Collapse of the World Trade Center Towers

[ELVIS]

Council On Tall Buildings Explains Heat, Not Structure, Caused WTC Fall

http://www.caddigest.com/subjects/wtc/select/clifton/images/image001.jpg

BETHLEHEM, Pennsylvania, September 21, 2001 - In a statement issued September 14, the Council of Tall Buildings explained the collapse of the World Trade Center towers:

"Tuesday, September 11, 2001 is a day that will forever be remembered. It is a day when thousands of people lost their lives and it is a day when the grand twin towers of New York fell to the ground.

"The Council on Tall Buildings and our chairman Ron Klemencic, president of Skilling Ward Magnusson Barkshire, have been flooded with inquiries. Of course the most frequently asked question is why did they fall. Although we may never know the exact answer, Jon D. Magnusson, partner to Ron, in a report to Engineering-News Record stated, "It appears that the floor diaphragm, necessary to brace the exterior columns, had lost connection to the exterior wall." Once stability was lost, the exterior columns buckled, dropping the floors to the floor below, overloading each one as it went. The airplanes compromised the structural tube and the fires that followed in all probability burned to temperatures beyond the integrity of the fireproofed steel, which is designed to withstand 1500 to 1600 degrees F. heat.

"Les Robertson, a structural engineer who participated in the original design of the World Trade Center and former chairman of the Council, has his offices in New York's financial district. He was, however, in Hong Kong at the time of the attack. On Thursday we received an email from Les. In part, it states, 'Yes, fire brought down the towers, but the structural integrity created by the engineers allowed perhaps thousands of persons to evacuate the building prior to the fire-induced collapse.'

"In the next week we will attempt to put together a list of the most frequently asked questions and answers for posting on our website. In the meantime all inquiries should be directed to Ron Klemencic at 206/292-1200 or by email rk@skilling.com.

"The Council would also like to thank all of its members throughout the world who have been offering words of support and encouragement."

LINK (http://www.caddigest.com/subjects/wtc/select/council.htm)

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[ELVIS]

Elaboration on Aspects of The Postulated Collapse Of the World Trade Center Twin Towers

G Charles Clifton, HERA Structural Engineer, December 13, 2001 (http://www.caddigest.com/subjects/wtc/select/clifton/elaboration.htm)

Scope of Paper

This paper provides elaboration on aspects of my paper [1] entitled Collapse of the World Trade Centre Towers, written 17 September 2001 and revised three times since then, with Revision 3 dated 11 December 2001.

Since that paper was written, there have been several minor errors noted in it. Of more importance, two important aspects of it have been queried; these being:

The postulated structural load distribution in the North Tower (the first tower to be struck) following the impact and leading to the collapse ; and
The intensity of the fire being underestimated because of distance and scale effects.
These points of concern require a response. The principal purpose of this paper is to provide that response.

It also briefly details some of the known errors in revision 2 of [1], dated 8th of October, and which have been either corrected or noted in Revision 3 to [1]. These details are given below.

This is followed by a brief coverage of the structural load- carrying system before impact, listing the assumptions made which impact on the postulated collapse mechanism for the North Tower.

Elaboration on the material presented in [1] relating to this collapse mechanism is then given.

This is followed by further material that has come to hand, in the two months since the attack, relating to the likely structural fire severity of the fires in each tower before the collapses occurred.

The paper ends with brief conclusions and references.

As with the original paper [1], the details herein are of a general nature. They do not present calculations or detailed metallurgical or structural observations. In the former case, this is because there are too many unknown to make a ¡§correct¡¨ set of calculations possible. In the latter case, I don¡¦t have access to material / data from the wreckage of these buildings so I am not in a position to make detailed observations.

What I do have is a good general overview of the structural system and method of construction used in the Twin Towers, plus my knowledge from 17 years of research into and development of design guidance for the response of steel buildings to the extreme events of severe earthquake and severe fire.

The details presented in [1] and this paper are consistent with that knowledge and background, plus the material I have available on the attack and destruction of these two magnificent buildings.

Also, as with the original paper [1], the details presented herein are my opinions. It is for this reason that the paper and [1] have been written in the first person.

Inaccuracies Noted in The Original Paper.

These are as follows:

(1) The times given for impact and collapse of each tower in the original version of [1] were based on published details as of mid-September. Some variation in these details was noted at that time. The generally agreed times are now given in Revision 3 of [1]. These are based on seismological recordings of the impacts caused by, first the plane hitting the building and, secondly, the building collapsing.

(2) The directions shown on the site plan (Fig 2 of [1] ) are approximately 40o off the true directions. If one rotates the site plan 40o clockwise, thus making the direction shown as North read N40E, then the map is correctly orientated.

(3) Some minor typographical errors have been corrected.

Structural Load Distribution Before Impact.

Overview

The section of [1] entitles ¡§Details of the buildings ¡§ and presented on pages 2-5 therein provide an overview of the structural system used.

In summary, this comprised:

A closely spaced perimeter frame around the four external walls, providing lateral strength and stiffness and also providing vertical support to its tributary area of the floor slab.
A cluster of compression load carrying columns in the core, forming the principal gravity load carrying system and supporting the vertical load from half the open plan floor system plus all the structural systems, services and components within the core.
A light-weight, long spanning floor system running from perimeter frame to outside edge of core. This floor system comprised bar joists as girders (primary beams) supporting secondary joists which carried a 100 mm thick light-weight concrete slab on profiled steel deck. The presence of secondary joists connected into the bar joists and made integral with a composite slab (see Fig 6 from [1]) made for a light, stiff floor system with good capacity for two-way action under severe fire conditions.
Assumptions made about the structural system design

In postulating the collapse mechanisms for both towers (but especially relevant for the North Tower), I have made some assumptions about the structural system used.

These as follows:

(1) The bar joist/floor system is connected to the perimeter frame/gravity core using a top flange mounted seat system as roughly indicated in Fig.7 of [1]. This system is designed to support the applied dead load from half the floor joist clear span. The actual connection between each joist and the supporting girders at perimeter frame and core is a typical bar joist connection detail, designed to carry principally its tributary design vertical load and with some nominal lateral load transfer capacity.

(2) There is a shear stud or some form of physical connection of the slab into the perimeter frame girders, through eg. shear studs from girder into slab and slab reinforcement passing beyond the line of connectors or alternatively some type of starter bar arrangement from the perimeter frame into the slab. Some form of this is evidenced from photos of the still intact perimeter frame remnants at the site. This would presumably have been sized on the greater of diaphragm transfer forces from floor into perimeter frame at each level or code minimum requirements for the interconnection, as applying at the time of design

(3) The visco-elastic dampers added from the bottom chord of the bar joists back to the perimeter frame did not noticeably increase the shear or tension capacity between floor slab and perimeter frame.

