He did not do so bad with it, at least did not over-reach.
His focus on what he called “false work” - lets just call it temporary support - is not wrong, but suggests gross obvious mismanagement. First off, there wasn’t any, period. Pinning the collapse on this suggests that the bridge could not be set without temporary support, could not support itself without temporary support, and somebody made the grossly obvious error of not using any temporary support.
I don’t think thats what happened.
I suspect they were following a strict installation plan, and if temporary support was required it would have been there. Would it have been prudent? Yes. Saved lives? probably. But required by the calculations - apparently not.
What that means is that the failure was more nuanced, and its not obvious from observing the collapse or the aftermath if it was an installation error, material deficiency, or design error. You just can’t tell.
What you can see is where it failed, and how it fell. I suggest finding the dash cam video which actually captures the entire span at the time of the collapse. It did not happen quite as described in the video, but he probably did not see it. What you do see is there is a lane closed and a crane in that lane holding a piece of equipment above the bridge - this is likely the device used to tension the post-tensioning steel. From this positions its probably working on one of the steel tendons that follows the diagonals between the deck and roof of the bridge. What you see happen is bottom deck cracks right below the second diagonal coming out of this spot on the roof. Once that cracks both halves of the bridge rotate around the other ends, and fall to the street. The longer part hits the street (and cars) and then sequential cracks along each joint along its length with most of the deck falling to the road, and the roof on top to it. The other side rotates to the street and amazingly more or less remains in one piece.
So what happened? I could write a book. Here is the short tell. The bridge was in the form of a truss with a top member and bottom member and diagonals connecting them in triangular form. The top and bottom are much too small to span as far as the whole truss, and not nearly strong enough. But the diagonals tying them together enable them to span much further than they do alone. So what happens if you break one of those diagonals? Well the whole house of cards will fall down.
So what I think happened is the work that was happening with the steel tendon in the diagonal went wrong - the steel tie broke. It was tightened too much, or the wrong tension value was used, or that piece of steel had a defect, who knows right now - but it broke. Now suddenly the strength of the truss configuration was gone, and all the force of the weight came to bear on the bottom deck alone - and it cracked right there, then the whole thing came down.
The questions around this are too many and too deep to figure out here what was the actual mistake or failure. I don’t think it was an obvious mistake like it should have had temporary bracing. That would have been a precaution, sure, but not likely the source of the failure.
My best guess is there was some confusion about the dual spanning modes for the part of the bridge. It was installed as a simple span - truss spanning across the road. But it was apparently supposed to be a cable supported bridge. So that would mean it would have to be designed for both modes. And the tension requirements on the steel tendons may have been different for both those conditions. Something may have been adjusted wrong for this stage of the work, or the temporary spanning condition may have put the steel closer to its ultimate strength in a way that made it susceptible to a defect. No way to know now. We won’t find out until a detailed investigation is done.
