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Opal Tower - Sydney Australia
27

Opal Tower - Sydney Australia

Opal Tower - Sydney Australia

(OP)
https://www.news.com.au/national/nsw-act/news/30st...

https://www.smh.com.au/national/nsw/opal-tower-res...

This could be an interesting and developing story in Sydney Australia. A 34 storey near new residential apartment tower in Sydney has been evacuated this afternoon over fears it is in structural distress with cracking noises heard during the day and one or more cracks developing; emergency services are treating it as a major incident.

Given we already have some of the toughest building codes in the world (although little to no registration requirements for engineers) it will be interesting to see how this plays out and what the crack(s) looks like to cause such a major emergency response.

RE: Opal Tower - Sydney Australia

Merry Christmas! Sheesh. Poor blokes.

I'm VERY impressed the fire department has quickly whipped out a laser range finder to monitor the building movement.

I'm also surprised they shut off the power. Why? How does this help anyone now having to shelp up and down 34 stories. How do they get pets out down 34 stories?

Keith Cress
kcress - http://www.flaminsystems.com

RE: Opal Tower - Sydney Australia

Quote (itsmoked)

I'm also surprised they shut off the power. Why? How does this help anyone now having to shelp up and down 34 stories. How do they get pets out down 34 stories?

Shutting off electricity and gas is pretty essential to prevent fire. Who cares about pets when there are hundreds of millions of dollars and lives and stake.


(There is every chance it will all play out fine in the short term with no harm to pets or anybody else. But the immediate concerns need to be addressed with a high degree of caution.)

RE: Opal Tower - Sydney Australia

Quotes from various media outlets below. Slightly conflicting, as I wouldn't expect the transfer to occur at level 10.

Quote (Media)

Engineers will spend Christmas Eve alongside firefighters examining a large crack on level 10 to establish whether the building is safe and investigate the source of the cracking, Fire and Rescue Acting Inspector Greg Wright said.

Quote (Media)

Wood & Grieve Engineers, who worked on the building, said online: “The large structural offsets at the base of the towers created a particular challenge. The difficulty was in the coordination of transferring sewer and storm water services through the deep transfer beams and large transfer slabs.”

“Due to the height of the building which imposes excessive pressures on the pipework and fittings installed on the lower half of the building, the WGE team came up with a unique dual stage pressure control concept and conducted a series of experimental tests to simulate the real working condition of the system before specifying it for installation in the building.”

RE: Opal Tower - Sydney Australia

Quote (Trenno)

Quotes from various media outlets below. Slightly conflicting, as I wouldn't expect the transfer to occur at level 10.
I'd normally take such media reports with a grain of salt..

Plenty of plans and picture on this site:

https://www.skyscrapercity.com/showthread.php?t=17...

What does seem almost certain is that several tension members, most like post tensioned strands have failed in the floor of level 10. The sounds were heard from as far as adjacent buildings. The slab has moved. Doors needed to be smashed open to get to some residents. At best it would be confined to one or two floors, but according to reports it seems to be several. Floor 10,12&13....

RE: Opal Tower - Sydney Australia

I'm not sure if it is a visual affect or if there are discontinuities in the columns due to openings in the structure for greenery.

RE: Opal Tower - Sydney Australia

So residents are being let back in. But this failure does seem to affect the serviceability of quite a few apartments and is not confined to just a few floors.

RE: Opal Tower - Sydney Australia

150 units in this building. It is reported now that about 2/3 of the residents have been allowed to return to the building. Someone, not clear who, has made an assessment that 51 units are uninhabitable for the time being. So obviously they have decided that the whole thing won't collapse, but some sort of localised distress makes a part of the building hazardous.

RE: Opal Tower - Sydney Australia

So the metaphor for the collapse of the Sydney housing market has been avoided...watch out Melbourne and Brisbane

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

I wonder if it’s one of the walls/columns at one of those garden slots?

Possibly - see this photo from Level 10:



Source: Link

RE: Opal Tower - Sydney Australia

Looking at the plans linked above, it appears to be grid 20 wall. Compare L9 and L10 plans, and see how that grid 20 wall is supported largely on a column below. Apartment 1005 is where it occurs.

Could wall be failing/crushing where the wall transitions/transfers to the column(s) under? Ie localised bearing failure?

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

Looking at the plans linked above, it appears to be grid 20 wall. Compare L9 and L10 plans, and see how that grid 20 wall is supported largely on a column below. Apartment 1005 is where it occurs.

Could wall be failing/crushing where the wall transitions/transfers to the column(s) under? Ie localised bearing failure?
My thoughts too. I have been hesitant to trust the structural accuracy of the architectural plan by they do seem good.

You can see the level 4 transition here:


Open the photo to zoom in and have a look at the far left.

RE: Opal Tower - Sydney Australia

Interesting.

It seems a common transition. I wonder why it happened up higher? Stronger concrete further down?

They must be working pretty hard right now assessing it all. I wonder who gave the green light for all the other units to return? The designers?

RE: Opal Tower - Sydney Australia

The Australian newspaper has reported that the NSW government will conduct an inquiry into the problem with this building. Based on many government inquiries in Australia, this could expand to be bigger than Ben Hur. Maybe that is a good thing.

RE: Opal Tower - Sydney Australia

I think it is pretty hard to speculate at this stage whether it is a design failing or a construction failing. Based on the state of the industry these days I'd GUESS that it is a failing on the construction side of things. Naturally a design failure would likely imply similar issues at the other connections.

Regarding giving the all clear for most of the building. I suppose it was based on the fact that it has been standing for four months, what's going to change in another couple of months. (Summer heat expansion is the only thing I can think of.)

I would presume that the initial determination is just short term. Long term structural safety of the structure can't have been determined this quickly. And remediation of the damage done will be eye wateringly expensive.

RE: Opal Tower - Sydney Australia

Yeah, hard to say whether it’s design or construction issue, or both, but it wouldn’t surprise me if it’s design issue. Someone neglecting to consider that the wall needs to locally yield at the stiff point before it can engage elsewhere.

They’re taking about 1-2mm movement, so maybe that’s whats going on.

RE: Opal Tower - Sydney Australia

Have seen that 1-2 mm referred to, but not sure how you measure that when it has already occurred

RE: Opal Tower - Sydney Australia

Guessing that the movement referred to is possibly relative movement either side of a crack that can be observed after the fact. Will be interesting to see what went wrong, without the structural drawings and the exact nature of what occurred it's a bit of a guessing game.

RE: Opal Tower - Sydney Australia

The 1-2mm is a comment from first responders and really needs to be forgotten about. It was made in the context of the building as a whole and immediate measurements from first responders.

It is pretty clear that some floor have moved significantly more than that. Several residents require emergency services to pry/smash open doors to be able to leave their apartment. This implies significant interfloor movement.

Meanwhile it would seem that the developer involved is being a little unprofessional and making big claims which I would be surprise if anybody has enough information about.

'Absolutely no danger': Developer defends evacuated Opal Tower building
"The developer of a new high-rise apartment block in Sydney's west, which was evacuated after residents heard cracking noises on Christmas Eve, says there is "absolutely no danger for residents" and the company is confident the "localised" damage to an internal wall can be fixed."

What we DO know is that some slab floors have moved. And that loud cracking sound where heard throughout the day. This crack was loud enough that some residents fled the building of their own accord. None of that sounds like an easy fix. The developers say it is an internal wall, it is a structural wall.

RE: Opal Tower - Sydney Australia

Taking a more optimistic view - if it’s some localised crushing of the wall at the support point prior to engagement of the transfer beam (compatibility yielding), maybe it’s now finished and they can just patch it up?

RE: Opal Tower - Sydney Australia

I'm not on board with any of this. 1-2mm by first responders, if the reports of the doors jamming are true than the displacements prolly around the 10mm mark. That video shows the column adjacent to unit 1005 which has spalled, don't know what happened to the column transition or transfer below it at Level 10 floor slab. If they are banning people from the units above and below this column, when I scrolled thru the drawings I counted at least 76 units which you could say fall within the tributary area of that column. From when this news story first occurred at 3pm to someone giving it the "OK. Building is at no risk of collapse at 1:45am". Hopefully it was an independent engineer with 20+ years high rise experience who conducted that 8-hr review. Given the nature of what happened there is no-way that building should have been re-opened. It should be closed until at least two independent parties completely review the design, completely review every site inspection report and site photograph, completely review every concrete cylinder report, every PT extension and every site survey, and carry out survey now that the failure has occurred.

I'm okay with 30% moment disstribution negative moment to positive moment provided that the reinforcement and displacements are accounted for, by the sounds of it, this slab('s) had to re-distribute prolly 3,000+kN in an instant.

RE: Opal Tower - Sydney Australia

Agreed. Hopefully this will be a big wake up call to the industry and the authorities that supposably oversee it. The state government have already announced an independent investigation.

It would seem that sagging slabs are not entirely uncommon. In a nearby structure "some balconies have sagged as much as 180mm on the outer edges over three years".
https://www.smh.com.au/national/nsw/huge-pressure-...

Not dissimilar to the flammable cladding and the Grenfell Tower fire. Until the public and authorities are slapped in the face with the dangers, much of it gets ignored. Due to the nature of joint ownership and here-one-day-gone-the-next companies lots of these problems just end in protracted legal battles. Maybe this will be a wake up call.

RE: Opal Tower - Sydney Australia

My thouthts only here. Destruction of a concrete wall with no lateral loads e.g wind or seismic is very serious.

But how can they say that it moved by 2mm ? The movement is insignificant in this building and in much smaller 1 storey buildings.

RE: Opal Tower - Sydney Australia

The 2mm comments were made by first responders on the day. They certainly were not made by engineers. They might have been made of the basis of monitoring after responding. AKA it means nothing, but the media will happily report.

RE: Opal Tower - Sydney Australia

3
Starting to hear that the wall panels were precast wall panels, which I think you can see a vertical panel joint just outside the glazing though it may be a dummy joint. And the spalled concrete looks like it has mesh each face. 2 thoughts:

- Grout beds, grout beds normally get detailed 20mm with 10mm steel shims placed around the panel dowels. The grout beds aren't as good as RC. They settle with load and create localised bearing points at the shims which can initialize cracking and spall the cover concrete, and could account for the vibration and sound that went thru the building. I remember reading about an Adelaide highrise early this year which didn't have the failure of this building but did have the ugly cracking of load bearing precast panels.

- Simplified wall calcs in AS3600. I think wall calcs using this equation must use a minimum e of yDim/6. I'm guessing from photos that the parameters for this wall panel would be xDim=1600;yDim=250;fc=65;Le=0.9*2900 (the f'c is a guess):
simplified wall calc using e=0mm = 7,900kN
simplified wall calc using e=yDim/6 (41.6mm) = 6,600kN
concrete column calc (and assuming the vertical bars are restrained) = 5,100kN.
I hate the divergence between simplified wall calcs and column calcs when Le/r>30.

RE: Opal Tower - Sydney Australia

Oh wow. Precast!

RE: Opal Tower - Sydney Australia

Oh and a backflip. Now doesn't that fill you with confidence....
https://www.theage.com.au/national/nsw/all-opal-to...

Hundreds of residents of Opal Tower at Sydney Olympic Park were told on Thursday that everyone who lived in the building would be "relocated" to allow "comprehensive investigations" into the damaged pre-made concrete panel.

"The building is structurally sound and the temporary relocation is a precautionary measure to allow engineers to work around the clock to comprehensively investigate and remediate the site in the quickest time frame possible, without further disruption to residents," the builder, Icon, said in a statement."

What horseshit. You wouldn't be evacuating the entire building [AGAIN] if you didn't think there was a safety risk. Yet a few days ago it was rapidly declared safe in under 8 hours.

RE: Opal Tower - Sydney Australia

Some more fine journalism (the blame games started), I'm glad all the experts in the public are onto the case at the end.
https://www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=12182960

Something looks odd about that concrete in the top photo, like it resembles masonry block texture. Could be an issue with the concrete strength/mix. Not even sure it's concrete from the closeup, sort of looks like grey polystyrene?

RE: Opal Tower - Sydney Australia

That bit is Hebel and most defiantly won't be carrying load. It's been crushed

RE: Opal Tower - Sydney Australia

Quote (Wiki)

Hebel can refer to:
...........
A brand of aerated autoclaved concrete from CSR Limited

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Opal Tower - Sydney Australia

It is just a close up of the internal damage as already posted. It isn't structural. The media are just being particularly poor.

It is just the top part of the wall in this photo.

RE: Opal Tower - Sydney Australia

@rscassar

My immediate thoughts as well, hard to say until we get more information but I agree, there is a disconnect between chapters 10 & 11 in AS3600.

I personally have seen several design firms detail blade elements as CL10 "columns" but use CL11 "wall" capacities, and they don't even question the disparity. Just boost the concrete to 65 or 80MPa and just cheer at the extra capacity without Reo or ties.

Although the new 2018 3600 has some stricter rules on walls/columns, I believe 3600 should follow ACI and have walls and columns under the umbrella of "compression" members that must be designed for a minimum moment. Slenderness cannot be ignored. Therefore a magnified moment must be designed for.

If the magnified moment doesn't induce tension in the cross section, then the simplified method might be appropriate, but you simply can't ignore slenderness.

RE: Opal Tower - Sydney Australia

In my opinion it would be a real shame if you had to design every wall as a column.

By all means reduce the capacity of the simple wall calcs if using simplified method (I’ve often considered them generous), but let’s not throw the baby out with the bathwater and demand complex analysis for everything. AS3600 has a nasty habit of doing that. Every edition gets worse.

RE: Opal Tower - Sydney Australia

Im hardly saying every element needs to be designed as a column, rather that compression elements need to be designed appropriately, and if slenderness is an issue, then it must be addressed.

Confinement in compression members cannot be understated and simply upping the concrete strength to avoid ties is reckless, in my opinion.

Using an interaction diagram, considering biaxial bending, and moment magnifier hardly constitutes "complex analysis". In actuality, the moment magnifier is the simplified method to avoid complex second order analysis.

RE: Opal Tower - Sydney Australia

Tomfh

How long does it take to design a column compared to a wall.

Part of the problem is that simplified methods which were developed in times when materials were a lot lower in capacity, eg concrete strength of 50MPa maximum up to 2001 and 65MPa up to 2009 are now being used for very high concrete strengths and with details which are completely inappropriate (central mesh reinforcing) for very tall walls. Something had to be done to limit the application of the very simplified methods.

Other things that have become more complex are crack control (because reinforcement strengths increased to 500 and now 600Mpa) and the old simplified rules simply no longer apply.

With computers, there should be no problem with removing some of the inappropriate design methods that were included in the code in previous generations because hand calculations were simply too hard to do.

RE: Opal Tower - Sydney Australia

Quote (QSINN)

Im hardly saying every element needs to be designed as a column, rather that compression elements need to be designed appropriately, and if slenderness is an issue, then it must be addressed.
That is certainly the way that I interpreted your comments and I agree.

The other thing is that I'm very surprised that such discontinuous connections be designed without deeper analysis. Even without potential stress concentrators of shims like rscassar mentioned, you are always going to get a very uneven load distribution in the wall. Stress analysis approaches should readily lead you to that conclusion.

RE: Opal Tower - Sydney Australia

Qsinn,

It’s more complex than I’d want to do when checking the simple capacity of a wall!

But in general yes I agree with you that these simplified methods can go too far, and give capacities beyond what seems reasonable. I believe stricter limits should apply, and I don’t believe walls should be giving significantly higher capacities than an identical column.

RE: Opal Tower - Sydney Australia

What do you think the panels were sitting on? What sort of transfer members?

How would you design the interaction between discrete panels, transfer beams, and columns/walls under? What software would they have used?

RE: Opal Tower - Sydney Australia

Opal Tower certifier previously disciplined by building watchdog

Not sure how it is in Australia, but in NZ walls cannot carry gravity load greater than 0.3f'cAg. This is due to poor performance under higher loads (lack of confinement). For higher levels of axial load I believe you can design using column provisions (much higher degree of confinement). I'm guessing we have a much higher confinement requirement anyway due to seismic issues, my previous experience with AS3600 is 10+ years ago and at that time it seemed miles behind our NZS3101 code in some aspects.

RE: Opal Tower - Sydney Australia

does not bode well longterm for the bldg if it is already showing signs of distress under gravity loads alone....
how does the "certifyer" system work or not work in Australia and who has overall responsibility for the design?...

RE: Opal Tower - Sydney Australia

Quote (SAIL3)

how does the "certifyer" system work or not work
Many have argued and are arguing more that it doesn't work. Of course the powerful and influential construction industry is arguing the opposite and largely opposing increase independent oversight.

My uninformed opinion. These sort of buildings get built, and sold (usually apartments are sold before they are even built) and hopefully no problems arise before the short term warranty is up. For many smaller builds this warranty might not mean much if the company conveniently no longer exists.

Opal Tower is seen by many as simply another in a whole line of problems that have been facing the residential building industry for a while. What makes this one a bit different is the severity of the failure (evacuated high rise buildings get plenty of media coverage).
https://www.news.com.au/finance/business/other-ind...
https://www.weeklytimesnow.com.au/how-sick-buildin...
https://www.sbs.com.au/news/some-residents-of-crac...

The flammable cladding issue is a big one. The most prominent one took 4 years to resolve the dispute, remediation hasn't occured yet. And this is just one in the line of many.
https://www.theage.com.au/national/victoria/apartm...
https://www.afr.com/real-estate/four-years-after-l...
https://www.theguardian.com/australia-news/2018/ma...
https://www.abc.net.au/news/2018-04-11/flammable-c...

I would say there are many in Australia who would like to see a major review of the entire industry.


On the structural side of things there are a few articles reporting that there is now concern of the 15 other identical panel connections in the building. Why this didn't concern the engineers from the very beginning is certainly puzzling but probably a reflection of the lack of responsibility taken by te building industry. The entire approach has been and continue to be more about protecting reputations that ethical engineering.
https://www.news.com.au/finance/business/other-ind...-

Another photo. Presumably the same level, same location but above a different column from the previously seen photo.

RE: Opal Tower - Sydney Australia

I suspect designers didn’t twig to the localised stresses. Maybe they assumed the transfer slab would carry it as UDL?

Presumably they’re now working out how it’s the precasters fault for inducing high localised stresses.

RE: Opal Tower - Sydney Australia

I think everyone is making up stories and we all need need to wait until we actually have some information to base our discussions on!

RE: Opal Tower - Sydney Australia

That's the most sensible comment I have seen in this thread, rapt. Based on what I know, I know nothing.

RE: Opal Tower - Sydney Australia

There’s enough information available to at least discuss the topic.

We know it’s load bearing panels, sitting on transfer floor, and they are locally yielding, particularly where there is columns/walls under.


RE: Opal Tower - Sydney Australia

2
It’s impossible to say much based on available information.
That said, there is a lot of difficultly modeling building of this size with such an unclear load path. Precast wall are extremely stiff compared with the transfer beams and tend to attract loads that they have difficulty carrying. The drawings show a major load path shift at level 10. The load path is very dependent on construction sequence and differential creep and shrinkage in the vertical elements of such differing proportions. The fact that the failure occurred several months after completion with no high wind loads suggests to me that creep or shrinkage is a factor.
My guess is that basic strength is there but it is really poor detailing that has crack due to local excessive stress.
The previous discussion highlights the problem with using simple wall design in complex structures. Although addressed in As3600-2018 there is still a lot of lack of clarity. The rule to design a wall as a column allows no confinement ties for concrete below 50MPa and no need for having sufficient steel to match concrete cracking stress. The current code, As3600-2009 allows this for all strengths. This is exactly the sort of failure you would expect in a lightly reinforced wall without ties with a complex stress state.
As3600-2018 remains vague as to how a wall is to be designed as a column. A column should should have minimum steel and confinement ties yet the various exemptions allow this to be ignored. It is not clear if minimum moment is applicable in the in plane direction and if biaxial checks are required.

RE: Opal Tower - Sydney Australia

Aside from the wall design questions most of which I will dispute as to whether they are actually problems in the 2018 code, as being told to design something as a column in accordance with the column design chapter means to use the column design rules with any specific variations that are defined in the walls chapter (if a variation from the column design rules is not defined, then it is not allowed), the biggest problem with precast walls is the detailing at the ends. There is some very bad detailing out there which basically means that the walls are essentially unreinforced at the ends, resulting in a plain concrete compression member. But no one knows if that is the problem in this case.

1 - 2 mm movement will not cause doors to jam. That is just about all of the information we have, so we have no information. We have no structural design or detailing information.

RE: Opal Tower - Sydney Australia

Agreed there is a lot of nonsence misinformation from reporters. But the topic is still interesting. Obviously there are serious problems with the building since it cannot safely withstand DL + partial LL.

From what I have been reading in this thread the walls were designed as walls and not columns ? I doubt that this would be the problem, just doesn't seem right to me.

What about workmanship issues and sloppy building practices (and also self certification doesn't help either) ?

RE: Opal Tower - Sydney Australia

I suspect that a first responder saw a crack that he estimated to be 2 mm and commented on it.
The number stuck.
There are most likely other cracks that are much wider but no ones talking about them.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Opal Tower - Sydney Australia

Quote (civeng80)

Agreed there is a lot of nonsence misinformation from reporters. But the topic is still interesting. Obviously there are serious problems with the building since it cannot safely withstand DL + partial LL.
Agreed. So there is IMO a still room for a discussion. Is there any room to determine the exact cause(s)? No, but there rarely is in this forum. The reality is we are always going to be dealing with a small subset of information.

