Perth Bridge Collapse - Does Anyone have a theory?
Perth Bridge Collapse - Does Anyone have a theory?
(OP)

Evening everyone, a pedestrian bridge in Perth Collapsed and I was wondering if anyone had any theory or information as to why it might have happened? I've linked to a video I made talking about the collapse.
https://www.youtube.com/watch?v=YQIn_XkmSrU
RE: Perth Bridge Collapse - Does Anyone have a theory?
Pause the video at 1:07, close up view in the upper left. You can see the rotated ledge, a right trapezoid shape in cross section, and a diagonal failure plane. There must have been reinforcing in the lower portion of the ledge, which is why it's still hanging there, but it also needed it in the upper portion.
What I didn't see in the article is why the area was cordoned off prior to the collapse. It looks like they were expecting it, and the reason someone suspected trouble would be relevant to the investigation.
Aside: I learned that a trapezoid is called a trapezium outside N America.
RE: Perth Bridge Collapse - Does Anyone have a theory?
They noticed some cracking earlier.
RE: Perth Bridge Collapse - Does Anyone have a theory?
TTFN (ta ta for now)
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RE: Perth Bridge Collapse - Does Anyone have a theory?
Also the underside of corbels are often sloped back to the support to more closely match the load path which you don't see here. The bottom is just flat. Which would be ok if the corbel was deep enough. But the corbel doesn't look to be deep enough. You can see there is plenty of depth in the supporting floor for the corbel to have been deeper but perhaps the bridge was a pre-manufactured component and they weren't able to change the bearing height without a mismatch in the floor.
Below is a typical corbel configuration and reinforcement. You can see the top steel, the slope of the bottom, and the depth of the corbel in relation to the width of the shelf.
Nice microphone btw. I just got that one myself. Made in Aus I think.
RE: Perth Bridge Collapse - Does Anyone have a theory?
RE: Perth Bridge Collapse - Does Anyone have a theory?
Also those clearances (5/8") might be for precast which are smaller than for cast-in-place (3/4").
RE: Perth Bridge Collapse - Does Anyone have a theory?
That makes sense for the face cover, but not the top and slant cover.
RE: Perth Bridge Collapse - Does Anyone have a theory?
Slab corbels don't look like that, that's a beam corbel. But otherwise yeah, the lack of top steel is a bit of a problem :)
RE: Perth Bridge Collapse - Does Anyone have a theory?
More than just some cracking. The corbel is clearly failing prior to the collapse. It's bent down.
RE: Perth Bridge Collapse - Does Anyone have a theory?
Our slab corbels for highway bridges look exactly like that.
RE: Perth Bridge Collapse - Does Anyone have a theory?
RE: Perth Bridge Collapse - Does Anyone have a theory?
It is a structural failure at one support side.
It wasn't design as a corbel. In UK we call it a nib. In a standard design design it should have upper and lower reinforcing steel off a standard link or stirrup.
The failed nib does not seem to have two layers of rebar. Australian design follows closely ACI from what I have involved in the past.
RE: Perth Bridge Collapse - Does Anyone have a theory?
And yes the top bars appear to be missing, leaving it hanging off the bottom layer. Maybe the top bars stopped short and no one picked it up?
RE: Perth Bridge Collapse - Does Anyone have a theory?