The skyscrapers of the World Trade Center, or twin towers, were a memorable part of New York, a city that itself became a symbol of America, its indomitable character, forcing the whole country to constantly strive forward and upward, overcoming obstacles. The creation of this architectural and technocratic masterpiece was not only an engineering and economic task. By his very appearance, he was supposed to inspire the idea of the inviolability of Western civilization, its eternity and power.
Again about the terrorist attack ...
In the first year of the third millennium of the New Era, namely on September 11, the twin towers were barbarously destroyed. To destroy them, the terrorists used tools to match the era: two huge passenger Boeing 767s, which also symbolize the power of American industry, like the skyscrapers they hit. A lot has been written about these events, and there is no point in repeating known information to everyone, as well as dubious assumptions about the involvement of a wide variety of forces in the terrorist attack, including the CIA and the US State Department. Journalists did not miss a single detail of the disaster. Even the number of the plane that crashed into the twin towers was scrutinized for fatal coincidences and omens. Having bowed our heads before the memory of the innocent people who died, it is worth thinking not about death, but about the birth of these structures, which for almost three decades have personified the American technological genius.
Background of the grand project
The roaring sixties became for the USA not best time. The fundamental foundations of a free society declared by the founding fathers were under threat. The moral crisis has reached alarming proportions, like a cancerous tumor affecting an increasing number of young people. Drug addiction has become part of the very popular hippie subculture, and patriotism has become something both funny and indecent. In Vietnam, there was a war that seemed to have no end (at least not a victorious one). Girls who came from Indochina were often greeted not as heroes who fought for democracy, but as child killers. Something grandiose could restore to the Americans a sense of dignity and pride in "the world's freest homeland". Flight to the Moon or Mars, for example. Or the world's tallest twin towers.
Difficult construction
The overall project belonged to Minoru Yamasaki, by that time already a famous architect. Behind the external brevity of the outlines of the buildings, a very difficult content was guessed. Even in demonstrative uniformity, a feeling of power was assumed, as if saying: "If necessary, we will build more!" Digging of the pit began in 1966. Actually, Manhattan is a rocky island, and all of its skyscrapers are built on naturally solid foundations. The twin towers were an exception; they were built on soft ground. The second problem concerned the creation of infrastructure. You do not need to be an expert to understand the complexity of the task of wiring and replacing communications in a busy metropolis. It is possible to block traffic on some street for a year, in New York this is unacceptable: both roads and crossings must work. And one more circumstance made the construction process difficult - the subway station, where passengers boarded underground trains going to New Jersey. The terminal had to be created new, and the old one worked all this time.
Some numbers
Now about the numbers and quantities that American builders love to list when talking about their achievements. More than a million square meters of soil was removed, and before that, of course, dug out. Each of the mounting wall blocks, made of steel, weighed 22 tons and had a height of a four-story building. The total weight of the metal used in the construction of the complex was 200,000 tons. Stone masonry was not used. Elevators (there were 239 of them) lifted people and goods to a height of one hundred and ten floors at a speed of 8.5 m / s, and their shafts were made so that they increased the rigidity of the entire scheme. Numerous financial difficulties had to be overcome, but in the end the first skyscraper was generally completed by 1971, and in 1973 both twin towers were solemnly commissioned. Their death in 2001 demonstrates the helplessness that is sometimes experienced by the most developed intellect and boundless diligence in the face of brutal violence. The only consolation is the invincibility of intellect and diligence - these best
Finite element model of the WTC floor, which allows evaluating the structural system of the building
The dimensions of the building in plan are 63.4 x 63.4 m, the stiffening cores are 26.8 x 42.1 m. walls or columns. This was achieved due to the fact that the outer wall of the tower, in fact, was a set of columns installed side by side, taking on the main vertical load, while the wind load fell mainly on the power columns located in the center of the tower (stiffening core). Starting from the tenth floor, each wall of the tower was composed of 59 columns, 49 power columns were installed in the center of the tower. All elevators and stairwells passed in the core of the stiffness, leaving a large free space between the core and the perimeter of the tower for office space.
The structure of the storey ceiling was 10 cm of lightweight concrete laid on a fixed formwork made of profiled decking. The corrugated board was laid on secondary (auxiliary) trusses (beams) resting on the main trusses, transferring the load to the central and peripheral columns. The main trusses had a length of 11 and 18 meters (depending on the span), and were laid in increments of 2.1 m, and were attached from the outside to the lintels connecting the peripheral columns at the level of each floor, and from the inside to the central columns. The floor was fastened through elastic dampers designed to reduce the impact of building vibrations on people working in it.
This truss system allowed an optimized load redistribution of the floor diaphragms between the perimeter and the core, with improved performance between different flexible steel and hard concrete materials allowing the moment structure to transfer the impact into compression on the core, which also mainly supported the transmission tower.
The towers also included an "outrigger (console) truss" located between the 107th and 110th floors, which consisted of six trusses along the longitudinal (long) axis of the core and four along the short (transverse) axis, which served to redistribute the load and raise the overall stability of the building, as well as to support the antenna spire, which was installed on only one of the towers. NIST determined that this design played a key role in the sequence of events leading to the towers' complete collapse.
Fire and Aircraft Resistance Capabilities
Like all modern high-rise buildings, the WTC towers were designed and built to withstand normal fire. Many fire protection elements were laid down during the design and construction phase, others were added after the 1975 fire that engulfed six floors before being contained and extinguished. Tests carried out before the disaster showed that the steel structures of the towers are in line with current fire resistance requirements, or even exceed them.
Structural engineers who designed the World Trade Center considered the possibility of an aircraft colliding with the building. In July 1945, a B-25 Mitchell bomber became disoriented in fog and crashed into the 79th floor of the Empire State Building. A year later, a twin-engine C-45 Beechcraft collided with a skyscraper at 40 Wall Street, and another aircraft came close to another collision with the Empire State Building.
NIST stated that “American building standards do not contain requirements for the stability of buildings when hit by an aircraft. … and thus buildings are not designed to withstand the impact of a fully fueled commercial airliner.” However, the designers and architects of the WTC discussed this problem and recognized its importance. Leslie Robertson, one of the chief engineers at the World Trade Center, recalled that the scenario was considered for a Boeing 707 jet airliner that was disorientated in fog and flying at relatively low speed in search of JFK airport or Newark Liberty Airport. John Skilling, another WTC engineer, said in 1993 that his subordinates were conducting an analysis that showed that the biggest problem in the event of a collision between the WTC towers and a Boeing 707 would be that all the aircraft's fuel would get inside the building and lead to a "terrible fire" and many human casualties, but the building itself will remain standing. FEMA wrote that the WTC buildings were built with a Boeing 707 jet weighing 119 tons and a speed of about 290 km / h in mind, which is much less in weight and speed than those aircraft used in the September 11 attacks.
NIST found a three-page report in the archives summarizing a study that simulated a Boeing 707 or Douglas DC-8 hitting a building at 950 km/h. The study showed that the building should not collapse as a result of such a hit. But, as the NIST experts noted, "the 1964 study did not contain a simulation of the effect of a fire caused by the spraying of aviation fuel on a building." NIST also noted that in the absence of initial calculations used to model the situation, further commentary on this topic would be mostly "speculation". Another document found by NIST was a calculation of the building's oscillation period if an aircraft hit the 80th floor of the World Trade Center tower, but it made no assumptions about the fate of the building after the collision. In a property risk assessment report prepared for Silverstain Properties, the case of an aircraft hitting the World Trade Center towers was considered unlikely, but possible. The authors of the report referred to WTC structural engineers, who believed that the towers should have survived in the event of a major collision. passenger aircraft, but burning fuel flowing from the aircraft to ground level would damage the building's skin. Part of the documents related to the analysis of the scenario of an aircraft hitting the towers was lost as a result of the destruction of WTC 1 and WTC 7, which contained documents from the Port Authority of New York and New Jersey and Silverstain Properties.
