Photographic evidence proves beyond a doubt that floors sagged, pulling perimeter columns in. An event some conspiracy sites suggest never happened.
With the fire proofing blown off, the fire only needed as little as 600 degrees C to deform the naked truss steel. Conspiracy theorists point to the UL tests which show the trusses sagged but never fail to say the building should have stood. But what conspiracy theorists don't tell you is that the test was done with a minimum of fire proofing on the trusses. The test was never meant to find out what caused the truss to fail. It was testing the fire proofing to see if it was up to code.
The 1968 New York City building code - the code that the towers were intended but not required to meet when they were built required a two-hour fire rating for the floor system.
Shyam Sunder, lead investigator of the NIST WTC investigation, explained that the four laboratory tests provide only a means for evaluating the relative fire resistance rating of the floor systems under standard fire conditions and according to accepted test procedures. Sunder cautioned, "These tests alone cannot be used to determine the actual performance of the floor systems in the collapse of the WTC towers. However, they are already providing valuable insight into the role that the floors may have played in causing the inward bowing of the perimeter columns minutes before both buildings collapsed."
"The fire conditions in the towers on 9-11 were far more extreme than those to which floor systems in standard U.S. fire rating tests are subjected," Sunder said to a group that gathered to watch yesterday's final test at Underwriters Laboratories (UL) in Northbrook, Ill. "Our investigation's final assessment of how the floor system performed in the WTC fires also must consider factors such as the combustible fuel load of the hijacked jets, the extent and number of floors involved, the rate of the fire spread across and between floors, ventilation conditions, and the impact of the aircraft-damaged towers' ability to resist the fire," Sunder said
http://www.sciencedaily.com/releases/2004/08/040829130757.htm This is more evidence conspiracy theorists are being dishonest when they point to these tests and suggest the building should not have collapsed. They KNOW this because this is old news.
So the fire expands the naked truss steel and it pushes against the perimeter columns. At this early stage the perimeter columns are strong enough to resist the expansion and cause the expanding truss to sag.
Computer simulation of expanding truss pushing out on a perimeter column and sagging
As the fires moved on to find new sources of fuel (Desks, seats, paper, plastic, etc..) the expanded truss cools and contracts. This contraction happened over a period of time and over many floors. This is a very important point, because had it only been one floor contracting the perimeter may not have buckled as much.
If a floor sags, it pulls both the perimeter columns and core columns toward the center of the floor. Because the core columns are stronger than the perimeter, the perimeter is the side that gets pulled in.
There are plenty of photographs from every angle which show the slow progression of sagging of trusses and bowing perimeter columns. It would be impossible for the NIST or anyone else to fabricate the photos. It was one of the most photographed and videoed events in history. It would be easy to prove the NIST is involved in a mass murder if they doctored photos. Yet this is exactly what some conspiracy theorists suggest.
Other conspiracy theorists say it's an optical illusion created by heat. But it would be impossible for this illusion (Heat/Light refraction) to happen only to one side of the building even when that side of the building cooled. Light refraction changes with the position of the person looking at it. So no two cameras would have shown the same degree of bowing. Here conspiracy theorists seem to want it both ways: they want to say light refracted due to the heat, yet they also say the fires were almost out toward the end when the bow was greatest. They need to have it both ways but they can't.
This illusion also happens to be where the collapse started.
A "scholar" says the bow was due to the core columns being cut. He points to the movement of the north tower antenna which some originally thought moved first. But this was not the case..
"Photographic and videographic records were reviewed to identify structurally-related events. Where possible, all four faces of a building were examined for a given event or time period to provide complete understanding of the building response. Observations from a single vantage point can be misleading and may result in incorrect interpretation of events. For instance, photographic and videographic records taken from due north of the WTC 1 collapse appeared to indicate that the antenna was sinking into the roof (McAllister 2002). When records from east and west vantage points were viewed, it was apparent that the building section above the impact area tilted to the south as the building collapsed." (NIST 2005)
The "scholar" is starting from a false premise and building a case around it. Something the "scholar" suggests the NIST did.
