When I talk about the trusses failing one by one, I am not talking about the moment the building collapsed. I am talking about the time leading up to the collapse. Let me break it down (35 minutes 'till test... lol - free time!)
1. Fire erupts on floors of building.
2. Fire dies down but is still hot enough to continue to gradually heat the metal supports (trusses, I-Beams, box-beams, etc...)
3. Metal trusses which help support the floor AND hold the outer-shell in place start to sag under heat.
4. Some trusses are exposed to more heat than others. Eventually, one of them fails after sagging low enough to snap the bolt holding it up.
5. As other places reach this same state, they too start to fail. Gradually the internal support structure of the building is collapsing, transferring it's load to other trusses.
6. When enough of the trusses have failed, the structure no longer has the rigidity to support its own weight. The outer wall, no longer held in place by enough trusses to support the load it is bearing, folds.
7. At this point, the remaining trusses and all else SNAPS under the monstrous loads that are transferred in that split second. This is when the building starts to collapse.
8. By the time the upper 15-20 stories of building falls the 10 or so feet down to the floor underneath, the weight that the impacted floor has to support is EXPONENTIALLY greater than the static force exerted on it when the building was stationary. As a result, ALL TRUSSES and everything simply snap under the weight. Remember that the floors underneath were held up by the outer wall. Now that the outer wall has been compromised, the structure has enough trouble holding each floor up on its own, much less the force of 20 stories crashing down on it.
Anyway test time! C u all in 2 hours!
1. Fire erupts on floors of building.
2. Fire dies down but is still hot enough to continue to gradually heat the metal supports (trusses, I-Beams, box-beams, etc...)
3. Metal trusses which help support the floor AND hold the outer-shell in place start to sag under heat.
4. Some trusses are exposed to more heat than others. Eventually, one of them fails after sagging low enough to snap the bolt holding it up.
5. As other places reach this same state, they too start to fail. Gradually the internal support structure of the building is collapsing, transferring it's load to other trusses.
6. When enough of the trusses have failed, the structure no longer has the rigidity to support its own weight. The outer wall, no longer held in place by enough trusses to support the load it is bearing, folds.
7. At this point, the remaining trusses and all else SNAPS under the monstrous loads that are transferred in that split second. This is when the building starts to collapse.
8. By the time the upper 15-20 stories of building falls the 10 or so feet down to the floor underneath, the weight that the impacted floor has to support is EXPONENTIALLY greater than the static force exerted on it when the building was stationary. As a result, ALL TRUSSES and everything simply snap under the weight. Remember that the floors underneath were held up by the outer wall. Now that the outer wall has been compromised, the structure has enough trouble holding each floor up on its own, much less the force of 20 stories crashing down on it.
Anyway test time! C u all in 2 hours!