Aircraft hitting towers
The terrorists sent two Boeing 767 jets, American Airlines Flight 11 (767-200ER) and United Airlines Flight 175 (767-200) into the towers. The North Tower (1 WTC) was hit at 8:46 am by Flight 11, between the 93rd and 99th floors. Flight 175 crashed into the south tower (2 WTC) at 9:03, between floors 77 and 85.
The Boeing 767-200 airliner has a length of 48.5 m, a wingspan of 48 m, carries on board from 62 tons (-200) to 91 tons (-200ER) of aviation fuel. The planes crashed into the towers at a very high speed. Flight 11 was traveling at approximately 700 km/h when it hit the north tower; flight 175 crashed into the south at a speed of about 870 km / h. In addition to severely destroying the supporting columns, the hits caused an explosion of approximately 38 tons of aviation fuel in each tower, resulting in an almost instantaneous, massive fire spreading to multiple floors containing office furniture, paper, carpets, books, and other combustible materials. The shock wave from hitting the north tower traveled down to the first floor, along at least one high-speed elevator shaft, shattered windows on the first floor, injuring several people.
Fire
The light construction of the towers and the absence of solid walls and ceilings led to the fact that aviation fuel spread in a fairly large volume of buildings, leading to numerous fires on several floors close to the aircraft impact zones. The jet fuel itself burned out within minutes, but the combustible materials in the building itself kept the fires intense for another hour or an hour and a half. It is possible that if more traditional structures were in the way of the aircraft, then the fires would not be so centralized and intense - aircraft debris and aviation fuel could remain mainly in the peripheral area of \u200b\u200bthe building, and not penetrate directly to its central part. In this case, the towers would probably have survived, or in any case, would have stood much longer.
Development of the situation
- 9:52 a.m. - Fire department helicopter radios that "Large pieces of the building may fall from the upper floors of the south tower. We are seeing large parts of the building in limbo.”
- 9:59 a.m. - Helicopter reports that south tower is falling.
Helicopters also reported on the development of the situation with the north tower of the World Trade Center.
- 10:20 a.m. - Fire department helicopter reports that the upper floors of the north tower may be unstable.
- 10:21 - It is reported that the southeast corner of the tower is warped, and that the tower is beginning to lean towards the south.
- 10:27 - It is reported that the roof of the northern tower may collapse at any moment.
- 10:28 a.m. - The fire department receives word that the north tower has collapsed.
Overloaded dispatchers and poor communication performance meant that the New York City Fire and Police Departments experienced great problems in ensuring timely communication, both with their units and with each other. As a result, the fire brigades stationed in the towers did not receive an evacuation order and 343 firefighters died in the collapse of the buildings.
The collapse of the WTC towers
At 9:59 a.m., the south tower collapsed, 56 minutes after impact. The north tower stood until 10:28, 102 minutes after the aircraft hit it. The collapsed towers created a huge cloud of dust that covered much of Manhattan. In both cases, a similar process occurred, the upper damaged part of the building collapsed on the lower floors. Both towers fell almost vertically, although there was a significant deviation from the vertical of the upper part of the southern tower. Debris and dust were also observed flying from the windows of the building below the rapidly advancing collapse zone.
Tower collapse mechanism
The NIST investigation showed that due to the fact that the planes hit the towers differently, the process of destruction of the north and south towers was also somewhat different, although it was generally the same in both cases. After being hit by aircraft, the internal force columns were seriously damaged, although the external columns were relatively lightly damaged. This caused a serious redistribution of the load between them. A significant role in this redistribution was played by the upper power structure of the towers.
Aircraft that hit the buildings stripped the refractory coating from a significant part of the steel structures, which led to the fact that they were directly exposed to fire. In the 102 minutes prior to the fall of the north tower, the temperature of the fire, although well below the melting point of metal, reached a sufficient magnitude to cause the power columns in the center of the building to weaken, which began to warp and buckle under the weight of the upper floors. The NIST report describes this situation as follows:
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A similar situation was in the south tower (the internal power columns were seriously damaged). The peripheral columns and floor structures of both towers were weakened by the fire, causing the floor to subside on the damaged floors and placing a significant load on the peripheral columns towards the interior of the building.
At 09:59, 56 minutes after impact, the subsiding floor caused severe inward flexing of the outer columns on the east side of the south tower, the upper structure transferred this bending force to the central columns, causing them to collapse and the building to begin to collapse, while the top of the tower deviated towards the damaged wall. At 10:28 am, the south wall of the north tower warped, causing roughly the same sequence of events. As a result of the ensuing collapse of the upper floors, the complete destruction of the towers became inevitable, due to the enormous weight of the part of the buildings that were above the damage zone.
The reason that the north tower stood longer than the south tower was a combination of the following three factors: the zone of impact of the aircraft in the north tower was higher (and the weight of the upper part of the building, respectively, is less), the speed of the aircraft that hit the tower was lower, in addition, the aircraft hit floors, the fire protection of which was previously partially improved.
Theory of complete progressive collapse
The ruins of the South Tower (right) and North Tower (left), as well as other buildings of the World Trade Center
A huge cloud of dust covered the collapsing towers, making it impossible to determine the exact duration of the destruction based on visual evidence.
Since the NIST report deals mainly with the mechanisms of the initial collapse, it does not address the issue of the subsequent complete collapse of both WTC towers. Initial analyzes attributed the collapse to the fact that the kinetic energy of the falling upper floors was much greater than what the interfloor floors could withstand, which also collapsed, adding kinetic energy to the falling building. This scenario of events was repeated with increasing speed until the towers were completely destroyed. Although this is the most widely held view among structural engineers, it has been criticized for not taking into account the resistance of the underlying structures, which should have slowed down the collapse of the towers, or even stopped it.
7 WTC building collapse
The initial FEMA study was inconclusive, and the collapse of 7 WTC was not included in the September 2005 NIST final report. With the exception of a letter published Metallurgical Journal, which suggested that the steel frame of the building could have been melted by fire, no other studies of this issue have been published in scientific journals. The fall of 7 WTC was investigated separately from the fall of 1 WTC and 2 WTC, and in June 2004, NIST released a working report that contained several hypotheses of what happened. One hypothesis was the collapse of one of the building's critical supporting columns, caused by fire or large debris from falling towers, resulting in a "disproportionate collapse of the entire structure".
NIST diagram showing the bending of Column 79 (circled in orange) that started the progressive collapse of the building.
Destruction order of 7 WTC in a diagram from a 2004 NIST preliminary report. Column 79 is marked with a circle in the center of the red zone.
7 WTC fall model developed by NIST. In the first part of the video clip, columns 81, 80 and 79 are shown from left to right.
