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building brick walls on "propped" structure ? Now it cracks after de-propping

building brick walls on "propped" structure ? Now it cracks after de-propping

building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
Hi, I have some problem because the contractor was building brick walls on propped structure.
Now what happens after they "de-propped" the slabs, the bricks started to crack here and there.
How can I prove to the contractor that this was wrong? Obviously he is now arguing that why was he not supposed to build the brick walls on propped structure.
Where can I get some written proof that this is not allowed? Do the building regulates and codes mention it?

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Building codes don't cover every eventuality, but it stands to reason that a structure which is loaded while propped will deflect when the props are removed.

BA

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

I agree with BAretired. Everyone involved with the job should have seen that one coming!

www.PeirceEngineering.com

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

at least in the US, the contractor is responsible for his means and methods, safety, quality control and protection of the work. it is not up to the owner or engineer to direct any part of the work. so it is entirely his problem to deliver a wall that is not cracked. it doesnt really matter how or why it cracked

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Unless this is so bad and the contractor doesn't fix things, it may be cheaper to hire someone to replace it than to hire a lawyer. However with an attorney you will have the best way to solve it.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

I've got into this before (i.e. about when to remove forms/supports). A lot of people just cover it with a note on the drawings saying do not remove until concrete gets its 28 day strength. But contractors always want to move on ASAP.

Probably one of the first things you need to do (if you don't already know) is figure what the deflection of the "slabs" would be long-term and what they would be at the point he removed the supports/forms. If the former is in excess of the latter.....you don't have a leg to stand on. You may not have one anyway if the long-term deflection exceeds something like L/600. (IIRC that's the requirement for supporting masonry under some circumstances.)

If he's not following your directions (or the drawing notes) and the deflection meets the criteria I was talking about in the previous paragraph.....it's time to talk to the owner/PM about getting him off the project.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Been telling consultants about this one for years in my RAPT training sessions.

Specifications and design drawings should specifically require that slabs and beams be unpropped before masonry and brittle finishes are added.

Any engineer who does not specify this cannot base their design on the deemed to comply deflection / span/depth ratio rules in design codes because they assume unpropped conditions and "incremental" deflections are controlling the design, not total deflection.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

It's been my experience when doing modifications to existing structures that involves any change to the existing load regime that you can have 'unexpected' consequences and other issues. You may not be able to pass this off as a contractor's 'means and methods'; courts in these environs also put a requirement of 'reasonable' to contract work.

Can it be remedied in a simple and cost effective manner?

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
that you guys, you all say the same basically, you all are also experts in this field but now an weak contractor wants to argue and I would like to show it to him somewhere written down. I need something to relate to.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

There's a requirement in the MSJC for beams supporting masonry to have a maximum service deflection of L/600. My MSJC is at home so I don't have the section number in front of me but I can get it tonight.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Lolobau,

It is the designers responsibility to both specify it and check that it is done correctly in my opinion.

The contractor is supposed to do what he is told.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Lolobau:
Maybe the brick wall should have been designed as a deep beam, with a substantial bond beam, tension reinfr’g. region at the bot. of the wall height, to distribute the tension forces and provide some self spanning ability, and better distribute the wall DL. You might have been better off waiting to build the wall until the slab didn’t need to be propped for early strength, deflection and curing reasons. Thus, some deflection would already exist when starting the wall and some added deflection due to wall weight might be accommodated by a softer wall which was still compliant. Maybe the slab should have been formed and built with some camber in this wall area so that it would still have a bit of camber after the wall was built. Some of this problem falls back on the EOR for not designing the wall and the slab in anticipation of this sort of potential problem.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

TME: It's unlikely that the Contractor knows about L/600 deflection and how to create it...

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

dhengr

Sorry, Precamber does not help! It is the amount of movement that affects brickwork, not the final deflected position. Precamber has no effect on the amount of movement, only on the visible deflection, unless you make it an arch, and I doubt that you want that much Precamber!

Otherwise, yes some Engineering input into it as you have described might have been useful.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
@dhanger: you right could have been done this way but not needed.

