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Flaws and omissions in NIST hypothesis
Topic Started: Jan 20 2008, 08:09 PM (1,721 Views)
Chris Sarns
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Revised: 2-16-08, 6-8-08

Flaw in NIST hypothesis, Heat

http://wtc.nist.gov/progress_report_.../appendixl.pdf

L-38 [42 on pg counter]
I4.2 Unbraced Columns: If floor systems failed, one or more columns may have lost lateral bracing.
At a floor where fires were noted, interior columns were comprised of W14x730 cores and reinforcing plates, and could support several stories unbraced without failure. …… This column, ….. would be approaching its load carrying capacity for an unsupported length of four stories if it was also subject to a uniform temperature of 500° C.

L-44
I4.6 uniform steel temperatures of approximately 570º C [1058º F] would result in column failure.

1] Core columns 79, 80 and 81 weighed 15,000 pounds per floor

2] Core columns were 2 stories high and the splices were about 3 feet above the odd numbered floors.
For a core column to fail at 3 splice joints, 4 floors would have to collapse around that column.

3] There were fires on floors 8, 11, 12 and 13, at different times in the area where the collapse began.

These fires were not sufficient to heat a column weighing 15,000 pounds per floor to more than 1000º F on 4 contiguous floors.


Fire time line:
NIST L 22–26
11:30 a.m. to 2:30 p.m.: fire on floor 22 on south side
fire on floor 12 burned west to east across the south side
[there were no other fires reported in the east half of the south side]

2:00 to 2:30 p.m.: fires on floors 11 and 12 at SE corner, progressing north

Posted Image

About 3:00 p.m., fires on floors 7 and 12 near the center of the north face
The fire on floor 12 spread in both directions, eventually reaching the NE corner

Posted Image

Sometime later, fires on floors 8 and 13
Fire on floor 8 eventually burned to NE corner and moved to east face

Posted Image

Around 4:45 p.m., a photograph showed fires floors 7, 8*, 9 and 11 near the middle of the north face. The fire on floor 12 had burned out by this time.
[NIST did not publish this photo]
*fire on floor 8 had already burned that area out.
Edited by Chris Sarns, Jun 30 2008, 07:17 AM.
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Chris Sarns
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Revised: 6-9-08

Weight of columns 79, 80 and 81

Core column 79
NIST [pg] L-40 shows column 79 had 3"x 26" cover plates.
columns 79, 80 & 81 were W14x730 [730 pounds per lineal ft.]

Rolled steel: 495 lbs per cu. ft.
http://www.reade.com/Particle_Briefings/spec_gra2.html

Cover plates 3” x 26”
2x3x26x12=1872 divided by 1728 [cu. in. per cu. ft.] = 1.0833 cu ft per lineal ft.
1.08 x 495 = 536 lbs. per lineal ft.
730 + 536 = 1,266 lbs. per lineal ft. x 12 ft. = 15,195 lbs. per floor.

Core columns 80 and 81
Core columns 80 and 81 had web plates. NIST doesn't say specifically but on pg L-14 they say the web plates were 1.5" to 8". Since the area in question is floors 7 - 13, the web plates are in the 6" - 8" range.

Shape W14X730
Depth: 22.4"
Flange width:17.9"
Flange thickness 4.91"
Web thickness: 3.07"
http://www.constructionknowledge.net/metal/images_metal/w%20Steel%20section%20tables%20080307.pdf

Top & bottom
17.9 x 4.91 x 2 x 12 = 2019.336 [cu. in. per lineal ft.]
Web
22.4 - (2x4.91) = 12.58 x 3.07 x 12 = 463.447 [cu. in. per lin. ft.]

2019.336 + 463.447 = 2483 [cu. in. per lin. ft.]
Divided by 1728 [cu. in. per cu. ft.] = 1.436 cu ft. x 495 = 711 pounds per lin. ft.
[the other 19 lbs. is the curved part where the web meets the top and bottom flanges]

Added web plates @ 6" thick:
6 x 2 x 12.58 x 12 = 1811.52 [cu. in. per lin. ft.]
divided by 1728 = 1.04833 [cu. ft.] x 495 = 518.92 lbs. per lin. ft.
730 + 518.92 = 1248.92 lbs. per lin. ft. x 12 [ft per floor] = 14,987 pounds per floor.