Quote (civeng80)

From what I have been reading in this thread the walls were designed as walls and not columns ? I doubt that this would be the problem, just doesn't seem right to me.

What about workmanship issues and sloppy building practices (and also self certification doesn't help either) ?
We don't this at all, we have no windows into how theses connections were designed nor about workmanship issue.

All indication do point to:
-partial failure of precast panel on the base of level 10, grid line 20
-this failure seems to have occured above the two supporting columns underneath with visible damage above these areas
-this failure seems to have resulted in the significant floor movement during which louds noises were heard over a period of hours

The speculation for the failure is simply that. But I think some pretty good points have been raised both about potential issues in the application of AS36000 and general concerns and risks when detailing such transitions.

RE: Opal Tower - Sydney Australia

I think the news reporting on this tower suffers from Christmas Holiday Reporting Syndrome. All the reliable reporting staff are enjoying time off. AAC is precast and that is what is seen cracking in the interior. Obviously not the problem but rather a symptom.

This is the only photo I have seen of real concrete damage, though the diagonal nature of the crack is not good. I don't think these are precast walls. It is hard to tell from construction photos. The "garden" walls rise after the core but in advance of the columns before the flat slab is finally poured.

RE: Opal Tower - Sydney Australia

I believe it has been reliably established that these are precast walls.

Professor Mark Hoffman and John Carter, the two engineers tasked with figuring out why the building began to fail, will investigate the precast concrete construction method used for part of the Opal Tower.

Despite engineers narrowing in on the precast concrete, Professor Hoffman said the building method was extremely common worldwide. “If our investigation uncovers an issue relating to precast concrete, that information will be shared with our report to government,” the two engineers said in a joint statement.



These are official statements from engineers tasked with and independent examination. I wouldn't expect them to get it that wrong. In other reports the actual precast panel manufacturer has been named.



I think it needs to be emphasised. This incident is one building, one failure and might well not have any link systemic failings in the industry. However due to the media and politics it cannot be considered inconsequential to the wider construction industry. Sure this isn't engineering, but engineering is influenced by the systems and politics that surround it. There is plenty of indication that this may become the catalyst for a wider look into the industry. We already have politicians jumping onto the issue. With an election coming up this only stokes such fires.
https://www.abc.net.au/news/2018-12-30/opal-tower-...
https://www.news.com.au/national/nsw-act/news/the-...

(Personally I think reform is absolutely necessary. Somewhere, sometime there might be an engineering conclusion on this building. But it will almost certainly be minor compared to the other reviews this has already triggered.)

RE: Opal Tower - Sydney Australia

Most of us commenting here are in Australia. But to attempt to answer SAIL3's question above, the certifier system in most Australian states has essentially replaced the local government building inspector system, and is not working well, at least in my opinion. Part of that is because the certifiers are appointed by the builders or developers. They are paper pushers, with most of their paper about things like energy efficiency. I doubt many self respecting structural engineers have decided to become certifiers. Part of that problem may be our historic reluctance to "certify" anything, and especially not the work of others. Many of us don't even like to "inspect", and that is mostly to do with insurance requirements.

RE: Opal Tower - Sydney Australia

So in Australia as an engineer are you not undertaking (or required to undertake) your own inspections of the thing you designed?

Are inspections only undertaken by this (not) independent certifier?

RE: Opal Tower - Sydney Australia

I'm going to start speculating again from what I have.

The crushed hebel panels are at the entry to 1005, somewhere concealed within that party wall should be a column of some sort on grid 20 and from what I've seen on the Architectural DA drawings 2015, it is probably located about where the glazing line is for the skygarden.

The second photo which looks more damning with the large segments of precast walls crumbling looks like its the level 10 skygarden looking down onto Brushbox Street where it turns onto Bennelong Hwy which is on Gridline 6 and adjacent to apartment 1009. So if the as-built scheme is similar to the DA scheme, there should be circular RC column sitting behind those walls and those panels might have been detailed as non-loadbearing (but became load bearing with whatever happen, also the RC column may have been VE'd out of the design). Also the chunks of concrete that have popped of seem largely unreinforced so the panels may only have a single layer of reinforcement.

RE: Opal Tower - Sydney Australia

My interpretation of is a bit different rscassar. But we are dealing with old architectural plans and limited photos...

Quote (rscassar)

The crushed hebel panels are at the entry to 1005, somewhere concealed within that party wall should be a column of some sort on grid 20 and from what I've seen on the Architectural DA drawings 2015, it is probably located about where the glazing line is for the skygarden.
I see no column on the architectural drawings nor in any construction photos. So I have presumed this wall is load bearing and the column beneath it seems to be position at the glazing line. (See floor plan for level 9 and overlay it with level 10)
Apartment 1005 Floorplan


Quote (rscassar)

So if the as-built scheme is similar to the DA scheme, there should be circular RC column sitting behind those walls and those panels might have been detailed as non-loadbearing
This column does appear clearing in the floor plans. However From what I can observe I cannot spot this column during construction. Thus I have presumed that the entire precast wall is load bearing with two columns underneath on level 9 and on top at level 16.


<EDIT> An additional sales floor plan for APT2204 has been found. You can see here that the third column in the corner is not included in the floor plan but the other two are. The missing column is where adjacent to the precast panels.


That has been my interpretation. But I'm open to alternatives. We pretty much only have photos and old architectural plans to go off. I might try trailing some old real estate advertisement for additional photos.

Most of my construction photos I've observed have been taken from here:
https://www.skyscrapercity.com/showthread.php?t=17...



RE: Opal Tower - Sydney Australia

Human909, I view it similar to you. A wall bearing down on a transfer slab, supported primarily on the the L9 columns.

I wonder if the transfer slab and precast walls form a very deep beam (as opposed to precast walls *supported on* transfer beam), and the wall failure at the columns is effectively a web bearing failure, which the wall panels may not have been designed for.

RE: Opal Tower - Sydney Australia

Agent666,
That is my interpretation of the current state of play. I am out of the game now, so am just giving my impression of what is happening. It didn't work that way when I was practicing, but from what I understand now, site visits/inspections by the design engineer on commercial and residential buildings are increasingly rare. A good reason to stick to industrial structures.

RE: Opal Tower - Sydney Australia

This image is from Google maps. It clearly shows the wall at L10 is load bearing with no column as shown in the DA plan. The wall is sitting on the L9 column with a limited bearing area.
The wall above L10 is supported appears supported on 3 columns, so is statically indeterminate. Depending on relative stiffnesses (including creep and shrinkage) the actual load at this transfer may not be what simple load takedown may indicate. It would be useful to know if all three go directly to the foundation or there are additional transfers.

RE: Opal Tower - Sydney Australia

Quote (degenn)

The wall above L10 is supported appears supported on 3 columns, so is statically indeterminate.
I count only two on the architectural plan. There appears to be a third column at the intersection of Grid lines 20 and 2 but the panels doesn't extend this far. The entry and internal wall is here. My interpretation anyway, I'm open to here others.

Quote (tomfh)

I wonder if the transfer slab and precast walls form a very deep beam (as opposed to precast walls *supported on* transfer beam), and the wall failure at the columns is effectively a web bearing failure, which the wall panels may not have been designed for.
Well you could consider it a deep beam if you wanted, it wouldn't be 'wrong'. It is just a designation that helps one apply appropriate analysis. But in this case I don't think describing the slab/wall as a beam is particularly useful. The key loads are mostly vertical compression loads on the wall, moment is minor in comparison.

Also calling the slab a transfer beam would imply that the slab has been designed provide stiffness in bending to the vertical loads imposed by the walls/columns. I don't think this has been done as you would need a significantly deeper slab to be stiff enough to carry the weight of 20 floor above. Instead, I am assuming that the design and analysis treatment of the slab is simply to support the bearing load of the wall/columns. That is my interpretations.

A corollary of this is that the wall is essentially only bearing on two points. These points being the ones above the columns. These points are also where the visible damage has been seen to have occured. ie, concentrated stress at two points along the wall.

Quote (tomfh)

(as opposed to precast walls *supported on* transfer beam)
If the design did treat the slab as a transfer beam then I'd suggest that is a key failing. The slab just isn't thick enough to provide the necessary stiffness to bear much load.

A quick rough and ready FEA of the wall to column-slab-wall behaviour and stress distribution. (Not loads are arbitrary, what matters is the distribution.)

(Note the above assumes perfect and continuous attachment between the slab and the wall. This is a generous approach and certainly not conservative. But even with this approach the stress concentrations are obvious. More realistic modelling of would result in even higher stress concentrations.)

RE: Opal Tower - Sydney Australia

As RAPT has pointed, often the major issue of precast is the connection design and detailing. I've seen precast panels with heavy Reo and ties (therefore technically "column" design) have only 4 heavy bars pass through the joint, and all other bars terminate in the panel. "The concrete takes the load". I hardly think this satisfies strain compatibility, and other fundamentals assumed by the code. Additionally, improper connection details can mean plane sections won't remain plane, therefore the whole analysis is pointless.

Many design offices merely put all the loads onto their RAM transfer models and take the output as gospel, without even scrutinising the results. Graduate level engineers are out there designing these major elements.

Not to mention that most site inspections are conducted by grad level engineers, if conducted at all. Generally contractors push for photos only... Details are easily missed.

RE: Opal Tower - Sydney Australia

@human909

Great image. What's the bet that the total G & Q load is applied to the transfer as a UDL, and that the wall is simply designed for the same UDL stress distribution? Not many would be doing that sort of FEA analysis..

RE: Opal Tower - Sydney Australia

Quote (QSINN)

@human909
Great image.
Thanks! I appreciate that. It only took me a few minutes. But it just puts a visual to what I was trying to say in words.

Quote (QSINN)

What's the bet that the total G & Q load is applied to the transfer as a UDL, and that the wall is simply designed for the same UDL stress distribution? Not many would be doing that sort of FEA analysis..
IMO, any engineer that considers the transfer as a UDL is failing in their task badly. It could never be a UDL or anything close to that due to varying stiffnesses. You could avoid FEA by considering the bearing forces through the slab as a 45degree flow which is how some pile cap analysis is approached. As far as what most would do. I am the ignorant one here. My direct experience in concrete design is pretty minimal. All that said it would not shock me if that is exactly what has happened.

Just forget the calculations and ask yourself does that wall look appropriately wide compared to the column widths above and below it?

My gut says that a skinny wall supporting some fat columns doesn't add up!

RE: Opal Tower - Sydney Australia

many of the reports mention the "building industry"...are they a separate entity, self-regulating and where does the practicing engr fit into the system?....the engineering society seems to have a reduced influence on the the quality of the design until something goes wrong.....what are the qualification requirements for a certifier and who certifies the certifier?.....no system is perfect but the objective should be to reduce the probability of error wheather it is human or a result of corruption of the system.....here in the USA, the independent/peer review for major bldgs, while it can be a PITA for the design engr, has allot of merit as it introduces an independent oversight....I had expected all hell to break loose after the cladding problem but as time goes on there seems to be only a muffled response...

RE: Opal Tower - Sydney Australia

QSIIN,

And the 4 bars through the joint are really dowels and their connection and development is debatable if it exists at all!

I have also seen details where the wall reinforcement terminates before it reaches the dowels as there is too much conflict with the two sets of reinforcement, so there is no continuity of reinforcement!

RE: Opal Tower - Sydney Australia

Assuming vertical stress will flow through a joint at 45 degrees means that there are very large horizontal stresses in the lower edge of the wall in order to pull the forces back to vertical. I’m not sure the wall would have this horizontal reinforcement along the lower edge. A detailed FE will show these forces but the code column forces through a slab does not include a check. Traditional design assumed the column above and below were of similar shape so the issue was not as significant as for a thin wall on a much bigger diameter column.

RE: Opal Tower - Sydney Australia

Human909,

By deep beam I simply meant the thing you modelled, which as your excellent image shows gives you really high “web bearing” stress at the support.

RE: Opal Tower - Sydney Australia

QSINN,

yes my first thought was the princess and the pea.

Many people would indeed just provide a normal mattress.

RE: Opal Tower - Sydney Australia

This plan of level 3 shows what looks like 3 supporting columns below the grid 20 wall.
It is statically indeterminate how these three will share the load.

RE: Opal Tower - Sydney Australia

Hi, I was wondering what everyone thinks of this theory:-
The “transfer beam” is a concrete upstand beam that it acts both as a beam and as the planter wall. (When you look at the balcony photo, the top of the beam that runs along the apartment wall should align with the top of the planter hob that runs into it. However, they are now misaligned as the top of the upstand beam is now lower than the top of the planter.)

The other photo showing a crack has some kind of white sleeve or conduit sticking out of the mess, that could indicate that this beam was post tensioned. Perhaps the post tension wires failed. I remember reading resident’s accounts of banging and screeching sounds.

Another thing I was contemplating was whether the temporary anchors for the “Doka” self climbing protection screen could affect the integrity of the post tensioned slabs. They have videos showing systems that anchor from the top of the slab and also from the slab edge. Could these possibly affect the post tensioning?

https://www.youtube.com/watch?v=vvQPXtvCuQ0

https://www.youtube.com/watch?v=LazbCGDiRWM

RE: Opal Tower - Sydney Australia

Quote (degenn)

This plan of level 3 shows what looks like 3 supporting columns below the grid 20 wall.
It is statically indeterminate how these three will share the load.
That isn't a plan of level 3 is is a plan of level 5-9. Zoom in on the image and it says 5004 and 5005.

Also the wall you are calling is not a precast structural wall as far as I am aware. It is an internal wall and presumable not structural. ( I've seen the only precast walls have been adjacent to the garden openings.

Here is an overlay of level 9 and level 10, it shows TWO columns underneath a 6m wall. (3 columns over 6 meters would be highly problematic for practical floor layouts)


Also note the discrepancy in the wall opposite to the one which we know has cracked. I would presume that final structurals would have meant a longer precast wall and moving the apartment entrance to the opposite side of the column.

RE: Opal Tower - Sydney Australia

I'm becoming an all too frequent poster. I am sick and on holiday so that is my excuse. I hope some people are finding my contributions informative and not too frequent!

Quote (SAIL3)

what are the qualification requirements for a certifier and who certifies the certifier?.....no system is perfect but the objective should be to reduce the probability of error wheather it is human or a result of corruption of the system.....here in the USA, the independent/peer review for major bldgs, while it can be a PITA for the design engr, has allot of merit as it introduces an independent oversight....
That is the second time you have asked that very good question and it hasn't been properly answered!

I would prefer somebody with better insight to answer it, as am ignorant on the specifics. I'll attempt to briefly answer it and not be too inaccurate! Certifiers in NSW state seem to be an administrative box ticking role. In my work I've never seen independent (outside party) reviewing of structural engineering, to my knowledge it isn't common. As others have reported site visits from the responsible structural engineers can be quite uncommon in residential and commercial construction.

Quote (SAIL3)

many of the reports mention the "building industry"...are they a separate entity, self-regulating and where does the practicing engr fit into the system?....the engineering society seems to have a reduced influence on the the quality of the design until something goes wrong.....
The big players in the building industry are:
-the developers who are the financiers running the show (Generally they buy the land and sell the building. They engage the architects, structural engineers and a principal builder.)
-the principle builder, for big build these are usually an 'engineering company' though often they are more about project and contractor management than engineering. For small builds the builder may not contain any engineers.
-the practicing structural engineer is often just a small player in the scheme of things with little ownership and oversight over the build.
(I'm sure you can join the dots here of where potential problems can arise.)

Quote (SAIL3)

I had expected all hell to break loose after the cladding problem but as time goes on there seems to be only a muffled response...
The issue here is similar to asbestos in buildings, it will take a good decade to get sorted. The scale of the issue is so large that dealing with it in a timely fashion is difficult except in the most dangerous implementations. Also delaying the process are lawsuits working out who is responsible.

As a side comment. In society, commerce and industry Australia generally has more extensive oversight and government protections than the USA. But in building industry Australia seems to have regressed considerably in the last 30 years. The general lay public are not blind to this. Which is why this single incident has trigger such a big media and political response.

Quote (mangotree)

Hi, I was wondering what everyone thinks of this theory:-
The “transfer beam” is a concrete upstand beam that it acts both as a beam and as the planter wall. (When you look at the balcony photo, the top of the beam that runs along the apartment wall should align with the top of the planter hob that runs into it. However, they are now misaligned as the top of the upstand beam is now lower than the top of the planter.)

The other photo showing a crack has some kind of white sleeve or conduit sticking out of the mess, that could indicate that this beam was post tensioned. Perhaps the post tension wires failed. I remember reading resident’s accounts of banging and screeching sounds.
You raise some interesting points. However I'm not sure there are transfer beams in play with the precast slabs. For a couple reasons:
1. No transfer beams can be seen in the photos at the top of the wall. (Levels 15/16) If one is necessary below, then one would likely be needed above.
2. To my knowledge there has only been mention of transfer beams once by the Wood & Grieve Engineers. “The large structural offsets at the base of the towers created a particular challenge. The difficulty was in the coordination of transferring sewer and storm water services through the deep transfer beams and large transfer slabs. (They are not the primary engineers, they just chose to speak to the media about the plumbing)
3. The deep transfer beams and slabs can readily be seen at the top of ground floor. Presumably they have larger spans on the ground floor that was original detailed in the architectual drawings. Larger columns are evident.

.
All that said I had noticed that item that looks like a conduit. I can't explain it, beyond assuming it isn't a conduit. Post tensioning a wall along that axis would likely give poor performance. All reports have said that it is precast walls that have been damaged.

RE: Opal Tower - Sydney Australia

Human, sorry to hear you are sick and hope you get better soon.

I am finding this post and your commnets very interesting and informative.

RE: Opal Tower - Sydney Australia

Thanks for your response human909. I really appreciate that and hope you get better soon!
I was thinking that perhaps there was a sequence of failures that started off with the post tensioning that led the floor to crack and drop 40-50mm, which in turn damaged the precast wall above it.
This is based on the tendency of designers to want to make joints and other building elements to “line up” for visual neatness. Eg. Top of the planter to line up with the top of a beam.
I haven’t seen construction drawings, so my theory is just based on a guess.
Many thanks again human909.

RE: Opal Tower - Sydney Australia

Quote (civeng80)

Human, sorry to hear you are sick and hope you get better soon.

I am finding this post and your comments very interesting and informative.
Thanks. I'm a little embarrassed to admit on this forum, but I am actually fairly fresh into the industry and my day to day work isn't directly structural. So my real world structural design experience is not extensive. But I'd like to consider myself as thoughtful so I try to contribute. I am more than open for people calling "bull-shit" on any of my comments, because I'm sure many people posting here have more experience than me! smile

(To me, debate and discussion is the way I learn. I've learnt plenty already from others in this thread. My knowledge of concrete barely extends beyond what I learnt in my degree. I'm mostly a steel guy, currently working in a niche industry in bulk materials handling and it is booming. I don't do enough formal structural work, but I've recently renegotiated my employment terms and intend to change that.)

RE: Opal Tower - Sydney Australia

Quote (mangotree)

The other photo showing a crack has some kind of white sleeve or conduit sticking out of the mess, that could indicate that this beam was post tensioned. Perhaps the post tension wires failed. I remember reading resident’s accounts of banging and screeching sounds.

I doubt that upstand was used to transfer the wall loads above as it looks about a 450mm upstand supporting 25 levels, if it where used as a beam it should have had heavy-ish shear ties whereas it doesn't appear to have any ties present.

That upstand may have been built at 32 or 40MPa with single layer of reinforcement, and I'm guessing the panels would be detailed somewhere between 60 and 80MPa, so the discontinuity between wall concrete grade and upstand concrete grade could be 1 point of failure.

The white thing sitting on top of the planter upstand doesn't look like a PT tendon. Tendons, even when they pop off the cover concrete and become exposed are more of a metallic grey appearance. And there shouldn't be a tendon placed in the top of the planter wall.

RE: Opal Tower - Sydney Australia

I would also like to see a survey of the building verticality, I went to the Kings game yesterday and had a bit of a look from a distance and it looked a little tilted when trying to gauge it against the neighbouring buildings. It is hard to gauge verticality by eye, I look at every tall building and think it's tilted.

RE: Opal Tower - Sydney Australia

To an EE, this is a completely new world. Interesting, even if I don't get it all. I'm impressed by the way different views are presented and the matter-of-fact tone.

Or is it my positive attitude combined with lack of knowledge that makes me have that opinion?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Opal Tower - Sydney Australia

CivilEngAus, good link.
Those are some might heavy duty props.

Very curious to hear the findings and the outcome. I certainly hope the investigations and reports are made public.

RE: Opal Tower - Sydney Australia

Hello all,

This is a great discussion. I have had a lot of experience in forensic engineering and reviewing failures on-site across Australia.

Here is my take on what has happened:

Local Column/wall failure has occurred due to insufficient grouting within the grout-bed interface between pre-cast element (wall/column) and in-situ element (beam/slab)

Here is some further explanation:

- Reports have confirmed pre-cast has been used

- Witnesses have indicated that there has been loud bangs/explosion and cracking sounds, even heard from neighbouring building. In my experience with this form of failure, it is brittle, sudden and very loud (if you have ever witnessed a high strength concrete cylinder core test to failure you will get some kind of idea on a smaller scale).

