×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Overhead sign crushes car on freeway in Melbourne Australia.
3

Overhead sign crushes car on freeway in Melbourne Australia.

Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
This happened a few days ago, but the article has just been updated with dash-cam footage from the car immediately behind the one involved.
very quickly it can be seen that the failure point is at the welded joint for the bolted connection. the grainy footage makes things harder to see, the base off the standoff looks weird, why would you close the end off the SHS to be welded to the main beam? Galvanising requires drainage points and a minimum area open between closed sections. Unless that is a solid block off steel? I'm not sure why they would have used a solid block off steel though.

https://www.abc.net.au/news/2019-01-08/tullamarine...

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Here's some screenshots from a better copy of the video; it really doesn't look like anything is obviously broken, though, aside from some sheet metal? Truly amazing that the driver escaped with "minor" injuries.








TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Overhead sign crushes car on freeway in Melbourne Australia.

IRstuff,

What's broken are the welds between the two upstands and the gantry horizontal. MDEAus is correct in that the bottoms of those upstands look weird.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
How the driver managed to avoid being crushed is astonishing, if they hadn't swerved the post would have laid down directly over the driver and not to the side.

I don't work with road signage at all but I do work with vehicles and structures made from SHS/RHS, about the only thing I can think off is that the ends weren't capped instead the gantry part now has to holes were the steel has fatigued and torn away around the welds. It looks like a painted/powder-coated structure rather than galvanized which would explain the absence of 'weep holes'.

In typing this I re-watched a news reel of the event and you can see two holes where the sign once stood. So my first though off failed welds was wrong it appears inssufficient strength in the gantry member.



RE: Overhead sign crushes car on freeway in Melbourne Australia.

Well, if those dark spots are holes where the upright penetrated, then the connection must have just been fillet welds around the perimeter. So the connection failed, not the gantry member.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
I don't think the upright penetrated the gantry member. I would have thought the short SHS upright would be butt welded to the gantry member. If the SHS member passed through the top of the gantry member I'd have expected buckling of the upright before the sign would have fallen. You can see in the closer image the cracks propagating from the corners of the torn out section. The Gantry member appears to have been to thin to resist fatigue loading from the sign.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I did find it humorous that the police (Acting Sergeant Jason Lane) said wind was not a factor. He might as well have said gravity wasn't a factor either!

RE: Overhead sign crushes car on freeway in Melbourne Australia.

MDEAus,
That would be very thin, and I doubt it. Hopefully, some more information will come through.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
Hopefully more information does come out, unlike in the US NTSB the ATSB only investigates Air, Rail, and Marine incidents. I don't think we will get a publicly released report unless someone files a freedom of information request a few months later.

It would surprise me that it's very thin but that's what it looks like to me. The sign has been in place for a little over 1 year having been installed at the end of 2017. What is concerning is that it was a relatively new structure.

P.S. Acting Sergeant Jason Lane is part off the Highway Patrol.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

This is a case where I think we should find out. The press will be like a dog with a bone until there is a result. This failure will be something very simple, as opposed to many transport failures.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Based on those other pictures, it does not look like it was really bolted to the gantry at all. Had it been bolted, the bolts would have torn 4 holes in addition to the hole from where the welds failed.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Overhead sign crushes car on freeway in Melbourne Australia.

It looks to me like the mounting flanges were just fillet welded to the overhead gantry.
In the frames that IRStuff clipped the bolted connections are intact.
I wonder if that type of sign was ever supposed to be mounted there?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Acting Sgt. Lane may have just meant it wasn't windy on the day of the incident.

About 20 years ago, NYSDOT had a series of issues with cracking sign structures. They found that the wind load from trucks passing under them caused excessive movement and resulting fatique. I can't find it, but there was a video of a cantilever sign structure deflecting a foot or more after a box truck passed under it.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

RE: Overhead sign crushes car on freeway in Melbourne Australia.

