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In some of the imagery, that’s been posted in other threads, you can see what might be the kingpost from the pier 6 east truss, buckled and flattened against the SE side of the pier. Poor camera angles and grainy enlargements make it hard to tell for sure, that might be something else.

If that is the SE kingpost, there’s a shard of another box beam attached to it that may be the root of the east truss span 7 bottom chord.

You can also see a steel box beam, about where’d you expect to find the top chord of the span 7 east truss near pier 6, but it appears to be too small to me. In the pictures, the west truss top chord is visible, and shows the same width, flat side on to the camera, as this other one does, diagonal to the camera, such that you can see three of its corners. Since the unidentified beam is closer to the camera, is should look thicker than the known top chord box beam, but it doesn’t.

Five possibilities:

1. We see what we think we see. The bottom chord then, is probably folded up under the debris of the span 7 pier 6 west truss, or possibly in the river. If the east pier came apart at or just north of pier six, this is a logical arrangement for the debris.

2. The span 7 east truss panels that used to be at and just north of pier 6 are in the water, probably in pieces. If the east pier initially failed a panel or two north of pier six, this is a logical arrangement for the debris. If so, they can probably yield a lot of information about the collapse.

3. The span 7 east truss panels that used to be at and just north of pier 6 are now under the northbound deck pavement and floor truss assemblies. If this is the case, it’s logical to look hard at the sway bracing between the trusses at pier 6, because both trusses fell eastward, early in the collapse sequence. I’d also want to look back at the span 5 crossbeam/endbeam/rocker bearing assemblies. I think the span 8 trusses failed when relieved of the counterbalancing cantilever weight of span 7. While they rotated, shoreward, about pier 7, as a unit, an early failure in the southside approach span could have produced similar damage, or, induced similar damage with a rotational component which rocked the pier 6 truss panels back towards the shore, and also to the east.

4.The span 7 east truss panels that used to be at and just north of pier 6 are now under the southbound deck pavement. This would be more likely if the SE kingpost buckled and rotated shoreward. Instead of leaning to the east, it would have dropped more nearly vertical. Both road decks could be carried east since the floor trusses were single transverse units that carried both northbound and southbound lanes.

5. None of the above.

Like you, I’d really like to know for sure where the east pier 6 truss panels came to rest. If not critically involved in the failure sequence, maybe even the trigger for the collapse, knowing where they ended up could permit analysis of the stresses that failed them, which in turn could point towards the first member that failed.