- Reports have now come out that the pre-cast wall/column itself is not to blame

- The images indicate that the cover concrete has "blown out" from the side of the column. This is the first thing to go as it is not confined by any reinforcement or ligatures. This form of failure doesn't mean that the column itself is no good, but rather the column has been over-stressed locally due to reduced contact area where grouting has not made full contact with entire column cross-sectional area.

- Reports saying that the building is "structurally sound" gives a glowing appraisal or the building itself and may be somewhat misleading, however would be technically correct as after local failure and crumbling of the base of the column occurs the contact area actually starts to increase and the grout-bed connection approaches full contact bearing area.

- However after the above has occurred, you end up with anywhere from 5mm to 20mm of "settlement" meaning that every floor above which that column supports will drop the same amount. This would explain the crumbling of the adjacent hebel wall at the level in question. This would also confirm reports that doors have binded in their door frames and some residents required police services to break them out of their apartments.

- Grouting of columns is generally not inspected by the building surveyor or the design engineer, you are leaving it up to the contractor (more specifically the subbie) to get this element right.

- This is frequently the most common "structural failure" I see in the industry at the moment as you rarely get much else go wrong, to be clear our construction industry is of high quality, is robust and we are more advanced than most first world countries. However this particular failure mechanism has been around for over a decade and actually leaves me scratching my head as to why this hasn't been rectified or the approach changed to mitigate risk.

- This has not been in the media previously as the failures I have seen occurred during construction and was able to be rectified while the public are none the wiser. Unfortunately on this occasion, while the grout connection may have been poor, perhaps not poor enough to cause failure under structural self-weight only but required service load to tip it over the edge.

- This is not a local state construction issue, I have reviewed projects where this has occurred in Melbourne, Adelaide and NSW.





RE: Opal Tower - Sydney Australia

Thanks for the insightful comments SheerForceEng. By the sounds of things you have significant experience in local construction of this nature. Certainly much more than myself.

Just a couple of questions:

Quote (SheerForceEng)

to be clear our construction industry is of high quality, is robust and we are more advanced than most first world countries
Could you elaborate further on this? Particularly in residential construction, my perception isn't like this. (Though my perception is based layman percerception rather than on professional assessment.) I'd expect northern Europe to put us to shame in robust residential construction. In infrastructure, new industrial construction and particularly OH&S I do see Australia being robust if not somes over the top for the latter, residential not so much. (All that said, Opal Tower does seem to be one of the higher quality residential builds. I've seen far worse. But despite being 'higher quality', one critical mistake can still ruin it all.)

Apart from the grout what are your thoughts on the column to wall load transfer? Does the wall not seem undersized in your experience? Even with perfect grouting it is hard to avoid large stress rises with the centre of the wall barely carrying any load and the transition.



Quote (Skogsgurra)

I'm impressed by the way different views are presented and the matter-of-fact tone.
Or is it my positive attitude combined with lack of knowledge that makes me have that opinion?
I would put it down to being a forum of professionals but it seems you are a very long time member here so I presume you are speaking in terms of eng-tips forum. My only explanation is that the uncertainty and lack of information creates an environment for open discussion. In some contexts I can be opinionated, brash, argumentative and forthright. But it is hard for me to do that here given the number of unknowns AND recognising that I'm far from the most experienced person in the room. If most people consider themselves in a similar position then you can get constructive discussion. (In contrast if everybody has a fixed opinon and everybody thinks they are the smartest in the room then welcome to unconstructive arguments!

Quote (QSIIN)

Very curious to hear the findings and the outcome. I certainly hope the investigations and reports are made public.
The planning minister has said that reports will be made public, but politicians change their minds all the time. Not to mention he might not have a job in 4 months which could be later than when the final report is finished.

RE: Opal Tower - Sydney Australia



Quote (human909)

Could you elaborate further on this? Particularly in residential construction, my perception isn't like this. (Though my perception is based layman percerception rather than on professional assessment.) I'd expect northern Europe to put us to shame in robust residential construction. In infrastructure, new industrial construction and particularly OH&S I do see Australia being robust if not somes over the top for the latter, residential not so much.

In terms of concrete technology, we are very advanced. Ironically enough even though they are swimming in sand over there, we taught Dubai how to use their sand in their concrete mixes to achieve high 80MPa plus concrete.

We have been leaps and bounds ahead of majority of the world in post-tensioning of slabs.

If your talking finishes/fixtures quality and also energy saving initiatives (insulation, glazing technology etc.), we are far behind, but unfortunately this is driven more by the dollar and developers than the skill of our local contractors (we don't have much legislation to force the issue). You can also say that we aren't as advanced as other nations when it comes to structural steel construction (it is done here but we don't have anywhere near the volume per capita compared to say the US).

Quote (human909)

Apart from the grout what are your thoughts on the column to wall load transfer? Does the wall not seem undersized in your experience? Even with perfect grouting it is hard to avoid large stress rises with the centre of the wall barely carrying any load and the transition.

I agree, it does look "lean" and may be a possible reason for some local failures no doubt. I believe however for the apparent "Funnelling effect" of the load to be the root cause (i.e. half the walls supported load being asked to go through a small cross-section due to corner support from column below) we would see more significant failure of the wall itself (it wouldn't have stopped failing and potentially would have continued to collapse...I don't see anywhere else for the load to go).

It is definitely a critical junction and something that would have little redundancy and margin for error if its working close to its the theoretical limit. May be a combination of a critical junction (perhaps one of a handful of very highly stressed connections) that has exposed less than satisfactory construction practices due to its critical nature.

What you are identifying is indeed a structural engineering "headache" but not out of the norm for most large scale buildings. The engineering firm WSP (who mind you were also the original structural engineers on the design not just the current engineers looking at the problem) are a huge reputable organisation and I don't see them getting a junction like this wrong (I have reviewed a lot of their projects in Australia and yet to find anything "dodgy") however stranger things have happened and may not be something to rule out just yet!!

RE: Opal Tower - Sydney Australia

Thanks Sheerforce for answering my questions so well! smile What you have elaborated on also aligns with my layman perceptions.

Also in support of your assessment that it is likely grouting issues, there have been clear statements to the media that no flaws have been found in the precast panel construction (or something to that effect). Those statements puzzled me, but if the main damage is to grouting then that explains it.

Quote (Sheerforce)

The engineering firm WSP (who mind you were also the original structural engineers on the design not just the current engineers looking at the problem) are a huge reputable organisation and I don't see them getting a junction like this wrong (I have reviewed a lot of their projects in Australia and yet to find anything "dodgy") however stranger things have happened and may not be something to rule out just yet!!
I agree that it is pretty elementary to get such junctions wrong. Thanks for clarifying that in your opinion such oversights are unlikely to have been made.

RE: Opal Tower - Sydney Australia

Quote (SFE)

The engineering firm WSP (who mind you were also the original structural engineers on the design not just the current engineers looking at the problem)

I thought Bonacci Group were the structural enguneer on the original building.

Of course Bonacci may have been purchased/acquired/merged by WSP in recent times...

RE: Opal Tower - Sydney Australia

I had thought Bonacci were the original engineers too. Either way, just because it's a large "tier 1" firm doesn't mean much; I've seen some questionable details from both big and small groups, not pointing any fingers, though haven't had much to do with either of these two.

Both large and small consultants are subject to the tight deadlines, fees and pressure placed on them from the contractor, and would have similar potential QA issues, generally speaking of course. And of course, both firms only look to 3600-2009 for wall and column design.

Touching again on the precast, if the panel design itself is sound, the fact that the connection/joint has failed is still a major issue, in my opinion. Any structure could be pretty much built like Jenga blocks for gravity, with dowelled connections everywhere, but subject them to wind loads* and the whole system fails. The fact that this is happening under gravity alone is concerning, regardless of how well the panel itself is performing.

*(and EQ, assuming the engineers haven't ignored them, because you know, "we don't get earthquakes in Australia")

RE: Opal Tower - Sydney Australia

Quote (Ingenuity)

I thought Bonacci Group were the structural enguneer on the original building.

Quote (QSIIN)

I had thought Bonacci were the original engineers too. Either way, just because it's a large "tier 1" firm doesn't mean much; I've seen some questionable details from both big and small groups, not pointing any fingers, though haven't had much to do with either of these two.

No, unfortunately fake news strikes again which looks like the Sydney Morning Herald has since retracted but damage may already be done it seems to Bonacci Group reputation...

https://www.smh.com.au/national/nsw/extreme-urgenc...

If you scroll down to the fine print you will read...

"An earlier version of this article incorrectly listed Bonacci Group as the structural engineers."

RE: Opal Tower - Sydney Australia

Channel 7 news just showed large quantities of propping being installed behind plywood privacy hoarding, with apparently more propping being brought in from overseas. They had quite a few pallets of props there already.

RE: Opal Tower - Sydney Australia

SheerForceEng, you seem very keen to lay the blame on the workers, eg saying tier 1 firms like wSP almost never make mistakes, and saying its most likely just a poor grouting issue and that the consultants would therefore have no responsibily there.

Assuming it is merely just poor grouting (and we don’t know that) it’s not ok for consultants to leave it up to workers to ensure critical load bearing elements like these are grouted. If you need 80MPa grout across the whole bearing area for your walls not to explode then you need to check it’s gone in and that it’s the right stuff.

RE: Opal Tower - Sydney Australia

My interpretation of SheerForceEng's comments certainly haven't been that. I don't think he has been unduly blaming workers and absolving the consultants.

He has a view and backed it up with clearly explained reasons. To me none of it is about blaming one party or another. It is about finding the immediate and associated source(s) of the failure.

Regarding the lack of oversight that occurs at grouting connections. I'd expect SheerForceEng would agree with you. He has already mentioned that he is puzzled why this failure area hasn't been addressed.

RE: Opal Tower - Sydney Australia

Here's a screenshot of the propping from the channel 7 video.

RE: Opal Tower - Sydney Australia

Quote (tomfh)

SheerForceEng, you seem very keen to lay the blame on the workers, eg saying tier 1 firms like wSP almost never make mistakes, and saying its most likely just a poor grouting issue and that the consultants would therefore have no responsibily there.

Hi tomfh, appreciate your input. I don't wish to lay blame unwarranted to any party (bearing in mind that this discussion is filled with hypotheses that precede my comments which you can either look at as being a blame game or a discussion amongst interested parties and enthusiasts based on limited information that is out in public currently). I simply came to my conclusion based on the information that I know is currently being circulated in the public domain mixed with my past experience and dealing with these very failures on projects across Australia....

- Photos show that local failure at the wall base has occurred, but not total failure of the wall itself, I believe a design error (i.e. under-sizing of the wall strength or thickness) would mean the wall would have continued failing rather than crumbling until a point of larger contact area was reached.

- An error in design would be picked up by now during these investigations noting that there is also a third party engaged by the developer checking the design. If a design error existed in this local area a couple of days should be enough to spot check this. The potential poor grouting issue is not readily detectable and in fact if my theory is correct they may never find out as the failure has now occurred and full bearing is now achieved, we may never know weather there was adequate grouting or not unless another lightly loaded column (that hasn't failed) is found and investigated to have poor grouting undertaken on it. This is the reason why the engineers, builder and developer are scratching their heads and sadly not able to give the residents the answers they need in my opinion.

- Playing the averages, in all the constructed failures I have been involved with investigating approximately 15% are design related with the remainder being a mixture of workmanship/materials or a structure being loaded beyond what it had been designed for with its intended use.

Quote (tomfh)

Assuming it is merely just poor grouting (and we don’t know that) it’s not ok for consultants to leave it up to workers to ensure critical load bearing elements like these are grouted. If you need 80MPa grout across the whole bearing area for your walls not to explode then you need to check it’s gone in and that it’s the right stuff.

Your comment has probably hit the nail on the head regarding why I don't understand why there is no code coverage or regulatory guidance considering this issue has been around for over ten years now.

Regarding presence of the design engineer on-site, you could argue that every piece of the structure is important not just select critical locations. The standard across the board in Australia is that generally the design engineer does not have a full time site presence to hold the builders hand through every step of the construction process. Notwithstanding this status quo, this junction is particularly hard to inspect and I will try to explain why in my elaboration below...

There are two methods to grout column connections which are adopted in Australia, Option 1 is quicker and easier to build and is the obvious builders proffered, however impossible to visually inspect as an engineer. Option 2 is far more labour and time intensive however results in a better outcome for the structural integrity of the connection itself and the quality however is used far less and not as common, as the builder generally decides what construction methodology they want to use even sometimes against the engineers recomendation.

Option 1

1. Plastic packers/shims are placed on surface of slab/beam
2. Pre-cast column is placed on packers
3. "Ram Pack" grout is then used around the column perimeter to grout up the contact surface i.e. a dry or semi-dry grout mix.

The above procedure when completed makes it impossible to visually inspect weather full contact area has been achieved. IT is also tricky to get the grout all the way to the centre of the column/wall if it is of a large cross-section.

A visual inspection can show that the full perimeter is covered (which it generally is) however voids may exist internally which are not visible. This is a primary reason why, looking at the photo of the failure, I theorise that the cover concrete has blown away because that is where the higher stress is most likely generated (perimeter of the wall/column) until the wall then locally fails and therefore closes up the potential voids within internally.

Option 2

1. Plastic packers/shims are placed on surface of slab/beam
2. Pre-cast column is placed on packers
3. Exterior perimeter of column is sealed up temporarily with one breather hole for grout access
4. A "flowable" grout mix is then pressure injected into the gap between column and slab,
5. Usually a breather hole or two is cast into the column itself via grouting tubes which would allow the grout to extrude out of the column therefore indicating that the joint is fully "filled". Generally flow of grout from the breather holes is allowed to continue for several seconds to ensure no air pockets remain.




RE: Opal Tower - Sydney Australia

The hypothetical design error is a stiffness compatibility problem between wall and transfer stiffness, such that walls end up locally yielding at the hard points, but not fully failing. As you put it “crumbling until a point of larger contact area was reached.”

Human909s December 30 post shows that concept.


Maybe it was that. Maybe it was that and was exacerbated by poor grouting. Or maybe it was just poor grouting alone. Or maybe something else entirely. Hopefully we find out.

RE: Opal Tower - Sydney Australia

WSPs statement today:

https://www.wsp.com/en-AU/news/2018/opal-tower

Guy Templeton, President and Chief Executive Officer of WSP, Australia & New Zealand says, “We have found no other areas of damage to the extent of that in one part of level 10. There are fewer than 20 parts of the building with a similar configuration to the connection between pre-fabricated and in-situ poured concrete that was damaged on Level 10. Two of these areas, both on level four, show evidence of some but lesser damage.”



As a precautionary measure, propping is being installed to support level four and this will be completed by Icon Co by the end of today.



The building is structurally sound overall.

RE: Opal Tower - Sydney Australia

If a wall is designed as a column then its capacity is limited to about 0.45f’c. If designed a a simple wall it would be less. The load at the time of failure would be only about 0.75 of the design load. The failure therefore occurred at about one third of the expected capacity.
It seems unlikely that construction only can account for this.

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

The hypothetical design error is a stiffness compatibility problem between wall and transfer stiffness, such that walls end up locally yielding at the hard points, but not fully failing. As you put it “crumbling until a point of larger contact area was reached.”
Human909s December 30 post shows that concept.
Exactly. Local yielding resulting in stress redistribution. Thanks for highlighting this, I was about to do it myself! smile Though I'm starting to be persuaded against my own arguments.


As much as I would like to continue pushing the line of thought I have been, there are a couple other things that support the grout description of the failure. Most notably the quote from you own post.

"There are fewer than 20 parts of the building with a similar configuration to the connection between pre-fabricated and in-situ poured concrete that was damaged on Level 10. Two of these areas, both on level four, show evidence of some but lesser damage."

They focus really does seem to be on the connection BETWEEN the elements. So that likely implies grout. (alternatively shimming, dowels etc, but grout makes good sense)

SheerForceEng, you have convinced me for the moment! smile In time we will hopefully get more details.

RE: Opal Tower - Sydney Australia

@SheerForceEng

We are seeing more commonly, heavy duty couplers being used to connect the precast panels vertically, and install two, sometimes three lifts of panels at a time, leaving a space for the insitu slab to be poured in between. Due to shrinkage, high strength grout is often required to fill the gap that developed between the slab and panel. Wouldn't assume that has been done on Opal, but the two options you've highlighted aren't the only methods for precast.

Using the couplers highlights other issues though, as generally not all bars are coupled (as already mentioned by RAPT and myself) meaning strain compatibility and bar development at the joint is questionable. Interaction between continuous coupled bars, precast concrete and insitu concrete is complex too, though I question how often this interaction is thoroughly checked.

Regarding the original engineers and investigation, wouldn't it be prudent that a third party engineer, with little to no vested interest, do the investigation and report, not just the original consultant...? Isn't there a conflict of interest there? Of course they are going to say "overall structurally sound"...

RE: Opal Tower - Sydney Australia

Human909, they are propping heavily below L4, which would suggest they are concerned with the slab as well and not just the connections to the panels supported by L4.

RE: Opal Tower - Sydney Australia

The “transfer” you are talking about looks to be only a 200 slab, like all the rest. The floor to floor height looks consistent. With 20 floors above, you can’t expect any reasonable redistribution without punching the slab.

The problem with propping to ground is how the get a say 10000kN foundation for the props.

RE: Opal Tower - Sydney Australia

Propping is occurring from the basement upwards and and probably is aimed to extend at least to level 16. It would be to reduce the load on the existing compression members so that no further damage is done and to allow remediation once they figure exactly why and how. Remediation becomes a whole lot more difficult once the slabs has moved!

Quote (QSIIN)

Regarding the original engineers and investigation, wouldn't it be prudent that a third party engineer, with little to no vested interest, do the investigation and report, not just the original consultant...? Isn't there a conflict of interest there? Of course they are going to say "overall structurally sound"...
The main investigation and remediation is being carried out by the responsible company, WSP. I would suggest that they are being very thorough now, they are engaging other engineers from within the firm as well as engaging engineers (presumably specialist) from another private company.

On top of this the state government has formed a engineering investigation that is participating in all this. (This isn't a normal action, but given the severity and the high profile the government has jumped on this.)

I would say from an engineering standpoint things are going to be pretty thorough from now on.


I can't explain why the early decisions and statements were made about the building's structural soundness. But it does seem like they were driven by the vested interests of the developer "Ecove" and builder "Icon". These are the ones with their necks mostly on the line in terms of immediate costs and reputation. WSP obviously will face issues if there is a structural design flaws.

RE: Opal Tower - Sydney Australia

(OP)
https://www.dailymail.co.uk/news/article-6544623/D...

I'm not sure how reliable The Daily Mail is although they have a new photo from apparently inside an apartment.

Quote (Daily Mail)

Apartments have already been - or will be - gutted on levels four, six, seven and 10. ...

This will include, but is not limited to, removing the walls to assess the structural damage.

New images show the interior of one such apartment that has already been assessed, showing a temporary metal wall in lieu of the plaster and exposed wires hanging from the roof.

The cost of the metal props currently holding the building up is said to be in the hundreds of thousands, and more are currently on their way from international sources to due a shortage of supply locally.

The ground level of the building has also been jackhammered and pavement ripped up.

Engineers are allegedly calling for the further inspections to garner a more holistic understanding of the causes and impacts of the current debacle.

They are also arguing it will allow them to assess the extent of the damage, amid rumours the engineers involved are currently at a loss as to how to go about repairing the building.

The new details come just days after allegations surfaced that two new cracks on level four had been found.



RE: Opal Tower - Sydney Australia

Just a bit of bad grouting hmm...

RE: Opal Tower - Sydney Australia

If it is the grout beds of the precast walls and it went unchecked through construction, the cracking of these walls could be extensive throughout the whole building. When they take off the finishings for all the walls & columns up the tower there could be more surprises yet. I don't think this building will be re-opening anytime soon, and I'm not sure there is a successful remediation for this building.

This is going to send shockwaves throughout the whole highrise building industry in Australia.

RE: Opal Tower - Sydney Australia

Whatever the reason for vertical displacement, even if it is just 'bad grouting', the consequences can be severe. This part we have known pretty much from the start. When you have slabs on multiple levels moving enough to jam doors rectification is always going to be challenging. Appartments gutted and ground jackhammered is likely just inspections and installation of props. If you have a tiled ground floor you are going to want to remove them before placing the props. (Which must extend down the the basement foundations.

That said, that picture above looks like they are possibly still concerned about the strength of the precast panels. (despite comments their comments to the contrary) But I feel like I'm doing too much guessing now, I've done enough already! smile


One thing to observe. If anything the media coverage of this is getting worse. Reporting rumors as fact which have forced denials.
EG on the previous level 4 cracking:
Design firm WSP — one of the investigators being employed by the building company Icon — denied reports the cracks on the fourth floor had widened from 3mm to 20mm over the past week, with chief executive Guy Templeton declaring them “completely not true”.

