40-ton timber arches collapse in Hickory, NC
40-ton timber arches collapse in Hickory, NC
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40-ton timber arches collapse in Hickory, NC
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RE: 40-ton timber arches collapse in Hickory, NC
The guy-wires kind of ruin the aesthetic of the arches being otherwise free-standing, and I wonder if this came late in the design? Certainly the pier crosshead was designed to be wide enough for these.
Also, interesting excerpt from the article linked:
The first arch was lifted in March with no problem, but crews stopped work after they tried lifting the second arch. They said they heard popping noises, so the arch was reinforced and re-inspected before it was raised in July 2021.
Officials in Hickory confirmed that the splintering issue last year was “repaired with adhesive, clamps and self-tapping screws.”
RE: 40-ton timber arches collapse in Hickory, NC
so, who's the structural engineer who affirmed that it was not only clever and attractive, but could also stand up for a long time?
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
This seems like an improbable structure but then, once again, hindsight.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
It is ONLY decorative.
It was interesting about how the general contractor passed the blame off to a subcontractor who seems to be passing it off to a place FAR out of town (in OREGON!!!), and thus obviously at fault.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Even worse, with the hinge points approximately 1/3 the height, the guy wires become even less effective, maybe just enough resistance to tease the installation.
As we can see in these images, the top portion buckled from the hinge points while the ends fell inward.
RE: 40-ton timber arches collapse in Hickory, NC
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
(With help from Google Earth and other)
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
It's sure as hell going to be cheaper to deal with than Millennium Towers. But, as you say, no respectable structural engineer designed......
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Tapered wood onto a metal plate with the grain the way it is wasn't sensible either.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Think they must have used my wife as a consultant. That's her solution to any wood work broken. And its never yet worked. But she keeps trying....
RE: 40-ton timber arches collapse in Hickory, NC
https://www.fox46.com/news/hickory-iconic-bridge-p...
Western Wood Structures appears to be well qualified for designing and fabricating wooden structures. This is not their first or most ambitious project.
https://www.westernwoodstructures.com/our-story#h
https://youtu.be/MDl21tNpjXs
The shape was interesting when it was standing - almost like a DNA strand.
RE: 40-ton timber arches collapse in Hickory, NC
It was more the wording of the reporting that amused me.
And agree they have done some lovely structures.
These white papers are interesting
https://www.westernwoodstructures.com/index.php/wh...
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Link
Big pic of the top
RE: 40-ton timber arches collapse in Hickory, NC
Maybe those wires are like the ones on the FIU bridge and there to prevent the bridge from bouncing too much?
Google street view hasn't updated with it built unfortunately but there are plenty of pictures out there.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
Link
It's not apparent from most of the pictures, but this is a single inclined arch
Opening was delayed for some time until everyone was sure it wouldn't collapse.
Brad Waybright
The more you know, the more you know you don't know.
RE: 40-ton timber arches collapse in Hickory, NC
A black swan to a turkey is a white swan to the butcher.
RE: 40-ton timber arches collapse in Hickory, NC
The base connections in the image above also appear to have been flimsy; whatever screws they used to secure the wood to the metal plates simply pulled straight out, while the hinge connection screws simply splintered their way through the wood.
This is a pretty good picture
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: 40-ton timber arches collapse in Hickory, NC
I agree that it looks frighteningly unstable at first glance, but most of that is resolved by internal bracing. I think the interplay of the two arches confuses the shape - some of the 'straight-through' shots make it look symmetrical. The global shape appears to be roughly parabolic, and 3 pinned arches are relatively common. So no moment is transferred from one half to the other at the middle connector by design.
Regarding fasteners in the connector plates, I wouldn't go so far as to say they "pulled through easily" - perhaps they did, but perhaps that was because the joint experienced 10x its design stress due to a failure elsewhere in the structure.
Check this from the picture IRstuff posted. This looks suspiciously like a terminal connection of a cable to the concrete pier. I would not expect this to be a secondary failure - if the arch itself had failed a wind of only 30mph our so would not be sufficient to blow it out and maintain significant tension as it went down. It likely would have crumpled and come down, leaving those connections in tact.
My theory: the incredibly inefficient cable brace angle led to excessive tension in the cable, and it precipitated a failure in the cable connection. (I wonder if there was a request to use adhesive anchors for the cable terminals...) When that came out, the arch lost all lateral stability, which then caused the joints to experience out of plane moments for which they were not designed.
RE: 40-ton timber arches collapse in Hickory, NC
That would seem to argue that the cable brace was woefully inadequate, given that it was a single-point failure mechanism.
Given that the cable was a single-point failure, the joints should have been designed to handle the loads that would arise from that failure, one would think.
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: 40-ton timber arches collapse in Hickory, NC
Not to pretend to stabilize the arch.
RE: 40-ton timber arches collapse in Hickory, NC
That it would. I never said it was a good design.
If that were the case, it wouldn't be a single point failure. And if this were an integral part of the bridge and not decorative, you'd probably be right. But as the failure of the arch had nothing whatsoever to do with the stability of the bridge itself, I'm guessing it didn't undergo the same kind of scrutiny with respect to design adequacy and redundancy.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The connectors require more info:
1. Is the connector from the top of the arch or from the pier crosshead?
2. The cable appears cut close to the loose connector. Is that from tension prior to collapse or from being restrained/sheared from the momentum of the collapse? The loose ends do not appear to be frayed, at least not significantly.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
How much tension?