(4) There was a network of beams interconnecting the 44 core columns, such that the core formed an effective moderately rigid box. Some details of these are given in [2].

(5) The perimeter frame assemblages were spliced by mid-span bolted web connections (this known) and columns spliced with bearing splices having some moment/tension capacity (this assumed).

(6) The gravity columns were spliced by slot and tab splices, with the ends prepared for compression bearing. That much is known; I have assumed that these column splices also had an integral connection capacity for shear (possibly 15% of design shear capacity, as would be stipulated by NZS 3404 [3]). If so, this could have been formed by blind bolting of the tabs of the supporting column through the walls of the supported column, or more likely, by incomplete penetration site butt welds between the abutting surfaces, with these welds of small size and formed using a ductile weld metal.

Prior to the impact, the applied vertical loads on the core would have been carried to ground through the core columns. The applied loads on the perimeter frame would have been carried to ground through the perimeter frame. The vertical loading on the floor system spanning between core and perimeter frame, including its self-weight, would have been carried effectively equally by the supports at core and perimeter frame.

Postulated Structural Load Distribution in the North Tower Following Impact

The plane hit the North-East face of the North Tower, flying near level, at around the 94th and 95th floors. It cut through the perimeter frame leaving a hole in this frame some 2-4 floors deep and impacted into the core, causing an unknown amount of damage there.

In my original paper [1], I stated that the impact on the core would have ¡§removed many of the core supporting columns, at least on the North side of the core, and leaving the remainder buckled and stripped of their passive fire protection¡¨. At that time (mid-September) I did not want to speculate in the paper on the number of core columns destroyed in the impact region. Since then I have been advised of estimates up to 40%.

This loss of core columns would have had the following immediate effects:

(1) The load from the still intact upper floors would have had to be carried by alternative load paths to the still intact core columns. This redistribution would have required vertical sagging of the core region to become effective, with this sagging occurring immediately on impact and to a very noticeable extent on the floors above, especially above the impact side of the core.

I believe that this immediate sagging offers a possible explanation as to why many people jumped from the North Tower upper floors before the effects of fire on those floors became very apparent. If this sagging hypothesis is correct, then it would have cut access to the stairs by jamming doors, etc. It would also have given a clear message of impending collapse, leaving the people trapped on these upper floors with a terrible choice; jump and die or stay in the building and die in the collapse.

(2) The compression load on the remaining core columns would have significantly increased.

(3) The vertical load being transmitted through the floor system into the perimeter frame would have increased , as the core region sagged immediately following the impact and in a progressive manner from then on to the final collapse.

(4) The gravity columns which had been severed by the impact would now act as tension ties between each of the floors above the impact region, through to the top floor. The amount of tension so transmitted upwards would have been limited by the strength of the column splices to transmit tension, and possibly by the amount of redistribution occurring within the core region.

(5) At the top floor, these ¡§tension¡¨ columns would have exerted as additional unbalanced downward load on this floor, adding to the overload stress on the floor to perimeter frame connection.

Following the impact were the fires. Fires adjacent to the damaged core region would have impacted on core columns already suffering various extents of local and member buckling from the plane¡¦s impact and loss of insulation material. As these columns heated up, they would have been subject to additional compression forces from restrained thermal expansion. In the case of columns with member buckling, this would have increased their lateral deflections between points of effective lateral restraint, leading to increased P-delta (P-ƒÔ) actions and reduced compression capacity. The temperatures required for this effect to become significant, on already damaged columns, is not high - I would estimate no more than 400-500oC would have been needed to cause significantly reduced compression capacity in the residual core columns.

In my opinion, based on the available evidence, there appears no indication that the fires were as severe as a fully developed multi-story fire in an initially undamaged building would typically be. (More on this below). However, the observations show that fire temperatures of over 500oC would have been probable over enough of the core to cause an ongoing loss of compression load carrying capacity in the remaining core columns.

This would have increased the pull-down action of the floors on the perimeter frame, with this effect greatest on the top floor. I believe that final failure would have been through detachment of the top floor from the perimeter frame, starting at one point and rapidly spreading around the top floor. This would have been followed by near instant tearing away of all floors above the impact region from the perimeter frame, with the pancaking effect then proceeding to the ground.

As detailed in [1], the above relates to the North Tower. The explanation of collapse for the South Tower is quite different, as given in that paper.

How Severe Were the Fires: Revisited

Having carefully studied all available material available to me and collected since the original version of [1] was written, there is nothing in points 1-5 of [1] under the section ¡§How severe were the effects of the fires?¡¨ that I would amend on the basis of this new material.

In fact, the new material provides further support for the fires not being particularly severe. Additional points to 1-5 of [1] in this regard are:

(6) Almost every building occupant below the impact floors (including up to the 91st floor on the North Tower) survived. Given that the fire separating walls around the stairs & lifts over the impact region were destroyed, then there must have been negligible spread of burning fuel/debris down into the breached stairwells to allow them to remain tenable.

(7) There is a survivor account of a group trapped in a lift, which had the cables severed by the impact. They were able to stop the lift on the 53rd floor, open the doors/escapes hatch in the top & cut their way out through the drywall fire separation. Their account says little about the effects of any fire above; nor could these effects have been significant or they would not have survived.

(8) Close scrutiny of close-up views of the burning buildings that I have received since mid-September (i.e much more detailed pictures than Fig 9 from [1]) show little evidence of temperatures above 600oC (i.e. fully developed fire conditions) within the impact region. These same pictures also show that, on some of the upper floors where fully developed fire conditions are observed, the fire-rated suspended ceilings appear largely in place and so the likely effect of these fires on the structure is minor.

(9) A fire engineer (Martin Feeney from Holmes Fire and Safety, Auckland NZ) has advised that theoretical consideration of the fire severity based on the quantities of combustibles in the planes and impact region of the buildings give answers that are not supported by observation. The observed fire behavior points to temperatures in the building not being particularly severe ¡V say no more than about 600 to 700 Deg C. Possible reasons for this may involve the coating of combustible material in dust from pulverized concrete and wall linings and the volatility of the aviation fuel leading to large amounts of fuel being pyrolized but not burned in the interior of the building.

