40-ton timber arches collapse in Hickory, NC 35

[bugbus]

https://www.wsoctv.com/news/local/n...king-busy-highway/N7L3RUTIKJE23LLTGYBXGJPM5U/

Before:

After:

 

[bugbus]

First thing that sticks out to me are the guy-wires at mid-span. It seems like a pretty inefficient arrangement, the slope being about 1:5 or thereabouts. I would have thought that this kind of structure would have been proportioned so that the end supports would be enough to make it stable under wind.

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.”

 

[spsalso]

The steel girders under the bridge, plus the fact that the actual walkway is still standing, hints strongly that this wood thing was only decoration.

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

 

[Sym P. le]

So the timber arch is a decoration, not a structural member. It is top heavy and has hinge points in its lower portion and at its summit.

This seems like an improbable structure but then, once again, hindsight.

 

[verymadmac]

is the arch structural or decorative. Is it me or does that arch become a beam in bending if you break / loss tension in one of those guy wires (assuming them are not just to stabilize the arch against wind side loads.

 

[spsalso]

If that wood structure was structural, it would have to support a load. The only connections between any part of the arch and the roadway are the two steel cables dropping down from the middle. And it is VERY curious that they land right on the top of a pier. Could the wood arch be secretly holding the pier up, keeping it from sinking into the ground? I think not.

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

 

[dik]

It's a shame... it looked like a beautiful structure. It would have looked better with concealed connections...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Sym P. le]

First thing that sticks out to me are the guy-wires at mid-span. It seems like a pretty inefficient arrangement ...

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.

 

[spsalso]

Note that what you see in the picture with all the colored lines and circles and arrows is NOT the completed structure that fell down.


spsalso

 

[Sym P. le]

Note that the complete structure includes two arches, one within the other. The failure axis extends through the hinge points on both arches. This is a very bad, no good, horrible design.

 

[Sym P. le]

Winds at the time S 30 km/hr (Feb 17/18 midnight)

(With help from Google Earth and other)

 

[hokie66]

No respectable structural engineer designed that unstable thing. Go find the architect. His monument fell down.

 

[spsalso]

"No respectable structural engineer designed that unstable thing."

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

 

[Alistair_Heaton]

Think those wires will actually make matters worse for the top joint.

Tapered wood onto a metal plate with the grain the way it is wasn't sensible either.

 

[AutisticBez]

I think the gods of engineering are smiling whenever non structural pieces fall over. Just a good thing they are ignoring Melbourne. We have so many such things here. (Bolte bridge)

 

[Alistair_Heaton]

There are some gems in the reporting

Officials in Hickory confirmed that the splintering issue last year was “repaired with adhesive, clamps and self-tapping screws.”

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....

 

[Brian Malone]

The project had the installation repair solution reviewed and approved sometime in May 2021

https://www.fox46.com/news/hickory-iconic-bridge-project-delayed-over-safety-concerns/

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.

 

[Alistair_Heaton]

unfortunately Europe blocked to the fox46.

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/white-papers

 

[Brian Malone]

Yes - WWS has some very interesting white papers. Their bowstring truss analysis PDFs will have me looking overhead whenever I am in a structure with glulam construction.

 

[Alistair_Heaton]

Link

Big pic of the top