22-04-2011, 08:30 PM
James H. Fetzer Wrote:(1) Orling makes the assumption that every floor represents equal mass (steel) in comparison with every other, which is grossly false. The steel diminished in its thickness from 6" in the basements to 1/4" at the top. As poster #28 displays, for Orling to be correct, 1.4% of each building's mass would have to overcome 98.4%.
(2) Jeffrey has persistently ignored the key point that, if the fires had burned hot enough and long enough to weaken the steel, since the fires were asymmetrically distributed, there should have been a gradual asymmetrical sagging and tilting of those upper floors, not the complete, total and abrupt demolition which we observe.
(3) What he proposes, therefore, can be illustrated as follows. Assume you had a stack of 50-cent pieces, say, welded together, and another stack of quarters atop of them, also welded together and to the stack below. If a small stack of dimes, welded together, were dropped on that massive stack, would a collapse ensue?
Jim you show amazing denseness in not understanding what I have described as the structure of the twin towers. There were basically two types of floors throught the 104 floors above the 6 story lobby.
Tenant floor which were assembled from pre fabricated units with truss supports. These were composite construction with 4" np stone aggregate lightweight concrete. There were 88 main trusses and 6 cross trusses assembled on site linking the assemblies. All the trusses were supported on angle truss seats. The angles truss seats were welded to the spandrels of the facade and a channel on the core side which was in turn connected to the perimeter core columns witj beam stub outlookers of increasing length as you ascend up the tower... at the top they were 32" long. There were 96 of these floors and they were essentially identical.
Then there were the 8 mechanical floors. These had thicker slabs, heavier concrete and instead of truss supports the slabs were supported with steel beams. There were also additional 16 columns about 8 foot in from the facade on the mechanical floors.
The core columns stepped in thickness from the bottom to the top because the lower column supported the 3 floors attached to it, plus all those above.
When the building came down the columns were no destroyed by the fall mass. The floors were. The columns however were not able to stand without the bracing which for the facade was the floor trusses. The core bracing also was largely, though not completely destroyed by the falling debris. Most of the core survived the collapse of the floors to as tall as floor 77. Most of those core columns buckled from Euler buckling - too tall and too thin without adequate bracing a column becomes unstable and will buckle from its own weight. Please read up on Young's modulus and Euler Buckling. Perhaps Chuck can explain them to you and why they apply. Several of the core columns survived for about 20 or more seconds before they too buckled. These have been call "the Spire". Both towers had surviving core columns to as high as 70+ stories.
The floor collapse was inevitable once a sufficient mass came down upon an undamaged floor to overcome its design parameters. A collapsed floor is NOT a pancake but a floor which has shattered apart like a dropped plate or pane of glass... its mass becomes dissociated and falls... the mass does not disappear, though some is turned to dust and is carried aloft. The vast majority of the mass becomes KE energy and enough to destroy each floor successively. All of the tenant floor being of equal design, if one will fail, all below it will in sequence. The mechanical floors were stronger and would require a greater mass to crush them. But it's unlikely that floor 76 (mech floor) could support the mass of the 34 floors above - NOT THE COLUMNS ON FLOOR 76, but the floor system. The floor systems failed - not the columns.
There is no such moment created applied to the columns by even the asymmetrical random failure of the floors. The collapse of the floors was driven by gravity and that was straight down. The columns were unaffected and would therefore not tilt.... no lateral force was applied and no moment developed.
The top section of WTC 2 DID tilt just before the initiation of the global collapse. This was a result of asymmetrical column failure. But this also caused severe overloading of the remaining columns which DID buckle and bend like a pretzel. Once they buckled there was no longer and axial load transfer, the top was dropping and in so doing destroying itself at the bottom and the top floors of the lower section. This mutual destruction created that threshold mass which kicked off the collapse of the floors from 78 down to the ground as in WTC1.
There was have been engineered intervention to kick off the destruction of wtc 1 and perhaps to destroy the columns asymmetrically in tower 2. We don't KNOW THE CAUSE. Fires DOES weaken steel, but it seems unlikely that it would weaken it enough to kick off the collapse of the floors... truss seat and truss failures.
I am doing some calculations at this date and the safety factor for the core columns seems to be about 1.5. For example CC501 was A36 steel at 36,000 psi at floor one was rated for load of about 21,000,000 pounds at floor 50 it was rated for 8.5 million pounds. I'll have the actual loading of the column shortly, but the column itself weighed 1,262,990 pounds and the loads were approximately 12,000,000 pounds.
What I propose is what happens when you drop (or rest) something too heavy (or overlaod) a floor - it collapses. QED.