“We’ve gone through the rest of the building, that (cracking) has been there for an indeterminate amount of time, not necessarily the same,” he told The Australian. “It’s been monitored and it hasn’t moved at all. It’s just a bit of cracked concrete, not very exciting.”

RE: Opal Tower - Sydney Australia

I'm actually surprised that they are speaking with the media openly as they are. Given what is at stake, I would expect any interviews with the media they would be very polished and deflect questions without given a definitive answer. Like a politician does when they get grilled by a journo.

RE: Opal Tower - Sydney Australia

Human909,

You have had an awful lot to say about this considering your own admission to having very little experience in this area and no knowledge of what has actually happened with the building.

Some comments like

"The main investigation and remediation is being carried out by the responsible company, WSP. I would suggest that they are being very thorough now"


could be regarded as slanderous. I would be confining myself to known facts, very few if any of which have been aired by anyone on this site.

RE WSP, they merged with Winward Structures several years ago when WSP moved into Australia. Winward were previously part of Bonacci Winward but they split in the early 2000's to form Bonacci Group and Winward Structures. There is no other connection between the 2 groups that I know of.

RE: Opal Tower - Sydney Australia

Quote (QSIIN)

We are seeing more commonly, heavy duty couplers being used to connect the precast panels vertically, and install two, sometimes three lifts of panels at a time, leaving a space for the insitu slab to be poured in between. Due to shrinkage, high strength grout is often required to fill the gap that developed between the slab and panel. Wouldn't assume that has been done on Opal, but the two options you've highlighted aren't the only methods for precast.

Hi QSIIN, you are spot on, however the two methods I have outlined remain the only standard approaches for the base where a wall/column starts at footing level (or in this case where a discontinuity or transition occurs and the wall/column doesn't continue to levels below in the same configuration.

For the "block-out" method, you are still left with the conundrum of how to grout the gap that is left between underside of column surface and top side of slab (you have one of two options which I have outlined above).

Quote (QSIIN)

Regarding the original engineers and investigation, wouldn't it be prudent that a third party engineer, with little to no vested interest, do the investigation and report, not just the original consultant...? Isn't there a conflict of interest there? Of course they are going to say "overall structurally sound"...

There is definitely a conflict of interest however this is generally the first port of call in a situation such as this for a few reasons:

- The original engineer already has significant analysis and understanding of the building (hopefully!!) and at short notice in critical situations can hopefully give some fast answers after re-checking or internally peer reviewing the design to either confirm or disprove that design is an issue.

- To get another engineer at short notice means approaching the firm, getting the scope agreed, getting the fee sorted, then the contract. With occupants inside, this is not ideal.

- Some firms steer clear from getting involved in these kind of situations altogether for fear of having their name associated with the debacle.

When the situation escalates and a logical answer is not found (or the prevailing answer is one that the developer/builder etc. is not satisfied with) a third party is then involved which now looks like is happening...

It looks like Rincovitch and Cardno are also involved now so there are plenty of eyes looking at the situation (with no vested interests, albeit one vested interest to one-up a competitor and get some PR out of the process which when scrutinising a design in this case would be a good thing as it gives added motivation to do a thorough peer review!!)

As a side comment, I've never seen so much significant propping in a "structurally sound" building before which is exhibiting cracks that are "not very exciting"

RE: Opal Tower - Sydney Australia

Quote (rapt)

Human909,
You have had an awful lot to say about this considering your own admission to having very little experience in this area and no knowledge of what has actually happened with the building.
Some comments like
"The main investigation and remediation is being carried out by the responsible company, WSP. I would suggest that they are being very thorough now"
could be regarded as slanderous. I would be confining myself to known facts, very few if any of which have been aired by anyone on this site.
That emphasis is yours not mine. Slanderous, well that is your opinion. I believe I have stuck to the known facts and where conjecture has taken place I believe that has been clear. I don't believe I have misrepresented unknowns as facts. This discussion, and certainly my comments, are meant for the interested parties in this forum. If we wanted to wait until all the facts were public before discussing the topic then the topic would never get discussed.

If you consider my contribution as useless, then that is your opinion. Personally I have valued the contributions of everyone here, even those who I have questioned or who have questioned me.

**Failure/accident analysis is a fantastic way of learning and a great way of not repeating past mistakes. Open discussion is a great way to engage the mind on the topic. Honestly I wish it was promoted more heavily in all aspects of engineering.

RE: Opal Tower - Sydney Australia

Wow, sounds like a structural engineering soap opera!

Thanks rscassar for your reply on the 31st Dec 2018. I appreciate that.

I learnt a lot from your comments too, SheerForceEng. Your explanations are very clear and thorough, and it’s great to have someone with your experience sharing your thoughts.

I happened to come across an article from the Financial Review, titled “Opal Tower: Ecove developer Bassam Aflak says builder Icon bears liability” by Michael Bleby dated 1st Jan 2019.
If you google search the title, you can read it online. Here’s an excerpt:-

Quote (Financial Review - by Michael Bleby dated 1st January 2019)


Start of Quote
“Tensions rise to surface
As technical experts scramble to understand the cause to cracking in the building that has dominated national news headlines over the past week, tensions are bubbling to the surface between the main players. Mr Aflak said his own project managers were party to the structural investigations taking place but he was not aware consultancy WSP was putting out a statement late on Monday saying other cracks had been found but that the building was structurally sound.
"You would have seen a release by WSP Australia last night, which we only found out about this morning as well," Mr Aflak said. "There appear to be two locations where they're identified a crack. We're still waiting for a full report."
The problems had occurred in "garden slots" – recesses in the facade on the fourth, 12th, 16th and 26th levels of the building – where precast concrete panels joined structural columns and engineers needed access to about 40 apartments to inspect those connections, Mr Doyle said.
"What caused it will play out over a long period – whether it's precast related or related to the column connections."
He said one potential cause, the grouting sealing the connection between panel and column, was not a problem.
"The type of grouting didn't raise any concerns," he said.
Both Mr Doyle and Mr Aflak said the building was safe for occupation. Mr Aflak said he hoped the majority of residents – apart from those living in units that still required invasive testing to determine problems – would be able to return home sooner than the 10 days Icon said was necessary, when it evacuated all the residents for a second time last week.
"I'm hoping once we have a plan and a resolution this week from the engineers, everyone will be in a position to put a plan of action in place – I think the majority will end up coming back earlier than anticipated – and working out a plan of action for the balance of them."
Mr Doyle, who said the timeline of any remediation work – and consequently, any return by residents – was subject to approvals given by the government-appointed engineers, was non-committal.
"I can't answer that," he said. "It's out of our hands at the moment." “
End of Quote

I’m not certain whether the grout in the article refers to the same under panel grout discussed here.

RE: Opal Tower - Sydney Australia

Human909,

Yes, we should all discuss failures more openly. The way everyone hides mistakes is really sad.

I often wish for The Big HandBook of Structural Screw-ups so we could all learn where the most common pitfalls lie. Too bad it doesn’t exist because everyone invariably clams up. It’s only ones like Opal which make the news which get out there for all to see.

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

Yes, we should all discuss failures more openly. The way everyone hides mistakes is really sad.

I often wish for The Big HandBook of Structural Screw-ups so we could all learn where the most common pitfalls lie. Too bad it doesn’t exist because everyone invariably clams up. It’s only ones like Opal which make the news which get out there for all to see.
Exactly. And although rapt may have a point about unnecessary speculation and analysis, there is also the counter point of not enough analysis or review.

There have been numerous times in my professional career that I have questioned things around me in the absence of all the facts. If you wait until you have all the facts you might be waiting forever. Sometimes I've had to eat humble pie after questioning things because I've been wrong. Other times I've caught errors before they have led to more serious issues.

There sorta is a "HandBook of BIG Structural Screw-ups", (note the rephrasing). But it readily misses all the small screw-ups which can include equally important lessons. One of my hobbies is a risky activity that involves plenty of risk assessment with analysis that engineers are often more adept with. Knowing and understanding past mistakes can keep you and others alive. Open discussion is important for the community to understand the risks and pitfalls.


EDIT:

In other news. This article (despite being from a tabloid media source) is one of the best summaries I've seeen regarding the chain of the responsibility for the construction.
https://www.news.com.au/finance/business/flawed-pr...

RE: Opal Tower - Sydney Australia

Quote:

Meanwhile, AAP has reported that structural engineers investigating the building’s cracks believe a prefabricated concrete panel was not inherently faulty.

Instead, they think the damage was potentially caused by how it was installed, or possibly by problems in the design or construction of the building itself.

From this news article, Link. If true seems to narrow down (or widen) the field of possibilities.


RE: Opal Tower - Sydney Australia

To throw something else into the mix, it's possible that whatever grouted connection is present between the insitu and precast was not grouted at all. This would seem consistent with the events/damage I'm extracting from the limited information that's avaliable.

Hokie66, I'm very surprised that engineers inspections are being neglected. Engineers are one of the important links in understand what is going on sometimes and understand the impact of changes, etc. They are the policemen of the construction world, putting you head in the sand thinking you are limiting your liability by not inspecting is potentially completely the opposite of the situation if something goes wrong (liability through professional neglect). You have an obligation to prevent problems that might lead to the design intent not being achieved in my view, and am obligation to protect the public. Shame Australia doesn't seem to have learnt from the NZ experience in the 90'swith regard to the leaky buildings fiasco (and we didn't learn from exactly the same Canadian experiences a decade or so earlier as I understand it).


Wondering in Australia are the drawings/calculations/specifications part of the public building record like in NZ, so anyone can simply request the building records from the local council? I'm guessing not, as my recollection of doing work in Australia 15 years ago was that I never even had to submit calculations or anything like that.

RE: Opal Tower - Sydney Australia

Human909,

The emphasis was added to show where I thought the problem was! You wrote it!

To suggest that they are being thorough NOW is to suggest that they were not previously, and that is still not known. In fact, were WSP the original structural consultants? Bonacci are listed as the structural consultants in the listing of consultants for the project. WSP are not mentioned, and are not related to Bonacci in any way.

In that comment above I was not referring to speculation about the cause of the problem, though I still find it amazing that there has been so much discussion without the existence of any factual information. As far as I know, no-one has seen a structural drawing or calculations, or even a final architectural drawing or even knows what the connection looks like.

RE: Opal Tower - Sydney Australia

Rapt, now that things have gone bad, WSP are obviously taking a much closer and more thorough look at the panels/grouting etc than they did previously.

So there’s nothing wrong with them saying they’re being much more thorough with it NOW that it’s failed. That’s what happens when things go bad.

You don’t do a forensic check of every square inch of grouting and concrete in normal practice. You don’t order apartments to be gutted so you can check the concrete.

RE: Opal Tower - Sydney Australia

Quote (IRstuff)

Can anyone confirm that the column configuration was definitely changed between the issuance of the architectural drawings and the actual construction?
Compare the photo with the drawing for Levels 5-9. There is a marked column that very much doesn't appear in the photo.
http://majorprojects.planning.nsw.gov.au/index.pl?...


Quote (rapt)

The emphasis was added to show where I thought the problem was! You wrote it!
To suggest that they are being thorough NOW is to suggest that they were not previously, and that is still not known.
The emphasis changed the meaning. The statement was never meant to be interpret the way you did, and to my mind most people wouldn't interpret it that way. The word 'now' simply means at presently or currently which is exactly what they are doing. They are doing the inspections later they are doing them now. Your emphasis changes can change the perceived meaning but the literal mean is still the same.

RE: Opal Tower - Sydney Australia

I know that we are all talking about something were we don’t know all the facts. What we do know is something serious failed under normal service. That is at about a third of what should be its actual capacity. There are twenty similar details in the structure. Although they may not have failed it is important to question whether they have an acceptable factor of safety.

My experience with forensic review of failures has always shown that these failed exactly as they should have once all the facts are known. Such reviews give you a great deal of faith in the design methods we use and the safety factors built into our codes.

It does lead you to question why in NSW we don’t have a formal process of external design review for structures where failure can have such serious consequences.

RE: Opal Tower - Sydney Australia

It's a good point. When working in the UK it was a requirement to submit a calculations package to the Authorities for review and I believe there is something similar in the UAE. From what I understand and I may be wrong as I have never worked in SA, but I believe that South Australia is the only Australian state that requires the certifying structural engineer to submit a calc's package or require the 'For Construction' drawings to undergo a complete Independent engineering review.

It might be a good time now to implement that throughout the country.

RE: Opal Tower - Sydney Australia

@degenn

Not just NSW, but the whole of Australia. Does anywhere do external design reviews? As you said, the structure is arguably the most important part of any project (concerning safety of life), yet we have tiny fees, and are constantly being pressured to deliver faster and more for less.

And having CPeng or RPEQ or any other form of qualification also doesn't mean much, anyone willing to pay the fee to be registered can sign off another Opal Tower...

RE: Opal Tower - Sydney Australia

I agree. Having to submit calculation packages and having designs reviewed would help to raise the bar far more than everyone sticking “CPEng NPER” on their business cards.

RE: Opal Tower - Sydney Australia

Tomfh guess what came out of NZ experience 20 years ago... Exactly that.

Another photo of damage to walls and floor that hasn't been posted yet (sourced from local news site). Appears to be some good punching shear / shear type of failure in the floor.

RE: Opal Tower - Sydney Australia

That was my thought when I first saw it. And the wall crack seems to line up with it.

Would be nice to know what the structure below it looks like.

Hopefully we will find out eventually.

RE: Opal Tower - Sydney Australia

I just got some engineering details:
- The precast wall adjacent to the skygarden above Level 10 is 200thk precast, don't have any details about the wall itself (eg. concrete grade or reinforcement).
- Level 10 slab is 200thk PT slab with 90mm setdown from internal to external. 40MPa generally with 65MPa puddle pours around the supporting columns below.
- L09 columns. Column closest to the slab edge is 700mm dia. Column closest to the entry of 1005 is 900x750 rectangular.

RE: Opal Tower - Sydney Australia

Wow. If there are punching shear issues then this is far more serious than anything reported.
And 200thk precast panels with 20 floors on top is pretty thin - and slender.

Similar to wall/columns, punching shear in 3600 is pretty vague, and again I've personally seen engineers outright ignore it because they don't "believe" in punching.

RE: Opal Tower - Sydney Australia

A quick calc...


30m2 x 10kPa x 23 floors = 6900kN
The area and load generous I think.

(0.7 + 2 x 0.2) x 0.2 = 0.22m2
Assuming a 45 degree dispersion

6900 / 0.22 = 31MPa.

Seems maybe a bit high for a wall but unlikely to cause an actual failure since the service load would only be about 70% of the design load.

I think something else is going on.

RE: Opal Tower - Sydney Australia

QSIIN,

Punching shear is a guess from the shape of the crack and what looks like significant vertical separation. We simply do not know enough. Another suggestion was prestress anchorage failure, but I doubt that it would damage the wall like that or that it would happen 6 months or more + construction time after stressing.

I did not realize that AS3600 or any other national code operated on a "belief" logic. We normally leave that to politics, religion and football! AS3600 is a minimum set of design requirements!

There is nothing vague about the AS3600 punching rules. Too prescriptive maybe, but any engineer who has read the development work it was based on should understand it sufficiently to apply it.

RE: Opal Tower - Sydney Australia

RAPT,you're exactly right, a minimum set of requirements. Meaning there's a lot more that might need to be considered that is not covered by the code. I wish more engineers understood that.

Regarding punching, I guess 3600 gives clear enough minimum requirements for an ideal situation, but these days, with all sorts of transfer, transitions, precast/insitu interaction, using the code method might not be most appropriate - again, just the minimum requirements. Most buildings aren't square columns, equal spans in all directions anymore- some require a little more thought.

RE: Opal Tower - Sydney Australia

That's the problem rapt, engineers have to think to apply..... Scary how many times in doing peer reviews of small and simple or large and complex projects that I've seen someone unfamiliar with certain provisions completely misunderstood the requirements. When you set them right they are generally missing some basic understanding of the principles on which the provisions are based, sometimes having never even read the associated commentary clauses.

It would scare me if anyone believed punching shear didn't occur. Brittle failure modes with little or no warning warrant some additional attention if nothing else in my opinion.

RE: Opal Tower - Sydney Australia

Agent666/QSIIN,

You are preaching to the converted. That is why they are engineers and have all of that training. Or it used to be!

And it is not just that they have not read the commentary. Many have not read the code. Apparently software does it all for them!! Means they do not have to think. Just press the go button and then the print button and the code is satisfied. And the more complex the software gets, the less they have to think.

RE: Opal Tower - Sydney Australia

Punching failure. good grief, that would be scary.

RE: Opal Tower - Sydney Australia

May have been initiated by the wall panel failure first.

- A 200thk panel bearing over a 1040mm length (700mm column + 2*0.85*200mm for dispersion thru the slab) = 4,050kN @ 80MPa.
- Working load at the time of failure 30sq.m x 7.5kPa x 23 floors = 5,175kN

If the wall underwent cracking to widen the bearing area then instead of going direct to the column it went thru the slab and cause the punching failure.

I'm not really happy that the company responsible for the engineering certification and an engineer appointed by the builder are heading the investigation. I think it would be more ethically if a reputable and independent consulting engineer was heading the forensics.

RE: Opal Tower - Sydney Australia

rscassar

You give the capacity of the wall over the column as 4050kN. This presumably includes a phi of 0.6. This is a safety factor and shouldn’t be considered in assessing an actual failure. Similarly the 5% eccentricity is a contingency but probably doesn’t actually exist with a symmetric floor load and high axial load from above.

The wall may be overloaded from a code point of view but failure shouldn’t be expected.

RE: Opal Tower - Sydney Australia

Degenn,

Agree. When assessing actual failure we need to look at actual expected capacity and actual loads, not code reduced capacities and code loading.

RE: Opal Tower - Sydney Australia

Quote (Agent666)

Scary how many times in doing peer reviews of small and simple or large and complex projects that I've seen someone unfamiliar with certain provisions completely misunderstood the requirements. When you set them right they are generally missing some basic understanding of the principles on which the provisions are based, sometimes having never even read the associated commentary clauses.

What experience/seniority have the people making these mistakes?

As for reading the commentary, the 2001 code didn't get one; the 2009 code didn't get one until 2014; the 2018 code doesn't have one. We probably can't learn much from the ACI code but their practice of publishing the commentary in the same document as the code itself is streets ahead of the Standards Australia shambles. (Can I coin 'Shambles Australia' or is that unfair?)

FWIW I didn't read the supposed slander in Human909's use of the word 'now'. If anything, it was a defence of WSP's professionalism when read in context.

RE: Opal Tower - Sydney Australia

There's a reason why a System Requirements Review (SRR) precedes Preliminary Design Review (PDR); it's a chance for the customer (or peers) to interact with the designer to ensure that everyone understands the meaning and intent of the requirements.

Finding out that someone misinterpreted a requirement, even at PDR, wastes time and money.

TTFN (ta ta for now)
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RE: Opal Tower - Sydney Australia

rscassar

That last picture would appear to show a near vertical crack in the wall. Not a compression crushing failure. The base of the wall at the floor appears to be intact as does the "grout" bed.

RE the review, there would appear to be several consultants involved as well as the Government appointed Deans from UNSW and Uni of Newcastle. From what I understand, WSP, Cardno and Rinkovitch are representing different groups as well as Kajima's own people.

RE: Opal Tower - Sydney Australia

I pieced this photo together from the NZ Stuff video. There is more going on than Agent 666's screen grab shows.


RE: Opal Tower - Sydney Australia

Keeps changing.

So it is not a wall according to that photo, it is an upturned beam! And it looks like a flexure-shear crack/failure. And it is right through the depth. You can see another much finer crack at the top right hand corner.

RE: Opal Tower - Sydney Australia

I thought it was some sort of fold in the slab, so that garden is below the units.

RE: Opal Tower - Sydney Australia

To me that seems like the window, the wall and the slab shown in this image (LEVEL 10, APT1005). The covering (?tiles?) and the planter box have been removed. The focus of the image is the top of the SQUARE column previously mentioned and the precast panel. My thoughts anyway. But it could be in a completely different area given we have no context.

Link

EDIT1: It also readily explains the 45degree cracking from what could be a steel shim between the wall and the column. This goes back to what rscassar conjectured earlier. The wall is offset on the square column, which is unideal but given the desire for clean architectural lines in the gardens it is understandable.

EDIT2: Added a picture to make it clearer what I'm suggesting. (Thicknesses of slab/wall and dimensions of column relying completely on rscassar's previous post.)
Link


EDIT3. I've gutted this post as I misconstrued the context of the photo. I believe ShearForce's post below is more accurate.

RE: Opal Tower - Sydney Australia

Meanwhile the insight into the political and legal quagmire continues:

'Design and construction issues': residents claim investigators not cooperating
“WSP and Icon are not cooperative with [the] engineer appointed by [the] body corporate,” the residents claim in the letter.
Chief among the residents’ concerns is their claim that WSP and Icon have denied Mr McMillan access to “equipment and drawings to facilitate his works”.

The headline and claim is a little bit inflammatory. The investigators (WSP) likely have no requirement to cooperate, and might be contractually obliged not to disclose such information. But it just exposes how powerless the actual OWNERS of the property are. As the owner (joint owners) of the property you would hope that access to structural drawings of your own property would be your right. As it turns out it isn't quite that easy.

