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There have been a lot of claims made about the circumstances surrounding the events of 9/11 and Building 7 in particular.

The central claim regarding Building 7, that I have heard personally, is that Building 7 fell in such a perfect fluid motion that its collapse had to be due to a controlled demolition. Furthermore since Building 7 wasn't hit by a plane directly, it is claimed that there can be no other explanation for how the building collapsed in such a seemingly controlled fashion.

Is there any evidence to support the claims that Building 7 was destroyed in a directly controlled fashion?

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No.

Fires ignited by falling debris (from WTC 1) are the sole cause of the WTC 7 collapse.

Short answer:

  • Debris from the collapse of WTC 1, about 350 ft. to the south, impacted WTC 7, igniting fires on at least 10 floors.
  • Other than starting the fires, the debris impacts were not a contributing factor.
  • Fires on six of those floors grew from the time of the debris impact (10:28:22 a.m.) and lasted until the building collapsed (5:20:52 p.m.).
  • After several hours, the heat absorption ability of the fire-proofing began to fail. The building's structural steel began to soak up heat from the fires.
  • A ''seated connection'' was used for some of the girders framed to interior columns. The girder was held by four "erection bolts" (''girders'' span between columns; ''beams'' span between girders).
  • A 13.7 m (540 in.) long W33x130 beam heated uniformly to 600 °C will expand along its length by 4.5 inches.
  • In doing so it will produce a lateral force of 6.9 million pounds (30.7 million newtons).
  • The four erection bolts resisting this force had a total shear capacity of 0.180 million pounds (i.e., 2.6 percent of the possible force).
  • By the time the girders reached 164 °C the four bolts had failed (i.e., torn in two, ripped apart, cleaved in twain, etc.).
  • With the failure of the bolted connection, further thermal expansion of the floor beams pushed a 13th floor girder, between Columns 79 and 44, off its seat.
  • The flooring system on Floor 13 subsequently failed, collapsing onto the floors below, resulting in the collapse of floors 12 through 6.
  • The floor collapse left more than 150 ft. of Column 79 without lateral support.
  • Without structure transferring load laterally, Column 79 buckled and failed.
  • The transfer of load, once supported by Column 79, overwhelmed the structural capacity of the other columns. They too failed.
  • After burning for 6 hours and 52 minutes, WTC 7 suffered a fire-induced progressive collapse. The building was completely destroyed.

Long answer:

1. Erection bolts are not structural connections

In a seated connection, the beam or girder was supported by the seat, which was welded to the column. Bolts were installed that fasten the beam or girder to the seat for erection purposes These erection bolts did not carry any gravity load; rather, they were installed to insure that the beam or girder was held in place during erection. NIST found no evidence that the girders or beams in WTC 7 were welded to the seats. In a similar way. an angle or plate was bolted to the top flange to prevent the beam or girder from twisting, but there was little restraint to bending in the plane of the beam. NCSTAR 1-9 Figure 8-21 Page 349 Consider the girder that spanned between Column 79 on the interior of the building and Column 44 on the exterior. Thermal expansion of this girder would have loaded the erection bolts in shear, since (1) there were no shear studs anchoring the girder to the slab (and thereby restraining elongation), and (2) the columns were prevented from lateral movement because they were embedded in the floor slabs which had considerable in-plane stiffness. Additionally, the expansion of floor beams that framed into this girder, because the framing was asymmetrical, tended to add additional shear load to the erection bolts. The combination of these two shear loads could have failed the bolts in shear. If the erection bolts were to fail, then there would be no positive attachment preventing the girder from being pushed off the seat. Source: (NCSTAR 1-9) VOLUMES 1 and 2, page 348.