If one side failed, then the horizontal vector up top for the other cable would surely add lateral force up there.
Would that be a bad thing?
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
(hickoryrecord.com)
The top connector resembles the loose connector found on the bridge deck after collapse:
In December 2021, after the installation of the second arch, it appears that a second cable is connected to the upper bracket, to the outside of the initial cables.
(newsadvance.com)
(newsadvance.com)
The lower connector is distinctly different from the loose connector on the bridge deck.
(newsadvance.com)
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Upper connector, enlarged from previous image:
(hickoryrecord.com)
RE: 40-ton timber arches collapse in Hickory, NC
I think you got it. The cables might have helped stabilise it, but they're essentially decorative. Decorative cables on a decorative arch.
In any case, those cables could be tensioned up fairly tight, like guitar strings. You're not tensioning a gravity load, you're tensioning between hard points (the headstock, and the arch).
RE: 40-ton timber arches collapse in Hickory, NC
(wset.com and newsadvance.com)
RE: 40-ton timber arches collapse in Hickory, NC
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: 40-ton timber arches collapse in Hickory, NC
Altogether a poor advertisement for exposed wood.
RE: 40-ton timber arches collapse in Hickory, NC
https://www.eng-tips.com/viewthread.cfm?qid=458618
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
https://www.youtube.com/watch?v=q-Vbe4ZqRak
https://www.bridgeweb.com/Report-published-on-fata...
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: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
The area circled in green appears to have been torn out. Could this tear-out failure of the pin have caused the arch to collapse? Alternatively, the other side of the clevis appears to have collapsed at its base, which is not surprising considering how thin it is. Could this have initiated the pin to become dislodged and tear out of the other side?
I would image that under wind loading, one side of the clevis would have been in tension and the other in compression. Perhaps this bending through the connection was overlooked, because it might have been thought that the guy wires would eliminate such an effect. But the guy wires appear to be awfully flimsy as well and not in a particularly effective arrangement as I mentioned in my first post.
RE: 40-ton timber arches collapse in Hickory, NC
(Video source)
Compare to the piece on the bridge deck ???:
EDIT: It appears that this clevis mount is indeed modified before the completion of the project. (see further posts below)
RE: 40-ton timber arches collapse in Hickory, NC
The structure likely experienced buffeting during its entire life. It is a large sail of significant mass so any movement would likely work over the joints pretty good.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Thanks, Sym P. le for finding that picture.
RE: 40-ton timber arches collapse in Hickory, NC
That was the purpose of those huge cable stays on the Florida pedestrian bridge that collapsed, too. No one seems to want to take really clear photos of the connections, it would appear. That top 'pinned' connection is really strange looking and really flimsy by the look of it.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
gusmurr:
"Wow! If this "connection" isn't the cause of the collapse, I will eat my hat."
When I look at the pictures of the completed decoration, I don't see a connection as shown in that photo.
The connection you are referring to appears to have been temporary and long gone. If so, it's kind of hard to see how it could cause a collapse, since it didn't exist anymore.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
agree Hokie... the similarity is that they, too, were decorative only, like the cables in this one. I don't know their function (even if only decorative) and what affect they had, if any, on the collapse. The Florida stays had the capability of supporting a load of several hundred kips... they weren't detailed as decorative... and they had nothing to do with the Florida failure.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
The Florida bridge stays may not have been detailed as decoration, but that was the intent, according to the project description. But the whole wooden monstrosity in NC was a sculpture, not a load bearing span. The cables may have been intended for lateral stability...maybe as an afterthought.
Tomfh, agreed. I would say that a traditional 3-hinge arch turned itself into a 5-hinge arch with the failure of those 'knuckles' at the top of the wishbones, and that is not a stable structure.
RE: 40-ton timber arches collapse in Hickory, NC
As I noted earlier, "I'm not sure what the cables are for... if to provide support of something below, they might have been OK. If to provide lateral support at the top, not so good. Any horizontal load at the top would greatly increase the force in the cable because of the 'steep slope'. We'll have to wait and see why it 'broke'."
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The thing does have an aerofoil look to it from certain angles. Including the one that the wind was blowing when it collapsed.
RE: 40-ton timber arches collapse in Hickory, NC
I don't know... if they were for dynamic response, it would likely be lateral since that's the weak direction. The steep slope would increase cable loads substantially, and the vertical loading on the arches. The arches had been subjected to greater wind loads earlier this year. We'll have to wait to find out the cause from some other source. I'm still curious about what the earlier failure was and the manner of repair. That, too, might have bearing.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I never saw any shop drawings of those pipes. Granted, the design drawings did show them with end plate connections to the top deck, but I always assumed there would be slip connections of some sort when they got around to installing them.
RE: 40-ton timber arches collapse in Hickory, NC
It's hard to say exactly how it all went down (so to speak) but I don't think any of the engineering imagined the degree of freedom represented in the following gif, which is what I tried to explain earlier in this thread.
