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Real life truss failure!
8

Real life truss failure!

Real life truss failure!

(OP)
I was called out to look at this truss which has failed. Its a Steel warren roof truss. The layout is shown below - but I’ve crossed out the vertical which doesn’t exist - which I think should have existed!

It looks to me as though the second last diagonal, the compression member buckled due to excessive compressive force, and as it buckled it pulled the last diagonal, which should be in tension, causing it to buckle also.

Any thoughts on the mechanism? There are hundreds of these trusses throughout the building and this one has failed.

Disclaimer - not my design!! I just got asked to review this failure!



RE: Real life truss failure!

(OP)
Here’s the type of truss... can’t seem to upload 2 images for some reason..

RE: Real life truss failure!

In the picture, looks like the top and bottom chords are angles. Do you have view with wider angle? Also, the actual shape of the members? What is the external force that seems pushed up from below.

RE: Real life truss failure!

Looks like a normal bar joist.

RE: Real life truss failure!

(OP)
Yeah, all members are angles. Funnily there is no external force below pushing upward. My feeling is the bottom chord bent upward, was pulled upward, when the compression member buckled so badly.


RE: Real life truss failure!

Seems like a lot of buckling and disfiguring in an isolated area with adjacent members undamaged. I wonder is someone bent the compression diagonal during construction or after so that it did not take much to make it fail. Is there a heavy point load above it that is new?

RE: Real life truss failure!

(OP)
That one truss supports significant copper bar services, which the other trusses do not. No point loads above. You could be right Ron about just enough damage during construction to cause disproportionate buckling.

RE: Real life truss failure!

The truss bottom chord is in tension with hinging weight (ceiling?). Both top and bottom chords seem straight in good shape, and the end support does not seem distressed, there is no good reason for the diagonal to buckle that much. Did the owner mention anything suspicious?

RE: Real life truss failure!

"Significant copper bar services" would add considerably to the force in that web member. That could be all or part of the problem.

BA

RE: Real life truss failure!

The single angle compression web failed. Whether due to lack of initial straightness or excess load, it is hard to tell. But single angle webs are tricky to analyze.

RE: Real life truss failure!

Uplift might cause such a failure. Was there an extreme wind event?

RE: Real life truss failure!

That looks a lot like someone tried to jack it up at the end of the bottom chord; the last tension diagonal does not look as if it was in tension when the rest of the damage was done. Likely it happened after the roof was on and whoever did it was glad to finish the drop ceiling.

RE: Real life truss failure!

I am more agree with 3DDave, an locally exerted external force from below.

RE: Real life truss failure!

Yes, that could have done it.

RE: Real life truss failure!

Is there any indication that this failure is a recent event, chipped paint on either side of the bent area, etc., or could it have been hit by a lift some time ago during installation of the drop ceiling, sprinkler piping, electrical work, drywall, etc.?

RE: Real life truss failure!

What are “significant copper bar services”

Bottom chor appears to be deflected upwards. Top chord appears to remain straight. If this was a loading failure I would expect significant distorting the top chord. Very suspicious failure.

RE: Real life truss failure!

Thanks for posting. But I figure this should be in the "Engineering Failures & Disasters" forum...

I agree, the failure is peculiar given the extent of damage to some members and the lack of damage to others. My initial thought are the top cord remained intact due to significant engagement of the roof diagram. The truss largely remain load supporting due to catenary action from the last tension angle and bottom cord. Also some load distribution to adjacent trusses is likely.

As to what load could have trigger the event. Hard to say without further information. Snow load, hanging loads, etc...

RE: Real life truss failure!

(OP)
Retired 13, thanks, yes the member circled red in the left hand side of your markup is also buckled. This is a bottom chord restraint which is inclined back to the deck level wind girder.

I’m not ruling out wind uplift. However that would have put the badly buckled member in tension.

Its the only truss that has been loaded with these heavy copper services and is the only truss that has buckled in such a way. These services impose heavy point loads hanging from the bottom chord.

That said, its still a very unusual mechanism and I agree, if I didn’t know better I’d say someone tried to jack it from below. I just don’t see how that would ever have been the case. The client hasn’t mentioned anything unusual either.

RE: Real life truss failure!

