New World Trade Center in New York. A memorial park was built on the site of the Twin Towers

Before September 11, 2001, the World Trade Center consisted of seven buildings. The World Trade Center was built in New York in 1973 according to the architectural ideas of Minoru Yamasaki. The impressive center of the complex is two skyscrapers, each with 110 floors - the South (415 m high) and the North (417 m).

At the time of completion of construction, they ranked first in height in the world. For almost three decades, the twin towers towered over Manhattan, symbolizing the financial power of the United States, but on September 11, 2001, attacks by fanatical terrorists caused the destruction of the skyscrapers.

The North Tower was rammed by a plane hijacked by a group of terrorists at 8:46 a.m., the destructive impact hitting the north side of the building between the 93rd and 99th floors. A strong fire broke out, cutting off the exit routes for the people above. After 102 minutes of burning, the skyscraper collapsed. The second plane struck the South Tower 17 minutes after the previous attack, striking between the 77th and 85th floors. The plane collided with the building in a space closer to the corner, so one stairwell remained intact - this helped many people escape.

The structures of the South Tower were severely damaged by fire and collision, so it collapsed 29 minutes before the North. Flying debris from the twin towers and the resulting fire caused the collapse of another building of the complex, WTC-7, at 17:20. The remaining four buildings were so badly damaged that the decision was made to demolish them. As a result of the terrorist attack, 2,752 people died, including crews and passengers of planes hijacked by terrorists.

Documentary video: see how it really happened.

After the disaster, a museum and a National Memorial were built at the site of the World Trade Center crash, which are two square pools on the site of the destroyed twin towers. Another World Trade Center is being built around the memorial, the center of which will be the new Freedom Tower. The height of the building together with the spire reaches 541 m - it will be the third tallest in the world and the first in the Western Hemisphere. Architects report that the Freedom Tower is a very reliable skyscraper: its foundation is reinforced with steel beams, and the first floors are built as a reinforced concrete base without windows.

This is what the Tribute in Light memorial looked like from the outside, September 6, 2011. (Photo by Mark Lennihan | AP). Two columns of light, each 1500 m high, shoot from the very place where the World Trade Center towers stood.

2 swimming pools located exactly on the site of the former “twin towers”. The underground museum is located directly below the memorial.

I was afraid to interfere. But some time passed, and this weekend we decided to check out the view from the new skyscraper.

I'll tell you about this observation deck, how to get there, and what you can see from it...

Construction of the tower began to be planned in 2001, shortly after the September 11 attacks, when the previous twin towers were destroyed. But the architects and the city competed for a long time with different projects, and as a result, the stand stood idle for many years. Construction began in earnest only in 2006. Then it was called the Freedom Tower. By the time it was completed last year, the patriotic fervor had waned, and it eventually received its current name, which simply duplicates its address: One World Trade Center.

It is quite difficult to look at the tower from below - your neck immediately begins to hurt. The building is 540 meters high and has 104 floors.

Right next door is a park where there is a memorial to the fallen twins and the people who died there. Behind the park stands a nearly completed transport hub designed by Santiago Calatrava, a Spanish architect known for his futuristic buildings. Many of them resemble skeletons of fantastic animals.

In the early 2000s, Calatrava built the City of Arts and Sciences in Valencia - one of my Top 10 places in the world. The construction of the WTC transport hub has already dragged on for 6 years longer than planned, and has cost twice as much as the original estimates (today the price is about $4 billion). ( .)

The memorial to the twins is very beautiful - it is made in the form of two fountains, which are gaping holes in the ground, exactly in the places where the towers stood until 2001. Water falls from the black stone walls, as if into an abyss. The names of people who died in the terrorist attack are carved on these stones.

The fountains are designed in such a way that standing next to them it is impossible to see their bottom.

Tickets to the observation deck currently cost $32 and are sold for a specific time. You can buy them in advance, via the Internet (), or at the entrance, standing in another line. The time on the ticket does not guarantee admission immediately - after your time is up, you will be allowed to stand in line outside.

And then another one inside. True, you can skip both of these lines by purchasing a VIP ticket for $54. Now that the rush has died down, these lines are not as long and move quickly, so decide whether you should spend the extra money to avoid the lines.

By the way, if you are a little late for the agreed time, the ticket can still be used. We bought at 3:15 and arrived around 3:40 without any issues.

At the entrance they check like at the airport - there is an X-ray for things, and a metal detector for visitors. There is even a machine in which you have to raise your arms up, but so far it has not been used. They force you to take everything out of your pockets - they take security seriously here.

A visit to the skyscraper begins with the elevator. They wrote about him a lot. Climbing one hundred floors takes less than a minute. At this time, the elevator shows passengers a mini-show about the history of New York on its wall monitors.

You can watch the elevator show

Once upstairs, you will be made to wait a few minutes, and then you will be taken into a small theater where they will show a mini-presentation. It seems like they decided to add a little interactivity to justify the high ticket price.

The performance consists of many pieces of New York life that are projected onto a relief wall. To accomplish this, a small theater has a ton of healthy projectors.

There's a mini surprise waiting for you at the end of this show, I won't spoil it.

We decided that we could do without him.

