Kceovaisnt- said:
While it's possible that there may have been some elastic strain on the structure before failure. I do not think it's likely that an explosion would allow the structure to remain elastic for a full oscillation cycle before failing.
If the blast came from above, it would need a full oscillation cycle to jump off the pylon.
I think the impulse came from below.
I suppose it's also possible that the explosion had a downward force on a different part of that bridge segment and this part was on the opposite side of the segment's center of mass which could cause the jump.
If there was an elastic deformation deflecting downward from the blast, then there would have to be a rebound elastic deformation upwards through the neutral point. It wouldn't have the same amplitude in it's upward movement, but there would be a net displacement upwards. That's just physics. The question would be the magnitude of the upward deflection - would it be large enough to displace it off the bearing/supports? I have no idea.
Also, the bridge would be twisting along it's longitudinal axis as well. The combined amplitudes would be additive at some points.
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