I just regrade that I did not have a note on my drawings which clearly stipulates that this is not allowed to built walls on a propped structure sad

RE: building brick walls on "propped" structure ? Now it cracks after de-propping


Quote (lolobau)

I just regrade that I did not have a note on my drawings which clearly stipulates that this is not allowed to built walls on a propped structure

I assume "regrade" should read "regret". The question is, if the props had been removed before building the walls, would there have been a cracking problem?

BA

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Quote (dik)

You may not be able to pass this off as a contractor's 'means and methods'; courts in these environs also put a requirement of 'reasonable' to contract work.
I agree with this, so the question is defining "reasonable". What knowledge should a contractor have? He is competent enough to know that he wouldn't build his wall 3 hours after pouring, so why not expect him to know that shoring affects the structure? Is building a masonry wall on a shored floor a common knowledge no-no? I would think so. Who told him he could build the day that he did? Was it his own decision? Wouldn't he have to coordinate his presence with the project manager in order to not conflict with the other possible trades there?

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

L/600 requirement for vertical deflection of masonry veneer is in section 6.2.2.3.1.5 of ACI 530-05. Not sure newer versions.

Brian C Potter, PE
Simple Supports - Back at it again with the engineering blog.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

if it cracked because of the specific means and methods used in the construction, than it is likely that most courts would place the liability on the contractor. If it cracked because the structure was not designed adequately to handle the load without excessive deflection than the engineer would be to blame. I wish I could anticipate every dumb thing a contractor might do and place a note on my plans to warn him not to do it, but I don't have a crystal ball. I don't expect them to read all the specs either, because they rarely do. A qualified contractor acting reasonably should have known better than to lay bricks on a structure that is temporarily propped up. Of course the engineer could not know ahead of time how much it would deflect after removing the props. It appears that this contractor may not have been qualified, due to lack of experience.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

CVG

" Of course the engineer could not know ahead of time how much it would deflect after removing the props"

Why wouldn't the designer know. It is part of the design calculations, if the designer wants to put in the effort to do them properly.

"I wish I could anticipate every dumb thing a contractor might do and place a note on my plans to warn him not to do it, but I don't have a crystal ball."

That is normally what Notes are for. So that the designer can tell the builder the limits on how he wants it built to suit the design. It is possible to design the floor to allow the brittle wall to be built on a shored floor if you want to do the calculations and pay the extra cost for the improved deflection control.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

well the designer could estimate it during design, but actual is likely to be different. he doesn't know much or anything about the actual propping, the actual strength characteristics of the slab. is the propping pushing the slab up, or is it sagging a little bit before or after removal? how many days since the concrete was poured? What mix was actually delivered to the site and what was the actual strength? Have environmental conditions or admixtures or something else delayed or accelerated the curing?

yes, a note should be on the plans and that will at least protect the engineer. But don't count on a contractor reading it

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

That would require a quaint old fashioned practice which used to be part of the engineers brief, often called inspection or supervision. And important requirements were often discussed at the beginning of a project to set the ground rules.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Rapt and CVG:

"" Of course the engineer could not know ahead of time how much it would deflect after removing the props"

Why wouldn't the designer know. It is part of the design calculations, if the designer wants to put in the effort to do them properly."

and, of course, you would expect the contractor to know this?

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

of course this "quaint old practice" is not always practiced. it is not the engineers job to supervise a contractor. contractually it is usually not allowed. and full time inspection is only done on some projects. maybe things are different in other countries.

apparently neither was done on lolobau's project.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

CVG,
"quaint old practice"

Probably not in other countries either, more in past times, before the age of project managers, where designers had more control and were actually paid to do their job properly, until the construction was completed. I should have added a smiley (or sad) face!

dik,
I have never made the assumption that a builder actually understands engineering or design. Some understood if explained properly, others simply have no idea what you are talking about. And getting them to read notes on a drawing!! And that is where the problem with lack on involvement of the building designers in the construction process and supervision/inspections rears its ugly head.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

rapt: Yup...