The overhead shots of the gantry are confusing to me, since the holes, which presumably correspond to the welded columns, are so close to the edge that I can't see how there could have been bolted connections on that side of the sign.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Overhead sign crushes car on freeway in Melbourne Australia.

In the picture showing the holes from above, I see what looks like a seam where the right red X marker is located. I'm wondering if what we see is only a sheet metal cover that obscures the actual structural members.

Brad Waybright

It's all okay as long as it's okay.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

https://bigbuild.vic.gov.au/newsfeed/new-gantries-...

No real info above. Just some good video of a similar, recently installed sign. To me, it appears the large gantry is fabricated from plate. Who knows if there's any internal structure. Should have run that HSS 'stub' through the whole member and not just attached it to the outside.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Well, that's what you get when you drive on the wrong side of the road and the sign is mounted backwords...

Mike McCann, PE, SE (WA)


RE: Overhead sign crushes car on freeway in Melbourne Australia.

My bet is it was near quitting time when was set. Plan was to come back tomorrow to weld or bolt it. Come tomorrow another job took precedence. Of course none of us members here ever were in that situation.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

IRstuff,

There were no bolts to the gantry. There was a welded stool with an end plate, and the sign uprights were end plate bolted to that. The stool, end plates, and bolts all went down with the sign. The welded connections of the stools failed, whether in the welds or in the base metal of the gantry.

It will be most interesting to me to find out if there was divided responsibility between the gantry and the sign supports. I have designed some gantries, not like that one, but over major highways. But I can't recall having designed the attachment of signs.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Australia's having a bad summer isn't it?

I'm with oldestguy. the lack of deformed material leads me to believe that the connection wasn't completed.

I guess the lesson here would be that if you have hundreds of welds to check, and can't be bothered, request a welding inspector to be hired to check them all?

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I think that hokie hit the nail on the head.
One party designed the gantry, another the sign (though it looks like a very standard sign and mount).
No one designed the integration of them.
At the least there should have been internal reinforcements in the gantry where the stools attached.
Perhaps both ribs and a heavier plate section.
But that would take planning ahead......

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Overhead sign crushes car on freeway in Melbourne Australia.

The holes in the gantry beam would seem to indicate a failure of the base metal at the toe of the welds around the structural tube base. For a sign in that position, fatigue from truck-induced wind gusts could easily be the culprit. I think it would be classified as Category E or E' fatigue detail. Depending on how it was welded, at best, it would be adequate for about 7ksi with the typical number of cycles for truck-induced gusts. At worst, it could fail at anything over 2.6ksi under what we call natural wind gust, which is the gust pressure it would see several times per day.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
The gantry does look like it was made up from plate sections.
At this point we know one thing for certain the joint connecting the stool/flanged stub post to the gantry member.
The videos and still frames shows a few things.
1) The flanged stub posts remain bolted to the sign at all times.
2) There are two holes left in the gantry while that material stays intact with the flanged stub posts.
3) Cracks around the area that the stub posts where welded to the gantry member.

Number 2 can rule out that the welded joint wasn't completed (the weld bead was stronger than the base material). There are a few scenarios to fit the video evidence which suggests a fatigue failure. Below is what I think happened that lead to the failure.

1) An undercut weld at the stub post/gantry connection on the gantry could have caused a stress riser.
2) Insufficient material strength for the gantry(lack of reinforcement, wrong material used or spec'd).

In my opinion the design safety factor for gantry material should have been enough to cover some welding defect like an undercut. However as others have noted this is likely a case of the designer of the gantry not knowing that the sign is going to be attached there at all and as such not being able to provide adequate strength.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

It has been reported that the sign is a new sign, installed after some significant roadworks - I wonder if the gantry is an older structure, and the new sign was attached to an existing gantry as part of the recent roadworks project?

