Reply #97: If I understand the basic construction of the WTCs- [View All]

There were built with a steel backbone, consisting of multiple vertical beams, encased in concrete. The floors were poured concrete that were supported by horizontal steel beams that tied to the exterior structure and the backbone.

If these horizontal beams weakened to the point of failure, the floors would pancake, no? Why would the backbone fail? The backbone would provide a guide for the floors to fall consistantly down one on top of the other....but I don't see why that core would come down with each floor.....unless that foundational supports suddenly vanished. Not that it wouldn't come down eventually...but I'd have expected to see some or all of it standing for some amount of time after the floors collapsed to the ground. If I recall, the only structure of significance after the towers collapses were some of the exterior walls.