[Yo-Yo]

It looks like the two main pillars (struts?) are gone. How the heck did that happen? How could that happen?

The pillars appear to be poured concrete. Concrete is only strong in compression. As soon as any side load is placed on those pillars, they crumble.

As to the flashes, my speculation is that like most bridges, they make a handy place to run power, water, and/or gas lines from one side to the other, so the flashes could be high tension power lines being snapped by the collapsing bridge.

Given the age and construction materials involved, I think you'll find that when the failure analysis is completed, it was a weakened concrete pylon that failed, not a terrorist attack.

[VanShuyten]

“... it was a weakened concrete pylon that failed, not a terrorist attack. “

Tony Soprano’s construction firm?