RE: 40-ton timber arches collapse in Hickory, NC
As for the wind loading being ok initially with one span and then fail with two.
I am thinking biplane.
Lift off the spans would put even more load on the wires.
RE: 40-ton timber arches collapse in Hickory, NC
This picture was posted earlier. These perforated metal strips must have been the repair as they're not visible in other images.
The arches seem to be flanged together in th lower 1/3. I question the strength of the flanges that connect the arches at 1/3rd height. They are so very thin. It's so bad it's as of someone forgot to carry a zero.
RE: 40-ton timber arches collapse in Hickory, NC
Make of these what you will. I don't understand them but that centre connection looks like a pin to me. Also the turnbuckles on the wires are nearly out of room on tension.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Alistair: you notice that the cable bracings are at a 'shallow angle' If they were at a steep angle, the tension load induced in the strand would be huge with any lateral loading on the and they would likely tear free from whatever they were attached to.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Does anyone know if an engineer was involved? Western Wood Structures is a fairly reputable supplier and I suspect the connections would have been designed by them or at least checked...
It appears the wind speeds were in km/hour, and not mph on my last post.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Dunno... the top hinge is fairly tall for the span and the reaction at the crown pin in horizontal shear, if half arch is 20T, would be approx 40x0.5x0.5 about 10K plus whatever wind loads are applied (they could be big)... these are not a real big loads, so the connection may be adequate. Looking at the framing, 80K seems like a pretty big weight for the timbers, but I haven't tried to see what the real load is.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Yes I did and there was no load fuse.
Thats why I think they were only envisioned to alter the natural frequency but only in one plane.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
When I say saw, it was a FEA model. The attachment to the support was many times stronger than the tensioning wire. It was a controlled failure analysis if that makes sense. The dynamic engineer took it off me once I had created the input deck for nonlinear geom, it was as well a piece of "Art" and I don't have a clue if it was ever made.
It was a welder that apparently triggered a more in depth look at the dynamics of it.
RE: 40-ton timber arches collapse in Hickory, NC
No drawings ???.... Then where are the ARCHETECT Drawings with his stamp on the corner ???
Why is no one discussing responsibility here ?????
MJCronin
Sr. Process Engineer
RE: 40-ton timber arches collapse in Hickory, NC
1) We're more interested in why it happened - we're engineers, not lawyers.
2) Until you know why it happened, it's difficult to determine who is responsible. Was it an inherently flawed design? Was there an error in the shop and the 1-1/2" plate callout on the drawings was recopied onto the shops as 1/2"? Was the epoxy adhesive applied correctly? Each of those has a different person who is "responsible" for the error. The EOR is involved at each of those stages, but we're not going to burn him/her at the stake until we know that it was his/her mistake that was the root cause.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I strongly suspect Western Wood Services provided the design, manufacture and installation.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
I expect those should come out in the near future. Unless, of course, there's a reason not to "share".
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
I think the articles say that the sub did the installation, with some support from Western Wood
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: 40-ton timber arches collapse in Hickory, NC
The link is blocked to the eu
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
https://res.cloudinary.com/engineering-com/image/upload/v1645563680/tips/Screen_Shot_2022-02-22_at_12.54.55_PM_v3xa2k.tiff
Skyline Ranch Road, Bend OR, by Western Wood Products
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
None the less, Western Wood Structures is pretty clearly not a run-of-the-mill 'design' firm as they have some simply phenomenal structures across the world (some of which I've seen in person) - which makes this arch creation (and failure) all the more baffling.
RE: 40-ton timber arches collapse in Hickory, NC
That bridge's arches are structural and required to keep the walkway in place
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: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
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: 40-ton timber arches collapse in Hickory, NC
https://hickoryrecord.com/news/local/govt-and-poli...
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
I cannot imagine it would take much horizontal load on that single pin joint at the top to cause it to tear out as it appears in gusmurr's earlier post.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
As soon as that failed and it started going, it would have put the windward side cable under massive tension and it would have pinged, which looks like what happened in the pics where you can see the broken cable. But that's a symptom not a cause imo. Looks like those crossover joints half way up just weren't up to the job.
EDIT: posted this before seeing the vid. It looks like this halfway up hinge failed on one side, that side then dragged the other half down and that would have pulled the cable as well.
RE: 40-ton timber arches collapse in Hickory, NC
Thanks for the neat comment but I think you missed the point. The gifs only purpose was to convey the idea of the freedom of movement, full stop. What might be obvious (and may not) is that once any movement starts, other factors quickly come into play and complicate the collapse sequence. I for one am not ready to meld half a dozen or more factors into one animation, let alone fine tune it to inches or less. The gif was neat but it's also wrong (I fear) and not because it moves south instead of north or moves to far. Much to my dismay, I finally took a closer look at the math of the guy wire and realized I was out to lunch, or should have just had lunch instead. In order for that gif motion to occur, something else had to break first (the guy wire or another connection).
Thanks for posting, I was looking for images relating to the repair or where the crew may have been working at the time but had not found any. That flimsy repair may be the key. A closer analysis of the videos just posted may reveal that leg buckling first.