No doubt none of these issues are new in the industry. They simply have been brought out into the spotlight by this drama. And this is all in the context of a brand new construction. Imagine the nightmare for the owners if the building was outside the 'warranty', which I believe is only 7 years.

RE: Opal Tower - Sydney Australia

Has there been an explanation of why the developer, builder & designer are in charge currently, rather than the owner's corporation? Is it by default or is there some law/contract that makes it so?

RE: Opal Tower - Sydney Australia

(OP)
A couple of screenshots taken from a Seven News video from two days ago.


No context on the location.


The image has been taken with a drone.

Quote (rapt)

RE the review, there would appear to be several consultants involved as well as the Government appointed Deans from UNSW and Uni of Newcastle. From what I understand, WSP, Cardno and Rinkovitch are representing different groups as well as Kajima's own people.

Who are Rinkovitch working for?

https://www.instagram.com/p/BaKu-MqH7S8/

Quote (Icon Social Media)

The Opal Tower Project at Sydney Olympic Park celebrated the #toppingoffceremony amoungst team member & clients. This milestone was achieved 19 weeks ahead of contract programme and the 36 levels above ground were completed at less than 6 days per level. Congratulations to the Opal Tower project team!
October 2017

I don't work in high rise although 19 weeks ahead of schedule sounds mighty impressive...

RE: Opal Tower - Sydney Australia

Quote (steveh49)

Has there been an explanation of why the developer, builder & designer are in charge currently, rather than the owner's corporation? Is it by default or is there some law/contract that makes it so?
Not there hasn't. But it can largely be surmised. (I am not a lawyer, nor do I know the contracts involved.) But in summary there is nothing that gives the owners or the owners corporation the power to 'be in charge'.

The Developer (Ecove) is the contractually obliged to the owners. There are statutory warranties regarding structural defects between the Developer Builders and the owners. The Builder (Icon) is contractually obliged to the Developers and they are the ones currently covering costs of investigation and relocation of residents. WSP presumably have contractual obligations to Icon and are also (as the original engineers) in the best position to assess the issue.

Icon has put itself in charge as it knows it it liable. Most of those involved have just played along willingly so far. (Though some owners initially and maybe still are, refusing to cooperate with offers and requests from the Icon.

RE: Opal Tower - Sydney Australia

My understanding is

WSP - Ecove
Rinkovitch and Kajima - Icon (majority owned by Kajima)
Cardno - Owners/Body Corporate

This could be wrong as it is gleaned from press reports!!

RE: Opal Tower - Sydney Australia

Human909, you just own the space between the structure. The joys of high rise strata living.

RE: Opal Tower - Sydney Australia

Quote (CivilEngAus)

I don't work in high rise although 19 weeks ahead of schedule sounds mighty impressive...

You might be on to something CivilEngAus.

It would be good if the construction programme was checked against when the concrete slab would be cured/ robust enough before it’s subjected to various loads eg. Load bearing panels, post tensioning, and also checked against weather conditions.

I’ve read someone’s comment that sometimes the recently poured slabs appeared diluted down with rain (a general comment NOT specific to the Opal Tower). Would that affect the structural engineering calculations? Or would there be no long term implications?

The problem is, the residents are talking about a class action lawsuit.
That’s the likely reason for the lack of co-operation with the external professional engineering investigators.

RE: Opal Tower - Sydney Australia

Am i correct in reading the latest photo as a vertical crack in the wall over the centre of the column? If so, it would appear that a tensile force existed in the base of the wall due to the rectification of the dispersed column force into the wider wall. This force would be say 10% of the axial compression and enough to crack the wall. It appears to have cracked the slab also. If the wall had only minimal horizontal reinforcement the yield would occur until to crack was long enough to have enough bars to contain the crack growth.

This L10 panel should have additional horizontal reinforcement. The panels above need not. The panels would otherwise be the same. Any chance of a mixup?

RE: Opal Tower - Sydney Australia

3

Quote (epoxybot )

I pieced this photo together from the NZ Stuff video. There is more going on than Agent 666's screen grab shows.

This photo really makes things very interesting.

I believe this photo is taken just inside the balcony at apartment 1005 (level 10). It is the blind side to the image I showed (from the garden side) on an earlier post of mine. It definitely looks like a beam of sorts, but there appears to be two joint locations (possible 2 grouting beds) which would mean this beam may also be pre-cast of sorts(?)



The shear failure in the slab makes sense considering the following sequence of possible events:

1. Local failure occurs at the wall/grout immediately above the supporting columns under which is the point of most significant stress as pointed out by Human909's diagram earlier, which I'll re-produce here (I'm sticking to my theory of in-sufficient grout but for those playing at home who don't like blame to be given to the contractor this could equally be due to under-designed wall thickness or under-specified grout and/or wall grade from the design engineer!!).




2. Once local failure occurs over the support columns, load then wants to transfer itself, via bending, to the upstand beam and slab system (mind you both of which would not have been designed as transfer elements considering their small depth in comparison to apparent applied load).

3. The up-stand beam and slab however can not go into bending because of the significantly stiff wall above, therefore everything is taken out in shear at the critical failure planes some distance away from the internal faces of the support columns below.

4. The upstand and slab system can not take the shear load so they fail, in shear. Local shear failure would then mean that a portion of the level 10 slab at this location is now "hung" from the support wall above.

5. By this time, the wall has failed enough to increase its bearing contact area with critical surface of the up-stand beam, this is either through closing up of grout voids and/or blasting off enough of the base of the wall to be rid of the chamfer you often find at the base of panels to prevent cracking/chipping in transit, thus increasing its contact area.

6. Local failure of the wall means all levels above drop by however much distance the wall/grout crushed. This explains the Hebel destruction at level 10 immediately adjacent and reports of doors sticking in their doorjambs on levels above.


RE: Opal Tower - Sydney Australia

Quote (SheerForceEng)

I believe this photo is taken just inside the balcony at apartment 1005 (level 10). It is the blind side to the image I showed (from the garden side) on an earlier post of mine.
I think you are spot on with the location. In fact your own photo posted earlier gives context.


This is the same position just before they cleaned the area up properly exposed the beam and wall. It looks a fair bit different but note the same angles in the slab cracking.

Also going over some of the other photos. From what I can see they have engaged in floor to ceiling continuous propping in the floors below level 10 along grid line 20. Propping here makes sense but until I started piecing together the available pictures of the props this had been less clear.

I just thought I'd add a few pictures and what I believe is the context.
Floor plans Levels 5-9


I believe this is showing the bedroom 1, in apartment 3 on one of the floors 5-9. They seemed to have smashed through the Hebel wall separating apartment 3 from 4 to install continuous propping along grid line 20.


Bedroom 1, apartment 4, floors 5-9. (facing built in wardrobe and props going through Hebel wall)


Bedroom 1 apartment 4, floors 5-9. (facing window)

RE: Opal Tower - Sydney Australia

Sheer force eng, in the photo the grout bed appears the same thickness on both sides of the crack.

RE: Opal Tower - Sydney Australia

An outsider's view:
1. Will most of the building come down? Or are there ways of saving it?
2. If so, who wants to move in again?
3. This thread will, or has already done so, influence the direction investigations take. Which I think is a good thing. More questions and more views. It will be difficult to leave any stone unturned.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Opal Tower - Sydney Australia

Quote (Skogsgurra)

1. Will most of the building come down? Or are there ways of saving it?
No (very unlikely). But we don't know the exact issue and have no indication of the potential extent. The remediation will be a costly nightmare, but likely less so than the alternatives.

Quote (Skogsgurra)

2. If so, who wants to move in again?
That is the legal battle that is looming. Not just that but the loss of value will be a big battle ground the resale cost has dropped not matter what the fix. And there would be a decent number of owners who are investors or short term owner-occupiers. A class action is openly being discussed and discussions between residents and lawyers is occurring. (Property prices in Sydney have already dropped 10%, some might see this as a way of recouping losses already incurred.)

Quote (Skogsgurra)

3. This thread will, or has already done so, influence the direction investigations take. Which I think is a good thing. More questions and more views. It will be difficult to leave any stone unturned.
No. On the engineering topics, the engineers involved are doing their investigation an have far more information than the tiny peep hole we have. On the legal and political stuff the media is keeping the spotlight on things.

RE: Opal Tower - Sydney Australia

ShearForceEng

A great diagram showing what has happened!

The interesting point is the crack in the lintel beam in vertical indicating a tensile crack. A true shear crack would be on an angle. The drop in the floor is a secondary effect.

The fact that is has tension suggests that the grout and shear connection has not failed. Otherwise the precast beam would just move in.

The fact that there is a single crack rather than spaced smaller cracks suggests it has less than 1% reo or it is not adequately anchored.

RE: Opal Tower - Sydney Australia

We must be looking at different cracks!

RE: Opal Tower - Sydney Australia

2
In the photos pasted by CivilEngAus, assuming its the same location as the photo I posted(?) it looks like some of the concrete has been removed to expose the reinforcement. However to me I'm not sure what I'm looking at, a beam/column/wall, reinforcement that is exposed doesn't appear to be consistent with what I would be expecting for either a beam/column/wall.

Quote (steveh49)

What experience/seniority have the people making these mistakes?

Everyone makes mistakes, from graduates to the most experienced engineers. Some of the most significant issues I've exposed over the years are from graduates, and people with several decades experience, there is no magic number here. It can happen on the smallest and simplest of jobs, or on the most complex and large jobs. In the worst cases I've driven complete redesigns of the structure causing months and months of delays, it's not really very fun being a peer reviewer, no one ever thanks you for discovering all their errors. You cop a lot of flack, but you have to stick to your guns and stand up for what you believe in.

Certainly sometimes there are repeat offenders, both individuals and companies. To some degree its down to the level of internal verification (and experience of those doing this internal review) or the lack of it in most cases. Things taught incorrectly 'on the job' by more experienced engineers tend to be adopted by less experienced engineers without a second thought and passed on further afield. You challenge this and you get the old this is the way we have always done it by some companies, sometimes it can be quite hard to convince people when you are changing cumulative decades of poor or inherited understanding. In the past on occasion I've had to go all the way to those that wrote particular code requirements to get them to personally explain/confirm the requirement to the designer in their own words. Sometimes the answer I hear back from the designer is 'well why didn't they say that in the code'... so code writers with all their collective knowledge could perhaps do a better job communicating the requirements considering some of the readers don't have their background knowledge.

It's interesting how people react to being proved incorrect or challenged on their understanding. For example some people are very receptive, and acknowledge the error once they have that 'lightbulb' moment and interpret what you are saying, others react defensively by producing 50 pages of calculations to refine their analysis to prove that extra bolt I asked for to get it to work for example doesn't in fact need to be added along with throwing you under the bus as being picky/pedentic, etc to all that will listen (Project managers/client/etc). Any delays are mostly due to the original designer getting it wrong, not attributed to the peer reviewer discovering too many errors......

I have more respect for those that listen and take on board what I am saying and make any changes required or respond to the queries to address the root cause, as opposed to those who play the numbers and refuse to accept that they might have made an error.

RE: Opal Tower - Sydney Australia

We have that in the 'lectric, too.

My last case, which is likely going all the way to the court-room, is about "old wisdom" and new reality. The old and common wisdom is that bearing problems occur only in larger electric motors while the new reality is that problems (as a result of energy-efficient motors and frequency inverters with very fast switches) now can be seen in motors from FHP up to tens of megawatts.

I think that the building/structural community sees changes over a somewhat longer time than they happen in the drives area where "revolutions" happen almost every second year. And the gain is not always obvious. Rather the opposite.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Opal Tower - Sydney Australia

From a recent news article (5th January), hopefully some more info/answers are coming.

Quote:

Professors Hoffman and Carter expect to release a more comprehensive update by the end of next week.

RE: Opal Tower - Sydney Australia

Quote (Agent666)

From a recent news article (5th January), hopefully some more info/answers are coming.
I won't hold my breath but I will be keeping an eye out.

I would be quite surprised if a "comprehensive" report was at all publically available, let alone at the end of next week. My reasons are due to my cynical nature regarding the transparency of Australia's building industry and the fact that this independent investigation is a couple of academics hastily employed for political reasons as much as investigatory reasons. (I have no reason to question the competency of the independent investigators, but the suggestion that a comprehensive report can be completed in a couple of weeks seems a little ambitious.)


Meanwhile the media is still having a field day on this topic. Residents are complaining about having their apartments ripped apart and their belongs pile in corners. Which is perfectly acceptable giving the structural concerns. However the optics are terrible. First it was evacuation. Then it was safe. Then it was evacuation again for a 'short period'. At every stage those running the show (Ecove, Icon) have been at pains to talk down the issues. But that has made things worse. If they had been upfront then they could have readily given residents the opportunity to remove their personal possessions themselves and avoided all this.

Here is hoping all this mess is a big wake up call to the industry. Going back to a post from 2 weeks ago.

Quote (hokie66)

The Australian newspaper has reported that the NSW government will conduct an inquiry into the problem with this building. Based on many government inquiries in Australia, this could expand to be bigger than Ben Hur. Maybe that is a good thing.
I agree. Though I'd hope for something federally led rather than state led. And given the lame duck nature of the current NSW government I wouldn't hold my breath from action from them.

RE: Opal Tower - Sydney Australia

"Lame duck" would seem to be a good description for the federal government as well. And with union controlled Labor governments, it won't be just holding your breath, you will have to hold your nose.

RE: Opal Tower - Sydney Australia

There was a statement that came thru on Linkenin yesterday:

Quote (LinkedIn Members)

Bonacci wish to highlight that the Sydney Morning Herald have incorrectly identified us as the structural engineer for Opal Tower at Sydney Olympic Park. The SMH has since published a retraction. Bonacci did not design or certify the structure of Opal Tower.

Our thoughts go out to the residents and all those involved over this difficult time and hope for a speedy resolution.

RE: Opal Tower - Sydney Australia

Here's a list of units which have had propping and inspections.



An image of unit 1005 without the room number blanked out.



RE: Opal Tower - Sydney Australia

If someone has time to highlight on the arch plans where the propping (and inspections) are, it might offer some insight if the propping is local to the areas previously highlighted, or if there is concerns in other areas that might have similar detailing to the area that is known to have failed?

RE: Opal Tower - Sydney Australia

I think the speculation in this thread could be better focused if we had some structural drawings to digest. From what I have seen, there is not even a good description available of the structural system.

RE: Opal Tower - Sydney Australia

Totally agree, with some drawings
we'll know a whole lot more. Hopefully some drawings will be included with the initial report that's been promised. Though if there has been construction changes due to the design/build nature of the contract there might not be a good record of what was built!

RE: Opal Tower - Sydney Australia

Pretty doubtful that the structural engineering drawings will be made available.

I have heard that even the engineers investigating are having difficulties getting the drawings from the builder and the consulting engineer.

RE: Opal Tower - Sydney Australia

A pity. This is in stark contrast to the situation with the recent pedestrian bridge collapse in Miami. Perhaps the designer and builder would rather hear wild speculation than learned opinion.

RE: Opal Tower - Sydney Australia

The difference between this and the Miami bridge though is that the bridge drawings were made public prior to the collapse, so they were already in the public space.

No engineer in Australia would like their drawings made available to the public, particularly after a collapse!

RE: Opal Tower - Sydney Australia

Agent666 here's the approximate location of propping in unit 301 and 302.

101,102 and 201,202 were also propped so I would assume they also follow grid line 15.


The partition wall between units 301 and 302 has been removed between B1.


Approximate prop location marked in red along grid line 15, same plans floors 1-3. The giprock along grid line 13 has been removed on the inside of 301.


Level 4 plan showing the approximate location of propping in unit 301 and 302 along grid line 15.

https://www.heraldsun.com.au/news/national/damaged...
Link to video of room 301.

Thanks goes to the member of another forum.

RE: Opal Tower - Sydney Australia

StructEng23,
Understood. But there is now a governmentally funded investigation, so the drawings will eventually become public. There is no point in delaying the inevitable.

RE: Opal Tower - Sydney Australia

We will have to wait and see on this promised report. But neither of the two professors who have been appointed by the NSW government to investigate are practicing structural engineers. One is a geotechnical engineer, the other I think mostly a materials specialist. Hopefully, they have help with understanding this apparently complex structure.

RE: Opal Tower - Sydney Australia

Professor Mark Hoffmann is the Dean of Engineering at the University of New South wales, and his areas of specific expertise are listed as including:
Structural integrity; fracture and failure analysis; ... ; structural modelling and life prediction ...
https://research.unsw.edu.au/people/professor-mark...
http://www.materials.unsw.edu.au/profile/mark-hoff...

Emeritus Professor John Carter is a geotechnical expert at the University of Newcastle https://www.newcastle.edu.au/profile/john-carter , and I suspect he was nominated to confirm whether there are any foundation / settlement issues which might have contributed to the damage; it may well be that the foundations are indeed perfectly sound, in which case, his role may be limited.

I wouldn't expect these two experts to tackle the investigation unaided - they will have ready access to the resources of their respective University Engineering faculties, and I would hope the Government will allow them to access other professionals and expert opinions as their investigations unfold.
I wouldn't expect a comprehensive report to be issued for several months.

http://julianh72.blogspot.com

RE: Opal Tower - Sydney Australia

Agreed.

RE: Opal Tower - Sydney Australia

Jhardy1

Most of whom are away on holidays for the Summer break!

RE: Opal Tower - Sydney Australia

@rapt:
"Most of whom are away on holidays for the Summer break!"
Hence:
"I wouldn't expect a comprehensive report to be issued for several months."

http://julianh72.blogspot.com

RE: Opal Tower - Sydney Australia

It does surprise/concern me that the chaps looking independently into it are not themselves structural engineers by trade. Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree. I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.

Something I picked up from the inspection and propping letter is that they are obviously looking at levels 15/16 & 25/26 as well and apartments all over the floor plate, presumably where there are similar details to that which has allegedly failed. I'd imagine any proposed fix/repairs would be to all similar locations unless the failed location had something else going on. Even if not strictly required the owners might demand it, hopefully those responsible do a good job to reassure the public that its safe again (typically if in cover your arse mode I'd imagine you are trying to do the least possible to bring it back to standard so you can say after some investigation that there was never an issue, no one was ever in danger, etc).

It's interesting sometimes the opposing views from different sides of the fence. Some will want the world while others are trying to get by on the minimum.

RE: Opal Tower - Sydney Australia

What I'd like to know is why there are no columns on L1-L3 and L10-L15 at grid line 20, above the point of failure. Why would the builder/designer unnecessarily load the slabs on L1 and L10. What's different/special.

Every other garden location where you have prefab panels installed at grid lines 1-2,5-6,8-9,12-13,15-16,19 from L1-L35 there are columns, you can clearly see them in photos of the building.

I know the panels are/should be okay to carry the load as stated earlier in the thread.

I apologise in advance for my lack of understanding. Cheers David

RE: Opal Tower - Sydney Australia

Quote (Agent666)

It does surprise/concern me that the chaps looking independently into it are not themselves structural engineers by trade.Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree.
Politicians wanting to be SEEN to be doing something.

The conversation probably went something like this:
"The media is having a field day and fingers are being pointed! Which department is in charge of investigating this stuff?"
"Nobody Mam. The private sector does it. We also privatised the building certification system decades ago."
"Well, we need an independent review! Who do we have who knows about this stuff but isn't in the private sector."
"Um.. Maybe try a University.


Quote (Agent666)

I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.
Exactly. I will give these guys the benefit of the doubt. They should be able to impartially analyse the situation and engage appropriate resources.

Quote (Agent666)

(typically if in cover your arse mode I'd imagine you are trying to do the least possible to bring it back to standard so you can say after some investigation that there was never an issue, no one was ever in danger, etc).
Which seems to have been the reactions from the developer and the builder from the very beginning. Sure the builder (Icon) did rapidly accept responsibility, however the public statements have always been on the optimistic end of the spectrum giving residents and the public much more hope for a quick resolution than was likely.

RE: Opal Tower - Sydney Australia

(OP)

Quote (Agent666)

Judging them by the cover I would imagine the average geotech professor potentially doesn't know the first thing about structural design, structural codes, current best practice, etc. A materials professor would be in the same camp to a lesser/same degree. I await their initial report, and I hope they are drawing on the experience of the structural forensics community where required.

In one of the media videos of the engineers leaving Opal Tower there was a very well respected concrete structural engineering professor amongst the group and who is presumably helping with the investigation.

RE: Opal Tower - Sydney Australia

CivilEngAus

Can you name the professor, or what university or forward a link to the video for us to see who you are talking of.

Interested to find out who is involved.

RE: Opal Tower - Sydney Australia

As per media reports the majority of residents have been advised by the builder that they can move back in this weekend. Not that I see that this is much of a development. It is just an indication that they do not anticipate any further risk or deterioration. Given the building is paying accommodation and other expenses for around 392 apartments residents it is obviously in their interest to give the all clear ASAP.

Meanwhile, there is conflicting commentary about the independent report that was reported to be made available today (an unrealistic expectation). Unsurprisingly it is not finalised, the state government has also said it needs time to digest the report.

For those wanting to read about some of the broader issues facing the industry here is a decent media summary:
https://www.theguardian.com/australia-news/2019/ja...

RE: Opal Tower - Sydney Australia

I thought this website was about engineering, something normally based on facts and science.