2. Thermal expansion will break stuff

The first failures observed were of the shear studs, which were produced by axial expansion of the floor beams, and which began to occur at fairly low beam temperature of 103 °C. Axial expansion of the girder then led to shear failure of the bolts at the connection to Column 79; and, at a girder temperature of 164 °C, all four erection bolts had failed, leaving that end of the girder essentially unrestrained against rotation. Continued axial expansion of the floor beams pushed the girder laterally at Column 79, as shown in Figure 8-26, in which failed shear studs and bolts were evident. When the beam temperatures had reached 300 °C, all but three shear studs in the model had failed due to axial expansion of the beams, leaving the top flanges of the beams essentially unrestrained laterally. Continued axial expansion of the girder caused it to bear against the face of Column 79, generating large axial forces that led to failure of the bolts connecting the girder to Column 44. When the girder temperature had reached 398 °C, all four erection bolts at Column 44 had failed, leaving the girder essentially unrestrained against rotation at both ends. After failure of the erection bolts in the seat at Column 44, continued axial expansion of the floor beams pushed the girder laterally, where it came to bear against the inside of the column flange. Axial compression then increased in the floor beams, and at a beam temperature of 436 °C, the northmost beam began to buckle laterally. Buckling of other floor beams followed as shown in Figure 8-27(a), leading to collapse of the floor system, and rocking of the girder off its seat at Column 79 as shown in Figure 8-27(b). The collapse process took time to occur in the LS-DYNA analysis, during which the temperatures had ramped up to their maximum values in the simulation. Source: (NCSTAR 1-9) VOLUMES 1 and 2, page 352.

3. Collapse Initiation

The simple shear connection between Column 79 and the girder that spanned the distance to the north face (to Column 44) failed on Floor 13. The connection failed due to shearing of erection bolts, caused by lateral thermal expansion of floor beams supporting the northeast floor system and, to a lesser extent, by the thermal expansion of the girder connecting Columns 79 and 44. Further thermal expansion of the floor beams pushed the girder off its seat, which led to the failure of the floor system surrounding Column 79 on Floor 13. The collapse of Floor 13 onto the floors below-some of which were already weakened by fires-triggered a cascade of floor failures in the northeast region. This, in turn, led to loss of lateral support to Column 79 in the east-west direction over nine stories (between Floors 5 and 14). The increase in unsupported length led to the buckling failure of Column 79, which was the collapse initiation event. Source: (NCSTAR 1-9) VOLUMES 1 and 2, page 611.

4. "Free fall" is a myth

To further clarify the descent of the north face, NIST recorded the downward displacement of a point near the center of the roofline from first movement until the north face was no longer visible in the video. Numerical analyses were conducted to calculate the velocity and acceleration of the roofline point from the time-dependent displacement data. The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel (a single element in the video image) at the roofline. This pixel became brighter as the roofline began to descend because the color of the pixel started to change from that of the building façade to the lighter color of the sky.

The approach taken by NIST is summarized in NIST NCSTAR Report 1A, Section 3.6, and detailed in NIST NCSTAR Report 1-9, Section 12.5.3.

The analyses of the video (both the estimation of the instant the roofline began to descend and the calculated velocity and acceleration of a point on the roofline) revealed three distinct stages characterizing the 5.4 seconds of collapse:

  • Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
  • Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall).
  • Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity.

:This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model, which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below. Source: Questions and Answers about the NIST WTC 7 Investigation.

NCSTAR 1-9 Figure 12-77 Page 603

Claims, assertions and questions :

Many of the claims and assertions by WTC 7 conspiracy theorists can be found at WTC 7 Draft Reports for public comment. The submission by Richard Gage of Architects & Engineers for 9/11 Truth is a good representation of how 911 conspiracy theorists rely on a lack of evidence to somehow draw conclusions (see: argument from ignorance).

Investigation by the National Institute of Standards and Technology*:

The National Institute of Standards and Technology (NIST) is responsible for conducting fact-finding investigations of building failures that resulted in substantial loss of life or that posed significant potential of substantial loss of life.

Final Report on the Collapse of World Trade Center Building 7 (The results of all NIST WTC investigations can be found at : NIST and the World Trade Center)

NIST: Questions and Answers about the NIST WTC 7 Investigation

How did the fires cause WTC 7 to collapse?

The heat from the uncontrolled fires caused steel floor beams and girders to thermally expand, leading to a chain of events that caused a key structural column to fail. The failure of this structural column then initiated a fire-induced progressive collapse of the entire building.

According to the report's probable collapse sequence, heat from the uncontrolled fires caused thermal expansion of the steel beams on the lower floors of the east side of WTC 7, damaging the floor framing on multiple floors...

How hot did WTC 7's steel columns and floor beams get?