I believe it's the connector of the lower arch on the east end of the structure. In the closeup, the timber to the right of the connector is of the upper arch. Only a fragment of the lower wishbone remains. That southeast leg fell off and under the bridge.
RE: 40-ton timber arches collapse in Hickory, NC
Seems like it. They needed to be rigid to prevent 5 hinged arch formation, and also to prevent it falling over laterally like it ended up doing.
RE: 40-ton timber arches collapse in Hickory, NC
The gif may have obscurred or detracted from the failure. Movement would be nowhere near that magnitude, and people seeing the clip might be expecting that type of failure.
Failure did not appear to be from a cyclical loading. From the clip posted by Hokie, it appears that there was no movement due to wind and that the one cable may have failed, allowing the top of the arch to fall to the right, bringing down the 'fixed' base parts. All is speculation; it's a matter of 'those in the know' posting the real cause of the collapse.
It would be nice to see the failure parts to see how the components fared... I suspect strongly that the one cable 'snapped' for whatever reason. Cable failure may have precipitated the collapse, or some component/connection failed causing the overload to the cable. I suspect that the one cable is 'broken', but I don't know for sure.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The failure looked pretty much like that from the first video. Isn't that all the gif was saying likely happened? That the top fell over? I didn't think he was saying it looked like that in service. Merely that it looked like that when falling over.
The wind was blowing in the video. Flags near horizontal. So likely it blew over in the end.
RE: 40-ton timber arches collapse in Hickory, NC
https://whky.com/wp-content/uploads/2022/02/2022-02-18-13-06-39-2.mov
https://whky.com/wp-content/uploads/2022/02/FPS-arch-video.mov
https://whky.com/video-footage-of-collapse-of-arches-shared-by-city-of-hickory/ (click on the video icon near the bottom of the story for a third video)
RE: 40-ton timber arches collapse in Hickory, NC
The blue is the trajectory of the cable and the red is the trajectory of the crown of the arch from the elevated 'base'. The white is the trajectory of the crown of the arch if the rotation were about a non-elevated base. The difference in the two schemes is the location of the elevated base.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
I just realised that in the Right Sketch, the cable is in tension. In the Left Sketch the cable is
mostlypartially in compression and the first rule of engineering is that you can't push on a rope... maybe we've solved the manner of collapse.Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Yes, that is what I was trying to say earlier, however from a pure technical standpoint, no matter how less effective the guy wire is, something still has to bend or break before the motion can proceed. But the idea that the guy wire might become irrelevant is of concern. As I've since looked at the videos closer, I do see the structure start to lean over at the top before anything else starts to fail, at least anything that can be reconciled in the videos.
RE: 40-ton timber arches collapse in Hickory, NC
Cable in compression will allow that to happen. I got the idea from your clips, because it appeared they started to rotate with little restraint.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Oh sh*t... I should have realised that.
If you look at the sketches, the white curve shows the approx cable location if the arches were pinned at the base... the red curve shows the cable location with the arch rotating about an elevated point... the effect is that the bracing is severely compromised. Earlier in my comments, I noted:
...and the first rule of engineering is that you can't push on a rope.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Yup, but because of symmetry you should have a fairly close static analysis. They may have chosen pins to do this. Moment connections with wood are a real b*tch... so maybe to eliminate these, too. Just WAGs until there is more information.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
We still don't have enough information to be certain of the cause; this is just another scenario. Elevating the base of the arch diminishes the effect of the cable bracing. Any movement of the base locaton to the left further diminishes the effect of the cable bracing.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
And you could get the ruff measurements off google maps.
RE: 40-ton timber arches collapse in Hickory, NC
In 2D space for sure, but maybe not in 3D space unless you can use symmetry, I think (I'm not 100% sure); I think it's reasonably close to use for analysis. BART knows these things. The bottom connections have to be 'rigid' else you have a mechanism (without plastic design).
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Hence we ended up with a visually pretty pure representation of the sketch, but now with seriously lower bending strength and essentially another hinge.
Doubt anyone will know why it just decided to fall over at that particular moment - maybe a gust of wind, maybe a wire did snap, maybe the hidden hinge between the two sections halfway along decided to bend.
Don't think those videos are going to give us those answers, but it sure looks to me like it bent at that connection from the wishbone to the strut.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
I understand the shop drawings were a b*tch and they ended up just getting a bunch of glulams and cut them to suit on site.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
However:
"A dedicated engineering department sets Western Wood Structures apart from the rest."
Does that mean apart from the others that DIDN'T fall down?
And the mayor says it's extremely unlikely they'll rebuild the arches. The mayor SHOULD have said "We're going to rebuild those glorious arches bigger and better and STRONGER than before. And our good friends at Western Wood Structures, and their insurance company, will be covering most of the costs!"
As is, he looks like a loser mayor of a loser town.
I'm going to mention that the more I look at the "before" photos, the more I like this non-structure. I would have liked to walk around/under it. It MIGHT have been a pretty neat piece of work. My biggest aesthetic problem is that there are three bridges here, all together. And the fact that the other two bridges are FLAT takes away from the visual interest. Can't exactly move the other bridges, but it would have looked better with this thing all by itself.
I think what they should have done with all this extra money that they had to spend is to put some nice shady sitting spots on the perfectly flat bridge, so as to allow folks to have a picnic while waiting for a train to watch pass by. THAT is a pleasant way to pass the time!!