Not conspiracy theories based on press reports by people who have no idea what they are talking about, guesses as to how a building is behaving without any knowledge of the structure or the design and complaints about reports and timelines for presentation of reports and those reporting even before the reports are finalised.

RE: Opal Tower - Sydney Australia

I don't know any engineer or company that would say any structure is 100% safe, especially one that's undergone a previous failure and with the reported doubt over what seems to have been designed/constructed. Those types of broad statements can easily be turned against you, by others or by nature taking its course and working its wonders. It complies with code, or it doesn't, that's all I'd be reporting on as this is the minimum benchmark that needs to be achieved.

David256, the architectural drawing that have been posted are not representative of the final structure based on what a lot of people have observed, guessing they are quite preliminary and lack coordination with the final structural scheme. So basically cannot be relied on for delving into the structural behaviour.



RE: Opal Tower - Sydney Australia

(OP)

Quote (StructEng23)

CivilEngAus

Can you name the professor, or what university or forward a link to the video for us to see who you are talking of.

Interested to find out who is involved.

I intentionally did not name them given that the media could potentially see them as another person to hassle for comment :)

Seven News 31/12/18

There is a copy of the video here; around 10 to 15 seconds in: https://www.instagram.com/p/BsDAo-qFoBs/?utm_sourc...

RE: Opal Tower - Sydney Australia

The news reports mentioned “remediation” and “stabilisation” works that were scheduled to be completed last Friday.
This suggests works to the structure, which is why they have all the heavy duty props, while those are carried out.

This is speculation- but perhaps they need the 4-6 weeks for the any new structural concrete elements to cure before removing the props and then start the fit out works.

If they were otherwise giving the all clear without structural works, and the props were truly redundant as purported in the press releases, shouldn’t they first monitor the building’s performance prop-less? Eg To see if there is further movement prior to fitout works commencing.

RE: Opal Tower - Sydney Australia

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?

RE: Opal Tower - Sydney Australia

Based on my vaguely informed opinion:

Quote (mangotree)

The news reports mentioned “remediation” and “stabilisation” works that were scheduled to be completed last Friday.
This suggests works to the structure, which is why they have all the heavy duty props, while those are carried out.

This is speculation- but perhaps they need the 4-6 weeks for the any new structural concrete elements to cure before removing the props and then start the fit out works.
It is very unlikely that proper remediation has even begun. At this stage works have likely been about stabilisation and investigation. It is quite unlikely that there have been any "new concrete elements"

Quote (mangotree)

If they were otherwise giving the all clear without structural works, and the props were truly redundant as purported in the press releases, shouldn’t they first monitor the building’s performance prop-less? Eg To see if there is further movement prior to fitout works commencing.
You don't install props if you think they are completely unnecessary. Statements made to that effect are about PR rather than engineering. Forget the PR. The building has had structural failure. Floors have sagged. This hasn't changed and this still needs to be addressed.

Quote (georgeeverghese)

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?
Quite unlikely. And I would call it a 'disaster' a bit extreme.

RE: Opal Tower - Sydney Australia

Quote (georgeverghese)

The Olympic Park underground line linking Lidcombe to the nearby Olympic Park station seems to pass very close or right underneath this Opal Tower - could this have something to do with this engineering /construction disaster?

Yeah some of the workers might have arrived on site via the train, perhaps even the designer took the train to the site... ponder maybe the report will cover this aspect.

The experts have already publicly noted that they didn't find any issues with the foundations about a week or so ago. Presumably based on this fact the designers accounted for the presence of the train station appropriately. Issues appear to be concentrated in the superstructure based on where the failure occurred and where the destructive investigations were noted as being undertaken in the letter posted above.

RE: Opal Tower - Sydney Australia

SBS World News managed to obtain Cardno’s letter to the owners, explaining their current professional opinion.
https://www.sbs.com.au/news/opal-tower-body-corpor...

The text was a bit blurry from the video, so I’ve typed out what I could make out.

Quote (Source: SBS World News, Cardno's Letter dated 11th Jan 2019)


11th January 2019
Dear Owners,

RE: OPAL TOWER

Before residents can return to the Opal Tower, the structural adequacy of the building should be confirmed in a totally unqualified manner by WSP that acknowledges the damage that has occurred to the structure, the temporary propping that has been installed to help prevent further damage, and the stabilisation works currently underway to reduce stresses in critical regions.

Before Cardno is in a position to even recommend that the building can be reoccupied in part, the Stage A stabilisation works must be fully completed and the investigations to:
a) Confirm concrete strengths in the damaged regions must be completed.

b) The investigation works to confirm finding of the non-compliant reinforcing in the precast on Level 10 and that suffered significant spalling is a one-off occurrence as opposed to a systemic problem must be completed.
Because of the considerable disruption that the completion of the major remedial works will cause to residents who may choose to return, Cardno is reluctant to recommend that residents return at an early stage.

Regards,
D. R. McMillan
Cardno

RE: Opal Tower - Sydney Australia

Thanks mangotree, an interesting and reserved letter from Cardno.

Having thought a lot about this failure, I would like to pose a question to the thread: what was different on 24 December from 23 December or earlier?

The building was completed in August, the elements in question at Level 10 were installed months before this, and the majority of the load they carry was in place when the structural works topped out, which would have been long before August. Some live load was added as residents moved in after August. Inadequate structural elements are likely to exhibit some form of distress during the construction phase when the concrete strength is lowest. Internal to the unit this would have been concealed by finishes, but the external face of the panel was always exposed.

It is unclear from the available information whether the failed element contributed to the lateral load resisting system. The wall appears stiff enough to pick up some lateral load, whether it was intended to do so or not, but the 24 December was not a 'windy' day and Sydney had experienced a significant storm on 20 December. So what changed on 24/12 to initiate failure?

Perhaps ongoing creep, shrinkage or deflection growth contributed, but for that to be a factor the element must have been particularly sensitive to such effects.

Cardno's letter mentions 'non-compliant reinforcing in the precast'. It seems unclear whether the precast panel was acting as a simple vertical load-bearing element, with a bearing failure mode per Human909's analysis, or a deep beam performing a transfer, in which case it looks more like a failure at the nodes anchoring a tension tie.

While we wait for formal comment from those conducting the investigation, I would welcome any thoughts on what changed on 24/12 to make the failure occur in seemingly benign circumstances.

RE: Opal Tower - Sydney Australia

Quote:

The investigation works to confirm finding of the non-compliant reinforcing in the precast on Level 10 and that suffered significant spalling is a one-off occurrence as opposed to a systemic problem must be completed.
Well that is the first indication of a primary cause of this failure.

Quote (tornear)

Cardno's letter mentions 'non-compliant reinforcing in the precast'. It seems unclear whether the precast panel was acting as a simple vertical load-bearing element, with a bearing failure mode per Human909's analysis, or a deep beam performing a transfer, in which case it looks more like a failure at the nodes anchoring a tension tie.
Considering it as a vertical load bearing element or a deep beam is just modelling simplifications. Regardless it doesn't change the bearing stress concentrations. Those stress concentrations are pretty unavoidable. But that doesn't mean it is bad or they are the issue. As far as a tension tie in a beam model goes, the beam is so deep the tension in the bottom flange is quite low. (the same rough and dirty FEA shows this) Compressive stress at the supports and shear stress next to them are both very high as you would expect. Both would need appropriate reinforcement detailing.

RE: Opal Tower - Sydney Australia

Tornear, what was different on december 24 was the stresses reached the failure point!

I suspect it was shriankge/creep/temperature/deflection etc. those cracks often take a while to appear.

RE: Opal Tower - Sydney Australia

A couple of snippets from the report being circulated:
https://www.news.com.au/finance/business/opal-towe...
https://www.theaustralian.com.au/national-affairs/...

"As an interim report into the cracking of concrete panels that triggered two evacuations of the building is expected to be released, investigators disagree as to whether the grade of reinforced concrete used in the support beams was strong enough to withstand the pressure of precast concrete panels installed on top of them.

Several sources close to the ­investigation have told The Australian that one theory is that the beams lacked sufficient strength, causing pressure on the concrete panels, which cracked and sparked the evacuations."


"But another theory is that grouting between the precast panels and the beams contributed to the cracking in the panels."

"Investigators’ reports handed to Planning Minister Anthony Roberts last week appear to have found the builder, Icon Co, ­appeared to have built Opal Tower according to the specifications it was provided with."

The last comment if accurate seems to point towards design issues. There might be reliable information available later today if the report is publicly released.

RE: Opal Tower - Sydney Australia

Another one

https://www.abc.net.au/news/2019-01-15/opal-tower-...

"We can confirm that, while the building is structurally sound, significant rectification works are required to repair and strengthen damaged hob beams and in some cases the panels that rest on them," they said in a statement.

The trio said while the "probable cause" was narrowed down to "localised structural design and construction issues", more information was needed to make a conclusion.

RE: Opal Tower - Sydney Australia

haha, sometimes you wonder if these things are proof read before going out...

Maybe its a problem with the PDF (I did try opening in adobe and bluebeam with the same result) or maybe its true, I suspect 'poor' was what they were after........ rather unfortunate potentially depending on what concrete tests throw up.





RE: Opal Tower - Sydney Australia

My first thought regarding the areas above the columns where the bearing failure/confinement failure has occurred:-

This hob beam is essentially a thin upstand wall, and as such there is zero confining reinforcement in the area directly above the column where the load is being dumped. (ties across the section would be expected in NZ, not sure in Australia what the requirement is, but gravity is the same). Very poor detailing for the transfer of loads into the columns.

The bit of the hob beam between the column is essentially not needed to carry the gravity loads, the bits over the columns below that are doing the work are required to act as columns, detailing it as a beam seems to be a fundamental error in appreciating how the loads are transferring form the panel above into the column below.

While there are dowels linking the hob beam to the column, seems to be very little reinforcement linking the hob beam to the column, guessing there will be tension/uplift here and a few stirrups seem to extend into the column but nothing more, you are presumable transferring a large force into a thin wall with no confinement. Dowels seem to have the hook/cog(?) turning at top of column into the slab so not tied/linked into the column (I'd expect to see some reasonable vertical reinforcement with horizontal confining links/stirrups extending down into the columns to lap with the column reinforcement, similarly in the bottom of the panel until the loads are spread out into the full wall width).

Plastic ducts seem like a poor detail, in NZ corrugated metal ducts are required. How is the bond or shear supposed to transfer through the soft plastic.

All in all the detailing observed in the photos seems quite poor based on my understanding of how they were using the walls as gravity walls, the report tends to read that the design was the first issue but is pretty light on details regarding this aspect. But still sounds like they are waiting for further information to flesh this aspect out.

RE: Opal Tower - Sydney Australia

Quote (Agent666)

haha, sometimes you wonder if these things are proof read before going out...
Yep. I noticed the same thing. Quite hilarious.

The report doesn't say too much in my brief perusing. I would really like to know the original design methodology. The need for the beam isn't obvious to me due to the stiffness of the wall. I'm surprised there hasn't been much comment on this. The beam doesn't seem to have failed as a 'beam' (from resisting moment), it seems to have failed due to bearing compression and shear. Can anybody shed some light on this?

To my mind there doesn't seem to be much sense in using a 500mm deep 'beam' as a 'beam' underneath a panel that is ~18m deep!

EDIT:

Quote (Agent666)

The bit of the hob beam between the column is essentially not needed to carry the gravity loads, the bits over the columns below that are doing the work are required to act as columns, detailing it as a beam seems to be a fundamental error in appreciating how the loads are transferring form the panel above into the column below.
Exactly what I am thinking. It seems to me they were assuming uniformly distributed load from the wall.

RE: Opal Tower - Sydney Australia

The report seems to be full of those spelling mistakes. But they got poor right once.
For a German reader, the Grandpa Tower (Opa Tower) doesn't make things easier to understand. Grandpa and turds. What happened?




Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Opal Tower - Sydney Australia

This

In-adequate tensile capacity in the horizontal direction in the bottom region of Panel A that rests on the hob beam spanning columns C21 and C38.

There is compelling evidence indicating that the wrong size reinforcing bars were placed in this area during manufacture of this particular panel  – 20 mm  diameter bars were used instead of 28 mm diameter bars (see  Figure8).

So :

It was either incorrectly manufactured or the wrong panel was used during construction or there should be columns C21 on L1-L3 and L10-L15 above and below unit 1005 and the initial failure point.

RE: Opal Tower - Sydney Australia

Human909 I suspect the upstand wall/hob beam is there due to the presence of the garden. Putting the joint lower would be a waterproofing issue. Yes agree the failure is via a compression mechanism vs bending mechanism.

Regarding the potentially wrong size horizontal bars, the way they phrase it, it sounds like these were a horizontal tie for carrying gravity load at base of the panel. I'm sure alternative strut and tie models could show this was adequate by using horizontal reinforcement further up the panel, really depends how it was designed in the first place I guess. Didn't sound like they were worried about the shear capacity (even 20 diameter bars would be unlikely for shear reinforcement typically).

RE: Opal Tower - Sydney Australia

A couple of things about the report of the three professors struck me. The first is their recommendation in several places in the report that the WSP design, both original and for rectification, should be "checked by an independent qualified structural engineering organisation". I assume by that the professors are not going to do that job.

We still haven't seen any structural drawings, including details of how the floor slabs, hob beams, precast walls, and cast in place columns interact. The report states that the professors have reviewed the design, but doesn't state to what detail.

Notwithstanding incomplete grouting issues, I am skeptical about the failures being primarily of a bearing/compression nature. Shortening of the floor slabs, shrinkage and post-tensioning induced, would be an issue I would want investigated, as the resulting restraint stress could well lead to some of the spalling which is shown in the photos.

RE: Opal Tower - Sydney Australia

So all the columns under align with the wall over?

RE: Opal Tower - Sydney Australia

Hokie66, I'd expect if it was predominantly due to the slab shrinkage (etc) that the damage would possibly be more localised at slab level and/or more cracking in the slabs? I have no doubt that it could contribute, but there didn't seem to be any slab damage at many locations, just wall damage including cracks going further up the walls. It could be that there was more slab damage, but on the basis of the pixelated photos its a bit hard to tell too much detail!

I guess at this stage we have more info (basically the photos, report didn't say too much apart from the reference/inference that the failure seems to stem from design issues). But as I see it we still don't have any concrete conclusions from the authors as I read it. I really hope the final report goes into a bit more technical detail, outlining loads, capacity, etc.

Regarding the "checked by an independent engineer" bit, checking the design is not part of their scope based on the outline in the report of the scope as I read it to.

Definitely it should be checked, but not only the remedial work, the whole thing should be checked and anything additional thats found should be addressed. During my peer review work often uncovering reasonably serious issues/omissions, I can tell you sometimes it didn't give you a lot of confidence that the people or persons that were capable of making these errors were the ones who basically had to determine and design the remedial design (at least in many situations you can lead them by the nose to something you could accept that would comply). Also, where there is one mistake, dig a little deeper and you often uncover more issues!

Interestingly on WSP's website they have been saying its been deemed structurally sound since 1st January, at least someone has confidence in their own design. Link

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

So all the columns under align with the wall over?

Seems so based on the plans that are marked up.

Wonder if there is any damage at the tops of the walls, as presumably a new column springs off the thin wall again at the top (sort of the upside down detail of the details that have failed)?

RE: Opal Tower - Sydney Australia

One thing I’ve been wondering - how would the slabs have been designed? Would it have been given to a D+C PT contractor?

RE: Opal Tower - Sydney Australia

One question I still have and maybe it is a silly one.. Is there a second grout layer as pointed out by SheerForceEng? Certainly the description and the photos of the form-work indicate that there wouldn't be... Likewise with the commentary in the interim report. And it would be an odd detail.

But like I've said, I'm not really a concrete guy...

SheerForceEng's markedup photo:

RE: Opal Tower - Sydney Australia

Quote (Tomfh)

One thing I’ve been wondering - how would the slabs have been designed? Would it have been given to a D+C PT contractor?

Yes, by APS, as stated on page 3 of the Interim Report:

Quote (Interim Report)

The design of the post-tensioned concrete floors was carried out by Australasian Prestressing Services (APS).

RE: Opal Tower - Sydney Australia

I saw no evidence for the second grout bed.

RE: Opal Tower - Sydney Australia

Ingenuity, thanks.

That’ll be a very nasty fight.

RE: Opal Tower - Sydney Australia

Hokie66, this article has a previously unseen picture of a floor crack in what looks like a carpark level. Not sure where it is, and they call them up as panel cracks so who knows, media can't tell if a wall is a floor and vice versa.



Looks like a fairly wide crack if its a suspended slab.

RE: Opal Tower - Sydney Australia

It looks like a number of restraint shrinkage cracks I have seen in post-tensioned slabs without adequate crack control reinforcement.

RE: Opal Tower - Sydney Australia

Looks like a slab on grade to me with a badly detailed expansion joint. Looks like joints in both directions meeting at one corner of the column. Above the column, the crack follows the joint perfectly. Below it wanders off by 50mm or so.

RE: Opal Tower - Sydney Australia

Yes it looks like slab on grade. I’ve seen that a few times where the crack wanders off.

I’m not sure it’s a correct photo.

RE: Opal Tower - Sydney Australia

@Tomfh:
"I’m not sure it’s a correct photo."

The Unisearch report https://www.planning.nsw.gov.au/-/media/Files/DPE/... mentions "These activities have focused on various structural elements in sections of the building located on Levels 3, 4, 9, 10, 16 and 26, as well as the basement level B3", but there is no further discussion or photographs of the damage observed in basement B3. (Basement B3 is the bottom basement level, so it is very likely that this slab is constructed as a "slab on grade".)

I would assume they saw the floor slab crack shown in this photograph, and concluded that it was "minor damage" only, and not associated with the "major" structural issues in the upper floors.

http://julianh72.blogspot.com

RE: Opal Tower - Sydney Australia

Yes, after looking again, I agree it is a slab on grade. But the crack does indicate poor attention to detail, which may be an indicator of the problems in the structure.

RE: Opal Tower - Sydney Australia

Agree, this is likely a pavement slab on grade at B3, Probably 120-140 thick with a light top mesh and saw cut control joints. The joint running north/south in image may be a pour break/expansion joint (concrete texture looks to differ. Suspect joint dowels may have bound up and no debond agent applied to slab face prior to second pour, or bonded to column footing below. Completely irrelevant in context. Media are funny.

RE: Opal Tower - Sydney Australia

My thought is as to how much care was taken in ensuring that the tensile horizontal reinforcement in the bottom of the panel was anchored and developed within and past the critical nodal zone directly above the column. The columns look to be very close to the end of the walls. A 180 panel is very slim to be detailing 2 layers of N28 rebar at 100 c/c, particularly with the central dowel tubes (probably 70 dia). The bars should be developed past the outer face of the CCT node. Cog anchorages for an N28 are very long, and likely would not fit within cover, and these only give 50% bar development anyway. There would have been severe congestion in this panel, which makes me think the N20's were intentionally substituted as N28s with cogs would not fit.

RE: Opal Tower - Sydney Australia

Also in the report photos, you can clearly see that the starter dowels for the panel in the critical column zone are not developed/cast into the column below. They are cogged into the 200 slab A flimsy attempt at a compression splice has been attemped by using 180 degree hook bars from the top of the insitu hob into the column, however I doubt this is effective in carrying much compression and and alleviating the unconfined compressive stress in the upstand concrete. And no transverse confinement reo within the upstand itself. All of this combined with the poor grouting, there goes the factor of safety.

RE: Opal Tower - Sydney Australia

You cannot develop any compression using a hook/cog. The only development you get is the straight bit before the bend.

RE: Opal Tower - Sydney Australia

And you probably get no transfer of bond stresses in the straight portion if the dowels are embedded into plastic ducts above the hob beam. Any tension/compression would just deform the plastic, so it stands to reason all of the axial load is potentially bearing through the concrete with lmited contributions from the dowels (as a reinforced member) if they cannot be developed above the base of the panel. Can someone comment if these plastic ducts are deemed acceptable practice in Australia?

RE: Opal Tower - Sydney Australia

Agent666,
Yes, I see plastic grout ducts commonly used in my local
Google "anchorage requirements for grouted vertical-duct connectors..." and you should find a report by FJ Brenes et al. Chapter 8 discusses embedment length issues.

Toby

RE: Opal Tower - Sydney Australia

Thanks Toby43, from that report it states "...galvanized steel ducts were able to resist tensile stresses 25 to 35% higher than those with plastic ducts". So if you are after full development as often required by codes it would seem to me that plastic ducts have no place in the type of detail connecting the panel to the hob wall?

RE: Opal Tower - Sydney Australia

Agent666,
Yes - required embedment lengths for plastic are typically 30% larger than for metal ducts. Whether the geometry was there for this particular detail at Opal, I don't know.


RE: Opal Tower - Sydney Australia

For anyone that's interested Icon have created a blog for communications with residents. Link

RE: Opal Tower - Sydney Australia

Video of a new crack in one of the apartments, tenant returned to pick-up their belongings and move out.

https://vimeo.com/312421160

RE: Opal Tower - Sydney Australia

How can they tell it’s new?

RE: Opal Tower - Sydney Australia

Because they didn't look for it two weeks ago obviously....