Due to the effectiveness of the spray-applied fire-resistive material (SFRM) or fireproofing, the highest steel column temperatures in WTC 7 only reached an estimated 300 degrees C (570 degrees F), and only on the east side of the building did the steel floor beams exceed 600 degrees C (1,100 degrees F). However, fire-induced buckling of floor beams and damage to connections-that caused buckling of a critical column initiating collapse-occurred at temperatures below approximately 400 degrees C where thermal expansion dominates. Above 600 degrees C (1,100 degrees F), there is significant loss of steel strength and stiffness. In the WTC 7 collapse, the loss of steel strength or stiffness was not as important as the thermal expansion of steel structures caused by heat.

Some people have said that a failure at one column should not have produced a symmetrical fall like this one. What's your answer to those assertions?

WTC 7's collapse, viewed from the exterior (most videos were taken from the north), did appear to fall almost uniformly as a single unit. This occurred because the interior failures that took place did not cause the exterior framing to fail until the final stages of the building collapse. The interior floor framing and columns collapsed downward and pulled away from the exterior frame. There were clues that internal damage was taking place, prior to the downward movement of the exterior frame, such as when the east penthouse fell downward into the building and windows broke out on the north face at the ends of the building core. The symmetric appearance of the downward fall of the WTC 7 was primarily due to the greater stiffness and strength of its exterior frame relative to the interior framing...

Graphic showing the buckling of WTC 7 Column 79 (circled area), the local failure identified as the initiating event in the building's progressive collapse

Did investigators consider the possibility that an explosion caused or contributed to the collapse of WTC 7?

Yes, this possibility was investigated carefully. NIST concluded that blast events inside the building did not occur and found no evidence supporting the existence of a blast event...

Is it possible that thermite or thermate contributed to the collapse of WTC 7?

NIST has looked at the application and use of thermite and has determined that its use to sever columns in WTC 7 on 9/11/01 was unlikely.

Thermite is a combination of aluminum powder and a metal oxide that releases a tremendous amount of heat when ignited. It is typically used to weld railroad rails together by melting a small quantity of steel and pouring the melted steel into a form between the two rails...

...Analysis of the WTC steel for the elements in thermite/thermate would not necessarily have been conclusive. The metal compounds also would have been present in the construction materials making up the WTC buildings, and sulfur is present in the gypsum wallboard used for interior partitions...

An emergency responder caught in the building between the 6th and 8th floors says he heard two loud booms. Isn't that evidence that there was an explosion?

The sound levels reported by all witnesses do not match the sound level of an explosion that would have been required to cause the collapse of the building. If the two loud booms were due to explosions that were responsible for the collapse of WTC 7, the emergency responder-located somewhere between the 6th and 8th floors in WTC 7-would not have been able to survive the near immediate collapse and provide this witness account.


*NIST is an agency of the U.S. Department of Commerce.

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    @jon_darkstar The main towers did not fail from side impact. They failed because the truss hangers for the concrete floors seperated from their perimeter supports and the floor started dropping....bang, bang, bang...all the way down. Why straight down ? Gravity.
    – Rusty
    Mar 26 '11 at 22:34
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    @jon_darkstar I can understand you might think that. Makes perfect sense. But the towers are not big poles. They are big boxes (an inner box and an outer box) and they are mostly hollow. The floors are basically just hanging between the boxes and when one comes off its hangers it can only go down. Down the inside of the box.
    – Rusty
    Mar 26 '11 at 23:03
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    Gentle but firm reminder: comments are not the place for discussion, use the chat for that. Thank you. :-)
    – Sklivvz
    Mar 26 '11 at 23:09
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    we can argue finer points of that forever, so lets not. return to the question at hand - building 7. can you propose any reasonable explanation for it that does not involve explosives? also, try to explain why the 911 Commission Report NEVER mentions building 7 in over 400 pages. Not a footnote. Nothing! @Sklivvz - sorry, read it right after Mar 26 '11 at 23:10
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    You may want to show pictures of the SOUTH side of WTC7 prior to its collapse. Most conspiracy theorists neglect the fact that nearly 25% of the first ten floors were missing on the south side (they only, conveniently for themselves, show the north side of the building which faced away from the collapse). Check pages 59-66 of 911myths.com/WTC7_Lies.pdf Sep 17 '11 at 3:39
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No. There are alternative explanations for observed characteristics of the collapse consistent with a fire induced collapse.