I would have expected that for a new-build design, you would have some internal stiffening under the top flange at the locations of the stubs, to transfer the base moment into the webs of the main gantry beam. However, the apparent failures of the top flange suggest that there was no internal stiffening, so the base moments are being resisted solely by flexure of the top flange plate. It is not hard to imagine fatigue of the fillet weld at the base of the square hollow section stubs if the sign is subject to fluttering / buffeting.

It is also possible that there might have been some sort of resonance between the torsional mode of the main gantry box beam and the sway mode of the cantilevered sign, which might amplify the moment at the base of the stubs (and increase susceptibility to fatigue of the fillet welds around the base of the stubs).

http://julianh72.blogspot.com

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)

Quote (jhardy1)

It has been reported that the sign is a new sign

I've seen it reported that the sign and gantry were installed in late 2017 at the same time(as part of a new build after roadworks). So to me there absolutely should be internal stiffening of the gantry; which admittedly could be obscured by shadows, but evidence points to it's absence.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Agree with most of what has been said by others. A thin gantry material combined with what was likely poor welding. Just poor detailing. All that was needed would be a piece of flat plate welded onto the gantry. That would give it a larger weld circumference, reduced load on the weld and parent metals and an all round stiffer connection.

There has been suggestions (unsure if confirmed) that it was fabricated overseas. Which has much more variable and usually poorer quality work than local fabrication. (We have had some good stuff done, but the last load of 'food grade' stainless steel work we had done needed weeks of re-work.)

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Hokie, I went by a previous news report that stated that the sign was bolted and welded. What you said makes more sense, but that was a mickey-mouse design, even to my eyes. The plate should have been welded directly to the gantry, and there should have been studs where the bolts went. That's how street light columns are installed, and those seem to work pretty well.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Overhead sign crushes car on freeway in Melbourne Australia.

No studs on street light columns where I am. They use bolts out of the footing.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I've done proof engineering for similar sign gantries in the past. It's worth mentioning that the fatigue requirements in AS5100-2017 for highway gantries refers to the 2015 AASHTO code, which doesn't explicitly disallow square/rectangular hollow sections for these structures, but requires some pretty onerous FE modelling of the weld details to demonstrate that the connections are suitable (the FE model - which must be solid by the way - has to be so refined as to provide several finite elements just along the toe of an individual weld - fractions of a mm. Simple welded connections may require 10s of thousands of solid finite elements to model). AASHTO heavily favours CHSs for these structures. In practice, it seems that the rigorous FE analysis required by AASHTO is not performed by designers, and equivalent fatigue categories for circular sections are simply adopted for square/rectangular sections.

My understanding is that RHSs tend to attract stress to the corners of the sections near connections, where they are relatively stiff and do not warp in-plane to the same extent as at the middle of the walls. This is particularly the case at connections with stiff plates. Additionally, where the end of one RHS (member A) is welded to the face of another (member B), especially where they are the same size, the relatively low out-of-plane stiffness of the face of member B allows member B to warp locally. The high in-plane stiffness of the RHS walls tend to attract a large share of the load instead and you end up with some fairly non-uniform distributions of stress. For a CHS, this isn't as big an issue. Based on my own FE modelling of similar RHS connections, the stresses in the walls may vary by a factor of as much as 3-4 from the corners of the section to the centre of the walls.

I can't say whether or not this would have contributed to this particular failure, but it's likely that not enough consideration was paid to the fairly complex flow of stresses through the RHS to RHS connection. My first thought is that a simple bracket clamped around the perimeter of the SHS gantry would have provided a simple weld-free connection that is better able to distribute the loads from the sign into the gantry (not so concentrated to a single wall of the section).

RE: Overhead sign crushes car on freeway in Melbourne Australia.

It looks like a short HSS upright with a bolted flange on top was welded directly to the top of the gantry. Due to the low height of the HSS and the width of the bolted flange they had to fillet welded it from inside the HSS further reducing the moment couple. This would also help explain the clean tear of the gantry material since the outer edge of the HSS acted like a brake.