Putting this irony aside, the real evidence that the core did not move over time is the fact that the other faces showed no signs of the core moving until the collapse.
Before I continue, it's important to distinguish between the events of the moment of collapse and the gradual progression of bowing of the perimeter columns. I am talking about the gradual progression of bowing. The NIST does not disagree with the tilting of the top sections of the towers and that the core was a major part of that. Where the "scholar" differs is that it was the core and not the trusses which caused the tilt/collapse. He needs it to be the core to explain away the bowed columns and still entertain the thought of thermite/thermate.
If the core tilts, pulling the columns in at the impact level in, you would see an equal but opposite reaction from the opposite face. If the east perimeter columns were being pulled in because the core columns tilt, the west would show signs of being pushed out. The top would also tilt, not just when it collapsed but over time as the perimeter is being pulled in. Think about it, the core is connected to all the floors above the impact point. If the trusses were in pristine or even merely slightly sagged condition as suggested by this "scholar", and the core and not the trusses pulled in the perimeter columns, then the core would have tilted pushing out the columns on the roof level. Why is there no sign of this happening? Because it didn't. It's just another attempt at throwing the kitchen sink in to explain this evidence.
Why is this important? Because no believable scenario exists to explain explosives or thermite creating this effect. NONE. How would thermite/thermate bow columns over time? It simply ignites and burns chaotically. So we're left with an effect which looks EXACTLY like the fire sagged the trusses, then contracted and pulled in the columns with no evidence of thermite or a credible scenario which would explain the drawn out event.
Here are some scholars from England who wrote a paper for a university which explains the bowing of the columns in detail.
http://www.era.lib.ed.ac.uk/bitstream/1842/1216/1/WTCpaper.pdf A helicopter pilot saw this about 10 min before collapse but had no way of communicating that to the people in charge.
A bow is clearly visible on the right hand perimeter wall as trusses sag and pull in the perimeter columns. The photo below is NOT from the NIST report.
The photo below is from the NIST report.
Collapse begins a minute later. View from another angle, not from the NIST report...
Below is a video from the moment the columns begin quickly buckling inward. Note there is no ejection of debris characteristic in Controlled Demolition before the event. Only after the building begins to fall do we see the debris from the pancaking floors eject outward as the floors force air out of the windows.
http://wtc.nist.gov/pubs/Media_Public_Briefing_040505_final.pdfStart at page 36 of the above NIST briefing. You can see photographic evidence that the building was pulled in. Not just one floor, but across many.
Note how the sagging floors pull the outer column in. There is enough visual evidence that the trusses were pulling the outer columns in. If you think a bomb blew up the building, you have to explain how a bomb pulled the walls inward well before they fell...
Starting with the moment the plane hit, survivors said the doors wouldn't open because the building was so out of alignment. The impacts alone BENT THE 110 STORY BUILDINGS. That building was made to sway. I grew up in NY and have been to that building many times. When the wind was strong you could feel the building sway. I can't imagine an impact that would cause the building to sway enough to knock it out of center. A humanly unimaginable energy. That alone should weaken the building. Once you start to pile on the fire, unique construction, sagging trusses, and shifted load distribution, it's not hard to imagine enough of these factors adding up to cause a collapse. Factors which weren't known at the time. NIST’s computer model even took the wind shifting into account.
"It is impressive that the World Trade Center towers held up as long as they did after being attacked at full speed by Boeing 767 jets, because they were only designed to withstand a crash from the largest plane at the time: the smaller, slower Boeing 707. And according to Robertson, the 707's fuel load was not even considered at the time. Engineers hope that answering the question of exactly why these towers collapsed will help engineers make even safer skyscrapers in the future. ASCE will file its final report soon, and NIST has been asked to conduct a much broader investigation into the buildings' collapse."
http://www.pbs.org/wgbh/nova/wtc/minu-trans.html
