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Question about structural beams, and columns ;)

post Aug 23 2008, 08:00 PM
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Some links on WTC1 & 2 Perimeter Columns:

FEMA Steel Collection

SEoNY Summary of Identified Pieces

WTC Modeling

NIST NCSTAR1-3 Section 2.3.1 covers Perimeter Columns of the 9th through 107th floors [55 of 184 in PDF, p.7]

Paraphrasing (since it won't copy/paste from the PDF):

14 different grades of steel were used, ranging from 36ksi to 100ksi in yield strength (F_y). [54 of 184, p. 6]

Flange spacing = 40.0 inch [1.02 m] between adjacent perimeter flange plates.

Spandrel thickness ranged from 0.375 to 1.375 inch, with spandrels 52 inches high [1.32 m], and the inner web was not present in the spandrel area (see Figs 2-3 and 2-4).

Perimeter flanges varied from 0.250 to 3.00 inch thick [57 of 184, p. 9]

2.3.2 covers Core Columns.

At the 83rd floor, the core is said to have changed from built-up box columns to wide flange (WF or I-beam) columns. [Fig 2-6]

Hat truss (floors 107 to 110) are covered in section 2.3.4 [61 of 184, p. 13]

"7.8.2 High Strain Rate Properties
The strain rate sensitivity and high-strain rate ductility of the perimeter and core column steels were similar to other structural steels of the WTC era.

7.8.3 Impact Properties
The impact toughness of steels from the perimeter and core columns, and floor trusses was consistent with literature values for the WTC construction era.

7.8.4 High Temperature Properties
The high-temperature yield and tensile strength behavior of WTC steels was similar to behavior of the structural steels from the WTC construction era literature.

The creep behavior of WTC steels was modeled by scaling WTC-era literature data using room temperature tensile strength ratios.

Laclede Steel Company's substitution of 50 ksi yield strength steel for A 36 in the lower chord of the [floor] trusses is expected to have provided significantly improved performance at high temperature." [164 of 184, p. 116]

Another discrepancy- Section 2.2 of NCSTAR 1-3 states: "Skilling, Helle, Christiansen, and Robertson (SHCR), structural engineers for the WTC towers." [53 of 184, p. 5]


Problem is, the North Tower blueprints state "Worthington, Skilling, Helle, & Jackson, Structural Engineers." [I looked at the 80thFloorPlan, the rough impact location for WTC2 South]

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post Aug 23 2008, 10:27 PM
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Given the above information about Perimeter Flange (red in the images below) variation, if I assume a roughly linear variation between the 9th and 107th floors, I find the following perimeter column profiles (assuming 0.250" thick inner and outer web plate [green in images], and taken to the nearest 1/16th inch as steel plate usually comes in 1/16" thickness increments):

NOTE: Units are inches [with cm in brackets]

Thinnest/upper columns (0.250" flange):

95th Floor (WTC1N impact floor, 0.5625" or 9/16" flange):

80th Floor (WTC2 So impact floor, 1.00" flange):

Thickest columns (3.00" flanges):

Here is an array of the 95th floor ~0.625" thick flange Perimeter Columns:

NOTE: According to NIST NCSTAR 1-3B, Fig. 3-5(B) [41 of 112, p. 13], both Flange plates(red) are termed "Plate 1," the outer web (upper, narrow green in pictures above) is "Plate 2," and the inner web (lower, 15.75" wide green) is "Plate 3."


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Leslie Landry
post Oct 1 2008, 04:17 PM
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QUOTE (Sanders @ Jun 2 2008, 06:50 PM) *
Sorry Leslie, I hadn't peeked in to this thread in a while and didn't realise I hadn't responded to a couple of your posts.

The only other explanation I have heard for the molten metal that is even plausible is one that involves the use of high-energy weaponry... but that would not have explained the molten metal oozing out of the side of the tower

Sanders..your reply to me was written 4 months ago but same as you...i haven't checked this thread in awhile. After what you said here...i think that i was understanding this whole thing wrong and if you are saying what i think you are saying..then i agree with you smile.gif
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post Oct 3 2008, 12:44 PM
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Have you got the 40% [perimeter only IIRC] severed column references handy TF? It would be good to have the NCSTAR section and page number(s) listed here for the benefit of "those who shall not be named here." wink.gif

EDIT: It looks like my green "web plates" above should have been thicker too, from my recent NIST readings. Someone else is welcome to correct those thicknesses with sources, too.
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post Apr 23 2009, 05:26 PM
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QUOTE (forester @ Oct 31 2006, 02:48 PM) *
the structural beams of the wtc and all buildings are designed to be able to hold up the weight of all the beams above them.