I don't see how that configuration could have worked without a taller HSS upright and stiffeners to the gantry. The thought of a 16 ft high sign fatigue bending the wide plates of the gantry is a bit terrifying.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

charlie,
Just how did they weld from the inside of the SHS with that plate on top? Limited access for welding may have played a part, but your explanation is not logical.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I think the plate is just a bolting flange welded to the top of the SHS with a full size opening or hand hole. That would have allowed them to weld from inside the SHS stand prior to bolting on the sign. The flanges look to be at least 4 inches wide and the height of the SHS stand is less than the flange width. I don't see how it could have been welded from the outside.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

OK, hadn't thought of an access hole for welding because that would be a poor detail, as it would decrease the strength and encourage corrosion. But if the stools are not high enough for welding, that is a poor detail as well. Something went wrong, either in the design or execution.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

As I read this I keep wondering;
"Was this the only similar sign installed in 2017?"

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

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (gusmurr)

I've done proof engineering for similar sign gantries in the past. It's worth mentioning that the fatigue requirements in AS5100-2017 for highway gantries refers to the 2015 AASHTO code, which doesn't explicitly disallow square/rectangular hollow sections for these structures, but requires some pretty onerous FE modelling of the weld details to demonstrate that the connections are suitable (the FE model - which must be solid by the way - has to be so refined as to provide several finite elements just along the toe of an individual weld - fractions of a mm. Simple welded connections may require 10s of thousands of solid finite elements to model). AASHTO heavily favours CHSs for these structures. In practice, it seems that the rigorous FE analysis required by AASHTO is not performed by designers, and equivalent fatigue categories for circular sections are simply adopted for square/rectangular sections.

AASHTO is poorly written IMO. Clause 5.6.2 does appear to outlaw SHS/RHS but then rules are provided for them, however there is nothing provided for them in terms of fatigue (aside from the impractical FEM requirements). I wouldn't be surprised if designers are getting it wrong.

[Edit: Or are the RHS/SHS rules only for assessing existing structures? I'd have a hard time justifying them in a new structure given what 5.6.2 says.]

This failure is intriguing because it seems as though there wasn't much wind which would tend to suggest fatigue failure, but it's a young structure. Could be a fairly diabolical oversight in design or construction, or material supply.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Retrograde; Thanks for answering my question.

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

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (steveh49)

This failure is intriguing because it seems as though there wasn't much wind which would tend to suggest fatigue failure, but it's a young structure. Could be a fairly diabolical oversight in design or construction, or material supply.

The lack of wind actually suggests that the failure was caused by fatigue. From the photos you can see that the gantry metal broke away cleanly in two squares, with only a small tear at one corner of one upright. This means that the gantry metal had been almost completely compromised by previous wind or gust effects and finally laid over in near calm conditions. If there had been substantial capacity in the connection then the gantry plates would have distorted and torn and it would have required a significant wind load.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I agree small load at time of failure makes fatigue the prime suspect but, at less than two years age, exactly how bad would the detail have to be? Standard sign structures with no particular fatigue consideration have lasted decades. I don't know when it was designed but I expect the criteria included infinite life to AASHTO.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

As it was posited earlier, fatigue of the base metal of the built-up box section that spans the roadway, may have never been considered - one engineer designs the box section to span the roadway while another engineer designs the sign supports, and each assumes the other (or someone else) checked the connection between them. Even in only a couple of years, it may have been subjected to tens of thousands, maybe hundreds of thousands, of cycles of truck-induced wind gusts.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

It should have been designed for infinite fatigue life for natural wind gust loading, and perhaps for truck-induced gust loading as well. Whether that particular connection was or wasn't is still speculation at this point, but since it's in Australia, it's unlikely it was to the AASHTO criteria. I can't imagine the Australian code is substantially different, though.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Interesting that it tore out two neat squares. I wouldn't have guessed that.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (HotRod10)

- one engineer designs the box section to span the roadway while another engineer designs the sign supports, and each assumes the other (or someone else) checked the connection between them.
Maybe, but I think it's probably likely that the connection was detailed somewhere, and through someone's oversight never got implemented when the sign was assembled. But, maybe not.