Conclusions

This paper, which should be read in conjunction with Revision 3 of [1], provides elaboration on aspects of the postulated collapse of the World Trade Center Twin Towers that are given in [1] and which have been queried by readers.

The details presented in [1] & herein are my opinions and are put forward to stimulate discussion and consideration of all aspects of this tragedy, in order that we can learn as much as possible to make buildings safer & more resistant to deliberate or natural acts of an extreme nature.

References:

1. Clifton, GC; Collapse of the World Trade Center Towers; HERA, Manukau City, New Zealand; written 17 September 2001; revised 19 September, 8 October and 11 December 2001.

2. Godfrey,GB (Editor); Multi-Storey Building in Steel, Second Edition; Collins, London, England, 1985, ISBN 0 00 38 3031 4.

3. NZS 3404:1997, Incorporating Amendment No.1: 2001, Steel Structures Standard; Standards New Zealand, Wellington, New Zealand.



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[ELVIS]

Structural Engineers on World Trade Center Collapse

LINK (http://www.caddigest.com/subjects/wtc/select/ncsea.htm)

CHICAGO, Illinois, September 11, 2001 - According to one of the designers of the World Trade Center (WTC), the towers were originally designed to take the impact of a Boeing 707; and the impact of the aircraft this morning did not take the buildings down. In fact, WTC One stood for 1 hour and WTC Two stood for 1 3/4 hours after impact. Engineers familiar with the chain of events suspect that heat from the massive and extraordinary fires weakened the structures and initiated the progressive collapses.

John Hooper, a structural engineer from Skilling, Ward, Magnusson, Barkshire - the structural engineering firm that evolved from Skilling, Helle, Christianson, Robertson, which was the structural engineering firm of record for the WTC - provided the following facts to NCSEA: WTC One was 1368’ tall, and WTC Two was 1362’ tall. Each 110-story tower had a floor plate that was 208’ by 208’. The central core of each was 86’ square. Around the perimeter of the buildings, columns were spaced at 3’-3” on center, with 48”- deep plate girders at each floor. At the third level, the columns transitioned in an arch-like formation to a 10’-0” spacing for the lower story. Floors were supported by steel trusses spanning 60’, from the core to the perimeter wall, on each side of the building. The buildings are also thought to have been the first buildings to use non-asbestos fireproofing. The fibers of the spray-on fireproofing product were reportedly ceramic rather than asbestos.

NCSEA has contacted FEMA and will coordinate and make available structural engineers in the New York and Washington D.C. areas. NCSEA will also coordinate and provide the services of Member Structural Engineering Associations throughout the U.S., as needed.

The National Council of Structural Engineers Associations is extremely saddened with the day’s news, including the collapse of the World Trade Center in New York City. Our hearts and prayers go out to all the victims and their families.



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[ELVIS]

http://www.civil.usyd.edu.au/latest/wtc_graphic.gif


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[ELVIS]

World Trade Center - Some Engineering Aspects (http://www.civil.usyd.edu.au/wtc.shtml)



Height: 1,368 and 1,362 feet (417 and 415 meters)
Owners: Port Authority of New York and New Jersey.
(99 year leased signed in April 2001 to groups including Westfield America and Silverstein Properties)
Architect: Minoru Yamasaki, Emery Roth and Sons consulting
Engineer: John Skilling and Leslie Robertson of Worthington, Skilling, Helle and Jackson
Ground Breaking: August 5, 1966
Opened: 1970-73; April 4, 1973 ribbon cutting
Destroyed: Terrorist attack, September 11, 2001


http://www.civil.usyd.edu.au/latest/wtc1.jpg


The Structural System


Yamasaki and engineers John Skilling and Les Robertson worked closely, and the relationship between the towers' design and structure is clear. Faced with the difficulties of building to unprecedented heights, the engineers employed an innovative structural model: a rigid "hollow tube" of closely spaced steel columns with floor trusses extending across to a central core. The columns, finished with a silver-colored aluminum alloy, were 18 3/4" wide and set only 22" apart, making the towers appear from afar to have no windows at all.

Also unique to the engineering design were its core and elevator system. The twin towers were the first supertall buildings designed without any masonry. Worried that the intense air pressure created by the buildings' high speed elevators might buckle conventional shafts, engineers designed a solution using a drywall system fixed to the reinforced steel core. For the elevators, to serve 110 stories with a traditional configuration would have required half the area of the lower stories be used for shaftways. Otis Elevators developed an express and local system, whereby passengers would change at "sky lobbies" on the 44th and 78th floors, halving the number of shaftways.



The structural system, deriving from the I.B.M. Building in Seattle, is impressively simple. The 208-foot wide facade is, in effect, a prefabricated steel lattice, with columns on 39-inch centers acting as wind bracing to resist all overturning forces; the central core takes only the gravity loads of the building. A very light, economical structure results by keeping the wind bracing in the most efficient place, the outside surface of the building, thus not transferring the forces through the floor membrane to the core, as in most curtain-wall structures. Office spaces will have no interior columns. In the upper floors there is as much as 40,000 square feet of office space per floor. The floor construction is of prefabricated trussed steel, only 33 inches in depth, that spans the full 60 feet to the core, and also acts as a diaphragm to stiffen the outside wall against lateral buckling forces from wind-load pressures."



Why Did It Collapse?

Tim Wilkinson, Lecturer in Civil Engineering

(This is an initial suggestion, originally written on Sept 11 2001 (with some minor subsequent changes) on one possible reason for failure, and should not be regarded as official advice.)


The structural integrity of the World Trade Center depends on the closely spaced columns around the perimeter. Lightweight steel trusses span between the central elevator core and the perimeter columns on each floor. These trusses support the concrete slab of each floor and tie the perimeter columns to the core, preventing the columns from buckling outwards.

After the initial plane impacts, it appeared to most observers that the structures had been severely damaged, but not necessarily fatally.

It appears likely that the impact of the plane crash destroyed a significant number of perimeter columns on several floors of the building, severely weakening the entire system. Initially this was not enough to cause collapse.

However, as fire raged in the upper floors, the heat would have been gradually affecting the behaviour of the remaining material. As the planes had only recently taken off, the fire would have been initially fuelled by large volumes of jet fuel, which then ignited any combustible material in the building. While the fire would not have been hot enough to melt any of the steel, the strength of the steel drops markedly with prolonged exposure to fire, while the elastic modulus of the steel reduces (stiffness drops), increasing deflections.