WTC 7 Technical Approach and Status Summary
December 18, 2007, pg 6:
The working hypothesis is based on an initial local failure caused by normal building fires, not fires from leaking pressurized fuel lines or fuel from day tanks.

A typical fire burns at around 800°C.[1472°F] As it passes through the building, the fire's intensity changes as flammable items are consumed. Fires usually average about 20 minutes in any location.
Edited by Chris Sarns, Jun 9 2008, 03:21 AM.
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Chris Sarns
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Revised: 2-13-08, 6-9-08

No horizontal collapse

L-50
H1.4 Truss #2 and/or East Transfer Girder: If one of the diagonals of truss # 2 and/or the east transfer girder was damaged or severed by collapse debris from the vertical progression, there would be
a horizontal force developed in the Floor 7 slab as columns 77 and 78 became unstable.

• H2.6 Collapse Does Not Progress: The Floor 7 slab may fail at adjacent columns prior to imposing lateral displacements sufficient to fail the columns or their splices.

• H2.7 Collapse Progresses: The horizontal tensile force would tend to pull the line of columns 74, 71, 68, 65, and 62 towards the east. The general absence of the Floor 7 slab and braced frames around the center core column line, due to the presence of elevators shafts, creates a more likely scenario for the
simultaneous lateral displacement of the center core columns without similarly displacing other core columns. The possible result is a failure of all the columns at their splices, as shown in Fig. L–49.
[column 62 not shown]

Posted Image

NIST is saying that the floor 7 slab between columns 77 and 74 pulled 5 core columns sideways simultaneously.
For this to happen, all the following must occur simultaneously:

Column 74 BENDS below floor 5 and breaks at 2 splice joints.
[there were NO fires reported below floor 6 at any time]
The other 4 columns break at 3 splice joints.
Four girder to column connections on the west side of column 62 fail
while the 24 intervening beam to column connections hold.
[62 was surrounded by an 8 inch thick, reinforced* concrete slab on floor 7]
36 north south, girders bend and start to break at column connection.
Sixteen 10 foot wide, reinforced concrete slabs, rip apart.**

The hypothesis assumes falling debris took out the east half of T2.
[this is impossible because the bottom beam of Truss #2 is one piece***]
This also means that the floor 7 slab between columns 80 and 77 is no longer there.
That leaves the slab between columns 77 and 74, to pull 5 core columns sideways.
Part of that area was the stairwell and a service shaft.
The girder between columns 77 and 74 was holding the slab to column 74.
The girder to column connection is not strong enough to bend column 74 and break 2 splice joints, much less pull 5 columns sideways.


They offer NO explanation as to how half the core columns failed.
[58,59,60,61,63,64,66,67,69,70,72 and 73]



* two layers of 5/8” steel reinforcing bar, 6”apart, in both directions.
**slab noted above and 15, 5 1/2" slabs with one layer of 6”x 6” W1.4 [5/8”] welded wire.
***
Posted Image

Source:
http://wtc.nist.gov/progress_report_june04/appendixl.pdf
http://www.fema.gov/pdf/library/fema403_ch5.pdf
Edited by Chris Sarns, Oct 4 2008, 05:53 PM.
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Chris Sarns
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Short version

NIST horizontal collapse hypothesis: 12-18-07

H1.4: ….. a horizontal force developed in the Floor 7 slab
The horizontal tensile force would tend to pull the line of columns 74, 71, 68, 65, and 62 towards the east
… simultaneous lateral displacement of the center core columns
… possible result is a failure of all the columns at their splices
, as shown in Fig. L–49.
[column 62 not shown]

Posted Image

NIST is saying that the floor 7 slab between columns 77 and 74 pulled 5 core columns sideways simultaneously.

The girder between columns 77 and 74 held the slab to column 74.
It is not strong enough to bend column 74 and break 2 splice joints, much less pull 5 columns sideways.


They offer NO explanation as to how half the core columns failed.
[58,59,60,61,63,64,66,67,69,70,72 and 73]


Edited by Chris Sarns, Jun 9 2008, 04:28 PM.
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