It could be from top loading. The second from last diagonal is normally a compressive member and I think it failed first by buckling. When that diagonal buckled it rotated the joint below counter-clockwise (in MIStruct's picture), causing a further upward bending deformation in the last diagonal, even though that member was and probably still is under some tension.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

(OP)
That’s my feeling on it ax1e.

RE: Real life truss failure!

Thought so, but I wasn't sure. As they say, "great minds think alike." smile
I'm not a believer of the jacked up from below theory. Don't see any reason to do that.
And damages done after construction are usually nearer to mid span, not against a wall.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

ON a fair number of similar examples I could see they all had a vertical member at the end.

That missing element, combined with some point loads on the lower element would seem to have pushed it beyond the limits, but it's very odd.

Did that extra load make both struts tensile and push the final strut into failure?

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

RE: Real life truss failure!

If it's uplift or overload, then where did the dent in the cross-piece angle (dark green side) lower flange come from? The part of the angle that looks to have no connection to any load path?

RE: Real life truss failure!

Dear MIStructE_IRE ,

Do you have any picture when the roof installed ( before suspended ceiling and mech. installation ) ?. IMO, The buckling of the second last diagonal, ( the compression web member ) can be explained with overloading but will not explain the plastic bending of bottom chord from the same node and plastic bending of last diagonal (which is tension element).
These kind of deformations is likely due to impact loading which could be a forklift impact. IMO , The ceiling or mechanical erection group made this mistake and kept silence..

RE: Real life truss failure!

By "significant copper bar services" I'm assuming you mean a large electrical distribution load center?

I'm having trouble with the overload from above theory. The location and nature of the failure suggests excessive shear - meaning it would have to be a point load or very confined distributed load on that joist near the wall. A load center could do that. BUT - if that were the case, wouldn't that severely degrade that joist's ability to resist the load? I would expect to see some sort of deformation in the deck and bending in the top chord of the joist now that the bottom chord and web members have failed. It doesn't seem to be there. That suggests to me that there was some sort of damage from below - whether it was jacking or hitting it with a lift or something else is impossible to tell - and the applied load from above has never exceeded the capacity of the damaged joist. It seems the most likely given the nearly pristine condition of everything else in the vicinity.

RE: Real life truss failure!

3DDave
Presumably the "dent" is a local flange buckle due to compressive stress in the flange caused by latent bending.

The paint there and everywhere else appears intact, suggesting no impact force, or excessive care if there was any high loading there.

Little Inch
A vertical member at that joint, if installed, might have contributed somewhat to resisting excessive rotation of the joint, but of course it wasn't there.

Pham
High load anywhere on the truss could have overloaded the compressive diagonal. Once buckled, there is virtually nothing to prevent upward translation caused by the tensile load in the last diagonal. An evenly placed heavy uniform load from above might not tend to show any local deck deformation.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

My bet this was done during initial construction. Damage in handling and they got away with that, unnoticed. No way with loads on top would,that end of bottom chord be bent up.

RE: Real life truss failure!

MISTRUST
I think your initial post nailed it dead on.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

OldestGuy
Naw.. Too hard to believe nobody noticed that since Day 1.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

(OP)
Here’s a closeup of the connection. The diagonals are welded to the bottom chord, which may have provided just enough fixity to bend the bottom chord upward as the diagonal buckled.

I don’t think It was the top chord loading. I tHink it was the relatively new bottom chord point loads (which other trusses do not have)




RE: Real life truss failure!

Thanks. Paint damage is noticeable now, showing nonuniform tnsion in that flange... from rotational bending? I think so.

Where, why and how do you get a point load from below there??? Especially the "why". Not buying that.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

RE: Real life truss failure!

Looks like some separation of diag at the joint. That would tend to indicate the compression diag rotated the joint putting tension there, rather than a point load from the right hand side, which would have instead compressed that bit.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

I will only believe that if somebody explains the reason for the supposed upward loading.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

These diagonals are the highest loaded members in the group shown, so any buckle would have quickly released considerable energy. Over-rotation counter clockwise, followed by tension diagonal pulling it back a bit.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

That upward loading was during handling when they dropped the overhanging end on the wall and it bent up the end of bottom chord and bent up that last diagonal. Explains that torn up end of last diagonal upward leg. Luckily the bending resistance of top chord still carried the load over that last few feet.