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
"Western Wood is dedicated to identifying the root cause of the failure of our structure installed by SOMEONE ELSE, and will work diligently with the city to show that it was not our fault, etc. "
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: 40-ton timber arches collapse in Hickory, NC
I suspect we all agree that the design of the structure was by Western Wood, with perhaps some artistic sketches contributed by a Hickory NC local. But they were the folks who ran the numbers.
Yes. It would be interesting to see the installation instructions. If any.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
To tighten it up. But with a 5 hinged arch it would only tighten so much. And like you say, the motion would have stressed the joints. This is likely related to the joint damage that was repaired earlier on.
RE: 40-ton timber arches collapse in Hickory, NC
https://www.youtube.com/watch?v=c_D6RfCLZA0
RE: 40-ton timber arches collapse in Hickory, NC
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: 40-ton timber arches collapse in Hickory, NC
that's what prompted me to do the sketches...
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Well, it wasn't actually "loose", so there was nothing to tighten up.
I wasn't actually asking why some person chose to do this. I was asking how the structure allowed so much movement.
The cables pulled downwards with a pretty significant force. This then put a compressive load onto the structure. And rather than being decently rigid, and refusing to compress much, it most likely did a whole lot of bending/bowing. And, yes, twisting of any joints in a way that was likely not contemplated by the designer.
I wonder if the thing would have been still standing if the cables were not used.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
It’s a 5 hinged arch.
RE: 40-ton timber arches collapse in Hickory, NC
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I don't think this one bent by design. If it DID, I surely look forward to the explanation.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Bending makes it less stable, and once it reaches the 'snap through' point, the cables become useless, no matter how well they are anchored.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The latest news from Hickory, NC regarding arches:
https://hickoryrecord.com/news/local/govt-and-poli...
RE: 40-ton timber arches collapse in Hickory, NC
As I watch various news sources and video feeds today, I do think the mayor just might be overstating his case.
Maybe they need a new mayor, who has a sense of proportion. Or just sense.
Meanwhile, Western Wood Products still has nothing to say about this on their website. Perhaps they feel there's no reason to rush.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
WWP is sensible say nothing until the facts are known. Even if they know already its not their fault.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Difficult to see how a structure which is less than a year old and fell down in nothing more than a stiff breeze isn't a design issue. They were supervising during construction so can't back away from that responsibility.
The joint between the A frames / wishbones and the rest of the arch would seem to be the key area of interest and likely failure location.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
Yes. But it wasn't. It fell down, went boom.
spslso
RE: 40-ton timber arches collapse in Hickory, NC
So, definitely catastrophic. And potentially fatal.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
I wonder what the mayor would have called it if several someones were killed in the process, or one or two bridges taken out. Would "mega" or "super jumbo" have been appended?
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
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: 40-ton timber arches collapse in Hickory, NC
If the town burned down, that would be a catastrophic event.
This seems more like having the decorative fountain in your front yard fall over and break, after you paid good money for it.
However. I have noted that I am unimpressed with the mayor's choice of terms. Others may not have that reaction.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Depending on the town, it might not be.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Oh boy - That will take years and have a value several times more than the Bridge.
I was once involved in a project which had 5 sets of parties involved between sub contractors, main contractors, operator, designer and owner - all different, each with their own set of insurance companies and lawyers.
As no one could agree on how much compensation to pay for the the damaged tank (in my example) they decided to repair it. Repair costs were easily 5 times what the tank was possibly "worth" and due to its location could not be feasibly demolished and re-built or a new one substituted. Was a great experience for me, but utter madness in terms of value for money.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
https://www.hickorync.gov/nc-127-road-closure-removal-city-walk-arches
RE: 40-ton timber arches collapse in Hickory, NC
They are some of the clearest images of the design choices in question that I have come across, including the (possibly infamous) 'pin' joint.
I do not want to directly link his images or upload them here (without permission), but the album in its entirety can be found and viewed on his flickr page:
https://www.flickr.com/photos/raddad/albums/72157719596386082/with/51332009377
RE: 40-ton timber arches collapse in Hickory, NC
That's where artistic impression of continuous strands of wood gave way to engineering reality and where the failure almost certainly came from
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
I thought it was attractive; now that they know what not to do, can they rebuild it?
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The extreme closeup (on the ground) seems to be one of the two pieces of the top connection. I note that the cable anchor is conspicuously missing, and assume it was added after the arch was assembled, and likely cut to length. It kind of messes up the "purity" of the single bolt connection.
In the photo shot directly from one end, you can look up towards the near "outer" connection and see three steel plates assembled together. What is weird is that they're not flat and flush with each other--"bent" would be the word I would use. I could wonder if the person who designed this structure spent much time on figuring out how it would be assembled.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
You are right. As I see it, each laminated timber member is fitted with a weldment which slots into the members end and extends proud of the member to allow for bolted connections to adjacent members. These individual members are then connected to each other with an additional weldment configured to accept the various members. At the connection to which you refer, you see two end plates and one junction weldment between them.
At the peak junction, you will find an end plate on each member and each of which is bolted to a mount plate. The mount plates then connect with a single bolt.