On November 20, 2008, NIST released its final report on the fall of 7 WTC. The NIST report cited the fire as the main cause of the destruction, along with a lack of fire fighting water for firefighters and the automatic fire suppression system. NIST reconstructs the sequence of events as follows: At 10:28 am, debris from falling WTC 1 caused damage to adjacent WTC 7. Fires also broke out, probably from burning debris from 1 WTC. By 7 WTC, firefighters immediately arrived, but at 11:30 they discovered that there was no water in the fire hydrants to fight the fire - the water came from the city's water supply system, destroyed by the fall of towers 1 WTC and 2 WTC. New York Fire Department ( English), fearing for the lives of the firefighters if 7 WTC were destroyed, at 14:30 withdrew the firefighters and stopped the fight to save the building. The fire was observed on 10 floors from the 7th to the 30th, and on floors 7-9 and 11-13 the fire got out of control. Thermal expansion of the approximately 400°C beams around Pillar 79 in the eastern part of the building in the 13th-14th floor region caused the fire-weakened floors adjacent to Pillar 79 to collapse from the 13th to the 5th floor. The destruction of the ceilings deprived column 79 of its horizontal support, and it began to bend, which was the direct cause of the complete destruction of the building after a few seconds. The bending of column 79 resulted in the transfer of load to columns 80 and 81, which also began to bend, as a result of which all the ceilings associated with these columns up to the top of the building were destroyed. Falling ceilings destroyed truss 2, causing columns 77, 78, and 76 to fall. As a result of the increased load transferred from the bent columns, falling debris from above, and the lack of horizontal support from the collapsed ceilings, all internal columns from east to west began to buckle in succession. Following this, in the area of floors 7-14, the outer columns began to bend, on which the load was transferred from the lowered inner columns and the center, and all floors above the bent columns began to sink down as a whole, which completed the final destruction of the building at 17:20.
Some writers have criticized the city's decision to locate WTC headquarters on the 23rd floor of 7 WTC Emergency Situations Office(English) Office of Emergency Management ). It was assumed that this could be a significant factor in the destruction of the building. Particularly noteworthy was the placement in the building of large tanks with diesel fuel, which were supposed to serve to power emergency power generators. NIST concluded that diesel fuel did not play a role in the destruction of the building, but the rapid evacuation of the Office of Emergency Situations was one of the reasons for poor communication between various services and loss of control over the situation. The main cause of the building's destruction was fire, debris damage from falling 1 WTC accelerated the building's fall, but NIST calculations showed that 7 WTC would have collapsed from an uncontrolled fire alone.
Progress of investigations
First reaction
The destruction of the WTC towers came as a surprise to the construction engineers. "Before 9/11," wrote the magazine New Civil Engineer, - we quite sincerely could not imagine that a structure of this magnitude could suffer such a fate. Despite the fact that the damage from the aircraft strikes was very serious, they affected only a few floors of each building. It became a challenge for engineers to figure out how such localized damage caused the complete progressive collapse of three, some of the largest buildings in the world. In an October 2001 interview with the BBC, English architect Bob Halvorson quite aptly predicted that there would be much "debate about whether the World Trade Center could have collapsed the way it did." A full analysis should include the WTC's architectural and design plans, eyewitness testimony, video footage of the destruction, wreckage survey data, etc. Highlighting the challenge of the task, Halvorson said that the destruction of the WTC towers is "far beyond ordinary experience."
Research Authority
Immediately after the disaster, a situation of uncertainty arose as to who had sufficient authority to conduct an official investigation. Contrary to the practice in air crash investigations, there were simply no clear procedures for investigating building collapses.
Shortly after the disaster at the base Institute of Building Engineers(English) Structural Engineers Institute (SEI)) American Society of Civil Engineers(English) American Society of Civil Engineers ASCE), a working group was created, which also involved specialists American Institute of Steel Structures(English) American Institute of Steel Construction ), American Concrete Institute(English) American Concrete Institute ), the National Fire Protection Association and Communities of Fire Protection Engineers(English) Society of Fire Protection Engineers ) . ASCE also invited the Federal Emergency Management Agency (FEMA) to join this group, which was later jointly managed by ASCE-FEMA. This investigation was subsequently criticized by American engineers and lawyers, however, the authority of the aforementioned organizations was sufficient to conduct an investigation and to provide access to the crash site for the group's experts. One of the most poignant moments of the investigation was that the cleanup of the crash site actually resulted in the destruction of the remaining components of the building. Indeed, when NIST released its final report, it noted a "lack of physical evidence" that became one of the main concerns of the investigation. Only fractions of a percent of the remains of the building remained available for investigation after the completion of the clearance work, in total 236 individual steel fragments were collected.
FEMA published its report in May 2002 . Despite the fact that NIST had already declared its involvement in the investigation in August of that year, in October 2002, under increasing public pressure for a more detailed investigation, Congress passed a bill creating a new group under the leadership of NIST, which published its report in September 2005 .
FEMA's "stack of pancakes" theory
In its early investigations, FEMA developed a theory to explain the collapse of the WTC towers called the "Pancake Stack Theory". pancake theory). This theory has been defended by Thomas Iga and widely covered by PBS. According to this theory, the connection between the lintels supporting the floor and the columns of the building failed, causing the floor to collapse one floor below, placing loads on its structure that it was not designed for. Some individual publications have suggested other sets of factors that caused the collapse of the towers, but in general this theory has been accepted by the majority.
Fires remained the main key factor in this theory. Thomas Iga, professor of materials science at MIT, described the fires as "the most baffling part of the collapse of the WTC towers." Although the fires were initially thought to have "melted" the steel structures, Iga stated that "the temperature of the fires in the WTC towers was unusually high, but still definitely not enough to cause melting or severe softening of the steel." Aviation kerosene fires typically result in extensive fires, but these fires do not have very high temperatures. This led Iga, FEMA, and others to believe that there was a weak point, and this point was named as the anchoring of the floor to the building's load-bearing structures. Due to the fire, these fastenings weakened and, when they collapsed under the weight of the floor, collapse began. On the other hand, the NIST report states completely and unequivocally that these mounts were not destroyed. Moreover, it was their strength that was one of the main reasons for the collapse, since through them a force was transmitted to the peripheral columns, which bent the columns inward.
At temperatures above 400-500 °C, there is a sharp decrease in the tensile strength and ductility limit (by 3-4 times), at 600 °C they are close to zero and the bearing capacity of the steel is exhausted.
NIST report
Organization of the study
As a result of mounting pressure from experts, construction industry leaders, and family members of the victims following the release of the FEMA report, National Institute of Standards and Technology(NIST) of the Department of Commerce conducted a three-year, $24 million investigation into the destruction and collapse of the World Trade Center towers. The study included a series of experiments, in addition, leading experts from many third-party organizations were involved in it:
- Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE)
- Society of Fire Protection Engineers (SFPE)
- National Fire Protection Association (NFPA)
- American Institute of Steel Construction (AISC)
- Council on Tall Buildings and Urban Habitat (CTBUH)
- Structural Engineers Association of New York (SEANY)
Scope of study and its limitations
NIST's scope of study was limited to studying the question of "the sequence of events from the moment an aircraft hits to the start of each tower collapse", and also included "a small analysis of the structural behavior of the tower structure after the conditions for its collapse were reached and collapse became inevitable" . Like many other engineers involved in this issue, the NIST experts focused on aircraft hitting turrets, simulating the effects of hits such as structural collapse, fire spread, etc. in a very high degree of detail. NIST has produced several very detailed models of various building components, such as lintels that support the floor, and entire buildings have been modeled, but at a lower level of detail. These models were static, or quasi-static, included modeling of deformations, but did not include modeling of the movement of structural elements after they were disconnected from each other. Thus, NIST models are useful for finding out why towers collapse, but they do not provide a way to model the collapse itself.
Parallel investigations
In 2003, three engineers from the University of Edinburgh published a report suggesting that fires alone, even without taking into account the destructive effect of aircraft strikes, were enough to completely destroy the WTC towers. In their opinion, the design of the towers made them extremely vulnerable to widespread fires that engulfed several floors at once. When the NIST report came out, Barbara Lane and the English engineering company Arup criticized its conclusion that the destruction caused by aircraft hits was a necessary factor for the start of destruction of buildings .