RE: Real life truss failure!

Maybe. If it is new enough structure and we are seeing this for the first, or second time ever, yeah, maybe. But still hard to believe the deck was built on top with it like that without any flags being raised. OK, stranger things have happened.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

RE: Real life truss failure!

when was that bare metal structure installed ?

another day in paradise, or is paradise one day closer ?

RE: Real life truss failure!

Hell, could have been damaged any where between the fabrication and finally setting it in place. Rush job. Bet bottom of the bottom chord end has paint damage also.

RE: Real life truss failure!

While I can intuitively see the buckling as being caused by a point load from the overhang, it's hard to imagine the inherent stress causing that much buckling with very little ancillary damage.

One other possibility, given lots of people wandering in the plenum during installs and maintenance, is that someone fell against the diagonal, which. when added to the compression. cause the diagonal to buckle.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Real life truss failure!

ax1e - I agree it should have been seen, but I've been on too many job sites with obvious damage that was never repaired that everyone else conveniently "didn't notice" until I pointed it out and then continued to "not notice" as I repeatedly pointed it out to them. It's rarely things as critical as this (in those cases I scream load enough to get the right person's attention), but the mentality is the same. When you've got the frame up and all the other trades lined up waiting to come in and get to work, the last thing anyone is going to do is hold up the whole project for a week or more while one replacement joist is manufactured and shipped to the site.

Based on the joist and the deck, I'd say this building is circa 1950s or 60s. Hard to say whether or not the people involved at the time were terribly concerned about this or not.

The new load on the bottom chord makes a lot of sense, especially since it looks to be localized near the end of the joist. Now that we know it's there, I agree that it's a likely culprit. That clamp connection looks terrifying. I see the unistrut markings - is it zinc coated? If not, and it's just bare steel, I'd be less likely to accept that as the reason as the joist bottom chord has rust where the paint has been damaged.

RE: Real life truss failure!

I'm with oldestguy. I think this happened during construction. If this had been from an overload scenario, I'd expect to see some distress in the deck or adjacent joists.

RE: Real life truss failure!

(OP)
This was built circa 1995. The trusses are 1000mm deep and the fiagonals are typically 50 x 50mm angles - so not something you’d damage by falling against.

It certainly could have been damaged by a forklift etc but I really don’t see it. This is a data hall. There’s no moving machinery etc. That’s not to say it didn’t happen during construction but again, I really find it hard to believe given its age and the fact that this is the only truss supporting heavy services and is the only one that’s failed.

Really interesting to get everyone’s view - so thank you all. Keep it coming!

RE: Real life truss failure!

1995? Wow. I was way off on that one. Different countries, different trends and nuances in design, I suppose.

RE: Real life truss failure!

(OP)
Yep - We’re miles behind you guys!!

RE: Real life truss failure!

Well, I don't know when the damage occurred. Is stand behind the point that if this type of failure happened due to overload you will see significant distortion in the top chord and the buckling and distortion of the web members will also come out in the top chord.

From your newest picture, it looks like the damage has been here for quite some time as the dust and dirt on the chord appears to be uniform. If this was something that was new, the dust would not be uniform on the members.

RE: Real life truss failure!

Can be damaged by high-lift during roof inspection, pipe/cable installation...

RE: Real life truss failure!

This got hidden early on with that suspended ceiling. So who's to know?

RE: Real life truss failure!

I guess this damage was uncovered by another ongoing/scheduled activity under the roof, don't think it has caused noticeable defect below the ceiling.

RE: Real life truss failure!

The most likely culprit is the additional load hanging from the bottom chord near the end of joist. The second diagonal failed in compression, causing the end diagonal to pull the end of the bottom chord up. Rotation of the bottom chord caused the kink in the end diagonal.

BA

RE: Real life truss failure!

I'll put my money on a manlift (scissor lift work platform).

The workers were going up with the manlift and not paying attention as they elevated the platform. The last two web members were "lifted" by a force coming up from below, i.e., the handrail around the manlift platform. The worker(s) involved aren't going to tell anyone if no one saw it happen. Their employer would have to pay to get it fixed the they would be out of a job.