The following image shows just how minimally, the timbers are connected at the wishbone:
RE: 40-ton timber arches collapse in Hickory, NC
By the way, were the bent members fully stable, including through temperature variation? i.e., did they have any tendency to unbend?
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
Quite right. I was horrified by the concept as soon as I saw the detailed pictures, and certainly didn't need to do any calcs to back up that impression.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: 40-ton timber arches collapse in Hickory, NC
That way, after proving the design (should that have actually happened), it could have been given to the city of Hickory on a platform with the adjoining bridges, and an HO scale train on the railroad track.
That way, it could even have been incorporated into the upcoming visiting (proposed) modular model railroad coming to town on April 1 and 2.
Would'a looked pretty cool if it had visually recreated the boo-boo, also. And saved some money and embarrassment.
A missed opportunity all around, I'd say!
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
(We'll overlook the toxic preservatives it contains.)
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
A whole month. Maybe they had the vapors.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
https://hickoryrecord.com/news/local/hickory-sues-...
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
I kinda liked it, before it fell down.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
Per say I think it could be engineered to work. Might not be as clean on the joint points but 95% of it would be the same.
But now the political legal wheels are turning it won't happen.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
I suspect that it was a short cut by the building contractors that killed it.
RE: 40-ton timber arches collapse in Hickory, NC
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Given the increasing frequency of invasive species, perhaps it was done in by an 'Axis of Weevil'?
Sorry.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
!!!
RE: 40-ton timber arches collapse in Hickory, NC
One of the engineering firms brought on to investigate the collapse (by the legal defense team representing the contractor that assembled the structure) has released a preliminary report of their investigation into the failure.
Greensboro News & Record has published an article here on the topic:
https://greensboro.com/news/state-and-regional/why-did-the-hickory-arches-fall-report-cites-faulty-design/article_ca281b3b-9cd6-5978-a6e6-3b8668592606.html
And included the report in PDF form available here:
https://bloximages.newyork1.vip.townnews.com/greensboro.com/content/tncms/assets/v3/editorial/4/f3/4f3c3a1d-152e-5e27-9bc4-3390ac47eeb7/62a51df1b05e4.pdf.pdf
The report is an interesting read and is harmonious with a lot of the structural and design observations made within this discussion thread.
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
So the lower arch cable attachment is suspect. The cable attachment bracket was attached asymmetrically with one bolt in the center of the lower arch. What?!?! The cable itself became frayed but stayed together while the welded bracket failed (not much weld visible either). There is no information regarding wind events that this structure experienced during its brief two month lifespan though a dump of local significant events for 15 years prior is provided. Did this cable fray solely in this event or was the damage initiated in prior events?
Edit: Was the bracket attached/welded only on one side ???? Answer: Not likely
Edit 2: I see now how the second bolt hole was utilized. The north side of the timber bracket is bent underneath the debris and would have been provisioned with a second attachment point. My comment on the welding is still in play. It seems like there is ample linear space for a robust weld connection so it brings into question the quality of the weld. Also with regard to the bolt connection, why the slots and did the bolts work themselves loose?
Photograph 14
Photograph 19
Photograph 20
RE: 40-ton timber arches collapse in Hickory, NC
Regarding the welds, I'm kinda surprised the confidence level is high enough to claim they failed while in the air vs the damage in question being the result of the twist and then impact. The area(s) in question clearly had a rough landing.
RE: 40-ton timber arches collapse in Hickory, NC
You're safe. Sorta. They made a worser one.
RE: 40-ton timber arches collapse in Hickory, NC
Key point.
Edit: The snap back would argue for the damage occurring while the structure was still erect.
RE: 40-ton timber arches collapse in Hickory, NC
Out of curiosity, what was the load on it at failure?
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Very good point if that final position is indeed from a snap back.
I do not see that indicated anywhere in the report. Just that the wind speed around the time of the incident was 18mph with 33mph gusts. The report also states that prior to this the structure: "...had not had high wind loads on it prior to the collapse." See page 6.
A re-occurring theme of the report is that the EOR only modeled a single arch (the upper) for the design/load calculations, and not the two arches tied together as a single structure. It also claims the EOR modeled the guy wires as solid rods in place of cables for the load calculations, possibly influencing the numbers by introducing support in compression. See page 9.
RE: 40-ton timber arches collapse in Hickory, NC
As noted earlier in this thread, a possible cause for collapse was due to the geometry. The effects of the cables became negligible, and the forces in them would increase substantially. If the project were mine, I'd likely have modelled it as an upper arch and looked at the effects this would have on the base, including the effects of the geometry. I don't find that to be at fault. I find the reliance on the FEM program to be distressing. For those wind speeds and gusts, I would think the failure wind pressures would be in the order of about 20 psf. The effects of gusts are local and not not on the entire structure at the same time. I didn't like the report.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
Also, a sharp arrow may have pierced the cable.
RE: 40-ton timber arches collapse in Hickory, NC
"Well. That's a VERY unusual design. Since we don't have a lot of history with something like this, let's go real conservative on both design and testing."
I will note that it does not appear that anyone involved in this project said that.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Looking at the first photo posted in this topic, it appears to me that, by the time the cable could have moved to intersect the bridge railing, it was all over.