Brad Waybright

It's all okay as long as it's okay.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

IRstuff, even with a perfect weld, small out-of-plane bending stresses on the base metal will result in fatigue. Given the size of the base relative to the size of the sign, the top plate of the gantry would have seen significant stress every time a truck passed under the sign. It was doomed to fail regardless of the quality of the welds.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Tomfh,

Neither would I have guessed that. Thus my guess above that the holes were made first, and the tube was inserted and welded in place. If we had a better resolution picture of the bottom of the upright, that could be determined. There does appear to be a shadow around the perimeter indicating that the walls of the tube extended below the plate.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Hokie66,

Plug welded it? Interesting.

I hope we get some good close ups.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

No, I think all the welding was just fillet welds. May have been intended to be full penetration, but that is not what happened. Yes, some close ups are needed, along with thicknesses of the gantry horizontal and size of the tube.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
Hokie66,

If the stub post was inserted into the gantry beam a short distance(on the scale of 10-20mm), what would explain the capped end? It would seem unnecessary as the flange would cap the stub post.

The shadows around the perimeter would be deformed metal as it tore away.

A new story about it but no new information just the best guesses (same as this thread, especially my input)of engineering professors.

https://www.abc.net.au/news/2019-01-16/melbourne-t...

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Hokie66, I meant the column stub "plugged" into a hole in the gantry tube.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (steveh49)


AASHTO is poorly written IMO. Clause 5.6.2 does appear to outlaw SHS/RHS but then rules are provided for them, however there is nothing provided for them in terms of fatigue (aside from the impractical FEM requirements). I wouldn't be surprised if designers are getting it wrong.

For those of us who do not have this standard would it be possible to post the words from clause 5.6.2?

Thanks

RE: Overhead sign crushes car on freeway in Melbourne Australia.

This photo suggests the base plate was part of the gantry fabrication, while the foot of the sign was part of the sign fabrication. The two mated at the jobsite and the gantry fabricator not making any great consideration or calculation for the demands of the signage attached. All those thick plates and bolts, secured with a zip-loc baggie weld.



RE: Overhead sign crushes car on freeway in Melbourne Australia.

Nice angle.

To me the whole assembly here looks to be related and is part of the sign fabrication. The paint, plate sizes, plate thicknesses, bolt pattern, and HSS size are all matched. The motivation also makes sense because this assembly would allow the sign installers to locate and weld the base to the gantry on one day with nothing but a man lift. Then they could come back and quickly bolt up the sign on another day to minimize heavy crane time.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
Charliealphabravo

I guarantee that the stub posts were welded on before the gantry was transported and installed, they use the stub post for easier transport. Easier to transport something long and skinny then something long with 5m branches off the side.

Epoxybot

As I've said earlier the video shows it wasn't the welds that failed in this case. However they may have contributed to the lack of fatigue strength in the base material. The investigation needs to uncover how and why the fatigue strength was so low, and how it was approved as such.

If that SHS post is 200mm square then those flanges are at least 20mm thick each and since (in my opinion) the gantry tore out around the weld (weld survived intact )the gantry can't have been constructed from greater than 6mm plate (judging from the grainy pictures based on relative size of what is still attached to the base of the stub post).

RE: Overhead sign crushes car on freeway in Melbourne Australia.

MDEAus - I agree the gantry metal failed not the welds.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (MDEAus)

If that SHS post is 200mm square then those flanges are at least 20mm thick each and since (in my opinion) the gantry tore out around the weld (weld survived intact )the gantry can't have been constructed from greater than 6mm plate (judging from the grainy pictures based on relative size of what is still attached to the base of the stub post).
Great
I concur with the estimation of max 6mm plate (possibly thinner) and 200SHS.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Failure of the base metal adjacent to a weld is typical of a fatigue failure. The allowable fatigue stress on the base metal at a fillet welded connection subjected to out-of-plane bending, as the top plate of the gantry would have been, is very low - 2.6ksi under the AASHTO (American) code. Since Australian steel is not substantially different than American steel, it's probably about the same. Given the 5m height of the cantilevered sign, it would not take much wind pressure to exceed that stress, even if the plate is 20mm thick.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

So are there 3 bad gantries or 3 good gantries out of 17?

