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As for only 4 of the 6 tendons being placed in the upper canopy, I would venture that the 2 unused positions were for the addition of continuity post-tensioning after both spans were installed and made continuous with concrete. There would then be a tendency for this two-span continuous...

Photos of the concrete blister on top of the truss canopy where the tensioning operation was taking place at the time of the collapse indicate that concrete chipping was necceasry. The surface around the anchorages is rough and uneven and there is a chipping hammer shown in bimr’s last post...

As to software that designs connections, what exists is only capable of designing standard, repetitive-type connections. The FIU bridge would not qualify and the connection details would first need to be drawn, preferably by hand, and then potential failure planes contemplated so that...

Just some thoughts on the design that might spur some thoughts by others. The midspan chord forces of a truss can be estimated by simply dividing the moment caused by the end reaction at midspan by the depth of the truss. Assuming under dead load the resulting force in the lower deck would be...

Dik, that's just shadowing due to the depressed pan shape of the top chord at night. Other photos above show the surface was the same light-colored concrete as the rest of the bridge.

Regarding the protrusion at the left end of the deck, shown in the time-lapse video right before the failure initiated, I think gwideman is correct, it is just the deck corner coming into view as the position of the camera continually changes position. We know that lower PT bar in member 11...

gwideman, given your assumed shear failure plane with the PT bar crossing it, tension in the bar would create shear friction, a clamping action tending to keep the two interfaces in contact. If the bar was detensioned, this would tend to reduce the shear friction and increase the likelihood of...