Truss Bridge Collapse 3

[CANPRO]

This just happened yesterday in rural Nova Scotia. The bridge was scheduled for replacement. Collapse took place while the contractor was moving equipment in to start the work. One worker in hospital (assuming the truck driver).

I of course don't want to see anyone get hurt, but I find these failures fascinating. The video and sound quality isn't great, but it sounds like there was indication the bridge was failing. The worker walking on foot on the far right seems to get off the span quickly just before the collapse. We will need to get more info, but my initial speculation is that one of web members failed.

https://www.cbc.ca/news/canada/nova-scotia/bridge-collapse-guysborough-county-worker-1.5641319

 

[Sym P. le]

And the tide rolls in!

 

[hokie66]

41.5 tonnes is a strange number. It would be interesting to know how the authority, or someone, came up with that number, and what it means. Uniform loading? Sum of wheel loads of a given type of vehicle across the span?

The driver certainly was being cautious. Creeping across the bridge like he was frightened of it. Glad he is going to be OK.

 

[3DDave]

Caution would have been letting the tracked vehicle be driven by itself.

 

[waross]

There is a curve on a very narrow road leading to a very narrow bridge.
On many site that I have worked on the safety department would demand a spotter in such tight quarters.
The truck probably had only a few inches or less of clearance beside the trailer.

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

 

[Sym P. le]

There was a spotter ahead of the truck. He backed off the bridge hurriedly at the last second.

 

[hpaircraft]

...The truck probably had only a few inches or less of clearance beside the trailer...

Given the generally positive correlation between size and mass of a vehicle, you'd think somebody would wonder if a rig that barely fits onto the bridge might be too heavy for it.

 

[davidbeach]

No, if it actually fits, how can it be too heavy?

 

[waross]

Like the farmer said when the horse died;
It never did that before!

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

 

[SwinnyGG]

Image below is as close as I could get on my laptop to the first frame of video showing movement.

Initial failure in the circled tension member?

Both vertical members on either side of my circle move between this frame and the preceding one - the top chord/vertical member joint to the left moves up initially, while the top chord/vertical member joint to the right moves down.

 

[IRstuff]

Whatever triggered that happened 3 seconds before this frame, roughly at 11.2 seconds, since that's when the front spotter turned away from the truck and hotfooted off the bridge. By the way, that particular video is relatively high quality and downloable. I was able to load it into Movie Studio and step through the frames.

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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[saikee119]

After going through the information available from the Internet this is my interpretation of the collapse.

I label the top chord of the eastern truss frame from north to south with node 1 to 7.

The Node 3 appears to fail first.

The condition of Node 3 from Google Street View looks like this (with colour brightened up). The top chord appears to be a continuous beam in permanent compression (strut). It looks like a made-up section with gusset plates welded at regular intervals to shorten the effective length to control the buckling. If the top chord were subjected to compression higher than the design capacity the made-up member could twist and buckle.

The eastern truss frame after the collapse with Node 5 submerged below the water, viewing from the northern shore.

An bird's eye view of the collapsed bridge from the west approach. Member 2-3 can be seen severely twisted while the corresponding member on the opposite western side remained plane and straight.

View of the collapse bridge from the southern shore and a close up view of the buckled/twisted member between node 2 and 3.

 

[IRstuff]

Note that the spotter turned to run from the bridge nearly 3 seconds before node 3 visibly deforms, so they heard something almost a second before that. I think something else broke, loudly.

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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