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Denny's Sign Failure 8

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But the bolts that remain on there look to be intact but deformed. They would have had to pull through the bottom plate (no plate washer??).

One look at that bottom plate would show any significant deformation at the bolt hole.
 
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We don't know the thickness of the bottom plate. We do know the top plate is very thin and the bolts are TOO far from the square column for such a thin plate. If the top, thin plate is flexing under load it loads the bolt head on one side which can cause the bolt to fail by bending. High strength bolts are very prone to this failure. I had an engine application that kept breaking
grade 8 bolts due to casting draft. Spherical seat washers resolved the problem.
 
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In this picture that I posted earlier:


[img

The lower bolt looks like it's kind of resting low, in the hole. I'm kinda wondering if those are 1/2" bolts through 3/4" holes. Or something similar.

It looks like the two remaining bolts were installed with their heads down (originally). A 1/2" bolt is 3/4" across the flats. So if you put one in a 3/4" hole, it would sorta work. And sorta not.

Thing is, those bolt heads do appear to have been pulled through the hole. And I REALLY don't think a proper sized bolt would have done that. Hence my suggestion.

Now. Why would someone do that? Because they didn't have the right size. Maybe they forgot them entirely. So they send Mikey to the hardware store, and it only has bolts up to 1/2". So Mikey takes what he can get and brings them back. Since the job "HAS" to get finished, they use the 1/2" bolts. And they WORK! Quite well, considering.

And then they don't.


I am having trouble thinking of another way to explain a bolt head pulling through its mounting hole, relatively intact.



spsalso
 
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Yes absence of plate washer and misfit bolt/hole combination. But why now? I don't suppose that the wind was max speed when the sign fell.
 
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TugBoatEng said:
We do know the top plate is very thin
Click to expand...

We effectively know the opposite of that.. look at Spalso's posted photos; the flange attached to the sign is at LEAST 1" plate. That's not 'very thin'.

Signs mounted this way are extremely common - most of us probably drive past dozens of them every day. And erecting a gigantic sign mast (the Denny's ones especially always seem to be enormously/excessively tall) is a non-trivial endeavor. I have a strong doubt that this install was performed by some fly-by-night contractor.... Based on the condition of the flange on the sign I'm betting the primary root cause here is corrosion. To my eye it doesn't look all that complicated.

I also suspect that what look to us like undersize bolts were perhaps a few sizes larger when originally installed, and before they were exposed to 25 years of heavy corrosion with no maintenance.
 
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I do want to walk back my rhin plate comment. The more pictures I see the more I understand it to be incorrect.

That doesn't change my weld distortion comments.

Then position of the bolts in the flange was still very wrong. They should be as close as possible to the support column.

As for the bolts pulling through, that's challenging. Corrosion will be focused in the higher strength steel so it's possible to say that the nuts reduced in diameter to cause the pull through.
 
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I think we have different usage of the "field" weld.

There was a change in the 80's i think after several failures offshore. Basically any weld that's not done in a fabrication shop with QA and certified welding supplies etc is deemed field.

Prior to that there was "oil" yards basically all over the place and stuff was being fabricated with a mixture of hand grinders suspect welders and virtually no QA on the materials. So stuff like this was welded up in a muddy yard in the rain at night on the top of a cliff. And they all had metal skips which were used as metal storage and they just used to grab something that would work. These days the scrap metal skips have cameras on them and if you want something out of them it has to be booked out and put on the job card. THe Norwegians banned it and then the post Piper Alpha regs came through.

I am wondering what inspection and sign off is required on structures like this now.

 
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Do they say anything about pre/post install requirements?

Was trying to think of anything similar scale in UK or near me in Europe. And can't. Even MacDonald's signs you can get to with ladder and they are not that common.
 
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Brian Malone has a good point, Doing a web search on the subject of sign inspection, finds a few locations like New York City that have explicit regulations dealing with sign inspection.
In most other US locations sign inspection would be governed by the local interpretation of the 2018 International Existing Building Code (IEBC) or something similar.

This same lack of regulatory inspection also occurs with many other structures, leaving the responsibility strictly to the owner (and perhaps his underwriter).
 
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So it would appear the sign was NEVER inspected; IF the failure was improper bolts, and you hold that an "annual" inspection would have revealed that failure, and prevented a death.

In reading Brian Malone's linked article, I notice that there was no statement that anyone ever inspected the physical sign, including during and immediately after installation.


spsalso
 
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TugboatEng said:
That doesn't change my weld distortion comments.
Click to expand...

In my opinion your analysis of the weld distortion creating that circular pattern of corrosion is exactly correct.

Alistair Heaton said:
I think we have different usage of the "field" weld. Basically any weld that's not done in a fabrication shop with QA and certified welding supplies etc is deemed field.
Click to expand...

We have the same definition.

A 100' tall sign mast is a highly engineered structure - it's not a 4" stop sign post that's stuck in the mud.

The welds on the post flange and the sign flange would have been performed in a fab shop, under an engineered WPS.

We're talking about late 90s/early 00s here as far as engineering control; this sign wasn't erected in the 60s.

 
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Looking at them I suspect they are a modular pick a height and the required number of reducing dia tubes turns up that fit on a lorry trailer and a "sign" crew turns up and mods it to the height required and type that's being installed.

But maybe I am just cynical on cost saving prowess of large franchise groups.
 
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Alistair_Heaton said:
Was trying to think of anything similar scale in UK or near me in Europe. And can't. Even MacDonald's signs you can get to with ladder and they are not that common.
Click to expand...

We have very few signs that are so high as those common in the USA; I don't want to say "none" but I can't think of any in my area (near Toronto). In the USA there's a forest of signs like this at practically every motorway junction, and non-stop billboards (which we also have fewer of). I suspect there's a permit process that puts limits on this ...

typical around here (note the McD's sign):
closer view of that one
 
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Rain getting in between the plates and freezing, I have seen icejacking break bolts, it's somewhat common for streetlamps here and a ski tram pole fell over because of it.
Now they use a set of extra nuts to give airspace between plates.
 
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Signs the property owner does not care about trouble me. This sign which still looks in reasonably good condition was installed in 1984.
Screenshot_from_2023-01-25_17-26-24_zdlyti.png
 
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Why would someone do that? Because they didn't have the right size
Click to expand...

There's quite a few ways to screw up the bearing area and allow pull-thru. Wrong fastener size, correct size but wrong head/nut profile (heavy hex vs standard hex vs thin), hole size/taper and embrittlement due to torching plates rather than drilling, corrosion of the fastener or hole, and cracking the plate itself come to mind.

I wouldn't be surprised if this was erected without washers, in this area relatively few sign/light posts have them. Most also cantilever everything off studs with the afordmentioned multiple nut method providing a space between plates, another terrible design practice IMHO.
 
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Alistair Heaton said:
Looking at them I suspect they are a modular pick a height and the required number of reducing dia tubes turns up that fit on a lorry trailer and a "sign" crew turns up and mods it to the height required and type that's being installed.
Click to expand...

Uh.... no.

The foundation for an 80' tall sign mast is a non-trivial endeavor. This is not your barn.
 
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