Modern structures are designed to resist fire for a specific length of time. Safety features such as fire retarding materials and sprinkler systems help to contain fires, help extinguish flames, or prevent steel from being exposed to excessively high temperatures. This gives occupants time to escape and allow fire fighters to extinguish blazes, before the building is catastrophically damaged.

It is possible that the blaze, started by jet fuel and then engulfing the contents of the offices, in a highly confined area, generated fire conditions significantly more severe than those anticipated in a typical office fire. These conditions may have overcome the building's fire defences considerably faster than expected. It is likely that the water pipes that supplied the fire sprinklers were severed by the plane impact, and much of the fire protective material, designed to stop the steel from being heated and losing strength, was blown off by the blast at impact.

Eventually, the loss of strength and stiffness of the materials resulting from the fire, combined with the initial impact damage, would have caused a failure of the truss system supporting a floor, or the remaining perimeter columns, or even the internal core, or some combination. Failure of the flooring system would have subsequently allowed the perimeter columns to buckle outwards. Regardless of which of these possibilities actually occurred, it would have resulted in the complete collapse of at least one complete storey at the level of impact.

Once one storey collapsed all floors above would have begun to fall. The huge mass of falling structure would gain momentum, crushing the structurally intact floors below, resulting in catastrophic failure of the entire structure. While the columns at say level 50 were designed to carry the static load of 50 floors above, once one floor collapsed and the floors above started to fall, the dynamic load of 50 storeys above is very much greater, and the columns were almost instantly destroyed as each floor progressively "pancaked" to the ground.

The only evidence so far are photographs and television footage. Whether failure was initiated at the perimeter columns or the core is unknown. The extent to which the internal parts were damaged during the collision may be evident in the rubble if any forensic investigation is conducted. Since the mass of the combined towers is close to 1000000 tons, finding evidence will be an enormous task.

http://www.civil.usyd.edu.au/latest/wtc_collapse5.jpg
Perimeter columns, several storeys high, and still linked together, lie amongst all the debris on the ground.

http://www.civil.usyd.edu.au/latest/wtc_collapse4.jpg
This photograph shows the south tower just as it is collapsing. It is evident that the building is falling over to the left. The North Tower collapsed directly downwards, on top of itself. The same mechanism of failure, the combination of impact and subsequent fire damage, is the likely cause of failure of both towers. However, it is possible that a storey on only one side of the South Tower initially collapsed, resulting in the "skewed" failure of the entire tower.

While the ways the two towers fell were slightly different, the basic cause is similar for both - a large number of columns were destroyed on impact, and the remaining structure was gradually weakened by the heat of the fire. Not much significance should be taken from the fact that one tower fell in 45 minutes and the other in 90 minutes.

The gigantic dynamic impact forces caused by the huge mass of the falling structure landing on the floors below is very much greater than the static load they were designed to resist.



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[ELVIS]

The Collapse: An Engineer's Perspective (http://www.pbs.org/wgbh/nova/wtc/collapse.html)

It wasn't until Dr. Thomas Eagar saw Building 7 of the World Trade Center implode late on the afternoon of September 11th that he understood what had transpired structurally earlier that day as the Twin Towers disintegrated. A professor of materials engineering and engineering systems at the Massachusetts Institute of Technology, Eagar went on to write an influential paper in the journal of the Minerals, Metals, and Materials Society entitled "Why Did the World Trade Center Collapse? Science, Engineering, and Speculation" (JOM, December 2001). In this interview, Eagar explains the structural failure, what can be done within existing skyscrapers to improve safety, and what he believes the most likely terrorist targets of the future may be.



NOVA: After the planes struck and you saw those raging fires, did you think the towers would collapse?

Eagar: No. In fact, I was surprised. So were most structural engineers. The only people I know who weren't surprised were a few people who've designed high-rise buildings.

NOVA: But you weren't surprised that they withstood the initial impacts, is that correct?

Eagar: That's right. All buildings and most bridges have what we call redundant design. If one component breaks, the whole thing will not come crashing down. I once worked on a high-rise in New York, for example, that had a nine-foot-high beam that had a crack all the way through one of the main beams in the basement. This was along the approach to the George Washington Bridge. They shored it up and kept traffic from using that area.

Some people were concerned the building would fall down. The structural engineers knew it wouldn't, because the whole thing had an egg-crate-like construction. Or you can think of it as a net. If you lose one string on a net, yes, the net is weakened but the rest of the net still works.

http://www.pbs.org/wgbh/nova/wtc/images/coll_traddesign.jpg
http://www.pbs.org/wgbh/nova/wtc/images/coll_wtcdesign.jpg
Earlier skyscrapers (top) had columns spaced evenly across every floor. The World Trade Center (bottom) broke with tradition by having columns only in the central core and along the exterior walls.


That's essentially how the World Trade Center absorbed an airplane coming into it. It was somewhat like the way a net absorbs a baseball being thrown against it. If you lose a couple of the columns, that's not the end of the world. It will still stand up.

NOVA: The World Trade Center was also designed to take a major wind load hitting from the side.

Eagar: Yes. A skyscraper is a long, thin, vertical structure, but if you turned it sideways, it would be like a diving board, and you could bend it on the end. The wind load is trying to bend it like a diving board. It sways back and forth. If you've been on the top of the Sears Tower in Chicago or the Empire State Building on a windy day, you can actually feel it. When I was a student, I visited the observation deck of the Sears Tower, and I went into the restroom there, and I could see the water sloshing in the toilet bowl, because the wind load was causing the whole building to wave in the breeze.

NOVA: Are skyscrapers designed that way, to be a little flexible?

Eagar: Absolutely. Now, there are different ways to design things. For example, Boeing designs their aircraft wings to flap in the breeze, while McDonnell Douglas used to design a very rigid wing that would not flex as much. You can design it both ways. There are trade-offs, and there are advantages to both ways.



"Most buildings are designed to sway in the breeze."

Most buildings are designed to sway in the breeze. In fact, one of the big concerns in the early design of the World Trade Center, since it was going to be the tallest building in the world at the time, was that it not sway too much and make people sick. You can get seasick in one of these tall buildings from the wind loads. So they had to do some things to make them stiff enough that people wouldn't get sick, but not so rigid that it could snap if it got too big a load. If something's flexible, it can give; think of a willow tree. If you have a strong wind, you want the building, like the tree, to bend rather than break.

NOVA: Brian Clark, one of only four people to get out from above where United 175 hit the South Tower, says that when the plane struck, the building swayed for a full seven to 10 seconds in one direction before settling back, and he thought it was going over.