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

If the brick is repaired will the problem persist? If the support structure was adequately designed then the contractor may have made a mistake. Things get very confusing in a courtroom and nobody comes out ahead. The team should address a solution and, unfortunately, the cost should be shared by all, including the owner.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

What did the owner do wrong?

BA

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

What was the deflection and span of the beam supporting the masonry wall? Assuming the slab is poured before the wall was built, the deflection that the wall will potentially see is the weight of the wall plus the floor live load.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Quote (jike)

...the deflection that the wall will potentially see is the weight of the wall plus the floor live load.

And don't forget that 'pesky' creep and shrinkage deflection that will occur over the lifetime of the slab.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

BART... he was the one benefiting from the 'reduced cost'...

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

dik...I should have known...

BA

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

jike,

You missed the bit about the slab still being propped when the wall was built. So the wall experiences the full deflection including the slab Sw and the wall weight as well as loads added afterwards and the resulting cracking effects. And the long term effects as mentioned by Ingenuity.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

rapt,

Yes, I missed that. So, what is the total deflection?

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
Hi guys, I am quite surprised about all the comments. Thanks for all the infos. Let me uplaod an image which will explain what was happening.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)


and this is what is happenign after removing of the propps

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
I just can't fine any any article on the net which would deal with this topic "building a masonry wall on a shored floor"

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Bottom line here to the original question - "why was he not supposed to build the brick walls on propped structure" is that the prop was a temporary construction feature - presumably included by the contractor - to assist with construction of the base slab. It was not part of the permanent design and therefore needs to be removed prior to building anything else on it.

So unless you told him to build the brickwork with the props still in place, the responsibility and schedule for any temporary construction works remains with the contractor. End of.

I'm a little surprised something that size moved enough to cause significant issues, but you have the evidence in front of you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Is the cracking at the mortar joints, or, through the masonry units... almost worst place for a door opening with the large cantilever on the left... Judging from the sketch, it appears cracking through the masonry units.

Dik

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

(OP)
@littleinch: thanks for support, you make feel better winky smile
I like your statement " "why was he not supposed to build the brick walls on propped structure" is that the prop was a temporary construction feature" this covers me a bit

I attached a photo of the site

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

That's some strange looking brick.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Are these walls serving as support for those little roof insets? If so then they likely needed the shoring in place to continue the construction sequence so not sure how this could have been avoided in that case other than specifying they would need to wait to proceed until the slab reached specified strength.

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

To me, the additional small self weight deflection of the cantilever doesn't seem like enough to be the primary cause of the cracking. The cantilever end of the slab seems to be carrying load from the trough (or whatever) at the roof, too.

I'd be interested to know whether sufficient reinforcing is in the correct position in the cantilever slab. I can't see cracks in the slab in the photo, but it seems like there's more at issue than just the timing of the shoring removal.

If all the reinforcing is in place and you're satisfied that the structure has the capacity that it needs, then you can patch the cracks, right?

RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Lolobau:
I second Wallache’s funny brick wall comment. It looks like your wall is pivoting on the left exterior window wall and conc. beam below, in your elevation view. The back span isn’t much longer than the canti. span, and it would appear that there is not enough rebar in the wall, at the door jambs, at the door head, or at the top of the wall. The wall is likely picking up a good share of the balcony slab loading too. Your wall is trying to act like a deep beam, but has not been properly designed, reinforced or supported. You may also want to check the concentrated reaction under your wall right at the ext. window wall.

(Edit) Also, it would be reasonable to assume that the canti. balcony slab and conc. beams below would be propped during the forming and pouring of your wall, and during its curing. Your wall and the slab below should be (should have been) properly tied together, bent tension rebars, etc. to tolerate this framing configuration. The forming joints don’t seem to make much sense, except as intentional stress raisers, or crack inducers.


RE: building brick walls on "propped" structure ? Now it cracks after de-propping

Was there any reinforcing in that wall? 2#5s around the opening or whatever?

Dik

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