Why the collapse resembled a controlled demolition

When discussing the similarity of the collapse of WTC7 to a controlled demolition, 3 points are often raised.

  1. Symmetry: The building was asymmetric. The damage was asymmetric. So how does the collapse become symmetric?

  2. Speed: Building 7 fell at freefall for 8 storeys. How is it possible to completely lose support over 8 storeys due to a fire?

  3. Totality: The collapse supposedly started with the failure of just one of 81 columns. So, how does such a failure bring down the whole building?

  4. And as a bonus, if the NIST version true, then how is any building safe?

There are a number of factors that made the very natural collapse of Building 7 resemble a controlled demolition as above.

The building collapsed from the inside out

enter image description here

As you can see above, the penthouses begin falling before the roofline. If you look closer, you can see daylight through windows on the top left.

The building was at least partially hollowed out over 6 seconds; a process that may have had substantial asymmetry. The walls survived all this because they were very strong; they had to brace the building against typhoons.

The damage was kind of symmetric

  • The collapse of the Twin Towers damaged the southwest side of the building.

NCSTAR 1-9 page 161 NCSTAR 1-9 page 161

  • The fire-induced collapse started in the northeast.

enter image description here

  • Building 7 at moment of global collapse

NCSTAR 1-9 page 588 fig 12-62 With impact and fire damage [NCSTAR 1-9 page 588] ![NCSTAR 1-9 page 594 fig 12-70 With only fire damage [page 594]

The building was severely damaged at the bottom before the global collapse began

  • The fires caused substantial damage to the floor beams, vital to column stability, as they marched across the building. An example of progression of damage on floor 13 is shown below.

NCSTAR 1-9 page 529 fig 11-47 NCSTAR 1-9 page 529 NCSTAR 1-9 page 530 fig 11-48 page 530

  • When the collapse started, the falling debris hit and damaged the adjacent parts of the building. This caused the already fire-damaged flooring near the bottom of the building to collapse in rapid succession, leaving the interior columns and outer walls without bracing.

NIST simulation NIST model [Source]

  • As a result, first the interior columns buckled, and the middle of the building stared falling:

enter image description here

  • And then the walls crumpled and fell at freefall for around 8 storeys.

NCSTAR 1-9 page 589 fig 12-63 NCSTAR 1-9 page 589

The picture that emerges is of several independent relatively small failures that accumulated all over the building over a span of several hours due to debris and fires, rapidly growing in size over seconds in response to a large localised failure.

In other words, an uncontrolled event with somewhat similar mechanisms to a controlled demolition.

Returning to those 4 points I mentioned above:

  1. the illusion of symmetry was created by the outer wall, which was the last component to collapse. The interior of the building collapsed in a highly disordered fashion. Adding to this was the symmetry created by the debris impact damage and fire-induced collapse being on the other side.

  2. Multiple storeys of freefall was enabled by internal collapses hollowing out the bottom of the building, followed by the hollowed out section crumpling.

  3. The totality of the collapse was due simply to the building misbehaving as if it was a 47 storey building standing too close to another collapsing 47 storey building. This was compounded by damage sustained over the past seven hours.

  4. And finally, such failures are rare, as there are few things that could cause them. A bomb could not be planted inside a skyscraper without someone noticing. A sufficiently large plane can no longer be flown into a building without substantial difficulty. And finally, a normal office fire would give hours of advance warning before a collapse.

Why the collapse did NOT resemble a controlled demolition

There are however some pretty clear differences between the appearance of this collapse and a controlled demolition

The noise

I don't know how to stress this enough. Go on Youtube and watch a controlled demolition. Odds are you'll hear:

  1. A serious of loud, sharp and sometimes quite annoying BANGs before the building even moves

  2. A (relatively) soft and gentle roar as the building slides down

#1 was completely absent at Building 7. A vivid example of this can be seen in this video

https://youtu.be/JnLcUxV1dPo?t=126

(Ironically, this is the clip that conspiracy theorists plaster around the web)

The time delay for sound from WTC7 to arrive in this video is 2 seconds. But 7 seconds after the east side of the building implodes, we can't hear anything.