I once had a colleague go out and do an insurance inspection for a person who was claiming their driveway was cracked due to a recent very mild earthquake that had occurred a few days earlier. They had never noticed the crack before, but it had grass growing out of it.... claim denied.

I've even found in my own house I noticed a lot more cracks after an earthquake, but only because I'd probably never noticed them previously because I never looked in great detail.


In fact one of the report photos shows the same location of the propping and the exact same crack (right at the beginning of the video). So the crack was probably there 2 weeks ago on the balance of probabilities. More uninformed people influencing the internet/media I say than a valid claim to new damage.

RE: Opal Tower - Sydney Australia

Agent666, I think you're right the person who took the video was in unit 301 and looking at the interim report it says floor between L3-L4.

Edit : Just had a look at earlier photo's and video of her apartment, they have definitely cut a much larger hole in the ceiling plasterboard since she was in there on the 3rd of January, maybe 1-2 meters larger down past the air-conditioner, where the earlier photos show the cutting stopped before the air conditioning.

RE: Opal Tower - Sydney Australia

the only sure things in life are death, taxes, and concrete cracking. all concrete cracks are not created equal. Many are fine. This is why we have an entire technical field of concrete crack control.

RE: Opal Tower - Sydney Australia

Just on the crack in the video posted by david256, that crack is clearly pictured in the interim report on page 16 in figure 11. Figure 11 only shows around the props but it is the same crack and doesn't appear to have changed since the photo in the report was taken (when compared to the video) and I doubt that it was taken last minute before the report was issued. In other words it would have been there 2 weeks ago.

RE: Opal Tower - Sydney Australia

MDEAus, here's an earlier photo of her apartment, you can't see the crack but you can see in the video how they have cut a larger hole in the ceiling plasterboard following the crack.



She probably didn't even notice the crack on the 3rd, she was probably in shock.

RE: Opal Tower - Sydney Australia

"The Urban Developer" website has an article by Ted Tabet dated 21st January 2019 that seems to have a new photo of cracks on the upstand beam.
It doesn't state what area or level this photo was taken at.



Here's the link to the article:-

https://theurbandeveloper.com/articles/opal-tower-...

RE: Opal Tower - Sydney Australia

mangotree

Quote (Opal tower investigation interim report)

Figure 10. Photographs of the damaged hob beam on Level 4 near column C34
before (top) and after (bottom) cracked concrete removed

That is not a new photo. It appears in the interim report as part of figure 10(likely where it was taken from; it's even linked in the article).

RE: Opal Tower - Sydney Australia

Yes, you're right MDEAus. That photo is in the interim report.
Thanks for that.

RE: Opal Tower - Sydney Australia

Statement from WSP regarding the repairs and reoccupancy. Link

This suggests they are concentrating only on strengthening/repairing 3 wall locations on each of levels 4, 10 & 16.

RE: Opal Tower - Sydney Australia

Interesting, that looks like a simple surface patch to replace the spalling concrete. Wonder how they strengthened it, and/or addressed the underlying design issues.

I was in all honesty imagining something completely different would be required if they were addressing what I'd see as the obvious issue/deficiency in the original detailing based on the observed damage. An apparent surface patch hardly addresses the apparent lack of confinement. Obviously no one has officially said what they think the apparent design errors were, so hard to say if this type of repair would address the underlying design and construction issues.

RE: Opal Tower - Sydney Australia

Agent666, yes it's definitely confusing especially considering the level of damage we've seen in photo's and videos.

RE: Opal Tower - Sydney Australia

If they’re building a new wall to bypass the hob junction wouldn’t they not bother strenghthening the cracked hob?

RE: Opal Tower - Sydney Australia

Have they used some kind of structural epoxy adhesive injected into the cracks?

I wonder what they found about the reo in all the other panels. Apparently there’s a “concrete scanning” service that uses ground penetrating radar (GPR) technology to locate reinforcement. Not sure whether the equipment can size them or not.

RE: Opal Tower - Sydney Australia

mango tree, it definitely looks like an epoxy it would be interesting to know if they are using it to strengthen or repair the panels. And it'd good to know what they're doing on the other side of the panelled wall. Hopefully we'll see more on Sunday night.

Took some screen captures of the 60 minute video, you can see the other side of the hob beam and you can see they have repaired a slab crack with something again looks like an epoxy.

https://imgur.com/a/vgcAnsV













RE: Opal Tower - Sydney Australia

Injecting all those cracks is not getting to the root cause of the distress. If the problem is with inadequate reinforcement, they are just pushing water uphill. Will be interesting to see further reports.

RE: Opal Tower - Sydney Australia

Yeah, it looks like they're just repairing the cracks, I was expecting some kind of permanent column supports would be installed on the inside of the panel wall, taking some load off the wall and hob beam.

RE: Opal Tower - Sydney Australia

These superficial repairs could just be part of the preliminary stabilising works vs being part of the final remedial to address any shortfalls in design or construction. Though its finished off so nicely at the base that it seems like that's it for the outside at the bottom apart from reinstating the waterproofing.

I would have thought that their would have been some further comments by the university professors by now if they are getting into the repairs, as the public still has no idea what the design issues are, that they are being effectively handled, etc. Yet a considerable portion of the tower has been opened up for reoccupancy based on WSP/Icon/Cardno agreement.


For those of us outside Australia, please post back on the 60 minutes programme content. Any idea if they stream it?

RE: Opal Tower - Sydney Australia

I thought they are casting a new wall inside to bypass the defective hob/grout junction?

RE: Opal Tower - Sydney Australia

Agent666,

I know we live in the information age (much of it mis-information) but I cannot understand why you would think they will give a running commentary on the whole project!

RE: Opal Tower - Sydney Australia

I can totally understand why the developer, builder and engineer wants to keep it quiet but do they have an obligation to explain more when there is such public interest and the entire industry is being brought into disrepute

RE: Opal Tower - Sydney Australia

Hi Rapt
That's not exactly what I meant but I can see it was a bad choice of words on my part. I thought their mandate was to produce a public report on cause and comment on proposed repairs (items 1 & 2 of their scope). These repairs seem to be underway of course, and one recommendation was that the design of any repairs was peer reviewed by independent and qualified engineers, which I assume and hope someone is at least doing.

I have not seen anything at all about this, but if I were a PR guy for the designer or contractor I'd be outlining to the residents that someone is at least doing this to alleviate their concerns. Otherwise its the guys who made the mistake fixing the mistake, and well that doesn't fill me with a whole lot of warm fuzzies to be honest based on my own experiences.

The professors issued an interim report, but it basically said nothing technical apart from raising more questions to a curious engineer reading it with a view to finding out what the root causes were.

As others have said, the explanation that seems to come out of the interim report is the suggestion that people moving in caused the overload resulting the damage and failures observed. I find it interesting that something that clearly had capacity issues, with possibly less than normal serviceability loads can have some propping added and the people involved are saying its all structurally sound and no worries so people can move back in while repairs are being undertaken (maybe they are advising they don't take their furniture back, just in case!...ponder).

I have a hard time believing that there are not more design issues throughout the structure than the areas that failed, but I'm a cynic. Too many years of doing peer reviews to know where there's one mistake, that there are generally more if you go looking.

I honestly have no idea what if any involvement the professors still have, but what I really meant was I would have thought they still owe a final report at some point that actually fully addresses the scope they were asked to report on, being:-

Quote (interim report scope)

1. - determine the basis of the failure, what happened and how?
2. - The immediate steps that need to occur to ensure the safety of the building for its occupants

I find it interesting on a personal level as this type of thing simply isn't supposed to happen in a country like Australia given all the checks and balances and modern codes and building practices that are in place. Like degenn notes, it reflects poorly on the industry as a whole and the media/politicians at least have certainly tried to turned it into a witch hunt on the whole construction industry in AU.

I am almost certain if this was a structure I was peer reviewing that the apparent lack of confinement (which I see as being a prime contributing factor to the damage we are aware of) would have been raised as a red flag and we would have insisted on something being done about it. However in Australia as I understand it you don't have the same level (or any) independent design review like NZ does. So when a designer potentially gets it wrong, it is wrong, there is no safety net, and every now and then it goes wrong when all the holes in the Swiss cheese align.

RE: Opal Tower - Sydney Australia

The logic that people moving in caused the problem is absolute rubbish.

Total dead load would be about 7 or 8kPa while full design live load is 1.5kPa. So live load is relatively insignificant compared to the building load before anyone moved in. And construction loads would have been similar or higher. Wall design loads from Wind and earthquake would have been higher than LL!

Like everyone else I would like to know what is happening and think there are major construction problems as a minimum. But I am not expecting any information in the near term.

Anything on 60 minutes will normally be sensationalist mis-information in my view so I will not be watching it. Making it worse will that the Tomic love-in will be on the same show!

RE: Opal Tower - Sydney Australia

I am also wondering when the professors’ final report will be issued, especially since people have already started re-occupying the premises.
It would give them a certain level of comfort if an independent public authority confirms the process.

This is after all, a defective structure built on public land.

If they don’t release any formal documents, all that would be circulating in the public domain would be the tabloid-oriented news, but at least the public gets some insight into the rectification.

Tomfh – I haven’t heard anything about a new wall. Are there any more details?

RE: Opal Tower - Sydney Australia

Current Affair is running a special this week, supposedly construction videos, it'll be sensationalised but the images will be interesting.

RE: Opal Tower - Sydney Australia

The ACA preview footage looked interesting. Spalling columns and lots of slab soffit cracks.

RE: Opal Tower - Sydney Australia

Columns shown in the ACA preview look like the result of concrete getting behind the plastic liner inside a formatube (or similar form system).

RE: Opal Tower - Sydney Australia

In this discussion I've been occasionally pulled up when my comments have been about political, legal or media perceptions rather than engineering facts. But the reason why I keep bringing up these issues it they are so involved in the way this is handled. With that in mind I'll go back to them.


Quote (Agent666)

I thought their mandate was to produce a public report on cause and comment on proposed repairs (items 1 & 2 of their scope). These repairs seem to be underway of course, and one recommendation was that the design of any repairs was peer reviewed by independent and qualified engineers, which I assume and hope someone is at least doing.
Yes, that might be their mandate of the independent review. But they have now power to control what actions the builder is currently choosing on taking.
The builder has EVERY incentive to:
-reoccupy the building as fast as possible
-perform superficial repairs as fast as possible to hasten reoccupation of the distressed areas
-complete an 'adequate' structural repair to prevent further damage

They have little incentive to allow peer reviews into the process. The peers might decide a more expensive solution is recommended and then they are facing a real PR nightmare. This is boots on the ground kinda of stuff. Better to get in the quickly and do it your way than have independent people try to dictate how you spend your money. Not to mention the independent reviewers would have minimal resources compared to the builder and structural engineers responsible. They have every reason to throw plenty of resources at the issue now.

Quote (Agent666)

Otherwise its the guys who made the mistake fixing the mistake
Yep. But not really any different from most consumer or commercial warranties. But I do share and understand your concern.

Quote (Agent666)

I have a hard time believing that there are not more design issues throughout the structure than the areas that failed, but I'm a cynic. Too many years of doing peer reviews to know where there's one mistake, that there are generally more if you go looking.
I agree.

To support your argument, it seemed there were quite a few mistakes in construction identified in the interim report which likely had no effect on the failure. I would have little doubt there are many more.

RE: Opal Tower - Sydney Australia

Quote (mangotree)

Thank goodness for whistle blowers.

Here’s a link to the ACA clip:-

Thanks.

Sure the clip focused on plenty of other corner cutting and imperfections in construction. But the smoking gun might just be that they placed the precast panel on level 10 upside down so the appropriate shear reinforcement was not present. Only got about 10 seconds of coverage at 6:28

RE: Opal Tower - Sydney Australia

Quote (mangotree)

Thank goodness for whistle blowers.

Funny how the I told you so brigade comes out of the woodwork after the horse has bolted so to speak. I wonder what if anything they did at the time.

We don't know what involvement the design engineers had in the construction repairs that were shown, they seemed to be implying it was a coverup (possibly by the contractor) but really offered no facts on this or rebuttal from the contractor or designer. But I do find it hard to believe the designer wouldn't have been consulted and had the final say on any significant repairs to the structure.

If properly repaired the column would still be absolutely fine I would have thought.

Slab looks a bit suspect, but I've never seen random cracking like that before so can't offer any insight as to what might have caused it, they didn't mention the thickness. Could be honeycombing though that's been patched up rather than cracks. Guy in the video stated they could drop a 2" nail through the cracks to the next level which sounds alarming to say the least and would certainly warrant more investigation if its an accurate reflection of the crack widths. Reporter also mentioned the possibility of adding water to the concrete trucks, but this sounded more like his opinion of what might have happened vs what was actually happening on site.

RE: Opal Tower - Sydney Australia

The crazing cracks on the 10th floor slab is probably a result of using a concrete mix with cement content above 300 kg/m3 to achieve early strength.

The reason a contractor would be willing to pay more for such a concrete mix is to cut down the waiting time before tendons of the post tension system can be stressed, thereby releasing the supporting formwork of the slab.

Unfortunately, too high a cement content results in uncontrollable shrinkage. Seen this happened in 1993 in an office tower project in Bangkok.

RE: Opal Tower - Sydney Australia

It's probably worth noting that A Current Affair, like many of our mainstream "news" media, is basically just a televised tabloid. They love vague conspiracy theories and are not known for their extensive, well-researched articles. Controversy gets ratings!
Having said that, they have at least managed to provide video and images, which have been useful it seems.

RE: Opal Tower - Sydney Australia

A few details of the repair thats been agreed to by Cardno/WSP. Details only for strengthening the affected upturn beam are shown, presumably the stell plates sandwiching the hob beam are intended to improve the confinement at the base of the wall.

I'm not sure if this qualifies for the independent review that was requested, given Cardno represent the body corporate but perhaps as good as its going to get for the repairs.

RE: Opal Tower - Sydney Australia

So the too skinny walls will be turned into fat walls. "Pay me now, or pay me later."

I would hope the state appointed professors will continue to insist on the overall independent review. We shall see.

RE: Opal Tower - Sydney Australia

Agent666,

Has it been agreed to by Cardno? The update says it's been issued to them for agreement but not whether it's been agreed to. It strikes me that the remediation work that's detailed has the wall the correct way around, given the shape of it and dowels on one end how would you even install it upside down?

If I'm drafting a fix for something I would show it in its as built state rather than its as designed. Now this might just be a 'media release only' draft to not release any info that might be damaging to one of the parties involved and the actual working draft could be different.

RE: Opal Tower - Sydney Australia

Those repairs would appear to agree with my guess a couple of weeks ago that the hob was poured at slab concrete strength and the walls were much higher strength plus the connection detailing was awful so there were serious development and bursting problems. probably introduced in a conversion from insitu walls to precast at some stage during the construction.

The concrete strength problem was confirmed to me a couple of days ago.

RE: Opal Tower - Sydney Australia

Quote (MDEAus)

given the shape of it and dowels on one end how would you even install it upside down?

I think what is meant by 'They placed the panel on L10 upside down' is that the reinforcement cage was placed in the mould upside down, and the rest of the hardware and ducts went in to design. As you point out, it is hard to lift a precast panel without lifting points on the top edge, not to mention getting it into place with the ship-lap joints inverted.

RE: Opal Tower - Sydney Australia

Quote (MDEAus)

Has it been agreed to by Cardno?
I'm guessing they have been party to early agreement on the concept involved, the remedial work has been in the works for a while and I can't imagine WSP not keeping them in the loop and getting agreement at each step. So while they still need to 'sign off' on it, I guess its possibly a done deal.

Quote (rapt)

The concrete strength problem was confirmed to me a couple of days ago.

Interesting, I see some media reports today stating that the final 'official' report will be issued shortly as well.

RE: Opal Tower - Sydney Australia

Just curious- is there something that’s stopping them from making the loads go directly down via new intermediate columns through the whole garden slot areas. (To effectively continue the columns down throughout all the levels)

Rather than sticking with the transfer beam scheme.

In terms of the visual impact of the elevation, it would appear more logical as the garden slot wall is presently treated as one large plane. To add little piddly pier-like columns that go up for one level then stop, risks looking odd when the void goes up several stories.

I guess the wall option “looks” better as it provides a continuous line through the wall width, but it does eat up quite a bit of someone’s floor area.

Edit: Perhaps they can ask the designers to work around their solution eg. maybe create maybe a niche wall-look so the add on piers/ columns don't look out of place...

RE: Opal Tower - Sydney Australia

Re. the concrete strength. Was it as per the design?, or did they place the wrong strength concrete?

RE: Opal Tower - Sydney Australia

Mangotree, that would possibly just be admitting that the original transfer beam structural scheme was the wrong one perhaps..ponder

What you are suggesting would be how I would have approached the design situation in the first place, column elements at the end of the wall. Heavily axially loaded walls make me nervous given the type of wall buckling failures observed over here in the Christchurch New Zealand earthquakes. Our codes were changed as a result, anything over I think 0.3f'cAg and you need confinement as per a column (i.e. a lot more confinement!).

RE: Opal Tower - Sydney Australia

I got the impression it was built as detailed, but cannot be sure.

RE heavily loaded singly reinforced walls and high concrete strengths and confinement, we have addressed this in the latest AS3600-2018, much to the displeasure of some consultants.

RE: Opal Tower - Sydney Australia

rapt,
It should be to the pleasure of engineers. Architects always want things skinny. I think I read that these bearing walls and upstands were only 150 thick. A minimum of 200 in multi-storey construction would be a good code requirement.

RE: Opal Tower - Sydney Australia

Hokie,

I think they were 180mm.

Anything more than lightly loaded walls (equivalent to about a 3-4 storey building) and any wall in a limited or moderately ductile earthquake design are now required to have reinforcement on both faces. No central reinforcing. That should force 200mm hopefully. And above a minimum stress level must be confined as for columns and above 50MPa concrete must be confined as for columns.

RE: Opal Tower - Sydney Australia

Quote (rapt)

and above 50MPa concrete must be confined as for columns.

Is this requirement only for limited or moderately ductile earthquake design, or for any wall with greater than 50MPa concrete?

RE: Opal Tower - Sydney Australia

All walls.

RE: Opal Tower - Sydney Australia

...and who pays/compensates the apartment owners who have now lost usable floor space with the thickened wall/column elements. Going to get ugly!

RE: Opal Tower - Sydney Australia

Ingenuity,

Hope you had not bought one!

They will lose a lot more in collapsed resale value than they will from 100-150mm off the side of a room. Add that to Sydney prices falling anyway and most will have debts higher than value forcing higher interest rates and impossible to re-mortgage, especially those who started on interest only loans. And they cannot just hand it back to the bank like they can in many USA states.

Doubt that consultants insurance company will volunteer to cover those losses.

RE: Opal Tower - Sydney Australia

Even with the changes to the 2018 code, there's no such thing as slenderness or second order effects for walls in Australia, remember? It just doesn't happen.

So consultants, don't forget to make all your columns D/b>4 (whoops, I mean L/tw, thank God for chapter 11) and you're good to go!! Confinement?, ductility?....earthquakes? What's that...?

RE: Opal Tower - Sydney Australia

QSIIN,

It is not just AS3600. Most design codes have a simplified wall design method and most are as basic as ours. The AS rules were based on the BS8110 rules when first written.

Even the changes we have made in the 2018 code to try to make them more robust have been heavily criticized in both the industry and some in academia as being far too conservative.

If you think they should be changed in some way, make constructive proposals for change!

RE: Opal Tower - Sydney Australia

Quote (rapt)

All walls.

AS3600-2018 gives cases, in 11.7.4, where wall can be designed as columns not requiring restraint of vertical steel according to 10.7.4. The new last paragraph says vertical reinforced is to be restrained to 14.5.4 if over 50MPa. I believe the correct interpretation of this only if restraint reinforcement is required by the paragraphs above. If the column complies with 11.7.4(a) then it is most likely below the dotted line in Figure 10.7.3.1(A) and doesn't need special confinement reinforcement anyway.

If a wall has a stress level less than about 0.2f'c, then it probably does not require vertical bars to be restrained (i.e. no ties though the wall thickness) , for strengths 50MPa to 100MPa.


RE: Opal Tower - Sydney Australia

RAPT,

Just because another code does something one way, doesn't mean we should assume it's correct and copy. How's the new Canadian beam shear capacity working out by the way?

Anyway, I've already expressed my opinions and recommendations on simplified wall designs in this very thread. Technology and computing power has come along far enough that some of these simplified methods can be done away with. Seriously, are interaction diagrams so difficult to produce?

As degenn states, you don't have to have ties in a column if you meet applicable criteria, and you can go less than 1% too. At least you're still checking for slenderness, cracking and strain compatibility. Let's at least get rid of the ambiguities as to when the simplified method is and isn't applicable.

And hopefully then we can stop seeing slender 200x800 "walls" being built.

RE: Opal Tower - Sydney Australia

DGENN

We are looking at the 14.5.4 referral. It obviously applies to all walls being designed for earthquake. And with the new earthquake code, any building using > 50MPa concrete is going to be required to be designed for earthquake anyway as no-one would waste money using > 50MPa concrete on the buildings that escape the minimum earthquake design requirements as the load levels would not be high enough to require it.



QSIIN,

You obviously do not know how hard it is to get something removed from the code or modified when it has been in a design code for 50 years and is liked by designers because of its simplicity.