Criticism
Some engineers have offered their insight into the mechanism of tower collapse by developing animated collapse sequences based on dynamic computer models and comparing the results with video footage of the crash site. In October 2005 the magazine New Civil Engineer regarding the computer model created by NIST. In response, NIST enlisted Colin Bailey of the University of Manchester and Robert Planck of the University of Sheffield to create the computer visualizations needed to work on correcting tower collapse models and bringing those models fully into line with observed events.
Other buildings
Portions of the outer wall of the north tower facing the remains of WTC Building 6, which was severely damaged by the fall of the north tower. In the upper right corner are the remains of building 7 WTC.
On September 11, 2001, the entire World Trade Center complex and the small Orthodox Greek Church of St. Nicholas, which stood on Liberty Street opposite the south tower of the World Trade Center, were destroyed. In addition, many buildings surrounding the complex were damaged to one degree or another.
Consequences
Clearing the crash site
The huge mountain of debris at the site of the World Trade Center continued to burn and smolder for another three months, with attempts to control the fire failing until a significant amount of debris and debris was removed. The clearance was a massive operation coordinated by the Construction Department (DDC). A preliminary clearance plan was prepared on September 22 by Controlled Demolition Inc. (CDI) from Phoenix. Mark Lozo, president of the CDI, particularly stressed the importance of protecting the mud wall (or "bath") that kept the WTC's foundations from being flooded by the Hudson's waters. The cleanup was carried out around the clock, involving a large number of contractors, and cost hundreds of millions of dollars. In early November, after about a third of the debris had been removed, the city government began to reduce the involvement of police and firefighters who were searching for the remains of the dead, and shifted priorities to garbage collection. This provoked objections from the firemen. As of 2007, the demolition of some of the buildings surrounding the WTC continued, amid construction of a replacement for the WTC, a memorial complex, and the Freedom Tower.
Controlled demolition versions
There is a version that the WTC towers could have been destroyed as a result of a planned controlled demolition, and not as a result of an aircraft hit. This theory was rejected by NIST, which concluded that there was no involvement in the collapse of the towers. explosives. NIST stated that it did not perform tests to search for explosive residues of any kind in the wreckage because it was not necessary:
12. Did the NIST investigation look for evidence of the WTC towers being brought down by controlled demolition? Was the steel tested for explosives or thermite residues? The combination of thermite and sulfur (called thermate) "slices through steel like a hot knife through butter."
NIST did not test for the residues of these compounds in the steel.
The responses to questions number 2, 4, 5 and 11 demonstrate why NIST concluded that there were no explosives or controlled demolition involved in the collapses of the WTC towers.
In a 2008 report, NIST also analyzed the WTC Tower 7 explosion hypothesis and concluded that the explosion could not have caused the observed effects. In particular, the smallest amount of explosives that could destroy column 79 would cause a noise of 130-140 decibels at a distance of 1 km from 7 WTC, but such noise was not noticed by either the sound recording equipment or bystanders. This theory has become a prominent part of most of all the "conspiracy theories" that arose as a result of the events of 9/11.
Notes
- Relatives gather at ground zero to mark 9/11 , The Associated Press/MSNBC(September 9, 2007). Retrieved November 3, 2007.
- PartIIC - WTC 7 Collapse (pdf). NIST Response to the World Trade Center Disaster. National Institute of Standards and Technology (April 5, 2005). Archived from the original on March 4, 2012. Retrieved November 1, 2006.
- Hamburger, Ronald, et al(pdf). Federal Emergency Management Agency. archived
- Snell, Jack, S. Shyam Sunder NIST Response to the World Trade Center Disaster (pdf). National Institute of Standards and Technology (November 12, 2002). Archived from the original on March 4, 2012. Retrieved July 27, 2006.
- Chapter 1 // . - NIST. -P.p. 6.
- National Construction Safety Team Final Report on the Collapse of the World Trade Center Towers . - NIST.
- Barrett, Devlin Steel type in WTC met standards, group says . The Boston Globe. Associated Press (2003). Retrieved May 2, 2006.
- Glanz, James and Eric Lipton. The Height of Ambition The New York Times(8 September 2002).
- Adam Long. PILOT LOST IN FOG; SCENE OF PLANE CRASH LAST NIGHT AIRPLANE CRASHES INTO SKYSCRAPER Ceiling Reduced by Fog , The New York Times(May 24, 1946).
- (pdf). NIST NCSTAR 1-1 Pages 70-71 archived
- Leslie E. Robertson. Reflections on the World Trade Center // The Bridge. - National Academy of Engineering, 2002. - V. 32. - No. 1. Archived from the original on February 28, 2010.
- Fahim Sadek. NIST NCSTAR 1-2. Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers. - NIST, September 2005. - S. 3-5, 308.
- Nalder, Eric. (English) , The Seattle Times (27-02-1993).
- Ronald Hamburger, et al. World Trade Center Building Performance Study. - Federal Emergency Management Agency. - S. 1-17.
- NIST's Working Hypothesis for Collapse of the WTC Towers (Appendix Q) . NIST (June 2004). Archived from the original on March 4, 2012. Retrieved December 21, 2007.
- NIST was informed by the Port Authority that the documents cited were destroyed in the collapse of WTC 1 and the WTC owners documents held in WTC 7 were also lost.
- Lew, H.S.; Richard W. Bukowski and Nicholas J. Carino Design, Construction and Maintenance of Structural and Life Safety (pdf). NIST NCSTAR 1-1 Page 71. National Institutes of Standards and Technology (2006). Archived from the original on March 4, 2012. Retrieved October 15, 2007.
- Jane's All the World's Aircraft Boeing 767. Jane "s (2001). Retrieved August 19, 2007.
- Field, Andy A Look Inside a Radical New Theory of the WTC Collapse . Fire/Rescue News (2004). Retrieved July 28, 2006.
- Gross, John L., Therese P. McAllister Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers (pdf). Federal Building and Fire Safety Investigation of the World Trade Center Disaster NIST NCSTAR 1-6 archived
- Wilkinson, Tim World Trade Center - Some Engineering Aspects (2006). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
- Lawson, J. Randall, Robert L. Vettori. NIST NCSTAR 1-8 - The Emergency Response P. 37. NIST (September 2005). Archived from the original on March 4, 2012.
- McKinsey Report - Emergency Medical Service response . FDNY / McKinsey & Company (August 9, 2002). Archived from the original on August 26, 2011. Retrieved July 12, 2007.
- McKinsey Report - NYPD (August 19, 2002). (unavailable link - story) Retrieved July 10, 2007.
- NY Firefighters attack Giuliani. BBC News, July 12, 2007 http://news.bbc.co.uk/2/hi/americas/6294198.stm
- Bažant, Zdeněk P.; Yong Zhou (2002-01-01). "Why Did the World Trade Center Collapse?-Simple Analysis". J Engrg Mech 128 (1): pp. 2-6. DOI:0.1061/(ASCE)0733-9399(2002)128:1(2) . Retrieved 2007-08-23.
- Bažant, Zdeněk P.; Mathieu Verdure (March 2007). "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions". J.Engrg. Mech. 133 (3): pp. 308-319. DOI:10.1061/(ASCE)0733-9399(2007)133:3(308) . Retrieved 2007-08-22.
- Cherepanov, G.P. (September 2006). "Mechanics of the WTC collapse". Int J Fract(Springer Netherlands) 141 (1-2): 287-289. DOI:10.1007/s10704-006-0081-8 . Retrieved 2007-10-07.
- Hayden, Peter WTC: This Is Their Story. Firehouse Magazine (April 2002). (unavailable link - story)
- Observations, Findings and Recommendations (pdf). World Trade Center Building Performance Study, (Chapter 8.2.5.1). Federal Emergency Management Agency. Archived from the original on March 4, 2012. Retrieved July 28, 2006.