Eagar: That estimate of seven to ten seconds is probably correct, because often big buildings are designed to be stiff enough that the period to go one way and back the other way is 15 or 20 seconds, or even 30 seconds. That keeps people from getting sick.

http://www.pbs.org/wgbh/nova/wtc/images/coll_pancake.jpg
Upper floors pancaked down onto lower floors, causing a domino effect that left each building in ruins within ten seconds.


NOVA: The Twin Towers collapsed essentially straight down. Was there any chance they could have tipped over?

Eagar: It's really not possible in this case. In our normal experience, we deal with small things, say, a glass of water, that might tip over, and we don't realize how far something has to tip proportional to its base. The base of the World Trade Center was 208 feet on a side, and that means it would have had to have tipped at least 100 feet to one side in order to move its center of gravity from the center of the building out beyond its base. That would have been a tremendous amount of bending. In a building that is mostly air, as the World Trade Center was, there would have been buckling columns, and it would have come straight down before it ever tipped over.

Have you ever seen the demolition of buildings? They blow them up, and they implode. Well, I once asked demolition experts, "How do you get it to implode and not fall outward?" They said, "Oh, it's really how you time and place the explosives." I always accepted that answer, until the World Trade Center, when I thought about it myself. And that's not the correct answer. The correct answer is, there's no other way for them to go but down. They're too big. With anything that massive -- each of the World Trade Center towers weighed half a million tons -- there's nothing that can exert a big enough force to push it sideways.


NOVA: I think some people were surprised when they saw this massive 110-story building collapse into a rubble pile only a few stories tall.

Eagar: Well, like most buildings, the World Trade Center was mostly air. It looked like a huge building if you walked inside, but it was just like this room we're in. The walls are a very small fraction of the total room. The World Trade Center collapse proved that with a 110-story building, if 95 percent of it's air, as was the case here, you're only going to have about five stories of rubble at the bottom after it falls.

NOVA: You've said that the fire is the most misunderstood part of the World Trade Center collapse. Why?

Eagar: The problem is that most people, even some engineers, talk about temperature and heat as if they're identical. In fact, scientifically, they're only related to each other. Temperature tells me the intensity of the heat -- is it 100 degrees, 200 degrees, 300 degrees? The heat tells me how big the thing is that gets hot. I mean, I could boil a cup of water to make a cup of tea, or I could boil ten gallons of water to cook a bunch of lobsters. So it takes a lot more energy to cook the lobsters -- heat is related to energy. That's the difference: We call the intensity of heat the temperature, and the amount of heat the energy.



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[ELVIS]

Engineer's Perspective Part 2 (http://www.pbs.org/wgbh/nova/wtc/collapse2.html)

NOVA: So with the World Trade Center fire, the heat was much greater than might have been expected in a typical fire?

Eagar: Right. We had all this extra fuel from the aircraft. Now, there have been fires in skyscrapers before. The Hotel Meridien in Philadelphia had a fire, but it didn't do this kind of damage. The real damage in the World Trade Center resulted from the size of the fire. Each floor was about an acre, and the fire covered the whole floor within a few seconds. Ordinarily, it would take a lot longer. If, say, I have an acre of property, and I start a brushfire in one corner, it might take an hour, even with a good wind, to go from one corner and start burning the other corner.

That's what the designers of the World Trade Center were designing for -- a fire that starts in a wastepaper basket, for instance. By the time it gets to the far corner of the building, it has already burned up all the fuel that was back at the point of origin. So the beams where it started have already started to cool down and regain their strength before you start to weaken the ones on the other side.

On September 11th, the whole floor was damaged all at once, and that's really the cause of the World Trade Center collapse. There was so much fuel spread so quickly that the entire floor got weakened all at once, whereas in a normal fire, people should not think that if there's a fire in a high-rise building that the building will come crashing down. This was a very unusual situation, in which someone dumped 10,000 gallons of jet fuel in an instant.

NOVA: How high did the temperatures get, and what did that do to the steel columns?

Eagar: The maximum temperature would have been 1,600°F or 1,700°F. It's impossible to generate temperatures much above that in most cases with just normal fuel, in pure air. In fact, I think the World Trade Center fire was probably only 1,200°F or 1,300°F.

Investigations of fires in other buildings with steel have shown that fires don't usually even melt the aluminum, which melts around 1,200°F. Most fires don't get above 900°F to 1,100°F. The World Trade Center fire did melt some of the aluminum in the aircraft and hence it probably got to 1,300°F or 1,400°F. But that's all it would have taken to trigger the collapse, according to my analysis.

NOVA: You've pointed out that structural steel loses about half its strength at 1,200°F, yet even a 50 percent loss of strength is insufficient, by itself, to explain the collapse.

Eagar: Well, normally the biggest load on this building was the wind load, trying to push it sideways and make it vibrate like a flag in the breeze. The World Trade Center building was designed to withstand a hurricane of about 140 miles an hour, but September 11th wasn't a windy day, so the major loads it was designed for were not on it at the time.



"You can't explain the collapse just in terms of temperature."

As a result, the World Trade Center, at the time each airplane hit it, was only loaded to about 20 percent of its capacity. That means it had to lose five times its capacity either due to temperature or buckling -- the temperature weakening the steel, the buckling changing the strength of a member because it's bent rather than straight. You can't explain the collapse just in terms of temperature, and you can't explain it just in terms of buckling. It was a combination.

NOVA: So can you give a sequence of events that likely took place in the structural failure?

Eagar: Well, first you had the impact of the plane, of course, and then this spreading of the fireball all the way across within seconds. Then you had a hot fire, but it wasn't an absolutely uniform fire everywhere. You had a wind blowing, so the smoke was going one way more than another way, which means the heat was going one way more than another way. That caused some of the beams to distort, even at fairly low temperatures. You can permanently distort the beams with a temperature difference of only about 300°F.

NOVA: You mean one part of a beam is 300°F hotter than another part of the same beam?

Eagar: Exactly. If there was one part of the building in which a beam had a temperature difference of 300°F, then that beam would have become permanently distorted at relatively low temperatures. So instead of being nice and straight, it had a gentle curve. If you press down on a soda straw, you know that if it's perfectly straight, it will support a lot more load than if you start to put a little sideways bend in it. That's what happened in terms of the beams. They were weakened because they were bent by the fire.

But the steel still had plenty of strength, until it reached temperatures of 1,100°F to 1,300°F. In this range, the steel started losing a lot of strength, and the bending became greater. Eventually the steel lost 80 percent of its strength, because of this fire that consumed the whole floor.