There are sprinkler pipes that were installed after the structure was "completed". You have wall panels that had to be placed. You have the metal studs erected. Workers often use the manlift to hoist materials during construction. They are looking at something that has drawn their attention from watching the other end of the platform and bingo, they hit the underside of the node with the handrail around the platform.



RE: Real life truss failure!

One way or another that end of bottom chord got a whack going upward. Not load related at all.

RE: Real life truss failure!

axle1 - the flange is in torsion, just like the other one. It's probably where the force was applied. A photo from the opposite side would have cleared that up.

gtaw - scissor lift makes the most sense. Probably when they were putting in the wires to hang the ceiling where they had to get to the underside of the roof. It's when the scissor mechanism has the greatest extension leverage and when all the structural people are off the site and/or not looking.

RE: Real life truss failure!

Probable fix, if required. Add hanger if it is not there already.

RE: Real life truss failure!

What's the bottom end of those extrusions look like? I wonder if they've been taking the load that should have transferred to the end of the truss. Probably best to leave them in place until a repair is made.

RE: Real life truss failure!

How many jobs have I been on that the contractor put something like this on his punch list and promised to fix.

RE: Real life truss failure!

My money is on the workers installing the dry wall or drop ceiling did it with a scissors lift.

RE: Real life truss failure!

Another situation might have led the owner to notice the damage - noise. As the connection is getting loose, when the joist deflects, some metal might rub against the other that produces a repeated squeaking noise.

RE: Real life truss failure!

Interesting failure. My guess is the additional load from the hangers has caused the final compression member to buckle, rotating the node and adjoining members.

Do you know the magnitude of the loads? If the truss has failed due to overload then are the other trusses safe?

RE: Real life truss failure!

It wasn't caused by overload, but the heavy localized load may have contributed to the buckling - upward forces near the joist end meeting the confining force near the first hinger, resulting in excessive compression in the web members. The roof was confined by the heavy load, so it remains flat, evident by the unaffected top chord.

RE: Real life truss failure!

Quote (retired13)

It wasn't caused by overload, but the heavy localized load may have contributed to the buckling -

You may be right, but you do not know it wasn't caused by overload. Copper is a pretty heavy metal. It would be foolhardy to recommend a repair without determining the magnitude of the load from the "copper bar services".

BA

RE: Real life truss failure!

(OP)
I will be doing analysis shortly, going into it with an open mind, and lets see how much compression was in that last compression diagonal.

RE: Real life truss failure!

The key for me is whether there is any deflection in that top beam.

If not then it got whacked from underneath at some point seems to be the consensus

If there is actually a visible or measurable dip or bend in the top T section then it could have been buckling under additional compressive force caused by the additional weight applied.

But the fact that the beam looks like it is surviving and hasn't apparently bent is very interesting. I can't see how the elements would bend that much without the top chord moving downwards and creating a hinge at the junction of the 2nd and third diagonal.

At the same time I would reinforce the attachment of those down tubes. They look like they are literally hanging on by their finger nails....

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

RE: Real life truss failure!

BA,

Whatever service was designed for, if overload, the top chord must deform too, and might not be just one place.

RE: Real life truss failure!

Looks like uniform corrosion under that flaked paint.
If that is correct (can't really tell from those photos), it indicates that the damage has been done long time ago.
I have no idea, but would there be a way to determine when the damage occured using the corrosio as an indicator? I'm thinking wall thickness measurement at that point a e few inches further, under "good" paint?
Probably to small a difference to work with?

RE: Real life truss failure!

Back to what happened and fixing it. My take it is more likely to have been damaged before placement some how rather than a mistake with a man lift gong too far. Then for any repair with replacement, etc. Ya gotta lift it during repair so you will put a load on it for service after repaired. Jack it up against that roof planking and load? No way. Likely to just damage it elsewhere. It won't move. The least any repair will do is provide help against further loading. However cutting out the damaged parts, which now do carry some load, then you run into final repair leaving it more deflected than it is now. Needs some careful thought before doing anything. Might even be best to do nothing.

RE: Real life truss failure!

who'd attach the out-of-plane stringer to a bent flange ?

At lest the fix is straight-forward … cut out the cancer, add new, paint, done.

another day in paradise, or is paradise one day closer ?

RE: Real life truss failure!