It's only after the roofline begins falling that we hear the cameramen shouting "whoa, whoa, whoa!"

The building fell over

From this angle, you can see the building clearly fall over to the south.

https://youtu.be/JnLcUxV1dPo?t=456

enter image description here

Therefore, the claim that the building fell symmetrically straight down onto it's footprint is not accurate

Moreover, look at this picture of the ruins. You can see a wall draped over everything else.

enter image description here

Collateral damage

MIT lost it's Fiterman Hall in the collapse

enter image description here

The Verizon Building was also heavily damaged by the fall of WTC7

enter image description here

Not a very "controlled" demolition.

Other steel framed buildings that fell due to fire

The Plasco in Tehran

On 19 January 2017, the 19 storey Plasco Building pancaked following a several hours long fire.

enter image description here

Architects and Engineers for 9/11 Truth went so far as to claim that this could also be a demolition!

Madrid Windsor Tower

This was a 32 storey building with steel walls and a concrete core

enter image description here

On 12 February 2005, a fire broke out, causing the steel portions, and the steel portions only, on the upper floors, to collapse.

enter image description here

It's possible that the collapse would have been even more destructive but an extra-strong mechanical floor at the middle of the building arrested Twin Towers style pancaking.

Appendix I: The University of Alaska Fairbanks study

Though not directly referenced in the question, this study is one of the strongest arguments used to claim that Building 7 was brought down by controlled demolition. Therefore, examination of this study is relevant to the question. The study concludes:

The principal conclusion of our study is that fire did not cause the collapse of WTC 7 on 9/11, contrary to the conclusions of NIST and private engineering firms that studied the collapse. The secondary conclusion of our study is that the collapse of WTC 7 was a global failure involving the near-simultaneous failure of every column in the building.

But the study has fatal flaws. Some of the greater examples are touched upon below.

Treating the building like infinitely strong rubber

To see how plausible NIST's progressive collapse model was, UAF ran a simulation with the NIST damage model.

From their figures 4.8 to 4.16, which shows the results of their analysis of the NIST scenario, we learn that they used a linear static analysis. What does this mean?

A linear static analysis is an analysis where a linear relation holds between applied forces and displacements. In practice, this is applicable to structural problems where stresses remain in the linear elastic range of the used material. In a linear static analysis the model’s stiffness matrix is constant, and the solving process is relatively short

Source

That means they neglected plasticity in a simulation of something being destroyed. The result: Their building was indestructible; they needed to remove columns manually at each step to keep the collapse going, as shown by the captions to their figures.

Violating Newton's first law

From the above, we can see that they used a "linear static analysis". The "static" in there is particularly damning.

Linear static analysis has two main assumptions:....

  • The loading is static.
    • Magnitude and direction do not change with time.
    • All loads are applied slowly and gradually until they reach their full magnitudes. Inertial and damping properties are ignored due to negligibly small accelerations and velocities.
    • Time variant loads that induce considerable inertial and/or damping forces may warrant dynamic analysis.

Source

By using this static model, they are ignoring all that momentum in the falling building, which would play a pivotal role in the collapse.

UAF analysis of NIST scenario Figure 4.15 Visualization of linear static analysis, from the southwest, showing the building tipping to the southeast after the hypothetical failure of Columns 76 to 81. The movement shown is highly amplified for clarity. The actual scale of the displacements are presented to the right.

Even when we account for their displacements being highly amplified, the above is ridiculous. Comparing the image with the scale tells us that the building is displaced 600 inches, or 15 meters. This can only occur from a collapse in progress. Yet if that building were to suddenly appear in Manhattan, it would not collapse - at least according to the laws of physics in their "simulation"!

The above is not exhaustive. But it is enough to see that this "study" has no basis to conclude that "fire did not bring down WTC7".

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    I was expecting that each of the four "points often raised" (three plus a bonus) would be explicitly addressed, but the structure of the explanation does not parallel the points, so it's a bit of work to make the connections. And I don't see any explanation of the third point, nor of the bonus point. Have I overlooked something?
    – phoog
    Aug 30 at 15:32
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    @phoog how about now
    – Abdullah
    Aug 30 at 17:00
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    Yes, I think that's somewhat better, thanks.
    – phoog
    Sep 1 at 14:55

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