If it had only occurred in one little corner, such as a trashcan caught on fire, you might have had to repair that corner, but the whole building wouldn't have come crashing down. The problem was, it was such a widely distributed fire, and then you got this domino effect. Once you started to get angle clips to fail in one area, it put extra load on other angle clips, and then it unzipped around the building on that floor in a matter of seconds.


NOVA: Many other engineers also feel the weak link was these angle clips, which held the floor trusses between the inner core of columns and the exterior columns. Is that simply because they were much smaller pieces of steel?

Eagar: Exactly. That's the easiest way to look at it. If you look at the whole structure, they are the smallest piece of steel. As everything begins to distort, the smallest piece is going to become the weak link in the chain. They were plenty strong for holding up one truss, but when you lost several trusses, the trusses adjacent to those had to hold two or three times what they were expected to hold.

Those angle clips probably had two or three or four times the strength that they originally needed. They didn't have the same factor-of-five safety as the columns did, but they still had plenty of safety factor to have people and equipment on those floors. It was not that the angle clips were inadequately designed; it was just that there were so many of them that the engineers were able to design them with less safety factor. In a very unusual loading situation like this, they became the weak link.

NOVA: I've read that the collapse was a near free-fall.

Eagar: Yes. That's because the forces, it's been estimated, were anywhere from 10 to 100 times greater than an individual floor could support. First of all, you had 10 or 20 floors above that came crashing down. That's about 10 or 20 times the weight you'd ever expect on one angle clip. There's also the impact force, that is, if something hits very hard, there's a bigger force than if you lower it down very gently.

NOVA: Miraculously, a number of firefighters survived inside Tower One. They were on the third or fourth floor in a stairwell, and immediately after the collapse they looked up and saw blue sky above their heads -- their part of the stairwell survived. How is that possible, with all the force of that 500,000-ton building coming down?



"They were very, very fortunate that they happened to be in an area that was somewhat shielded."

Eagar: Well, you have to understand the stairwells were reinforced areas of the building. The stairwells were in the central core, which had more steel than the outer areas, which were big open floors. So that extra steel formed a little cage to protect them. It's still amazing, though.

Now, there could have been someone two floors below who could have been completely crushed. It just depends on how the steel buckled. If you take that soda straw again, and you push it sideways, it will develop a buckle at some location, probably somewhere in the middle third. Well, if you happen to be where the buckling occurs, that area is going to get smashed, but if you're, say, below where the buckling occurred, basically the whole thing can push sideways. They were very, very fortunate that they happened to be in an area that was somewhat shielded and protected by all the extra steel in the central core.

I read one of those people's statements in the paper the other day, and he said that if they'd been in the lobby, they'd be gone. I was in the lobby of the World Trade Center years ago, and it was some three or four stories tall. What was going to buckle? Well, the lobby had the longest columns, so they were going to buckle. Those firefighters were just above that, so they were protected by the buckling underneath, within this sort of steel cage.

In fact, that's how they design automobiles for crashworthiness. They try to design the passenger compartment to be a cage, and the hood and trunk are supposed to deform and absorb the energy so that you're protected by this little cage of steel that hopefully won't deform.


NOVA: There's a theory that the aluminum of the planes caught fire.

Eagar: Yes, a number of people have tried to reinforce that theory. Now, the aluminum of the planes would have burned just like a flare. Flares are made out of aluminum and magnesium, so are fireworks, and they burn hot enough to melt steel in certain cases.

However, they have had people sorting through the steel from the World Trade Center, and no one has reported finding melted steel, which means that we didn't have that aluminum flare. In any case, burning aluminum would have been white-hot, about 4,000°F, and someone would have seen it even through that dense black smoke.

Of course, aluminum can burn. That's what demolished the [British destroyer] Sheffield in the Falklands War [when it was struck by an Argentinian missile]. It wasn't the Exocet missile that destroyed the superstructure of the Sheffield. The missile wasn't big enough, just like the plane wasn't big enough to bring down the World Trade Center. That Exocet missile did damage the Sheffield, but what doomed the Sheffield was the aluminum superstructure caught fire and burned. So you suddenly had something like 1,000 or 10,000 times as much fuel as you had in that Exocet missile.

Now, this is not a type of fire we have to worry about in buildings. We don't have anywhere close to those types of conditions. And we didn't have those in the World Trade Center, in my opinion.

NOVA: How soon will a definitive report of the causes of the collapse be released?

Eagar: Well, there's some very sophisticated analysis that various people in the government, at universities, and at structural engineering firms are doing to understand it. Most of those people have not yet published any conclusions. To do a good job of research on something like this can typically take one to two years. I don't expect to see any conclusive reports probably until about the first anniversary of the attack.



"There will still be people worrying about this ten years from now."

There are different levels of analysis. You can do the back-of-the-envelope, which was what I and other people did early on. But to do the full analysis will take much longer. I suspect there will still be people worrying about this ten years from now.

NOVA: In your back-of-the-envelope analysis, you concluded the World Trade Center was not defectively designed, but not everyone apparently accepts that conclusion.

Eagar: A lot of people said, Well, the building failed. That's true, but nothing is indestructible. The question is, why did it fail? In this case, as I've explained, it was the fire covering the whole floor in a few seconds that made this different from any other fire that anyone had ever designed for.

If people say, Well, couldn't we have designed it for this, I say, Yes, we could have. We could build buildings that could survive a jet running into them with a full fuel load. In fact, the military does. But they're bunkers. We build these things for the President and the rest of the 150 leaders of the country to go to as a secure area. You can do that, but your building costs go up by a factor of about 100. Well, do we want to have 100 times fewer homes for people to live in? Do we want to have 100 times fewer roads?

If we were to harden everything against a terrorist attack, we'd push ourselves back into the first half of the 19th century in terms of living style. Now, some people might consider that an improvement, but not everybody, so society has some important tradeoffs here. There's got to be some middle ground where we can make things more secure but not destroy our standard of living.

NOVA: Anything we should do now to retrofit existing skyscrapers like the Sears Tower?

Eagar: Well, one of the things that's really important and is relatively inexpensive is a public communication system. I've been in high-rises when the fire alarm goes off, and everyone looks around the room and decides, Should we just continue meeting and ignore the fire alarm, or should we evacuate? Fortunately, in most cases -- and I've had to be the person in a few of those cases -- people say, Look, it's a fire alarm. We don't know if it's real. Evacuate. So you need better public-address systems to inform people that this is not a test, this is not a false alarm, you'd better get out of the building.