Transurban's David Clements said an audit had found two other signs on the network were also missing the component, and have since been removed.

"There are 17 gantries that have similar signs supported in this manner, and of those 17 there are only three that have the stiffener plate required in the detailed design," he said.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I was confused by those sentences too. It sounds like only 3 have the required stiffener plate. Some contractor is going to be in hot water.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I read it that only 3 required the stiffener by design. I wonder if the detailing of the stiffener would have prevented the failure. A single central stiffener for example would really align with the stubs flanges for example.

I wonder how it was called up on drawings and how it was apparently easily missed 3 times. I bet there's a lesson to be learned there.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Sounds like there were 17 total similar gantries, but only 3 of them were supporting large cantilevered signs that required the base connection to be stiffened. Either it was missed that they were required in the fabrication and none of them included stiffeners, or perhaps several of the gantries were too similar and there are 3 out there with stiffeners, but they were installed in other locations. It's also possible that the other 2 that needed stiffeners actually do have them, but they have to get inside them to find out.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I can't see the stiffeners being installed inside. I visualize a stiffener plate thick enough that the welded stub will not break free and with a large enough perimeter that the weld from the stiffener to the gantry will not fatigue.

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

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I also saw the newspaper article to which dgallup refers.  As I read the sentence he quotes I was immediately struck by its beautiful ambiguity, and wondered whether the credit belonged to Clements or the reporter.  (Probably the reporter?)

RE: Overhead sign crushes car on freeway in Melbourne Australia.

If the story rapt linked to was accurate, the stiffeners were inside and not visible, which is why no one realized they weren't there until it broke.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
Yeah those two sentences are strange, but it reads like this. Out of the 17 similar signs left 3 had spec details for an internal stiffener; of those 3 gantries 2 were missing the spec'd stiffener. All three have had their signs removed for the investigation.

"Mr Clements said the stiffener plates were not visible to the naked eye and therefore could have been missed during the final inspection of the signs."

If something won't be visible on the final inspection maybe it should be inspected at a time when it is still visible.

Denial,
Given that they are quotes I'd say the ambiguity comes from Mr Clements rather than the reporter.

It'd be interesting to get a copy of the drafts to see what the "internal stiffener" is.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Is it usual in Australia for most structures as the engineer to get shop drawings for review before anything is fabricated?

If so, the way I see it is that there are probably multiple steps in the process where both the engineer and fabricator could/should have noted the deficiency or lack of stiffeners?

1 - Engineers internal design verification process (assuming the stiffener was not noted on the drawings but designer was aware they were required)
2 - Shop detailer reading engineers drawings (assuming the stiffener was noted)
3 - Engineers review of shop drawings (assuming engineer had it on their drawings and shop detailer inadvertently missed it, or if it wasn't on the engineers drawings then the engineer realises the mistake and corrects it)
4 - Welding inspectors QA checks (assuming it was noted on the shop drawings)
5 - other...

The media insinuate a fabrication error, but it could equally be an engineering error.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I'm having trouble understanding how a stiffener on the inside would prevent those pieces of metal from being torn out of the gantry.
Can anyone help me here?

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

RE: Overhead sign crushes car on freeway in Melbourne Australia.

