Now we begin to have a technical discussion, which is fine by me. We're talking about the columns in the 6 floors that were involved in the collision. I have made no assumptions about any damage from the collision itself, only that the fire occupied the central area of the floors. I have no idea what the structural factor of safety was, but I would expect it to be at least 2. Structural steel loses 70% of its strength at a temperature of 600 deg C (only 90% of the temperature of molten aluminum; wherever there was molten aluminum, there would have been critically weakened steel). The question becomes how much of the floor area was at this temperature or above, given that the flame temperature was over 2000 deg C. My point is that, through the loss of structural strength from high temperature, it is plausible to think that a very large fraction of the floor was incapable of supporting any structural load, and that this load was being carried by outer columns.
Columns would bend only if the applied stress was above the yield strength BUT below the ultimate strength. If the stress was above the ultimate strength, the beam would simply shear. Many of the central columns could have done this. When the conditions were such that the upper-story load equaled the effective limit load for the remaining columns. the catastrophic chain reaction could take place. Because the load conditions on each individual column would be different (different exact temperature, different exact loading) the failures would be stochastic---and would all happen in a matter of milliseconds, as I mentioned previously. In the course of those tens of milliseconds, the specific supports beneath the upper floors would be vanishing randomly at the rate of maybe 1000/second (or faster). There would be no consistent tipping moment. And there would be no tipping in that time interval; the rotational inertia of the upper floors would prevent it. If you doubt it, figure out the tipping moment from a support location that would be in place for only 5 milliseconds, estimate the rotational inertia of the upper floors, and figure out what the torque would be and how much tilt would accumulate in those 5 milliseconds. (Even so, it seems there was some small tilt that accumulated during the full collapse.)
Your logic is inside-out. If this can happen to one tower, it can definitely happen to the other tower. It does not depend on any unique configurations of columns, because ALL configurations go away in tens of milliseconds.
What you may think to be demolition explosions were probably catastrophic shear failures of the freshly loaded columns beneath the collapsing mass above. Do you think a shear failure is not a violent event?
Snide remarks? Did I call you a glowie or did you call me a glowie?
I would only say I have analysis and you have opinion.
But let me apologize for the "glowie" question. It is really hard to sort the thread when it gets into these extensions, and our discussion was remarkably similar to the discussion I was having with someone who did call me a "glowie." I didn't appreciate that.
Now we begin to have a technical discussion, which is fine by me. We're talking about the columns in the 6 floors that were involved in the collision. I have made no assumptions about any damage from the collision itself, only that the fire occupied the central area of the floors. I have no idea what the structural factor of safety was, but I would expect it to be at least 2. Structural steel loses 70% of its strength at a temperature of 600 deg C (only 90% of the temperature of molten aluminum; wherever there was molten aluminum, there would have been critically weakened steel). The question becomes how much of the floor area was at this temperature or above, given that the flame temperature was over 2000 deg C. My point is that, through the loss of structural strength from high temperature, it is plausible to think that a very large fraction of the floor was incapable of supporting any structural load, and that this load was being carried by outer columns.
Columns would bend only if the applied stress was above the yield strength BUT below the ultimate strength. If the stress was above the ultimate strength, the beam would simply shear. Many of the central columns could have done this. When the conditions were such that the upper-story load equaled the effective limit load for the remaining columns. the catastrophic chain reaction could take place. Because the load conditions on each individual column would be different (different exact temperature, different exact loading) the failures would be stochastic---and would all happen in a matter of milliseconds, as I mentioned previously. In the course of those tens of milliseconds, the specific supports beneath the upper floors would be vanishing randomly at the rate of maybe 1000/second (or faster). There would be no consistent tipping moment. And there would be no tipping in that time interval; the rotational inertia of the upper floors would prevent it. If you doubt it, figure out the tipping moment from a support location that would be in place for only 5 milliseconds, estimate the rotational inertia of the upper floors, and figure out what the torque would be and how much tilt would accumulate in those 5 milliseconds. (Even so, it seems there was some small tilt that accumulated during the full collapse.)
Your logic is inside-out. If this can happen to one tower, it can definitely happen to the other tower. It does not depend on any unique configurations of columns, because ALL configurations go away in tens of milliseconds.
What you may think to be demolition explosions were probably catastrophic shear failures of the freshly loaded columns beneath the collapsing mass above. Do you think a shear failure is not a violent event?
Snide remarks? Did I call you a glowie or did you call me a glowie?
A compelling argument, fren. I will definitely take this under advisement.
I don't care to debate this. You have your opinion and I have mine.
Moving on . . .
I would only say I have analysis and you have opinion.
But let me apologize for the "glowie" question. It is really hard to sort the thread when it gets into these extensions, and our discussion was remarkably similar to the discussion I was having with someone who did call me a "glowie." I didn't appreciate that.