A strange thing: I just did a search on Bing for "hickory north carolina bridge collapse" in images. There were none for this event. I wonder how that came to be. Google came through.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
A revision to my previous post copied here.
Edit 2 - I see now how the second bolt hole (in the lower cable bracket connection) was utilized. The north side of the timber bracket is bent underneath the debris and would have been provisioned with a second attachment point. My comment on the welding is still in play. It seems like there is ample linear space for a robust weld connection so it brings into question the quality of the weld. Also with regard to the bolt connection, why the slots and did the bolts work themselves loose?
RE: 40-ton timber arches collapse in Hickory, NC
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Birdcaging of the wire rope at the socket may be a clue to the sudden release of tension or indicative of other issues? It appears more pronounced in the south rope which had significant tension failure. Of course when the structure fell, the north rope would go completely slack so perhaps this is evidence of the structure flapping in the wind prior to its collapse or cycling during its short life span.
The upper arch
southnorth cable also exhibits significant birdcaging at the upper socket which would indicate that it was abused as welllikely prior to the falland in another image it is seen to be sharply kinked upwards at the socket so it likely sustained this damage from the fall.Photograph 20
Photograph 17 - south cable at the bottom and north cable at the top. The north cable is kinked at the socket but it is not readily apparent in this view.
RE: 40-ton timber arches collapse in Hickory, NC
Threaded rod epoxied in place but I doubt I can call it accurately from a photo.
So far, all of the anchor bolts I've seen have pulled out of the drilled holes rather than pull up any concrete so it would seem that they did not develop their intended strength. This may be a moot point given the base was entirely more stable than the upper portion.
Photograph 9
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
The photo 9 one has some shim plates surrounded by grout to support the base plate. The photo 11 one does not. It is extremely unlikely that the designer would spec two different styles of mounting, one with and one without.
So it appears that the mounting shown in photo 9 came up 3" short (photo 5), and filler was added. I suspect discovery of the need for this modification was made during the physical installation of the arch itself. It does not reek of prior planning.
Study of the photos shows that the hold-down bolts were not an additional 3" longer where the shimming was used. From photo 9, it appears the exposed hold-down bolt was engaged in about 3" of grout and 2 1/2" of concrete.
I have little experience in gluing bolts into concrete, but I do wonder whether the "glued-on stuff" (of about a 2 1/2" length) is concrete dust that was never blown out of the hole.
I question whether the grout is "Structural Grout". Which means that, structurally, it isn't there. So it would contribute nothing to pull out strength for the bolts. In addition, it would provide nothing for lateral movement. As I said, structurally, it isn't there.
I am sympathetic to doing an install, and finding the "bridge" is 3" shorter than the needed span. But this looks incredibly poorly designed. As an experienced electrical worker, with all the knowledge that that implies, I would have at least made the steel shims the full size of the base plate, and cut bolt holes through them. I would have added additional large steel blocks on all four edges to minimize lateral movement of the stack. And I certainly would have used longer bolts.
I am SO looking forward to finding out how this one "solution" turned out to be needed, and was so designed. I note that the Dara Thomas, the investigating forensic professional engineer, made no mention of the above in the report.
One additional point: for the base plate in photo 4, I question having two of the hold-down bolts located so far away from the location of the landing of the wood beam. Works OK for lateral, but pull-out???
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
I do see that the reason for this report was so that the PE could "...express my opinions, to-date, about the catastrophic failure...". So perhaps the thing about the design quality of the baseplates was not an opinion he wanted to express. Fair enough, I guess. I do suspect that the design of the baseplate is not the primary reason for failure, so perhaps it can be left out.
I AM interested, however, with what the design of the baseplate illustrates as to quality of design and installation.
It struck me, when I read that this installation cost $750,000, that that number seemed low (not that I have experience in judging). If it IS low, that could account for a certain style of approach to the task.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
I do a lot of stuff that is unusual... I thrive on it. I take great care in understanding the system to start with, and try to keep up with materials. Although not common, there was nothing distinctly different from a normal structure. Something was likely overlooked and not taken care of. I suspect it was the geometry... but don't know for sure.
The cable and geometry may have contributed. The effect of the cable may not have been as good as inticipated.
It would be neat to see actual detailed drawings of the arch and connections.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
The 1:5 vector ratio means that 6.2 tons of sideways force at the top anchor would break it:
12,400 pounds.
Subtract from that the "pre-tensioning" done by tightening those turnbuckles at the bottom. I wonder what that "pre-tensioning" figure was supposed to be and how it was achieved.
Once one cable is caused to snap, presumably by wind load, then the "pre-tensioning" load on the other side will add into the wind load that just caused the other side to snap.
Doesn't sound good!
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
If that rusty line on the inside edge of the loose twin socket bracket was where another piece of steel was butted prior to galvanizing, it does not not look like there was any fillet penetration whatsoever.
Edit: Not implying this is a trigger/cause. Perhaps a quiet indicator of a much larger issue...
RE: 40-ton timber arches collapse in Hickory, NC
Photograph 21 and 14
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
The thing that was interesting to me what that she didn't really look into that joint that failed and how it was modelled and designed.