One possible fix that would take more loading, but will look pretty bad is as follows. Weld an angle at the truss end support and another at the lower chord, at the end. Leave all other parts as is. Between these two angles install (weld) two threaded rods, one on each angle, one left hand thread. On these threaded rods install a turnbuckle (before they are welded). Due to space limits, I'd make this turnbuckle from a short length of pipe and would weld nuts to each end, one of which is left hand thread. Turn to tighten and get a substanti0asl tension load. Tack weld so it can't turn or use a lock nut. Looks bad, but will work. A cheap fix. Might add some more metal to the buckled angle . If there is difficulty getting large enough threaded rod diameter, use two of them, side by side.

Edit: The so called easy replacement fix ain't so easy. Unload the bent diagonal to the support first? The fix won't be loaded so easy.

RE: Real life truss failure!

Well before this drops off the first page, please be sure and let us know what you find and what you intend to do to repair it.

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

RE: Real life truss failure!

All the web members are single angles weld to one side of the top and bottom chords. Why couldn't new web members be welded to the opposite side of the damaged web members? Once the new web members are welded, the bent ones could be removed.

I would suggest checking the top chord member to determine if it is deflected downward from the roof load. It doesn't appear to be from the photographs, but you never know until you check it. Assuming the top chord is undamaged and there is no sag, you should be good to go.

It might be advisable to unload the open web joist to the extent possible, but it doesn't appear that the roof loads are that high considering the roof doesn’t appear to be deflected downward to the point where it is noticeable in the photograph.

Best regards - Al

RE: Real life truss failure!

Was the building smaller at one point in time. It looks like the far wall might have been added in recently. The only times that I've ever seen damage like that in a factory has been when there was either a hyster loader or a backtipping truck involved. A backtipper truck can bend a thick I beam like paper if the truck driver is not paying attention to what he is doing. Hysters are very similar, but obviously not as powerful.

What other source of upward force could you possibly have. Maybe a skyjack or boomlift operator? Both can push upward, but how will you be able to tell for sure?

RE: Real life truss failure!

Quote (MIStructE_IRE)

It looks to me as though the second last diagonal, the compression member buckled due to excessive compressive force, and as it buckled it pulled the last diagonal, which should be in tension, causing it to buckle also.

With every fiber of my being, I've wanted to believe that you did not, in fact, observe a unicorn. And by "unicorn" I mean a genuine, theoretically predicted, overload buckling event. I wanted it to be some pragmatic, pedestrian thing to do with forklifts or misbehaving construction workers. The usual. But, alas, I've come to the conclusion that your original explanation is my preferred explanation for what has actually taken place with this truss. Unicorn.

Below, I've attempted to tell a cohesive story of this truss failure as it might occur via overload. I haven't actually added anything to what has already been tabled above. What I have done, is attempt to put a bunch of it together into one cohesive story. I've also presented things as though they might have happened in sequence which is false. Obviously, all of this stuff would have happened, progressively, in unison. I just find it easier to conceptualize it this way.

Quote (human909)

The truss largely remain load supporting due to catenary action from the last tension angle and bottom cord.

I feel that aspect of things (yellow line below) is very important to the story of this failure and did not garner enough attention initially. I lean on it in what follows.

Everything below is also attached as a PDF in case others want to sketch over my stuff to show me how I'm wrong etc. Obviously, my theory is still just one theory of many. It's a pretty good story though... princesses and dragons.

RE: Real life truss failure!

Quote (MIStructE_IRE)

It looks to me as though the second last diagonal, the compression member buckled due to excessive compressive force, and as it buckled it pulled the last diagonal, which should be in tension, causing it to buckle also.

I disagree with the bolded part a bit, at least semantically:

1) The last diagonal is in tension and, I suspect, always has been.

2) What you've described as the "buckling" of the last diagonal is really it having been rotated at the bottom in order to keep the second web from compression buckling to the side infinitely. So it is a member currently experiencing axial tension and end bending but not buckling.

3) The last diagonal, as a result of developing the canternary mechanism shown above, has likey had it's axial tension increased as it has effectively become a shallower tension web than it originally was. I'm not sure "caternary" is technically the right term here but human909 chose that so I rolled with it. I'm sure that we all get the gist of it: a thing that moved and resisted greater shear in having done so.

