Dave Rogers
Bandaged ice that stampedes inexpensively through
I'm replying to this post at 9/11-investigator's request, and also because it appears to contain a very serious misunderstanding.
This is rather a blatant attempt at poisoning the well. It's clear that there must have been a series of impacts between elements of the falling block and the lower structure; it's impossible to envisage a scenario that doesn't involve this unless you're a certain Swedish marine engineer, who believes that the top section could have fallen through the bottom section without damaging either. It's equally clear that this wasn't as regular and structured a process as is suggested to the layman by the word "pancaking". In fact, it's more likely that there were several processes going on in the collapse. This probably included rubble from the already collapsed part being funnelled by the perimeter columns to impact the floors, which were unable to withstand the impact and collapsed, adding their mass to the rubble already falling in an avalanche-like progressive collapse; substantial damage to the lower core structure by impacts from falling debris, in particular the core structure of the upper section and the hat truss; peeling outwards of unsupported perimeter columns above the front of floor collapse, as they were by then unbraced and unable to withstand the horizontal component of off-centre impacts from other objects falling on them; and finally, the collapse of the last remaining spires of core columns - note that, despite your claim, it is visibly clear from the spire photographs that these spires contained many surviviing core columns of different lengths, with only the upper most part comprising one or two columns - which were now of too great an unbraced length to stand unsupported.
The "wet noodle" analogy seems bizarrely inappropriate to describe the progressive collapse of the lower structure. It's relatively trivial to calculate the force exerted by the falling block on the lower structure as it impacts during collapse, and it's well understood that this force is several times greater than the fracture limit of the lower structure. The mechanics of structural collapse is not one of the best-known aspects of structural mechanics, but it's had a very thorough airing on this forum. Overall we find that there is nothing surprising, once collapse has initiated, that the collapse propagated to the ground despite the lower structure being essentially undamaged at collapse initiation.
The simple answer is that it didn't, and I'm at a loss to imagine where you got the impression that it did. Have you not seen any of the videos of the collapse? IN particular, the Trinity Church video of WTC2 shows very clearly that the collapse initiated due to an inward deflection of the perimeter columns on the impact floors, leaving some 20+ floors above this level to fall on to the lower structure.
As would a simplified model of the collapse. This is in fact the exact collapse scenario determined by Bazant and co-workers in papers published on the dynamics of the collapse. In fact, some in the truth movement claim that this should not have happened, and that the upper block should first have been destroyed leaving the lower block undamaged, and some claim that this did in fact happen (if that's what they're claiming; often in the truth movement the need not to say anything that can trivially be proved wrong results in the inability to say anything at all). The exact details of crush-up vs. crush-down timing, again, are probably more complex than any simple model suggests, but it's clear that the falling upper block survived the initial stages of fall until it was obscured by dust from crushed non-structural elements of the towers.
Your argument, therefore, is that the collapse started at the top (which it did not); that the upper block did not stay intact (which it did); that the upper block did not fall on to the lower block (which it did); that the upper block did not destroy the lower block (which it did); and that the upper block was destroyed before reaching the ground (which it may have been, but neither is this certain nor suspicious); and that all this suggests the use of either impossibly quiet explosives, or a hitherto unknown method of cutting vertical structural members using incendiaries.
Please go back to your videos and study how the towers actually did fall. An argument based on reality will carry infinitely more weight than one based on a gross failure to understand, or even try to understand, the observed mechanics of the collapse.
Dave
This is rather a blatant attempt at poisoning the well. It's clear that there must have been a series of impacts between elements of the falling block and the lower structure; it's impossible to envisage a scenario that doesn't involve this unless you're a certain Swedish marine engineer, who believes that the top section could have fallen through the bottom section without damaging either. It's equally clear that this wasn't as regular and structured a process as is suggested to the layman by the word "pancaking". In fact, it's more likely that there were several processes going on in the collapse. This probably included rubble from the already collapsed part being funnelled by the perimeter columns to impact the floors, which were unable to withstand the impact and collapsed, adding their mass to the rubble already falling in an avalanche-like progressive collapse; substantial damage to the lower core structure by impacts from falling debris, in particular the core structure of the upper section and the hat truss; peeling outwards of unsupported perimeter columns above the front of floor collapse, as they were by then unbraced and unable to withstand the horizontal component of off-centre impacts from other objects falling on them; and finally, the collapse of the last remaining spires of core columns - note that, despite your claim, it is visibly clear from the spire photographs that these spires contained many surviviing core columns of different lengths, with only the upper most part comprising one or two columns - which were now of too great an unbraced length to stand unsupported.
The "wet noodle" analogy seems bizarrely inappropriate to describe the progressive collapse of the lower structure. It's relatively trivial to calculate the force exerted by the falling block on the lower structure as it impacts during collapse, and it's well understood that this force is several times greater than the fracture limit of the lower structure. The mechanics of structural collapse is not one of the best-known aspects of structural mechanics, but it's had a very thorough airing on this forum. Overall we find that there is nothing surprising, once collapse has initiated, that the collapse propagated to the ground despite the lower structure being essentially undamaged at collapse initiation.
The simple answer is that it didn't, and I'm at a loss to imagine where you got the impression that it did. Have you not seen any of the videos of the collapse? IN particular, the Trinity Church video of WTC2 shows very clearly that the collapse initiated due to an inward deflection of the perimeter columns on the impact floors, leaving some 20+ floors above this level to fall on to the lower structure.
As would a simplified model of the collapse. This is in fact the exact collapse scenario determined by Bazant and co-workers in papers published on the dynamics of the collapse. In fact, some in the truth movement claim that this should not have happened, and that the upper block should first have been destroyed leaving the lower block undamaged, and some claim that this did in fact happen (if that's what they're claiming; often in the truth movement the need not to say anything that can trivially be proved wrong results in the inability to say anything at all). The exact details of crush-up vs. crush-down timing, again, are probably more complex than any simple model suggests, but it's clear that the falling upper block survived the initial stages of fall until it was obscured by dust from crushed non-structural elements of the towers.
Your argument, therefore, is that the collapse started at the top (which it did not); that the upper block did not stay intact (which it did); that the upper block did not fall on to the lower block (which it did); that the upper block did not destroy the lower block (which it did); and that the upper block was destroyed before reaching the ground (which it may have been, but neither is this certain nor suspicious); and that all this suggests the use of either impossibly quiet explosives, or a hitherto unknown method of cutting vertical structural members using incendiaries.
Please go back to your videos and study how the towers actually did fall. An argument based on reality will carry infinitely more weight than one based on a gross failure to understand, or even try to understand, the observed mechanics of the collapse.
Dave
