I just thought of something on the harmonics/jackhammer theory on bringing down bridges. No, I don’t think a jackhammer can bring down a bridge.
Question: Was the crew overlaying the deck with asphalt? If so, could that asphalt compaction equipment be enough to shake loose a few things?
If this was a big asphalt job the crew may well have had 6 or 8 vibratory rollers working the asphalt. Rollers these days can get over 2000 rpms and throwing a lot of weight and vibration to the deck. Anyone, offer you thoughts on the vibratory rollers.
The harmonice possibilities are endless - but check out the russian pix in the other thread - it seems to show the collapse directly under a bunch of cement trucks that delivered material to the construction site.
No asphalt, it was concrete.