at the wtc towers, after the planes hit, many of the beams were severed. this puts a lot more of the weight of the building on the undamaged beams.

question 1: how many beams MUST stay intact for the buildings to stay up?

question 2: if the section of the towers above the impact does collapse due to the beams in the damaged section nolonger being able to carry the above weight, can the beams below the damaged section literally catch the fall of the collapsing section and keep the building up? i took physics many years ago but im sure their is an equation to figure out the weight or kinetic energy of a mass after it falls several feet.

if the section above the plane damage did indeed collapse, the undamaged section below it would have had to be able to hold up all the weight above it multiplied by its velocity...i assume. considering this, is it logical to expect the undamaged floors to be able to hold this weight? is there any precident for this?

1 - the buildings were standing after the jets hit. So; the question is not relevant as the buildings had sufficient structural integrity to stand as they were. After about an hour they then blew up. NIST now confirms this in their final reports, and no one that I know of is asking this type of question any longer. To further answer your obviously misleading question: had the damage to the impacted floors removed the structural integrity of those floors (which it did not), then the top floors would have fallen off to the side of the building due to the law of angular momentum (open a high school physics book). So even then the lower floors of the building would have in fact had the "beams" necessary to keep the overall building standing.

2 - yes they would have. This mathematical proof can be found in the following papers:
Response to NIST on Energy and Momentum (January 29, 2008)
Crockett Grabbe, Ph.D.

Collapse Time Calculations for WTC 1 (May 9, 2007)
Dr. Kenneth Kuttler, Professor of Mathematics

Analysis of Mass and Potential Energy in the World Trade Center Twin Towers (April 25, 2007)
Gregory H. Urich

3 - your cleverly worded assertion in your last section outlines what is known as the "sledge hammer hypotheses" It reads: The accelerated mass of the top floors came down on the rest of the building like a sledgehammer; thus smashing the building from the top down. NIST and all scientists studding the WTC have thrown that theory out along with the pancake theory. Their current theory is that FIRE caused the WTC destruction. When asked how in the world that would be possible their answer seems to be "because we said so".
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post Aug 11 2011, 04:20 PM
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According to the Architects of the TwinTowers the buildings were designed to withstand the impact of a Boeing 707 which is heavier and more rigid than a 2001 Boeing 757.Also a skyscraper tower is designed on the Cantilever principle; e.g. stronger and heavier Steelwork at the lower Third of the structure and lighter, higher up.The outside skeleton of columns and beams and trusses were welded together like a Shopping Trolley; i.e. much stronger, lighter and tensile.
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rob balsamo
post Aug 12 2011, 07:56 AM
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QUOTE (icarus88 @ Aug 11 2011, 04:20 PM) *
According to the Architects of the TwinTowers the buildings were designed to withstand the impact of a Boeing 707 ..........

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post Aug 13 2011, 11:18 AM
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The towers were not stiff enough.... able to act like a monolithic structure to be knocked over by a plane at ANY speed. Even a huge plane impacting at very high speed and energy would perhaps at best slice right through the structure somewhat similar to its profile... not unlike the holes we saw after the plane strikes. This could take out several columns but not enough... unless the plane was enormous (profile) but the remaining columns would support the upper part as the loads from the destroyed columns would be taken by the remaining undamaged ones. If the safety factor is sufficient then the remaining columns will do the job and hold the top up.

The speed (energy) of the plane is only significant as it relates to how much (how deep into the structure - core) could the mass of the plane penetrate to do damage to its columns. A slow lumbering craft might not even penetrate the steel facade columns... for example a blimp. If it collided it would hardly dent the towers.

The towers collapsed because there was a progressive destruction of additional core columns POST plane strike of yet to be determined cause... which then caused the top section to drop... the floor masses were freed and fractured as the came crashing down and set off a runaway collapse/destruction of the floors right to the ground. No columns were involved in the collapse once the floors at the top came down. No additional explosives or incendiaries were required. No columns below the strike zone were crushed or buckled... they all broke apart at their connections... the weakest part of the structure... from lateral forces for columns and dynamic loading for bracing.

Could the planes have delivered sufficient fuel or other pyrotechnic materials to weaken the structure further? That's a good question. Could planted devices do weaken it to failure mode? Another good question.
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post Aug 13 2011, 10:18 PM
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Yada, yada, yada.....
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