If it has indeed torn out of the wall it's likely failed due to fatigue, in a way too much concentrated stress on parts of the wall of the girder and too many reversals of this stress from wind/traffic etc until it cracks, crack propagates under further loading until it fails completely, an appropriately designed and detailed stiffener would likely provide a more distributed load path for the forces in effect better distributing or eliminating the peaks in stress that contribute more cumulative damage to an eventual fatigue failure.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
The stiffener could have been either gussets under each stub post or some plate on edge running the length of the gantry. It's goal would be to reduce the out of plane bending on the comparatively thin shell of the gantry (essentially acting like the web of an I beam). Or it could have been intended that a thick plate (20mm or greater) oversized around the stub post, I personally think this would be a terrible option; fatigue might still occur (at the same place) unless the skin is plug or spot welded to the thicker plate.

If the plate is large enough to avoid fatiguing at the stub post joint it would require plug or spot welding or the skin would still be able to pull away around the stub post joint.

This article doesn't add any new information but says the report is upto 8 weeks away.

https://www.theage.com.au/national/victoria/collap...

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Agree with some others that using stiffeners wholly inside a box member is fraught with danger. It just doesn't lead to effective control/inspection, even if the strength issues are addressed adequately.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Quote (HotRod10)

Sounds like there were 17 total similar gantries, but only 3 of them were supporting large cantilevered signs that required the base connection to be stiffened
Given the context that they removed signs from three gantries, I'd say the stiffener was shown on the design drawings for only those three gantries. But the quote also said 17 gantries with similar signs supported "in this manner". I hope they've asked the designer to confirm that 14 gantries didn't have the stiffeners deleted from the drawings by mistake. These things happen when copying drawings.

Quote (Agent666)

there are probably multiple steps in the process where both the engineer and fabricator could/should have noted the deficiency or lack of stiffeners?
1 - Engineers internal design verification process (assuming the stiffener was not noted on the drawings but designer was aware they were required)
2 - Shop detailer reading engineers drawings (assuming the stiffener was noted)
3 - Engineers review of shop drawings (assuming engineer had it on their drawings and shop detailer inadvertently missed it, or if it wasn't on the engineers drawings then the engineer realises the mistake and corrects it)
4 - Welding inspectors QA checks (assuming it was noted on the shop drawings)
5 - other...

I'd say it's likely that there was only one step when the mistake could have been noticed, but maybe two depending on where in the process the mistake entered.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Thank you for the explanations everyone.
I am sure that I am not the only one who has been wondering about this.

Quote (MDEAus)

The stiffener could have been either gussets under each stub post or some plate on edge running the length of the gantry.
I hadn't thought of this.

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

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I would think the stiffener, to be most effective, would take the form of a vertical plate aligning with the edges of the stub post and extending down inside the box of the gantry. Best if it attached to all 4 sides of the box, but straight down to the bottom would be fairly effective. Stiffening the stub against fatigue requires preventing the back edge (the one opposite the front vertical face of the gantry) from moving, so that the top plate of the gantry doesn't flex out-of-plane (vertically) and fatigue. A longitudinal stiffener could be some what effective, but again, it would have to align with the interior edge of the stub post and extend a significant distance along the gantry to spread the load along the top plate of the gantry.

The simplest and most effective is a configuration that essentially extends the stub post down inside the gantry, or better yet, actually extending the 'stub post' through the gantry and weld it on the top and bottom. That's what I would have done, as it eliminates the the possibility of moisture getting trapped inside the post, makes all the welds visible, and gives you the connection to gantry with the least amount of stress and flexibility.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

I was driving along the westgate freeway section of the M1 yesterday (not all that far away from where the sign fell) and noticed that two signs on a gantry had been removed and some white 'paint' applied at the top of the gantry that looked a lot like some NDE of welds had been occurring. The framework for the sign was all there, it was just the actual sign (large sheet) that had been removed.

I've seen similar gantries back in late 2017 painted the same colour at an industrial painter in Melbourne and I'm fairly sure the wall thickness was 8 to 10mm, though I can't be 100% sure I'm remembering the thickness correctly.

Here is a Link to what appears to be some of the research, including the FE methodology recommendations, that appears to have influenced the 2015 version of the AASHTO highway structural supports code.