Survivors from the World Trade Center have said that some people took four or five minutes to figure out there was something more than just some false alarm. Other people started moving immediately. Obviously, the quicker people started to move, the better chance they had of reaching safety.

NOVA: How about improving the fire safety of the building or putting in extra stairwells?

Eagar: These are very difficult things to redesign into current buildings. They can and will be added to future buildings. The simplest thing is the communication system. And better training of firefighters. Those things will definitely be done.

If you look at the World Trade Center disaster, it would have been greatly minimized if the safety personnel had been aware of the danger they were in. They didn't realize it was going to collapse. As I said earlier, there are only a few engineers in the country who had ever designed skyscrapers like this who would have realized, but they couldn't communicate within that first hour with the people at ground zero. Nobody could call to New York City at that time.

So better communication. The military's known that for years. They've invested tremendous amounts of money in better communications. That's been one of the differences in having fewer lives lost on the American side in recent wars. We've got much better C3I -- Command, Control, Communications, and Intelligence. They've spent billions of dollars, and it's saved thousands and thousands of lives in the military. We can do that on the civilian side as well for these big structures, though, in my opinion, skyscrapers are not the problem anymore.



"A terrorist is not going to attack the things you expect him to attack."

NOVA: What is?

Eagar: I think the terrorist danger will be other things. A terrorist is not going to attack the things you expect him to attack. The real problem is pipelines, electrical transmission, dams, nuclear plants, railroads. A terrorist's job is to scare people. He or she doesn't have to harm very many people. Anthrax is a perfect example. If someone could wipe out one electrical transmission line and cause a brownout in all of New York City or Los Angeles, there would be hysteria, if people realized it was a terrorist that did it.

Fortunately, we have enough redundancy -- the same type of redundancy we talk about structurally in the World Trade Center -- in our electrical distribution. We have that redundancy built in. I shouldn't say this, but this was how Enron was able to build up a business, because they could transfer their energy from wherever they were producing it into California, which was having problems, and make a fortune -- for a short period of time.

NOVA: Gas pipelines don't have redundancy built in, though.

Eagar: No, but one advantage of a gas pipeline is the damage you can do to it is relatively limited. You might be able to destroy several hundred yards of it, but that's not wiping out a whole city. The bigger problem with taking out a gas pipeline is if you do it in the middle of winter, and that gas pipeline is heating 20 percent of the homes in the Northeast. Then all of a sudden you have 20 percent less fuel, and everybody's going to have to turn the thermostat down, and you're going to terrorize 30 million people.

The lesson we have to learn about this kind of terrorism is we have to design flexible and redundant systems, so that we're not completely dependent on any one thing, whether it's a single gas pipeline bringing heat to a particular area or whatever.

Remember the energy crisis in 1973? That terrorized people. People were sitting in long lines at gas pumps. It takes five or 10 years for society to readjust to a problem like that. What happened in the energy crisis in 1973 was we had essentially all our eggs in one basket -- the oil basket. But by 1983, electric generating plants could flip a switch and change from oil to coal or gas, so no one could hold a gun to our head like they did before.

Thomas Eagar is Thomas Lord Professor of Materials Engineering and Engineering Systems at MIT. He was recently nominated to serve on a National Research Council committee on homeland security. To see Eagar's article, "Why Did the World Trade Center Collapse? Science, Engineering, and Speculation," which was coauthored by MIT graduate student Christopher Musso, go to www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html


http://www.pbs.org/wgbh/nova/wtc/images/coll_eagar.jpg


:elvis:

[Rikk]

Uh yeah...

...WARHAM, clean out your PM box.

[LoungeMachine]

Hmmm,

And all this time I thought GRAVITY brought 'em down.....

[ELVIS]

What do you mean by that ??

[Rikk]

I thought they were hit by a stray bird. Planes?? No shit!

[thome]

I specifically remember watching the first tower burn only minuets
after it was struck(post, seeing film of a airliner sticking the first tower) then seeing the second tower struck by a airliner.

I then saw them both fall due to the weight of the above floors
I'm some thing of a person who understands structural integrity
and i knew before they fell that if you cut a floor out of a building
what will happen next is common sense.

So what is the purpose of any other answer or question of the collapse?

[ELVIS]

Originally posted by Rikk
I thought they were hit by a stray bird. Planes?? No shit!

:rolleyes:

[thome]

Originally posted by Rikk
I thought they were hit by a stray bird. Planes?? No shit!

I wanna be like you when i grow up.LOL

5

[BigBadBrian]

Originally posted by Rikk
I thought they were hit by a stray bird. Planes?? No shit!

You haven't been poking your head in this forum enough to know why Elvis posted this thread.

I personally invite you to stick around to witness the silliness. :)

:gulp:

[Rikk]

LMFAO...I hear all the theories.

If anyone cares, I still think it was two planes loaded with fuel and the metal foundations melted to shit...something like that.

Hey, I love conspiracies. I consider myself pretty liberal...whatever the fuck that means in this day and age. But I've never bought the conspiracy theories concerning the actual cause of the collapse. Funny enough, I had a car conversation with a few people about this on Thursday night...and I was the only one in the car that bought the jet full of fuel and super-hot fire theory...

[diamondD]

Where's the TFBE crowd?

[Hardrock69]

Funny how the structural engineer conveniently does not take into account the numerous explosions resembling demolition charges witnessed many floors below the floor in question long after the planes struck the towers.

:rolleyes:

[thome]

Here's my theory who gives a FUK.some people sit in their cars and die
by the thousands. Nobody cares. Fuk the theories, their still dead and the buildings smashed their skulls to oatmeal.

Stop looking for bizzare causes.or don't, your time is well spent .

Did you hear Van Halen Has Sammy Hagar as a Singer??

WHAT!!!

NO, THAT'S INSANE.This is more important than the life & death soap opera we call Life.

:rolleyes:

[knuckleboner]

Originally posted by Rikk
LMFAO...I hear all the theories.

If anyone cares, I still think it was two planes loaded with fuel and the metal foundations melted to shit...something like that.




actually, they didn't melt, which is why a lot of the conspiracy theory crowd initially latched onto the...alternative...causes for collapse.

"but the fires weren't hot enough to melt the steel!" they'd say. and they were right.

but the fires were hot enough to weaken the steel. (technically, any heat weakens steel to some degree. the higher the temperature, the weaker the steel gets until it eventually melts.)

clearly, melted steel would not have been able to hold those buildings up. at the same time, there is some level of weakened steel, that, while still intact would also not be strong enough to hold up the mass of the floors above it.


well, that, or a bunch of cherry bombs in the toilets...