- Barnett, J.R.; R.R. Biederman, R.D. Sisson Jr. An Initial Microstructural Analysis of A36 Steel from WTC Building 7 . Features: Letter. The Journal of Materials (2001). Archived from the original on March 4, 2012. Retrieved May 12, 2006.
- Key Findings of NIST’s June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster . Fact sheets from NIST. National Institute of Standards and Technology (2004). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
- Interim Report on WTC 7 (pdf). Appendix L. National Institute of Standards and Technology (2004). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
- NIST Releases Final WTC 7 Investigation Report. National Institute of Standards and Technology (November 20, 2008). Archived from the original on March 4, 2012. Retrieved August 28, 2009.
- Robert MacNeill, Steven Kirkpatrick, Brian Peterson, Robert Bocchieri. Global Structural Analysis of the Response of World Trade Center Building 7 to Fires and Debris Impact Damage. - November 2008. - S. 119-120.
- Questions and Answers about the NIST WTC 7 Investigation. National Institute of Standards and Technology (21 April 2009). Archived from the original on March 1, 2010.
- Barrett Wayne Grand Illusion: The Untold Story of Rudy Giuliani and 9/11 . - Harper Collins. - ISBN 0-06-053660-8
- Replying to Giuliani
- Oliver, Anthony Lasting lessons of WTC . New Civil Engineer (June 30, 2005). (unavailable link - story) Retrieved July 28, 2006.
- Whitehouse, David WTC collapse forces skyscraper rethink . BBC News (2001). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
- Snell, Jack. "The Proposed National Construction Safety Team Act." NIST Building and Fire Research Laboratory. 2002.
- Experts Debate Future of the Skyscraper in Wake of Disaster, Engineering News-Record(September 24, 2001).
- Glanz, James and Eric Lipton. Nation Challenged: The Towers; Experts Urging Broader Inquiry In Towers" Fall". New York Times December 25,
- Dwyer, Jim. "Investigating 9/11: An Unimaginable Calamity, Still Largely Unexamined". New York Times. September 11,
- NIST. "NIST's Responsibilities Under the National Construction Safety Team Act"
- Thomas Eagle. The Collapse: An Engineer's Perspective. NOVA (2002). (unavailable link - story) Retrieved July 28, 2006.
- Eagar, Thomas W.; Christopher Musso (2001). Why Did the World Trade Center Collapse? Science, Engineering, and Speculation. JOM, 53(12). The Minerals, Metals & Materials Society. Retrieved on 2006-05-02.
- Clifton, G. Charles Collapse of the World Trade Center Towers (pdf) (2002). (unavailable link - story) Retrieved July 28, 2006.
World Trade Center. New York Twin Towers - fallen brothers
New Yorkers called the Twin Towers (Twins Towers) the skyscrapers of the World Trade Center, which were destroyed on September 11, 2001 as a result of a terrorist attack. This event became a national tragedy for the United States. It was not in vain that the terrorists chose the Twin Towers as their target, because they were the national pride of the country, a symbol of democracy and a symbol of the greatness of the American people. Today, Twins Towers reminds us of a huge memorial built on the site of the tragedy. In many Hollywood films released before 9/11, we can see a panorama of New York's Dream City, which necessarily includes the towers of the World Trade Center. On tourist postcards of those times, gigantic "twins" were also traditionally depicted. And how many souvenirs were made associated with these towers! Unfortunately, now these trinkets are more likely to remind us of the sad:
However, this article was not planned as an essay in memory of the fallen colossi, but rather as a story about an architectural masterpiece that has gone into oblivion, but, nevertheless, has retained a good memory of itself. It is natural that there is no project exactly copying the World Trade Center in the plans of American urban planners. Why strive to repeat success? May the Towers "live" in our hearts.
However, in addition to the memorial on the area once occupied by the World Trade Center, it was nevertheless decided to build several high-rise buildings. Indeed, such a tasty part of Manhattan should not be empty? Already at the stage of construction is the Freedom Tower skyscraper, which will have a height of over 500 meters. It is expected to be completed by 2013. In addition to this office building, there are 4 more projects, but so far they only exist on paper. 3 high-rise towers and one residential building have been developed. These giants will grow next to the memorial on Greenwich Street.
Before starting the story about Twins Towers, let's give a little explanation. The World Trade Center was actually a complex of seven buildings, which included the ill-fated North and South Towers. Each of the towers contained 110 floors, but the height varied - at the South Tower it was 415 meters, and the North - 417. Nearby was the 22-story Marriott Hotel, which had the abbreviated name WTC-3. Three more buildings of the WTC 4-6 had 9 floors each, and the WTC-7, located across the street from the rest of the complex, contained 47 floors.
Construction history
The idea to build a grandiose skyscraper was born in the post-war years. The US economy was actively reviving after the recession caused by the Second World War. In the 50s, most large companies located their offices in New York, namely in Manhattan. Influential businessman David Rockefeller, using the guarantee of his brother Nelson (who served as governor of the city), proposed to start building the World Trade Center here. The project was supported by the Port Authority of New York and New Jersey. The entire project was led by the Manhattan Creative Association, headed by David Rockefeller. It was assumed that the World Trade Center, upon completion of construction, will be about 4% of all office real estate in the city.
For some time, the project remained only in the minds of his associates, but at the end of the 50s, the World Trade Center got busy. This was mainly due to the political situation in the country. In those years, US citizens significantly lost faith in the further development of democracy and the country's prosperity. It was then that the authorities decided to bring Rockefeller's ideas to life, teaching the World Trade Center "under the sauce" of a national project. According to the authorities, the giant complex could rally the entire people of America around it. Eminent architects vied with each other to offer their projects, but preference was given to the development of Minoru Yamasaki. This American architect of Japanese origin was the author of many beautiful backgrounds, including: the airport in St. Louis, the Concrete Institute, the Institute of Arts and Crafts in Detroit. Together with Minoru Yamasaki, architect Antonio Britteci and Emiri Roth & Sons worked on the WTC concept.
In 1964, by order of the Port Authority, the first drawings of the future twin towers were created with a reduction of 130 times, and on August 5, 1966, the construction of skyscrapers began.
From the very first days, various technical problems began to arise at the construction site. At the site of the future construction, it turned out not to be stone, but artificial soil, which is a mixture of cobblestones, sand, and pebbles. Therefore, for the construction of the foundation of "Twins Tower" it took a lot more concrete than originally planned, this circumstance led to a sharp increase in the cost of building the facility.
Then it was necessary to solve a problem that was difficult in engineering and technical terms. On the site of future skyscrapers, it was necessary to demolish about 160 buildings, but at the same time preserve all engineering communications (gas pipeline, water supply, sewerage, electric cables, etc.), as well as the nearby high-speed highway and road network.
Another important problem was the line of underground railway passing at this location. It was impossible to close it, since every day tens of thousands of people traveled by subway to work and home. The authorities decided not to build alternative transport routes, as this would further increase the cost of building the towers. Therefore, the New York subway line functioned until a new one was launched, with a station in the lowest tier of the WTC complex.
More than 1.2 million cubic yards of earth had to be removed from the ground during the construction of Twins Tower. The formed foundation pit became not only the foundation of the twin towers, but also the Plaza was organized in it, which is a huge space that housed a car park for 2000 cars, a new underground railway station, restaurants, offices various firms, banks, warehouses, shops, etc.