RE: Real life truss failure!

Nicely presented, KootK. I think you have nailed it.

BA

RE: Real life truss failure!

Thanks for the vote of confidence BA. It'll be interesting to see what critiques inevitably come.

RE: Real life truss failure!

My concern with this as an explanation is this - how much energy was absorbed in that amount of distortion and where did that energy come from? In typical buckling the energy comes from a change in vertical height of some amount of weight, but here no other part of the structure appears to have moved at all.

So how much energy was required and where did it come from?

This is why the energy supplied by a lift is more attractive an explanation.

RE: Real life truss failure!

I agree with your analysis, KootK. I commented twice, once on each side of the argument, but hadn't focused at the time on the loading from those hangers.

RE: Real life truss failure!

All, please do me the courtesy of giving me 20 min to make one more contribution before we proceed. Some new information has been brought to my attention. I can weave it in, it's going to be killer, but I need 20 min to do the Blue Beaming. And, you know, a little work stuff...

Quote (3DDave)

My concern with this as an explanation is this - how much energy was absorbed in that amount of distortion and where did that energy come from? In typical buckling the energy comes from a change in vertical height of some amount of weight, but here no other part of the structure appears to have moved at all.

You're right, and I'll answer for that shortly.

RE: Real life truss failure!

(OP)
I agree Koot. The last diagonal tension member is bent, not technically buckled.

I fully agree with your theory above and from my initial calcs, this particular member is in theory overstressed - assuming the roof is even subject to its design imposed load, which it may never have been. However having gotten a closer look today - look at the localised damage to the bottom chord restraint. Its just at the tip of the angle flange (right hand side of the photo) and I don’t see how anything other than impact would cause this. Anyone disagree?

That said, the member is overstressed regardless and i think the slightest tip of accidental damage was enough to cause this failure!

RE: Real life truss failure!

(OP)
Another good photo..

RE: Real life truss failure!

So a friend has approached me offline and challenged me to explain the presence of the kink at the upper end of the last diagonal, as shown in the first sketch below. And I'm grateful for that because, while it represents an oversight on my part, I believe that piece of the puzzle can be also be woven into the story that I told earlier and, in the weaving, make it a richer and more complete tale.

Updated sketches below and attached. The difference:

1) Initially, I'd assumed that it was natural causes that created the perturbation in the second web that led to its eventual overload buckling. Misalignment, eccentricity etc.

2) Now, I proposse that there was some impact event delivered to the first web that created the perturbation in the second web that led to its eventual overload buckling.

So still genuine buckling but initiated and/or exacerbated by whatever impact event happened up near the seat. It's pretty common that real world failures are the result of a combination of things rather than by any one thing. So, in this story, most everybody ends up being correct to some degree. Princesses, dragons, and wizards as it were.



RE: Real life truss failure!

IRE,

Can you red-mark/pointing out the broken part on the overall view? I couldn't make the connection and get good picture of it. Thanks.

RE: Real life truss failure!

Quote (MIStructE_IRE)

Its just at the tip of the angle flange (right hand side of the photo) and I don’t see how anything other than impact would cause this. Anyone disagree?

No, I agree, that's pretty damning..

Also the twist that you see between the connection plate and the angle. The bottom chord tried to fight back.

RE: Real life truss failure!

(OP)
Sure, You mean this?

RE: Real life truss failure!

(OP)
I agree Koot. I think the already high stress combined with the impact created the perfect storm here. So everyone was right in a sense... gold stars all round!

RE: Real life truss failure!

I hate to say it given the amount of effort that I've already put in going the other way but I'm pretty solidly in camp impact now. The last web may well have compression buckled.

RE: Real life truss failure!

I do believe the overload contributed to the failure by impact from below. It needs the forces from both the top and bottom to cause damage like this. Note that this is a localized failure, the neighboring members and chords are conspicuously remained straight.



I was joking to pledge for star, but appreciate for getting it anyway. Thanks.

RE: Real life truss failure!

I think the impact explains why the tension tie is bulging upward. Also, the truss has rotated that caused the separation of the bridging.

RE: Real life truss failure!

did anyone see how the drywall was installed? Maybe the scissor lift operator hit the wrong lever.

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