[ELVIS]

Originally posted by Hardrock69
Funny how the structural engineer conveniently does not take into account the numerous explosions resembling demolition charges witnessed many floors below the floor in question long after the planes struck the towers.

:rolleyes:

Do you even hear yourself ??

[Hardrock69]

Yes.

[diamondD]

Those "explosions" were the sound of the support snapping. The sounds were the building coming down upon itself.

Do you think it would just come down quietly after reaching the breaking point?

[ELVIS]

Dude, you can't explain anything to these idiots...

They want so bad for the government to have taken the WTC down...

Keep these ideas in mind for the next conspiracy...

[Rikk]

I hate Bush. I hate the entire administration. I think they're criminals.

But I 100% believe that the steel was weakened to a certain point until it just gave out (thus, the breaking sounds...or "explosions") and the building(s) collapsed.

[Hardrock69]

Originally posted by knuckleboner
actually, they didn't melt, which is why a lot of the conspiracy theory crowd initially latched onto the...alternative...causes for collapse.

"but the fires weren't hot enough to melt the steel!" they'd say. and they were right.

but the fires were hot enough to weaken the steel. (technically, any heat weakens steel to some degree. the higher the temperature, the weaker the steel gets until it eventually melts.)

clearly, melted steel would not have been able to hold those buildings up. at the same time, there is some level of weakened steel, that, while still intact would also not be strong enough to hold up the mass of the floors above it.


well, that, or a bunch of cherry bombs in the toilets...


No they were not melted. Some of them were partially VAPORIZED.

Something that mere "fire" cannot achieve.

[ELVIS]

Keep on dreaming up "facts"...

[Warham]

Originally posted by Hardrock69
No they were not melted. Some of them were partially VAPORIZED.

Something that mere "fire" cannot achieve.

You were in the Towers just before they collapsed???

Please, tell us your amazing story!

[Hardrock69]

Originally posted by Rikk
I hate Bush. I hate the entire administration. I think they're criminals.

But I 100% believe that the steel was weakened to a certain point until it just gave out (thus, the breaking sounds...or "explosions") and the building(s) collapsed.

You can "believe" what you want.

I only believe factual evidence.

"Just the facts, man".

[Rikk]

Can we at least all agree that vagina tastes best after a shower?

[Warham]

Yep.

[Hardrock69]

Let's imagine, contrary to the evidence, that debris from the tower collapses damaged Building 7's structure, that diesel fuel tanks exploded, and that incredibly intense fires raged through large parts of the building. Could such events have caused the building to collapse? Not in the manner observed. The reason is that simultaneous and symmetric damage is needed to produce a collapse with the precise symmetry of the vertical fall of building 7. This building had 58 perimeter columns and 25 core columns. In order to cause the building to sink into its footprint all of the core columns and all of the perimeter columns would have to be broken in the same split-second.

To deny reality as Elvis and others do, means they really do not care about the "reality".

Their sole purpose is to simply troll around this forum with the intent of pissing people off.

Therefore I am not going to waste my time replying to people here who insist on posting their "delusional fantasies". They WISH the "official" story was true, and are extremely frustrated that they cannot prove that it is.

And no...I do not believe the "Government" brought down the WTC.

But I am not stupid enough to believe the "offical fairy tale" they have been spouting.

19 Terrorists my ass.
:rolleyes:

[knuckleboner]

Originally posted by Hardrock69
No they were not melted. Some of them were partially VAPORIZED.

Something that mere "fire" cannot achieve.


probably not.

but mere fire, combined with crashing/exploding airplanes and the immense pressure of a collapsing building?

could that partially vaporize a steel support beam or 2? or can only controlled demolitions explosions do that?

[ELVIS]

Don't forget being nearly a quarter mile up...

[Warham]

Originally posted by Hardrock69
Let's imagine, contrary to the evidence, that debris from the tower collapses damaged Building 7's structure, that diesel fuel tanks exploded, and that incredibly intense fires raged through large parts of the building. Could such events have caused the building to collapse? Not in the manner observed. The reason is that simultaneous and symmetric damage is needed to produce a collapse with the precise symmetry of the vertical fall of building 7. This building had 58 perimeter columns and 25 core columns. In order to cause the building to sink into its footprint all of the core columns and all of the perimeter columns would have to be broken in the same split-second.

To deny reality as Elvis and others do, means they really do not care about the "reality".

Their sole purpose is to simply troll around this forum with the intent of pissing people off.

Therefore I am not going to waste my time replying to people here who insist on posting their "delusional fantasies". They WISH the "official" story was true, and are extremely frustrated that they cannot prove that it is.

And no...I do not believe the "Government" brought down the WTC.

But I am not stupid enough to believe the "offical fairy tale" they have been spouting.

19 Terrorists my ass.
:rolleyes:

Who the fuck would do it if it weren't the government? Donald Trump's always looking for real estate, but I dunno...

I think you've got to give us a credible story of who, why, and how before we even START to consider that your possibility is true. Before that, it's the official story. Nobody here is frustrated by the official story, except for you, FORD, and Tin Foil Beanie Keeyth.

[Cathedral]

So, i ask you people this, How many controlled Demolitions have you ever attended live?

Remember Riverfront Stadium?
I was there when it went BOOM, and i also saw the events of 9-11 unfold on the tube and there was something missing from the towers collapse that is evident in every controlled demolition in history...the blasts that set it off.
There were no blasts as those towers began to fall, that is why it was deemed a "Collapse" and not a "Demoliton".

And also, since when are demolition charges NOT planted at the base of a building?
By the logic that the building couldn't collapse on it's own we would have see evidence of charges going off while they collapsed.

now i don't know what to believe about what came into play exactly with those towers. But a controlled demolition is a theory i would bet my life against.

I don't know much about building codes of the '70's, but i do know how to handle blasting caps and dynomite...it is sort of a requirement when you live on a farm with lots of tree stumps to remove.

There are many things that could have happened that day, but there is no fucking way it was a controlled demolition, the physics just do not support that theory, sorry.

[ODShowtime]

Originally posted by Rikk
I hate Bush. I hate the entire administration. I think they're criminals.

But I 100% believe that the steel was weakened to a certain point until it just gave out (thus, the breaking sounds...or "explosions") and the building(s) collapsed.

You don't need to get all crazy that they bombed the buildings. They just pulled assets away from investigating Atta & Company after whuppin' the beehive a bunch.

Easy as that. Next stop DICTATORSHIP