BTW, according to the seismic traces in this book, the collapse of each of the two towers took only about 10 seconds, not 25. However the same data shows WTC7 took 18 seconds to collapse, even though it was not nearly as tall. (Why did that one collapse anyway?)
If the columns failed as you describe, what was the cause for the failure? Was it a fire? Why did all of the columns fail at the same time - weren't there many of them in the core?
IIRC the NIST report said that the collapse started from a single floor slab, where the attachments to the columns were weakened by fire and let go, causing the rest to pancake.
For 10 seconds, the released power level would have been 6 trillion watts. As far as I am concerned, WTC 7 is a different story altogether.
The cause of the failure was exceedance of the limit load in compression. The columnns could support only so much load before failure in buckling or shear. The load was not increasing, but their limit load was decreasing with the heat and loss of strength of the structural steel. At 600 C, structural steel has only 30% of the strength at normal temperature, and at higher temperatures even less strength. So, the combined strength in compression of all the columns finally added up to less than the imposed load.
There will always be one column which is the least strong. It will fail first. But now the total carrying capability is even less than before, and the imposed load was sufficient to fail the entire column array. So there will be a next "least strong" column which will fail. The speed of sound in steel is about 4000 feet/second. If the columns were 10 feet apart in the core, the loads would have been redistributed within 10/4000 = 2.5 milliseconds. Then the next column failure. Then the next, etc. If all the failures are sequential and there were 100 columns, it would be over with in 0.25 second. Nobody can perceive that small a time interval. It is "at the same time" for all practical purposes. (I'm not saying these are the precise numbers, but am trying to indicate that the collective failure of the columns was very fast.) While this is going on, and stress waves were going up to the higher stories, there was not enough time for the upper story block to tilt, it was so massive and had much angular inertia.
Sounds like the NIST account tracks with reality. This collapse process would have proceeded with each succeeding floor, as the upper mass gained momentum from the downward movement, imposing a huge shock load with each succeeding impact.
BTW, according to the seismic traces in this book, the collapse of each of the two towers took only about 10 seconds, not 25. However the same data shows WTC7 took 18 seconds to collapse, even though it was not nearly as tall. (Why did that one collapse anyway?)
If the columns failed as you describe, what was the cause for the failure? Was it a fire? Why did all of the columns fail at the same time - weren't there many of them in the core?
IIRC the NIST report said that the collapse started from a single floor slab, where the attachments to the columns were weakened by fire and let go, causing the rest to pancake.
It is definitely an interesting book.
For 10 seconds, the released power level would have been 6 trillion watts. As far as I am concerned, WTC 7 is a different story altogether.
The cause of the failure was exceedance of the limit load in compression. The columnns could support only so much load before failure in buckling or shear. The load was not increasing, but their limit load was decreasing with the heat and loss of strength of the structural steel. At 600 C, structural steel has only 30% of the strength at normal temperature, and at higher temperatures even less strength. So, the combined strength in compression of all the columns finally added up to less than the imposed load.
There will always be one column which is the least strong. It will fail first. But now the total carrying capability is even less than before, and the imposed load was sufficient to fail the entire column array. So there will be a next "least strong" column which will fail. The speed of sound in steel is about 4000 feet/second. If the columns were 10 feet apart in the core, the loads would have been redistributed within 10/4000 = 2.5 milliseconds. Then the next column failure. Then the next, etc. If all the failures are sequential and there were 100 columns, it would be over with in 0.25 second. Nobody can perceive that small a time interval. It is "at the same time" for all practical purposes. (I'm not saying these are the precise numbers, but am trying to indicate that the collective failure of the columns was very fast.) While this is going on, and stress waves were going up to the higher stories, there was not enough time for the upper story block to tilt, it was so massive and had much angular inertia.
Sounds like the NIST account tracks with reality. This collapse process would have proceeded with each succeeding floor, as the upper mass gained momentum from the downward movement, imposing a huge shock load with each succeeding impact.