WTC7 was a very simple steel structure and not prone to any
classic progressive collapse of any kind, whatever it means.
There were 24
inner columns supported by external
wall columns as per simplified figure right.
The columns are primary load carrying parts. The columns are connected by
horizontal beams at every floor. The beams are secondary parts carrying local loads to the primary parts - the vertical columns. The floor panels, tertiary parts, are then hanging on the beams. There were 47 floors. Total height of structure was 147 meters.
The four
horizontal beams (secondary structure) carrying the floor panels transmit average about 200 tons (50 tons each) of weight to an
inner column at every floor and 50 tons of weight to a
wall column. You evidently have to adjust the actual load for different spans of beams, floor areas, unusual static loads, etc.
It means that the total load transmitted to the ground by each
inner column is on average 9 400 tons. A
wall column transmits one quarter that load to ground or 2 350 tons. Again the real values have to be adjusted for actual values of loads transmitted to the columns from the beams.
The columns have variable dimensions from ground to roof so that the compressive stress is always <30% yield at every floor level. Evidently the bottom columns are much stronger than the top ones.
The bottom column/pillar is 47X stronger than the top column below the roof! Note that the
inner columns carry about 81% of the total load in this simplified model.
The maximum combined stress in any horizontal beam is also <30% yield. The dimensions of the beams (adjusted for span) are similar everywhere as they only carry local loads. The floor panels are just thin structures carrying load to the beams.In figure right we see that an
inner column is removed between floors 11 and 13 adjacent to two
wall columns. It is similar to Column no. 79 in WTC7.
The load carried by that
inner column above floor 13 is, say, 6.800 tons and evidently the adjacent
inner columns carry the same load - 6 800 tons. The adjacent
wall columns carry one quarter that load - 1 700 tons.
The load - 6 800 tons - in the removed
inner column is then transmitted to adjacent columns - 1 700 tons to each adjacent
inner column and the adjacent
wall column via the
horizontal beams above the removed part.
The result is as follows:
The load in an adjacent
inner column increases from 6.800 to 8.500 tons and the load in an adjacent
wall column increases from 1.700 tons to 3.400 tons or the local compressive stresses increase 25/50%. As the stresses in the adjacent columns were <30% yield before removal of the column, the stresses are now still only <37.5/45% yield, i.e. well below any critical value. In reality there are more wall columns than shown in this simplified model, which are interconnected, so the load is shared between them.The bending stresses in the
horizontal beams above the removed column part will double, which is still <60% yield. It means that nothing will really happens to the complete structure except that named parts become a little more stressed.
There will be no vertical progression of failures due to removing one part of an inner column! To suggest, like NIST, that the whole structure collapses progressively is criminally absurd!
It can be noted that the load at ground of the
inner columns carrying the extra load of the removed column increases from 9.400 to 11.100 tons or only 18%. Similar happens to the adjacent
wall columns.
This effect, that you can remove a part of a structure, e.g. a piece of column, without, e.g. collapse following is called redundancy; the structure functions without that part; the part was superfluous and not really needed. The real reason for redundancy is safety; one part may get damaged for any reason and evidently the whole structure shall not collapse, if you have to modify the structure for any reason; shift the location of a column, etc.
None of the structural parts of the structure, columns and horizontal beams, will be subject to critical overload leading to any failure or buckling, when one part - a piece of column - is removed.
The report includes figures 3.10-13 showing the right side collapse below floor 16 (?) at 0.5, 2.5 (shown above), 4.5 and 6.5 seconds, while the left side remains intact. Apparently everything above Column 79 drops down due to vertical failures' progression - there are free-flying parts! But the remainder of the structure below floor 16 is just locally damaged during 6.5 seconds. Nothing drops down from below = there is no free debris there. You would then expect the upper, intact part to tilt to the right!
The horizontal failures' progression is not clear. What
energy is required to produce all these failures? NIST does not provide any data.
Then there is the whole, intact, undamaged part above floor 16 - the upper intact part of WTC7 above floor 16. How to handle it?