According to the plan proposed by Minoru Yamasaki, the Twins Towers were to become not only the tallest skyscrapers in the United States of America, but also the world. And this meant that the Twin Towers should be given a greater height than the Empire State Building, which at that time firmly held the palm of the championship of the largest building on the planet. For this, an interesting engineering solution was invented. In fact, the towers were a very strong hollow metal tube created from columns with trusses for the floors. Along the walls of the building there were 61 beams made of special steel. Each column had a diameter of 476.25 mm, they were installed tightly to each other. The distance between the beams was only 558.8 mm. The weight of each such steel block was as much as 22 tons, and the height was equal to 4 floors of the future building! In total, about 210,000 tons of heavy-duty steel were used in the construction of skyscrapers. Ceilings between floors were made of concrete slabs and corrugated steel, which were attached to the load-bearing elements of the entire structure. Inside the buildings, steel columns were erected for future elevators.
The twin towers were the first building in the world without the use of masonry, and the engineers were afraid that the high pressure of the air currents could disrupt normal work elevator shafts. Therefore, a special engineering system was developed for elevators, which later received the name "dry-walled". For a standard elevator system serving a skyscraper, it would have been necessary to use almost half of the entire floor space of the lower tier in order to place elevator shafts in it, which was not economically viable. Therefore, the specialists of the company "Otis Elevators" have developed a special system, called "fast" and providing for the transfer of passengers on the 44th and 78th floors of buildings. Such a system of elevators made it possible to reduce the number of elevator shafts by half, compared with the traditional system. As a result, 239 elevators worked in the Twins Tower complex, as well as 71 escalators. Each elevator was designed for a load capacity of 4535 kilograms, that is, it could lift 55 people at the same time. The speed of the elevators was 8.5 meters per second. By the way, the engineers also used this system of "transfers" when designing other skyscrapers that were born much later than the Twins.
During the construction of the facility, financial difficulties arose more than once, but despite this, construction not only did not stop, but also continued rapidly. In 1965-1970, New York authorities could not fully finance the construction, so credit loan bonds were issued. In 1970, a major economic crisis broke out, as a result of which the authorities stopped paying bonds. First, the administration decided to freeze construction for several years. But then this seditious idea was abandoned, because the prestige of the United States could suffer greatly from these measures. Then economists developed another way of financing and the money was found. Taxes for entrepreneurs were increased, contracts for the lease of office space in the skyscrapers of the World Trade Center (with prepayment), etc. were concluded.
The construction of the North Tower was completed in 1971, and the South Tower was put into operation two years later. The official opening date of the World Trade Center in New York is April 4, 1973.
Characteristics of the World Trade Center Towers
As a result, the twin towers became the tallest skyscrapers in the United States. Each "brother-giant" had 110 floors. The height of the 1st WTC building was 526.3 meters, including the antenna. The last floor in the South Tower was 411 meters from the ground, and in the North - 413! The depth of the foundation was at around 23 meters underground. The length of power cables exceeded 5,000 kilometers, and the total power of the electrical network was about 80,000 kW. Thus, the builders really managed to bring to life the "Project of the Century", which has become one of the symbols of the United States, the pride of the American people.
In the last years of the Complex's existence, about 50,000 people came to work at the World Trade Center daily, and another 200,000 people visited the World Trade Center as tourists a week.
An Observatory was organized in the South Tower on the 107th floor. From the observation deck there was a magnificent view of the city. In the North Tower, between the 106th and 107th floors, there was a chic restaurant "Windows to the World", which was opened in 1976 and was the highest "high-rise" food outlet in the world.
At that time, no one could have imagined that these towers would ever fall. After all, the frame of the building, according to the assurances of the engineers, could withstand the impact of colossal force, for example, when rammed by an airplane. The towers were especially not afraid of the strongest gusts of wind that raged at a height of 400 meters. The construction of skyscrapers was distinguished by high strength, stability, thanks to facades made in the form of steel frames and aluminum modular sections built into them. These elements had dimensions of 10x3.5 meters. All technical tricks were in vain, because when the planes crashed, it was not the destructive force of the collision that played a decisive role, but the high temperature. As a result of the explosion of fuel tanks containing over 5000 liters of gasoline, steel was instantly heated to 1000 degrees Celsius! This is what caused the collapse.
reference
Currently, on the site of the twin towers, three new skyscrapers are being built, under the working names Tower? 2,? 3 and? 4 and a tower 541 meters high, which received the symbolic name "Freedom Tower". All new buildings will be very different from the first towers that fell during the terrorist attack. The groundbreaking ceremony for the construction of the new World Trade Center was held in July 2004, and construction began on April 27, 2006. The site is being developed by Larry Silverstein, a real estate entrepreneur. According to the plan, the completion of the construction of the Freedom Tower should take place before 2013. In addition to this tower, the new World Trade Center in New York will also include a residential skyscraper, three high-rise office buildings, a museum and a memorial to the victims of the September 11, 2001 tragedy, as well as a concert and exhibition center. Many Americans dubbed the 540-meter skyscraper the "Tower of Fear", because. during its construction, innovative technologies will be used to prevent destruction during a terrorist attack of any force. In particular, it is planned to encase the first 52 meters of the building in a concrete frame, and use prismatic glass for the exterior, only in this way it will be possible to avoid the notorious visual effect of the "stone bag".
Exactly 45 years ago, on April 4, 1973, the World Trade Center designed by Minoru Yamasaki was inaugurated in the Financial District of Manhattan in New York. The architectural dominant of the complex were two twin towers, each with 110 floors - North (417 m high, and taking into account the antenna installed on the roof - 526.3 m) and South (415 m high). They became the symbol of New York known to the whole world.
The idea of creating a World Trade Center in New York was born long before that. In 1943, the New York State Legislature passed a bill allowing New York Governor Thomas Dewey to begin planning for construction, however development was halted in 1949.
In the late 1940s and early 1950s, New York's economic growth was centered in downtown Manhattan. To encourage redevelopment in other parts of Manhattan, David Rockefeller proposed to the Ports Authority that a shopping mall be built in Lower Manhattan. However, it came to construction another 30 years later.
The architects of the project were Emery Roth & Sons and Minoru Yamasaki, who came from a family of emigrants, who had previously built the buildings of the Pacific Science Center in Seattle, the Pruitt-Igoe residential complex in St. Louis (Missouri), etc. Yamasaki was afraid of heights, so all of his projects are distinguished by narrow vertical windows. The windows of the WTC buildings were only 46 cm wide. Yamasaki explained that in this way he seeks to create a sense of security for a person who could go to the window and lean on it with both hands, feeling safe.
Yamasaki's original plan was for the twin towers to be 80 stories high, but due to Port Authority building regulations, the height of the buildings was increased to 110 stories. Opened in 1973, the towers became the tallest skyscrapers in the world. In addition to the towers, the WTC plan included the construction of four low-rise buildings and a 47-story "7 World Trade Center" (built in the mid-1980s).
The main factor in curbing the height of buildings was the laying of elevators - the higher the building, the more elevators were required to service it, more cumbersome elevator shafts were required. Yamasaki and the engineers decided to use a new system with two "skylobbies" where people could move from a large high-speed elevator to local elevators that went to the correct floors in their section.
Preparation for construction began in 1965 with the purchase of the Radio Row area and the demolition of existing buildings, mainly residential and small shops. Many local residents refused to move to other areas, so the start of construction was postponed several times. A group of small business owners filed a lawsuit against the Port Authority, challenging the transfer of their business from the area, but the Supreme Court refused to accept it.
The complex was built on an embankment, so the foundation, 20 meters deep, had to be made using complex technology to prevent water from breaking through the Hudson into the construction zone. This work took 14 months. In August 1968, the construction of the North Tower of the center began, and seven months later - the South Tower.
Engineers at Worthington, Skilling, Helle & Jackson decided to build the towers in a tube-frame system, without the use of load-bearing beams and columns - steel columns in the core of the building, as well as in the outer wall, were located so close to each other that they formed a rigid wall structure , which could withstand almost all lateral loads: wind and gravity. This made it possible to increase the usable area of the twin towers.