You are not the first person to point out how simple it is to generate an interaction diagram these days. But for some reason, many on the code committee do not think designers should be forced to do real calculations that require a computer when a simple hand calculation method has been accepted for 50 years and not many have fallen down! And that includes some academics.

It is the 150 * 800's with central mesh and 80MPa concrete that I am trying to stop initially!

RE: Opal Tower - Sydney Australia

150 x 800, mesh, 80 MPa? Where have you seen that, rapt? Whatever the code provisions, that is nuts.

RE: Opal Tower - Sydney Australia

Hokie

Been told about them, especially by someone with a lot of experience in precast. He was fighting against it.

Even Opal was 180 * whatever and I understand 80Mpa centrally reinforced (not mesh at the ends at least) with N28's at 100 central at the ends. 2009 code does not say you cannot do it, and many designers these days will do it if their interpretation is that they are not specifically told they cannot!

RE the confinement provisions and DGENN'S case that walls will be under the limits of 10.7.3 for confinement, the problem is that the earthquake design load with mu and Sp factors for Moderately Ductile and Limited Ductile walls mean that the elastic design load that you are basing the need not to supply confinement reinforcement on are not the real loads under earthquake action where post elastic deformations are extreme. Using those rules with a mu = 1 would be ok, but not with mu = 3 and Sp = .67, where the design elastic load is thus reduced by a factor of 4.5 and ductility of the structure is supposed to make sure the structure can survive under the plastic sway after the elastic design load condition is passed.

We have had to make the same distinction for whether walls are in tension or compression. The decision cannot be made on the reduced design load. It has to be on the full earthquake load with mu = 1.

RE: Opal Tower - Sydney Australia

RAPT,

I totally agree, and I too have seen extremely thin 80MPa similar to what you are describing.
And you're right, I don't know how difficult it is, though I have tried to reach out to the code committee before regarding various matters and have been turned away. I imagine it must be very frustrating to deal with.

Regarding panels greater than 50MPa and wall ties to chapter 14, engineers will still use the logic of "if wind governs, then you can ignore earthquake". And therefore the mentioned requirement won't be applicable. The idea that earthquake and wind are two totally different mechanisms is still not well understood.

RE: Opal Tower - Sydney Australia

I do not know who you approached.

If you have any like that which really need looking at, send them to me on my work email and we can sort out a how to approach them. We do not know every stupid interpretation everyone is making! If you have specific clauses you think need improvement send them to me. I cannot guarantee anything but at least they will be looked at.

Agree with your second comment entirely. Unfortunately they are probably correct as far as ultimate strength design calculations go for section strength design. That is why we had earthhquake moved into the main code instead of as an Appendix. Now we just have to convince people that the reduced load to calculate strength for earthquake is not actually the full earthquake load and very special detailing requirements are needed to make it all stand up.

RE: Opal Tower - Sydney Australia

RAPT,

The code really ought to spell out the earthquake strength load vs the *full* earthquake load more clearly.

And if it’s not going to spell it out, the full load ought to be the starting point.

RE: Opal Tower - Sydney Australia

Tomfh,

We are limited on what can be said in the code itself. It is not allowed to be a text book. If we tried to add what you want in the code itself, even if it got through the main committee (we tried this time and failed), it would be rejected by the Standards editors and BCA. The commentary to the 2018 code will go into a lot more detail.

But any engineer designing to the earthquake provisions of the code should know the background or should be able to research the background logic before he starts designing. You do not learn to design by reading a design code.

It is not as if AS3600 is alone on this, the methods used are basically the same as NZS and ACI so there is a lot of information out there.

It is not the job of the design code to teach an engineer show to design.

RE: Opal Tower - Sydney Australia

And therein lies a big problem. A lot of engineers expect codes to be in cookbook form.

RE: Opal Tower - Sydney Australia

The code needn’t be a cookbook, but a clear statement that the code earthquake loads are a small fraction of the actual earthquake loads would be a useful thing to include.

I see many connections and walls designed based on assumptions that the code load is the load a wall to connection must resist. I’ve done it myself in the past. And I understand this is why some of the critical NZ failures occurred. The connections simply broke under the actual earthquake loads.

RE: Opal Tower - Sydney Australia

Tomfh

That was part of what we tried to add and it was watered down to what is in clause 2.1.2.

But when you divide your earthquake load by 4.5 (mu = 3 and Sp = .67), surely you can figure out the rest has to go somewhere. If you are unsure why, you research it.

Commentary to AS1170.4 goes into some detail on it.

Also, in several places in the 2018 code, it has been specified that the checks be done with a mu = 1 no mater what the design mu value, mainly in the Walls chapter.

We missed the one in confinement. It will be added in the next amendment.

RE: Opal Tower - Sydney Australia

Quote (rapt)

It is not the job of the design code to teach an engineer show to design.
Except that is how are universities have been approaching 'teaching' structural design for quite some time....

Quote (rapt)

But when you divide your earthquake load by 4.5 (mu = 3 and Sp = .67), surely you can figure out the rest has to go somewhere. If you are unsure why, you research it.
But when all you are doing isn't following the code letter by letter you aren't thinking about the why only about crunching the numbers. I must admit I am not immune from this but I try not to fall into such traps.

Just two days ago I had a call from a structural consultancy asking me why my supplied foundation loads had much greater earthquake shear in one direction rather than another. They seem confused in my reply I mention that the period of the structure differed considerable in either direction. They were about to send out a formal project RFI about the discrepancy, but I haven't seen that yet.

Quote (Qsinn)

The idea that earthquake and wind are two totally different mechanisms is still not well understood.
Very, very true.

RE: Opal Tower - Sydney Australia

Quote (Rapt)

We missed the one in confinement

Can you elaborate?

RE: Opal Tower - Sydney Australia

Human909,

Says something for our universities then doesn't it. Our design codes are already far too complex trying to bridge the gap between text books, design limits and allowed simplified methods.

A design code should simply be a set of limits. Theory is in text books. But design codes then started to define accepted simplifications to make design calculation easier. Some very basic examples are rectangular stress blocks for concrete, Branson's formula for Ieff and kcs factor for long term deflections and span/depth ratios for deflections. Using a slide rule or abacus, these things were too difficult to do on a daily basis so design codes gave acceptable simplifications. This has extended and extended until the line between a design code and a text book became blurred. But a design code will normally not define design theory, simply accepted methods and limits.

All of these simplifications are not accurate and can cause significant error in calculations! Designers have to understand these limitations and allow for them in their design.

Design is not simply plugging numbers into code formulae. RAPT or any other design program does that for people using it, but it is NOT a designer, it is a calculator.

Dgenn
I elaborated a few days ago about 8-10 posts up.

RE: Opal Tower - Sydney Australia

The final report is out, I haven't had a chance to read it yet.

Final Report

RE: Opal Tower - Sydney Australia

Quote (Rapt)

confinement provisions

So just to be clear, you believe the correct interpretation of 11.7.4 requires all walls designed as columns that are over 50MPa must be restrained to 14.5.4. In other words 11.7.4(a) cannot be used, even though not clearly stated.

Moving to 14.5.4, this clause in intended for an IMRF ie mu=3. Is this still applicable if mu is 1 or mu is 2. The reference from 11.7.4 places no qualifications. Should the reference simply say the provisions of Section 14 for columns be considered (which they obviously should be anyway).

You can have, say, 2500x250 65MPa blade column which doesn’t pick up much in plane moment if the core is much bigger, say 9000x9000. It may satisfy 11.7.4 or may not using mu=1. This would allow no ties or normal ties (at 250 centres) depending on load, if the first part of 11.7.4 is used and since it is Ok with mu=1, Section 14 has few requirements. If the last paragraph is used and no exemption is allowed for mu=1, then you need closed ties (not 90/135 hooks) at 125 centres for the full wall height.

There are big cost differences depending on how the clauses are read.

RE: Opal Tower - Sydney Australia

You will have to wait until the amendment is out. I cannot preempt what will be finally decided.

I am just pointing out that the 10.7.3 limits on special confinement in their current form are not really applicable for earthquake situations where there is a lot of plastic response required after the "nominal" elastic design load is reached. So the "nominal" elastic design load cannot be used to determine when special confinement is required.

RE: Opal Tower - Sydney Australia

Quote (rapt)

Human909,

Says something for our universities then doesn't it.
Yes. Pretty much.

In the context of many of the significantly experienced people commenting here, I'm relatively green and still inexperienced, especially in concrete as my career has taken me a different but still very interesting direction. I participate here out of curiosity and hopefully can learn and provide some thoughtful insight.

Plenty of structural engineers just seem to follow codes without thought or consideration of reality. I know my knowledge is limited. But when "inexperienced me" catches mistakes from people who are supposedly experts it positively scares me.


Meanwhile one of the more significant line items in the final report is this one:

Quote:

"The viability of residents re-entering the building extends beyond the structural issues considered here and hence beyond the scope of this investigation. Nevertheless, we would recommend that items 9-11 listed above be completed prior to re-occupation."

That is the line that residents and lawyers will be jumping on.

RE: Opal Tower - Sydney Australia

TomFh and DeGenn,

if you want some reading on it,

RE: Opal Tower - Sydney Australia

It would be good to have a Part 2 of the Final Report, with a follow up on the rectification work.

It’s not bad that there will be further checks in place on the professionals, but I think that is the easy and more politically palatable route.

The harder issue to deal with is that the builder/ developer are the party with the real control of the whole construction process. If one of the professionals insists on a rectification of a defect for instance, the builder may very well remind them of who exactly they are working for and paying their firm’s fee.
It’s a result of how the design and build contract is structured.

It’s difficult to envisage a future where the politicians would ever “crack down” on developers/builders!! If anything, it would be the exact opposite.

So if for instance, the builder insists on completing one floor every 6 days. Would the concrete floor or beam have reached adequate strength within the 6 days to support a load bearing precast panel, such that they can progress to the next level? Sure, if you test it after 28 days it would have adequate strength, but how about after 6 days?

Would the structural engineer be responsible for the builder’s or developer’s decision to achieve a certain completion timeline?

And what “power” exactly would the engineer have contractually to determine the procurement of the project- that’s the builder’s domain.

Even if all the professionals were registered, there’s an unequal power play in force, that is out of the professionals’ control.

(If the professionals' next pay cheque is coming from the builder they are checking)

RE: Opal Tower - Sydney Australia

If I'm following this correctly, the city nor any other geographical governing body retains a copy of the building plans, permits, inspections or approvals?

RE: Opal Tower - Sydney Australia

The rules are already in place for checking and certification of buildings. If they are not being performed correctly or are being corruptly manipulated, there are rules already in place for that too.

So what do we do, create more rules that say that the existing rules must be enforced! Oops they are already in place too.

Engineers are supposed to design to the building regulations. They are supposed to ensure that the building is built to spec. Certifiers are supposed to make sure that the checks have been carried out correctly.

I know I am old fashioned and come from an age when engineers and for that matter, most people in construction, felt an obligation to ensure that construction was performed correctly, but creating new rules and commissions and authorities is a waste of time and money. There have always been builders, engineers etc who were willing to break the rules to save/make money. That is human nature. It happens in all walks of life. Some are just worse than others.

You can regulate all you like but to me society is heading on a path where regulations do not matter to more and more people. More regulation just costs the honest people more money. It does not solve anything. And if you look back through history, it is simply repeating what has happened before to just about every age in human history.

RE: Opal Tower - Sydney Australia

I have total confidence in the honesty and integrity of the consultants wanting to do their job as expected of their profession.

Their traditional “position of authority” has been effectively taken away, however, if they are left vulnerable to progress payments from the builder to practice.

These “Design and Construct” contracts can be structured such that the developer only pays the builder. The builder then is in charge of the whole project and it’s budget, which includes paying the architect, structural engineer, civil engineer, mechanical engineer, hydraulic engineer etc.

The consultants have been effectively turned into nominated subcontractors, and are susceptible to be treated as such.

That’s a vulnerable position to be in, especially when these consultants are expected to “sign off” on the project.

If the consultants were not paid directly by the builder, but by the owner, then there would be more autonomy (which is the more “traditional” building contract).

If this weakness is not addressed, I fear the whole “registration” process won’t be enough to solve future issues.

RE: Opal Tower - Sydney Australia

The old model where the owner/developer appointed and paid the consultants has always been my preferred model. But once Project Managers took over the construction side of things and convinced the owners that it was better for them to control the whole process from design to construction, the current model became inevitable.

But there are many problems with your proposal that the PM/Builder appoint the consultants but they be paid by the owner/developer. eg
- Payments still have to be agreed/approved by the builder
- in many cases the builder and developer are not exactly at arms length and often are the same company

In my view, the consultants activities should not be negotiable, eg full supervision of the construction should be carried out by the design consultant. One developer/builder on the Gold Coast used to only require the consultant check every second floor pour. Unfortunately one time I know of, one of the "odd" floors was a major transfer floor with very large PT beams. And he did not check it! And full design should be at least overseen and approved by the consultant, even if some parts are subbed out to specialists at the request of the builder.

And checking by an independent 3rd party (not another group in the same consultancy) should be mandatory. This could be controlled by the Certifier and paid by the owner direct to the 3rd party checker.

The Certifier should be appointed by the relevant authority, not the developer/builder.

RE: Opal Tower - Sydney Australia

Quote (Rapr)

And checking by an independent 3rd party

And there needs to be some mechanism to limit the exposure of the third party checker to damages to reflect their reduced fee, otherwise no one may be interested in the work.

RE: Opal Tower - Sydney Australia

degenn, in NZ the company I used to work for doing peer review work would limit the liability to 10% of the original designers liability as part of the standard conditions of contract under which the work was usually done. This was an additional condition the company imposed for peer review work.

But I agree, if there is a problem in the future as the peer reviewer you could in theory get dragged into it an be liable. I've only heard of it happening once and the company who did the peer review were cleared of any wrong doing because if the designer had actually addressed the issues raised in the review (and to some degree been a whole lot more competent around some of the particular aspects relating to the construction), then perhaps the building would not have collapsed during a storm event.

As someone who has been constantly battling 'bad design' in peer reviews, I believe there should be some sort of independent audit of designs (random or targeted) to make sure minimum competencies are being meet within industry, it's been talked about for ages here as being required. Fail a review and get fined as an Engineer or loose the right to practice, personal accountability! Simply waving a rule book at engineers like rapt is noting does nothing, hit companies where it hurts. Make the findings public, let the market decide?

I suspect if you did this though, we'll run out of engineers in a few years and I'm busy enough already...

RE: Opal Tower - Sydney Australia

Also, it should be necessary for the structural designer to resolve all disagreements with the checkers to the satisfaction of both parties.

As I understand the situation with infrastructure D&C projects, as least in NSW, the structural designer is obligated to consider the checking engineers comments but not required to come to agreement on a resolution.

I know fee structures have been ruled against in Australia as being anti-competitive, but I also think there should be minimum fee schedules for different types of work to ensure that the designer has time to put in the effort to design and detail it properly.

It is farcical that the structural designer might get sigificantly less than 1% when the real estate agent gets 2.5% every time he sells it!

RE: Opal Tower - Sydney Australia

Quote (rapt)

It is farcical that the structural designer might get significantly less than 1%...

...and with liability for a lifetime. Crazy!

RE: Opal Tower - Sydney Australia

1%!?!? What kind of luxurious industry are you consulting in!!!??? Half that is considered generous!

But you are right about D&C and unfortunately we engineers have cannibalized ourselves by undercutting each other, further driving down fees. And if we don't be competitive with fees, the contractor boots us off the job in favour of their own engineer who will detail the job the way that suits them. We've been threatened multiple times by contractors to get rid of wall ties and make everything precast, singly reinforced and dowelled, because "their other engineer did it on their last job".

And the problem is, many chartered/registered/RPEQ or what-have-you engineers are the ones we are talking about in this thread, lacking in thorough understanding of seismic theory (amongst other areas). Hence why their fees can be so low, because they don't need to consider seismic, they don't need to consider progressive collapse! Because they don't even know what that is! And no one is there to stop them!

My main issue is that becoming registered is just a fee. You merely purchase your right to sign off on structures, and most companies pay that yearly fee for you. 3 to 5 years out, fill out a couple forms and write a report and (now) a phone interview, and you're qualified to sign off on a 50 storey building.... she'll be right.

Agent666, I don't think we'll run out of engineers, we'll just cut the fat. And the rest can do the job properly.

RE: Opal Tower - Sydney Australia

I did say < 1%!

Otherwise I agree completely!

RE: Opal Tower - Sydney Australia

(OP)

Quote (QSIN)


My main issue is that becoming registered is just a fee. You merely purchase your right to sign off on structures, and most companies pay that yearly fee for you. 3 to 5 years out, fill out a couple forms and write a report and (now) a phone interview, and you're qualified to sign off on a 50 storey building.... she'll be right.

Do CPEng and RPEQ applications not require face to face panel interviews anymore?

RE: Opal Tower - Sydney Australia

Quote:

Do CPEng and RPEQ applications not require face to face panel interviews anymore?

I believe it is now up to the discretion of the of reviewer.

RE: Opal Tower - Sydney Australia

In NZ the CPEng assessors just whittle down the applicants practice area until they pass. ~90% pass rate as far as I understand it, compare that to other comparable/equivalent licensing around the world (IStructE/PE/SE, etc), I think IstructE is something like 30% for first time applicants?.

So if you aren't deemed competent in a certain aspect that you wanted to be endorsed to do based on the evidence of work you provided (i.e. your best cherry picked work supposedly), then they remove this aspect until they end up with something they think you might be competent in doing based on what you submitted.

Its supposed to be based on demonstrating that you can operate on your own, to develop solutions to complex engineering problems, manage the process of design/construction etc. Very little applicants seem to hit this mark based on discussions with the assessors I personally know, but they feel obliged to pass them with caveats on their practice area. The danger is these people don't know what they don't know.

CPEng is not really seen as a measure of technical competency, which I personally believe it should be, because there is nothing else to distinguish engineer A from B to the unsuspecting public.

They talked a while back here about introducing a higher certification for 'complex structures' (which was never defined). As far as I know its gone nowhere and wouldn't have addressed the perceived failings of the original CPEng system.

RE: Opal Tower - Sydney Australia

CivilEngAus, I'm aware of a couple of people who have followed the process outlined (resume, forms, phone interview) to gain RPEng, which is then accepted by BPEQ as an acceptable assessment. I believe that BPEQ may have done their own assessments at one stage, but now its via an accredited assessment authority (EA, AusIMM, Professionals Australia etc).

The CPEng assessment requires a lot more report writing as far as I'm aware, as well as the panel interview, but there's a hefty cost for that compared to Professionals Australia. The people that I'm aware of that have followed the Professionals Australia path were all over 10 years experienced, which may have made a difference. None of them were seeking Structural though.

EDMS Australia

RE: Opal Tower - Sydney Australia

I believe that the RPEng was offered by Professionals Australia because the CPEng/EA assessment was considered too expensive (cost and time) by many people. I can see their point. About two years ago, an associate technical director asked me (as project manager) to sign off one of his project reports. I had to sign it off three times as he apparently wasn't quite able to guess the exact wording EA needed to see. The revisions came to me 1-2 months apart and I couldn't tell what had changed without having the different versions side-by-side. This was an engineer you'd have on all your projects if he was available and you had the budget.

Being a large company, we also had an EA-approved graduate program. This gave us a steady stream of 3-5 year experience engineers who gained the CPEng credential comparatively smoothly. The process seems flawed when you witness this sort of thing as it appears skewed to getting junior engineers into the CPEng system.

RE: Opal Tower - Sydney Australia

Quote (Rapt)

TomFh and DeGenn,

if you want some reading on it,

Hi Rapt

Are you aware that this paper suggests using the current (2009) rules for mu=2.


RE: Opal Tower - Sydney Australia

DeGENN.

Seeing it was written before the 20018 code was written, it could not really tell you to use it. But it does say somewhere that this is being revised in the 2018 code.

3 of the 4 authors were on sub-committees or contributed to the 2018 code development.

RE: Opal Tower - Sydney Australia

DeGenn,

Actually it says "Current Code"!!

Most of the requirements in that summary table have been included in the 2018 code. Many were not in the 2009 code!

RE: Opal Tower - Sydney Australia

Degenn,

I think it is important to understand, as we've been discussing in the other thread, that mu and sp are actually a function of the design, detailing and behaviour of your structure. Not the other way around. Therefore, this article recommends using limited ductile values, but that is still subject to the design, detailing and behaviour of your structure.

The article points out that many designers choose mu and sp of 2 and 0.77, but then proceed to detail with low reinforcement% and in some cases, low ductility mesh. In the latter case, it's hard to argue to have a ductile structure when reinforcing with low ductility reinforcement.

As RAPT has said, a lot of what is in this article has been adopted to the 2018 3600, such as the fourth category of non-ductile structure.

RE: Opal Tower - Sydney Australia

Part of the problem with the code is that there are specific provisions in the earthquake section of the code that over-ride the general design provisions, especially for walls and columns in sections 10 and 11.

Section 14.4, 14.6 and 14.7 all control wall design and detailing for earthquake situations, including boundary elements, minimum reinforcement and confinement.

Also, this discussion should probably move to AS/NZ code forum.

If someone wants to continue it, start a thread there.

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