Upper 31 Floors Part of WTC7 free fall drops for 2.25 Seconds
NIST has agreed/confirmed the finding that the upper part of WTC7, i.e. 31 floors or a 100 meters tall section, free fall drops (acceleration 9.82 m/s²) vertically with no tilting for 2.25 seconds during the collapse, i.e.
there is no support/resistance of the upper part above floor 16, when it displaces downward abt 32 meters. See e.g. figure 3.15 in the report (also below)
The 'finding' is however based on measurements from a
video and there is no evidence that the
video is real and no scientific analysis of the origin of the
videohas been made. The
video could be simple Computer Generated Images, CGI, and the acceleration of the CGI roof line just copy & paste of any free fall drop on Earth. That the complete top of any wide structure free fall drops on a
video is a very strong indication that the
video is fake, as no such big part part of any structure cannot free fall drop, if subject to demolition from below.
What a free fall drop is, is explained here! And here!
According non-regulatory agency NIST the constant acceleration of the complete roofline is 32.196 feet/s² or 9.814 m/s² between time 1.75 and 4 seconds, when the roofline velocity increases from 11.57 to 84.01 feet/s or 3.52 to 25.61 m/s!
This acceleration of the roof line is equivalent to gravity acceleration = 100% free fall drop. The average speed during this time is 14.56 m/s and the total free fall displacement is 32.77 meters. This makes some magic controlled demolition the OFFICIAL position of NIST.
Anyone who does not understand this, simply does not understand what free fall drop means. Free fall drop means NOT DOING ANY WORK - INCLUDING DESTROYING STRUCTURE BELOW AT ALL - OTHER THAN FALLING and ACCELERATING.
It evidently means that 32.77 meters height of structure below must have been destroyed completely before the roof line starts to free fall drop. Evidently the falling WTC7 top could not destroy the WTC7 bottom as suggested by NIST.
NIST suggests that this free fall drop was initiated by failure of column 79 between floors 11/13 followed by a vertical and horizontal progression of failures (no details of course except some strange figures) below floor 16 that apparently removed all support/resistance of the upper part for 32.77 meters vertically down at one side only and the complete structure horizontally.
If WTC7 is represented by three parts A, B and C, where part A is floors 0-6, part B is floors 6-14 (24 meters tall) and part C is floors 14-47 (see picture left), free fall of part C is only possible if, e.g. part B (or more!) is suddenly and totally removed! Then part C free falls on part A.
Free fall dropping upper part C of WTC7 (above floor 14) does not apply any loads at all on the structure below floor 14 during this time!
A free falling part C does not apply any forces or loads on anything (except the air (!) it drops through) until it contacts part A! So how can the upper part C above floor 14 damage the lower part below floor 14 as suggested by NIST during these 2.25 seconds? What kind of structural analysis is done ... when no loads except air resistance are applied?
Furthermore - NIST suggests that the upper part C deforms itself during these 2.25 seconds ... when no forces (except air resistance) at all are applied to it (all masses of the upper part are in free fall drop!). Same question ... how can a free fall dropping upper part C deform?
NIST has been asked these questions ... and could not reply. Actually NIST ignored all comments made by the public.
HOW to destroy WTC 7
An explanation how the 24
inner columns below floor 14 could suddenly 'disappear' simultaneously to produce the confirmed 32.77 meters
free fall of the structure above is given
here. The
inner columns between floors 6-13, carrying 81% of the total load, simply 'evaporated' at two locations or floor levels due to a compound applied to them that burnt extremely quickly. The load carried by the
inner columns was then transmitted to the
wall columns. The
wall columns floors 6-13, that previously carried only 19% of the load now carry 100% of it and cannot resist and buckle inward -
they are pulled in by the floor beams - as can be seen in the rubble. It explains the complete lack of parts of these lower inner columns in the rubble and also the presence of molten steel there and very strange looking pieces of junk! Further thoughts about this matter can be found
here.
There are a wide number of energetic materials and components that can be used to produce the local destruction of 24 steel inner columns by simply cutting them to destroy WTC7, and the charges had to be hidden in the lower floors, e.g. floors 6 and 13. But the result could not be hidden! The upper part - floors 14-47 - would not free fall for 2.25 seconds before being destroyed later in contact with ground.
) So in the end it would take some direct testing of this combination in conjunction with the corrugated material being welded to beams in order to determin exactly what "gives". Which as we all know, didn't happen. So its kinda hard to just take it on faith that the beams would dissociate from such a robust system and suddenly, all at once, spring there connections.