The SAP model and the report don't say exactly how nodes 4 and 22 were modelled. With the relative stiffness and strength of the lower wishbone compared to the rather flexible section above it that joint design is where the failure probably lies IMHO.
I've said before that maybe a better design was to have one solid section going through that joint with two angled connections to the joint so in the SAP model 3,4,5 and 21,22,23 would be a single solid piece of timber and 28 to 4 and 29 to 4 would be bolted connections to the main solid spar.
To not even try to model this herself in SAP is a real budget job of a report IMHO.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
https://m.mooresvilletribune.com/photos-arches-col...
you can see the south cable is not broken, and is stretched taught. Note the indent on the pedestrian bridge southern handrail (see shadow in photo) made by the cable. The other railing also has a dent, though lesser.
It appears it's the north side cable that is frayed. Which is a surprise to me, as mentioned/implied in a previous post. With the direction of the fall, there should have soon been no load on the north side cable.
Also, you can see most of the sideways movement of the structure happened above the pivot points called nodes 4 and 22.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
There are two cables on the north and two on the south. One each side for both the upper and lower arches. The arches are two separate structures, unconnected. The cable which remains tight is for the upper arch whereas the frayed cable is for the lower arch and runs a random path along the ground which is easily confused with its counterpart.
From a design aspect, the report touches on an interesting aspect, modelling for wind load. It appears that wind load was considered for each arch standing separately but without consideration for any proximity to adjacent structures, in this case a twin arch immediately adjacent.
Page 8
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Thank you for pointing out the four cables, as opposed to two. I do, however, wonder if the two arches WERE connected, after installation. If they were not, why wouldn't one, only, tip over? I supposed what could have happened is, when the lower arch tipped far enough, it started bearing on the north side cable for the upper arch. If it keeps going, it then also pulls the upper arch down, using the cable.
So, I believe you're saying one of the south cables snapped (the lower arch one). And the other south cable followed the structure down, as it tilted over.
There would then have been over 31 tons tension on the snapped cable, when it happened, to make the cable fail.
And the snapped cable is on the windward (south) side.
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Think this is a much smaller version of the FIU bridge. Very odd design, strange construction, no proper models or proven design methods. Probably very little independent review
Result, it fell down.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: 40-ton timber arches collapse in Hickory, NC
The jury is still out about the failure being precipitated by the failure of the cable... They likely don't have a clue about what caused it yet. The problem with the report that's out there is that it is poor and may not be correct. I hope the professional association is a little more on the ball... why lodge a complaint using such poor information?
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I haven't seen any indication that the two arches are connected. With the lower arch nested under the upper arch, between its two stays, the collapse of either one would take the other with it.
One of the lower arch stays is badly frayed down to a few strands. It's as though it was taken near to its limit but just prior to failure the load was released. I think that lends to the argument that it was the victim of another failure. As I alluded to earlier it's strongly suspected that it's on the windward side but we need confirmation.
I think from a structural design standpoint, this is far worse than FIU. This design didn't have a chance and the failure was sudden. There was no opportunity to protect the public or remedy the problems. FIU could have been salvaged had they taken appropriate precautions and undertaken to understand the as built structure (not what the final report said or the intended design).
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
1. Computer modeling appears to have been relied upon without having a complete analysis model.
2. The computer model appears to have been simplified for factors/scenarios that basic hand calculations would have called in to question the results presented by the computer analysis. Quite surprising, if the report by Dara Thomas is correct, that the design analysis only looked at the top arch and no moment control of the structure was employed during the analysis. Was the expectation the guy wires with very narrow included angles connected to relatively thin pinned joints at the arch apexes were going to provide all the necessary moment control?
3. The EOR has a stellar record and many accolades and has been an innovator in his field of design. Possibly, the EOR's reputation caused less scrutiny of the design analysis? Did the reputation of Western Wood Structures cause less scrutiny of the design?
4. During construction, failure modes were noted and remediation done but there may not have been a reassessment of the design analysis to account for the unexpected behavior of the partially completed structure.
This failure and the FIU pedestrian bridge failure are reminders to me to not get too casual or comfortable with my design expertise.
RE: 40-ton timber arches collapse in Hickory, NC
Assuming I am correct its not surpassing the structure was under designed for overturning since the rod would be like a kick stand on a bike.
RE: 40-ton timber arches collapse in Hickory, NC
And who might this blindingly overqualified engineer be?
spsalso
RE: 40-ton timber arches collapse in Hickory, NC
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I’m learning so much on this thread!
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: 40-ton timber arches collapse in Hickory, NC
RE: 40-ton timber arches collapse in Hickory, NC
Now if the user thought "well, of course it fails in compression!" and ignored it, then yes...that could be a big problem. That would be so many levels of big problems. None of them surprising, sadly, but still big problems...
RE: 40-ton timber arches collapse in Hickory, NC
Glad to help... that used to be (50 years back) one of the three laws of engineering.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I did... and, it's not well written. Don't waste your time...
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?
-Dik
RE: 40-ton timber arches collapse in Hickory, NC
I agree on the rod vs cable comment, I do they same thing but set them for tension only.
RE: 40-ton timber arches collapse in Hickory, NC
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates
-Dik