The walls were composed of 59 columns on each side, each modular part including three columns, three stories high, connected by lintels, which, in turn, were welded to the columns and created new modular parts.
The columns were protected with sprayed fire-resistant material. To ensure the comfort of the people inside the building, a series of experiments were carried out, after which the engineers developed viscoelastic dampers to absorb some of the vibrations, as some experienced nausea and dizziness in the towers.
A rectangular core 27 × 41 m was constructed in each tower. Elevator and communications shafts, toilets, and auxiliary premises were placed in it. It was built from 47 steel columns. The space between the outer wall and the core was covered with floor structures that were connected to the outer wall in such a way as to reduce the amount of vibration. Lateral loads were transferred from the outer wall to the central core.
The total construction costs for the towers amounted to $900 million. The complex was inaugurated on April 4, 1973.
The design of the newly built WTC drew criticism from urbanists and many architects. The Twin Towers have been called "glass-and-metal cabinets," "an example of the aimless gigantism and technological exhibitionism that is currently gutting the living fabric of every great city."
However, very quickly the towers became one of the symbols of New York along with the Empire State Building and the Statue of Liberty. Their image adorned postcards, the towers appeared in the screensavers of TV shows ("Friends", "Sex and the City") and movies ("King Kong" 1976).
Before the world-famous September 11, 2001 attacks, when the towers and other buildings of the complex were destroyed, the World Trade Center survived a major fire and another terrorist attack.
On February 13, 1975, the floors from the 9th to the 14th North Tower burned down. The fire spread due to the ignition of telephone wires in the shaft between floors. The fire was brought under control within a few hours and no one was hurt.
On February 26, 1993, a truck with 680 kg of explosives drove into the underground parking area of the North Tower of the World Trade Center. The explosion killed six people and injured more than 1,000 people. The goal of the terrorists was to destroy the North Tower, which, according to their calculations, was supposed to fall on the South Tower, which should have led to the destruction of both and mass casualties. After the attack, the alarm and fire safety systems were replaced.
On September 11, 2001, terrorists hijacked two American Airlines planes and sent them to the North and then the South Tower. The first plane crashed into the North Tower between the 93rd and 99th floors, trapping 1,344 people on the upper floors, unable to use the elevators or emergency exits.
In the South Tower, one of the stairwells remained intact, but not everyone was able to use it before the collapse. The south tower collapsed at 9:59 am, the north tower at 10:28 am. As a result of the attack, 2,752 people died - 200 of them jumped out of the windows. 20 people were pulled out of the rubble alive.
World News
11.09.2016The eleventh day of September 2001 went down in history as a global tragedy that dealt a crushing blow to the faith of the citizens of the democratic community in their own security and inviolability. September 11, 2001 terrorist attack claimed the lives of 2 thousand 752 people
The most important signs of the work of demolition workers in the World Trade Center
The rapid and strictly vertical collapse of skyscrapers (this happens during the point mining of a building for demolition), despite the fact that the “twins” collapsed vertically, the third building was also completely razed to the ground - WTC # 7, which was not rammed by aircraft, all structures were destroyed almost " crumbled” (this effect is achieved only with professional explosive dismantling), experts heard on the recordings the sounds of several explosions seconds before the collapse, which came from the first floors, filmed on many amateur videos, wisps of smoke and flashes almost forty floors below the level where the planes crashed , numerous fragments of glass, steel and human remains found in a very large radius, including on the roofs of houses, many vertical load-bearing beams were diagonally cut (this preparatory procedure is also typical for dismantling), the remains of burning Thermate, a substance commonly used for military purposes for thermal cutting of steel (discovered at the site of fished by independent experts), numerous traces of steel supporting structures melted to a lava-like state. The burning continued even on the fifth or sixth day and was recorded on NASA aerial photographs (aircraft kerosene is not capable of creating such high temperatures - a minimum of 1500oC is required!).
The names of specialists who disagree with the official version of the White House are impressive - leading scientists in the field of history, defense, psychology, philosophy and applied sciences. The conducted studies confirm the opinion that the World Trade Center buildings in New York were destroyed by controlled explosions, and the version of the authorities about the Pentagon attack does not stand up to scrutiny. Scientists are convinced that the government not only allowed the September 11 attacks, but staged them for political purposes. 
The names of people who made sensational accusations are striking:
Robert M. Bowman - Former Project Manager for Star Wars, USAF Space Defense Program (101 sorties).
Fred Burks is an interpreter for many American presidents and people familiar with American political cuisine firsthand.
Lloyd de Moos is director of the Institute for Psychohistory, president of the International Psychohistorical Association, and editor of the Journal of Psychohistory.
Eric Douglas - New York architect, chairman of an independent commission of the committee to review projects for the restoration of the World Trade Center.
James Fetzer is a renowned scientist, professor at McKnight University (Minnesota), former US Marine Corps officer, author and editor of more than 20 academic publications, co-founder of the S9 / 11T group.
Robert Fritzius is an electronic engineer, radar and telecommunications specialist.
Daniel Ganser - historian, representative of the University of Basel (Switzerland).
Michael Gass - explosives specialist (US Air Force), sapper, author of the development of demining techniques.
Kenyon Gibson is a former naval intelligence officer and the author of a number of books on the events of 9/11.
Rich Hellner - air traffic control, dispatcher.
Don Jacobs is a former Dean of the School of Education and Professor of Education at Northern Arizona University.
Andrew Johnson is a physicist, computer scientist, and software developer.
Stephen Jones is a professor of physics, co-founder of the S9/11T group, and creator of the website.
Peter Kirsch is a renowned pathologist.
Wayne Madsen is an investigative journalist and former intelligence officer.
Richard McGinn is Professor of Linguistics, Ohio University.
Morgan Reynolds is an economics professor, chief economist for the Department of Labor during the George W. Bush administration, and director of the National Center for Policy Analysis' Criminal Justice Center.
E. Martin Shotz - historian, psychiatrist, mathematician.
Glenn Stanish - pilot, head of the Airline Pilots Association.
Andreas von Bülow - ex-deputy foreign minister of Germany, head of the German intelligence services, member of parliament for 25 years.
Jonathan Wilson - Criminologist, University of Winnipeg (Canada).
This is far from full list, which allows you to get an idea of the level of professionalism of the people who made accusations against the American government. What gives them the right to question the official version of the White House? The answer to this question can be found on the website www.st911.org where 20 reasons for distrusting President Bush are published.
The commission of inquiry into the events of September 11 refused to study a huge number of testimonies and evidence. Even the former director of the FBI said that the mentioned commission hushed up the real events.
The recording of the interrogations of dispatchers who were on duty on September 11 was deliberately destroyed - the cassettes were broken by hand, the film was torn into small fragments, and its fragments were thrown into various bins.
Congressional investigators found that an FBI informant provided housing for two plane hijackers in 2000. When the commission wanted to interrogate this citizen, the FBI not only refused to comply with this request, but also hid the informant. According to some reports, the FBI took such steps after receiving appropriate instructions from the White House.
A retired U.S. Air Force lieutenant colonel and former Star Wars Project Manager recently issued the following statement: “If our government had done nothing that day, only enforced the normal procedure for such cases, the Twin Towers would have stood still and thousands of dead Americans would be alive. Our government's actions are treason!" 
Recently declassified documents show that in the 1960s the US High Command developed a plan to blow up US aircraft and carry out terrorist acts against US citizens on American soil.
