New 9/11 footage shows visible explosions in building 7

Di0genes wrote: »

Actually I've made none of those claims....

davoxx wrote: »

oh you're back again .. did you bring your theory too?

Di0genes wrote: »

You clearly are struggling with the basics of the search function still.



http://www.nist.gov/publication-portal.cfm?defaultSearch=false&q=wtc+7&authorlist=&researchfield=&seriesName=&datefrom=&dateto=#

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3.3 HYPOTHETICAL BLAST SCENARIOS
Considerable effort was expended to compile evidence and to determine whether intentionally set
explosives might have caused the collapse of WTC 7 (NIST NCSTAR 1-9, Appendix D). As a minimum,
the explosive material would have had to cause sufficient damage to a critical column or truss that it
became unable to carry its service load or that a lateral deflection would cause it to buckle.
Six combinations of explosive location and column/truss sections and two implementation scenarios were
considered. In the first scenario, there was ample time for optimized preparation of the structure
(including possible preliminary cutting of structural members) and use of the minimum mass of
explosives. In the second scenario, the explosive charge was to be placed in the shortest possible time,
which was to be no more than a 7 h to 8 h time frame.
SHAMRC, a software program that is used for analysis of explosive detonations, shock propagation and
structure loads due to blast and fragments, was used to simulate pressure histories from hypothetical
blasts. The pressure histories were then used to determine whether windows would have broken, which
would have provided visible evidence of a charge detonation to observers outside the building.
SHAMRC has a proven record of accuracy for explosive weights of less than 500 g (1 lb) to more than
4 x 106 kg (4,000 tons). A validated Shard Fly-Out Model (SFOM) was used to predict window
breakage. Simulations were performed for differing degrees of partitioning of a tenant floor.
Attention focused on a single hypothetical blast scenario. This scenario involved preliminary cutting of
Column 79 and the use of 4 kg (9 lb) of RDX explosives in linear shaped charges. The other scenarios
would have required more explosives, or were considered infeasible to accomplish without detection.
Calculations were also performed for a lesser charge size of 1 kg (2 lb) to evaluate threshold explosive
requirements for window fragility.

26 NIST NCSTAR 1A, WTC Investigation

Deriving the Probable Collapse Sequence

Preparations for a blast scenario would have been almost impossible to carry out on any floor in the
building without detection. Preparations would have included removal of column enclosures or walls,
weld torches to cut column sections, and placement of wires for detonation. Occupants, support staff, and
visitors would have noticed such activities, particularly since they likely would have occurred around
more than one column.
Figure 3–1 shows the results for the two shaped charges applied to Column 79 on a tenant floor that was
highly partitioned, such as Floor 12. Nearly all the windows on the northeast section of the floor
subjected to a blast would have been broken, even by the smaller charge. Simulations for a floor that was
not highly partitioned led to more extensive window breakage.

...

2.4
THE PROBABLE COLLAPSE SEQUENCE
The following is the NIST account of how the fires in WTC 7 most likely led to the building's collapse.
The collapse of WTC 1 damaged seven exterior columns, between Floors 7 and 17 of the south and west
faces of WTC 7. It also ignited fires on at least 10 floors between Floors 7 and 30, and the fires burned
out of control on Floors 7 to 9 and 11 to 13. Fires on these six floors grew and spread since they were not
extinguished either by the automatic sprinkler system or by FDNY, because water was not available in
WTC 7. Fires were generally concentrated on the east and north sides of the northeast region beginning
at about 3 p.m. to 4 p.m.
As the fires progressed, some of the structural steel began to heat. According to the generally accepted
test standard, ASTM E-119, one of the criteria for establishing the fire resistance rating for a steel column
or floor beam is derived from the time at which, during a standard fire exposure, the average column
temperature exceeds 538 °C (1000 °F) or the average floor beam temperature exceeds 593 °C (1100 °F).
These are temperatures at which there is significant loss of steel strength and stiffness. Due to the
effectiveness of the SFRM, the highest column temperatures in WTC 7 only reached an estimated 300 °C
(570 °F), and only on the east side of the building did the floor beams reach or exceed about 600 °C
(1100 °F). The heat from these uncontrolled fires caused thermal expansion of the steel beams on the
lower floors of the east side of WTC 7, primarily at or below 400 oC (750 oF), damaging the floor framing
on multiple floors.
The initiating local failure that began the probable WTC 7 collapse sequence was the buckling of
Column 79. This buckling arose from a process that occurred at temperatures at or below approximately
400 °C (750 °F), which are well below the temperatures considered in current practice for determining
fire resistance ratings associated with significant loss of steel strength. When steel (or any other metal) is
heated, it expands. If thermal expansion in steel beams is resisted by columns or other steel members,
forces develop in the structural members that can result in buckling of beams or failures of connections.