I don't have the 2015 code only the 2009 code so I can't see what clause 5.6.2 states regarding SHS/RHS - if anyone could elaborate further that would be much appreciated.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

This 7 News report has better resolution than I have seen previously. At about 25 to 28 seconds into the video, the base of the post which tore out of the gantry shows clearly.

https://www.facebook.com/7newssydney/videos/sign-f...

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
If that artists rendition of the stiffeners is anything to go by they may have been SHS/RHS running from front to back off the sign. I feel that would be less than optimal but probably would have been satisfactory. On second thoughts it's probably just a guess rather than any technical insight as the base off the sign isn't accurate at all.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Looks to me like the stub was located on the front of the gantry fright over the weld to the built up section, you can see what looks like the return of the front wall in the 1st photo, and what looks like a backing plate at the junction.

I thought and could be wrong, but for fatigue shouldn't any backing plates be removed?? Wonder what AS/NZS1554.5 notes?

2nd photo doesn't seem to show any fusion into the backing plate, I feel this is a key point if it was supposed to have full penetration as suggested by the presence of a backing plate, with the root of the weld to the gantry potentially acting as a crack initiator?

Partial penetration butt weld wouldn't require a backing plate.

You can see what looks like some of the tack weld where backing plate was attached to the wall during fabrication in the 2nd photo, and the 'shadow' of where it was placed in the junction. Its probably still attached to the gantry!




RE: Overhead sign crushes car on freeway in Melbourne Australia.

How would you remove backing plates from inside the closed section?

RE: Overhead sign crushes car on freeway in Melbourne Australia.

Don't ask me!... like I said I'm not sure now having looked through AS/NZS1554.5. It just states for permanent backing left in place, that it needs to have a similar weldability.

Definitely if you look at the top backing plate there is weld fusion on the backing plate, but the bottom one really doesn't look like there was any, but could just be my eyes playing tricks on me.

Shame these pictures weren't taken directly after so you could see what might have potentially been older rusted cracks vs fresh fractures?



RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
I didn't notice it when I watched the video but it would be interesting to know if that corrosion on the fracture site has happened pre or post failure. I would like to know the date of those images, I tried to see if I could find the source off those images to see if exif data was still attached but had no luck.

I doubt it was meant to be removed as those appear to be approx 50mm or longer stitch welds on the backing, which was likely used to help keep the top plate in position during fabrication. notice that the welds are only on what would have been the front face of the gantry and not the top plate.

I will revise my material thickness estimate up to 6-8mm (based estimates of a stub post of 125x125mm SHS and a M22 bolts I don't think it is 10mm). These could very well be what you saw at the industrial painter in 2017. I had a thought about estimating proportions from a weight I thought I saw in an article which I think was 4000kg but a rough estimate for the main structure of the sign itself is 1026kg using 200shs 10mm wall thickness. Now I can't see the rest of the sign making up 3000kg but I cant find what article I read that in anymore.

Until there is a report produced I don't think we will get much more new info.

P.S. whoops I thought I posted this half an hour ago

RE: Overhead sign crushes car on freeway in Melbourne Australia.

MDEAus,
For what it is worth, the sign fell on 8 January, and the photos were taken from the 7News video of 20 January. So less than 2 weeks after the failure.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

You can see it's already all brown and corroded in the original collapse video.

RE: Overhead sign crushes car on freeway in Melbourne Australia.

(OP)
Tomfh
I was mainly concerned with the fracture zone; while that shows the inside off the gantry it's about what I would expect from a fabricated steel section that has been painted/powder-coated. I.E. you can't sandblast and paint the inside of a closed section.

Thanks hokie66.

At this point in time though with the evidence we have corrosion would have only sped up the final result rather than been the cause; the gantry would have started to fail for corrosion to have formed. The corrosion may paint a picture of when the initial cracks started to form though and whether they should have been picked up on by inspections.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close