The US Defense Department, which is responsible for the safety of citizens, has been conducting exercises for many years, practicing the version of using kamikaze aircraft against the buildings of the World Trade Center and other American skyscrapers. "Various types of civil and military aircraft were used in the course of practicing actions in case of a possible terrorist attack. In other words, the Pentagon used REAL-EXISTING AIRCRAFT to simulate an attack on high-rise buildings, including the twin towers. Why did the department "turn out to be unprepared" - remains a question.
In addition, the military worked out options for similar attacks on the Pentagon.
On the morning of 9/11, US defense and intelligence agencies were conducting counter-terrorism military exercises using REAL planes and fake "radar tags" to mislead air traffic controllers.
It was on the morning of September 11 that the government carried out maneuvers simulating an air attack by terrorists on the World Trade Center.
Despite government claims of ignorance of the terrorist aircraft, the US Secretary of Transportation, testifying to the commission, claimed that Vice President Cheney personally monitored the pilots of the ill-fated Flight 77 many miles before the vehicle approached the Pentagon.
The third building of the World Trade Center (structure number 7) collapsed on September 11, despite the fact that it was not hit by terrorist aircraft. It collapsed as if it had no walls or ceilings. Before the tragedy, only small local fires were noted in the building. It is the only steel frame building in the world to be destroyed by fire, which by definition cannot happen.
According to a number of FBI officials, the WTC buildings collapsed as a result of the explosion of bombs planted inside it.
Broadcaster MSNBC claims that police officers believed that one of the explosions at the World Trade Center could have been triggered by a truck filled with explosives and located inside the building. In their opinion, explosive devices could be placed both in the building itself and in its immediate vicinity.
According to the New York City Fire Department's security chief, the explosions could have been caused by "bombs" and "secondary devices." Firefighters believe there were bombs in the building.
According to a spokesman for the National Demolition Association, the collapse of the twin towers resembled "a classically planned demolition of a building."
Eyewitnesses of the explosion claim that the explosions occurred much BELOW the area hit by the planes. Moreover, they happened BEFORE the first plane crashed into the building.
According to the testimony of a certain police officer, devastating explosions on the upper floors occurred at intervals of 15 minutes. The building collapsed after that.
The scientists managed to collect and systematize dozens of facts that were "ignored" by the authorities, distorted their essence or (which is especially scary) did not find a place on the pages of official reports. Every aspect of the official version is questionable by an inquisitive and literate reader who wants to know the truth about what happened.
Attack or controlled bombing? 
According to representatives of science, "fire (fire) could not lead to the destruction of the steel structures of the building." Supporters of the official (government) version of the tragic events hush up this fact. Moreover, according to a report signed by the Directorate of the National Institute of Standards and Technology (2005), the steel structures of the buildings collapsed allegedly as a result of fires. At the same time, no such fact is known to science.
Interestingly, the turrets were designed with aerial attack in mind and were built with a design strength to withstand a collision with such a colossus as the Boeing 767.
"They were designed to withstand all sorts of impacts, including tornadoes, bombings or collisions with huge airliners," says Hyman Brown, Project Manager for the construction of the Twin Towers (2001).
The theory about the destruction of the building as a result of a fire and the melting of load-bearing steel structures is also absurd. According to experts, the destruction of skyscrapers resembles a "controlled detonation" when a certain amount of explosives is placed in the supporting structures and fires in the right sequence.
In the course of a controlled detonation, the destruction of the building occurs suddenly - at first there is nothing, but the next moment the structure falls apart. The steel structure at high temperature cannot suddenly break. This happens gradually - horizontal beams begin to sag, and then vertical steel columns are deformed.
But the video filming, which captured the destruction of the towers, did not record such processes even on the floors located above the hole left by the aircraft. In addition, the art of controlled detonation of a high-rise building is to ensure that the exploded skyscraper does not scatter in all directions, but "sags" in such a way that the debris remains exclusively at the site of construction. This is what happened with the towers.
According to Marc Loisier, president of the largest controlled demolition company, such an explosion "must be completely planned, and the explosives must be placed in a certain order." All 110 floors of the twin towers collapsed very neatly. In an unplanned explosion, construction debris would have covered the entire area, but this did not happen.
In a controlled detonation, the remains of a building descend to the surface at the speed of free fall, which does not happen in a random catastrophe. To do this, demolitionists first lay explosives under the support systems of the lower floors, so the upper ones go down, practically without encountering resistance.
According to the commission's report, the south tower collapsed in 10 seconds, which corresponds to a controlled detonation. Moreover, this technique allows you to "cut" the supporting steel structures into pieces of a certain length, which was recorded in New York. The huge dust cloud that formed at the site of the towers after the explosion also serves as circumstantial evidence of a controlled explosion. Colonel of the US Corps of Engineers John O'Dowd came to this conclusion. "It seemed that the air at the site of the WTC explosion was saturated with cement dust."
Another proof of a planned explosion is a huge amount of molten steel at the site of the collapse of the towers. So, Peter Tully, the head of the construction company Tully Construction, and Mark Loisier reported on "lakes of molten steel" found at the site of collapsed buildings, in underground elevator shafts. Meanwhile, the collision of an aircraft with a building and the subsequent ignition of aviation fuel could not lead to the formation of temperatures at which steel structures begin to melt. The mystery of the explosion of the twin towers, according to scientists, still remains unsolved. But what about the government? It is inactive, refusing to divulge information that contradicts the official theory.
Shortly after the events of 9/11, over 500 New York City fire and emergency personnel gave oral testimony, in one way or another pointing to some of the inconsistencies noted during the aftermath of the terrorist attack. The City of New York has done everything to keep these facts from being publicized or denied.
It was not until August 2005 that The New York Times and a group of relatives of the victims succeeded, after a lengthy trial and a series of appeals, in forcing the mayor's office to publish the above-mentioned testimonies of direct witnesses to the destruction of the World Trade Center.
The words of the witnesses refute government theories, proving that the events of 9/11 are a well-planned act of intimidation.
Unfortunately, American officials are unwilling to conduct an independent investigation, establish the truth and punish those responsible. Why is this happening? To whom and why is it beneficial? These questions remain unanswered for the time being, but the public is not satisfied with the Bush administration's position, and the S9/11T group does not intend to stop its activities. Soon we will have new details that reveal the essence of these tragic events and the hypocrisy of officials. If the claims of American scientists turn out to be true, "controlled undermining" may well lead to an uncontrolled reaction of society - not only American, but also world. And then the authors of the largest hoax in the history of mankind may not be in trouble, writes Konstantin VASILKEVICH
THE BEHAVIOR OF THE US SPECIAL SERVICES INDISPUTABLE PROVES THAT THE SEPTEMBER 11 Terror Attacks in the USA IS THEIR WORK.
In their haste to blame the Muslims for this, in their haste to strike at Afghanistan, they made the investigation against the special services themselves impossible.
“The US government announced the creation of a new structure in the system of its special services (numbering 170,000 people with an annual budget of 37 billion dollars), designed to coordinate the efforts of various departments, as well as for the extrajudicial physical destruction of terrorists around the world, that is, to kill people, objectionable to the "world behind the scenes" (the CIA used to hide such operations, now it does not need it: it is enough to declare someone a "terrorist"). This was a new step in global war"against terrorism", declared after the terrorist attacks of September 11, 2001, which untied the US hands for the forceful subjugation of the entire planet. Even then, in many democratic countries laws were passed to facilitate surveillance, preventive arrests, wiretapping, the abolition of the secrecy of bank deposits; measures of political censorship were introduced in the democratic media, up to the closure of sites on the Internet that "spread hate propaganda". That is, the extrajudicial repressions of the special services against their own citizens were significantly expanded.” "TOMORROW", N30, 2002"
The BUSH administration used the Boeing attack as an excuse to invade Iraq and Afghanistan in order to realize its dream of world hegemony under the banner of fighting terrorism.
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