Right before the start of the beauty there are the next scammers of tourists. These offer to take a souvenir photo of you against the backdrop of skyscrapers. True, for some reason the skyscrapers are drawn on the big screen. Moreover, they use some special cameras, which, when you press a button, turn on for a second on all these monitors green color(to make it easier to photoshop different types later).

This photoshopography immediately reminded me of Chinese photographers who took similar pictures for tourists.

These various Special offers for tourists they occupy the entire hundred and first floor. The main part of the observation deck is located on the hundredth - there the entire perimeter space is open to visitors and it is easier to enjoy the views. By the way, the design of the site, and indeed all the interiors of the new skyscraper, are not very impressive. Typical modern glass and steel, most of the walls are plain white and the ceilings are hung low, reminiscent of your average office. They could at least come up with something better for the observation deck.

I don’t know if this was on purpose, but the first view that greeted us was the Stout of Liberty. There are surprisingly many different boats floating around it - the water is lined with white traces.

Here's a view of the west side of Manhattan. There is a wide, not too tall building on the right - this is my work. (You can read about it today from Varlamov)

Like any self-respecting skyscraper, there is a glass floor attraction.

But since there are no elements hanging over the abyss in this tower, the glass floor has to be simulated using LCD monitors. The effect is not at all the same, it turns out not scary. It’s a little awkward except to feel like you’re walking on TV with your feet.

On the main floor there are two stations like this, where city experts tell visitors stories about New York. While the narrator waves his hands, the picture on the screens changes in a circle. Then they invite visitors to point somewhere on the city map and tell them about this place.

At this height, the initially wide facades of the building converged into these narrow corner sections:

The view of the city is certainly stunning. For example, the financial district of lower Manhattan and Governor's Island.

Here are my favorite New York bridges. Next to the Brooklyn is the shamefully flat backside of Frank Gehry's apartment building. And the carousel in Dumbo is clearly visible, and “the ugliest building in New York” (a concrete block of Verizon).

There is a cafe-bar on the one hundred and first floor. If you're lucky, you can grab a table near the window, drink overly expensive drinks and enjoy the view...

The quality of service here is of course disgusting - we waited about twenty minutes for someone to come up and take our order. However, the impression was that the service corresponds to the quality of the food.

There is also a bar where you can use your mobile phone while at a great height.

But let's look through the windows again - this is what we came here for...

Here's a view of Midtown. The triumphal arch that stands in Washington Square Park is located here. Will you find it?..

Or for example Brooklyn Heights and downtown Brooklyn. A rather boring sight, a bit like Sim City.

But these brown matchboxes in the center are Stu-town, a town of the same type of housing. I have a couple of friends living there. I wonder if they saw me when I took this photo?.. I waved at them just in case.

Very colorful roofs of houses. They are not visible from the street, and owners often do what they want with them. And they want a lot of things.

Unique perspectives open up from above. Here is an example of a view of the Calatrava transit hub:

Or here - one of the fountains of the Twin Towers Memorial.

After five o'clock in the afternoon the crowd noticeably increases - we were there on Friday, and people probably come here after work. It becomes difficult to photograph anything without letting unnecessary people into the frame. And walk without getting into someone else’s frame.

Sometimes guards with a dog walk along the observation deck, and the dog tries to sniff out explosives from someone. Seeing the dog, I immediately felt very anxious - it serves as a reminder: “a terrorist attack could happen here.” But it quickly passed.

It's time to leave - the exit here, as always, is through the souvenir shop.

On the floor there is a very cool display of cute binoculars, but unfortunately they are not sold in the store, but rather a standard assortment of cups, T-shirts, pens and other similar crap.

When you find where the real exit is, it turns out that you have to stand in line to get into it. A VIP ticket will not help here; it only allows you to skip the entry lines.

Finally, look at another view of the southernmost tip of Manhattan:

While riding down in the elevator, its walls show another show. But it’s not as good as what’s playing on the way up, and in general, you don’t care about it anymore, because at this time your ears are stuffing up wildly...

Twin Towers: History, Pride and Tragedy of America

Buildings, like people, have something in common. Some live simple lives unnoticed by most and, when they die, remain in the memory of only their closest relatives. Others are visible, admired or hated; at least many people know them. When they die, they remain part of history, living in the minds of millions, even after passing into eternity, influencing the living.

It was the second option that fate chose for the famous skyscrapers, the Twin Towers in New York. Blown up as a result of the terrorist attack on September 11, 2001, these buildings seem to continue to exist: everyone knows them, remembers them, they continue to be replicated in thousands of photographs. In the end, they still subtly influence the life of a huge metropolis, and the United States as a whole.

Construction of the Twin Towers

It's easy to build, difficult to negotiate. Any building in the world, even a country house, is born not on a construction site, but in the minds of its creators. The World Trade Center in New York was no exception, the architectural and visual dominance of which were two skyscrapers, immediately called towers: North and South.

The idea of ​​​​building a grandiose complex was born in the USA during the Second World War. By 1944, it became clear that as a result, there was only one state left in the Western world that managed not only to maintain its economic power, but to significantly strengthen it, especially against the backdrop of destroyed Europe and Japan. America became this state. It did not take much intelligence to understand the simple truth: in the coming decades the country will become a superpower and will develop rapidly. And it will need a large financial and trading complex.

But a lot of time passed before the idea began to turn into reality. There were two main reasons.

The first is the inflamed arms race and the Cold War, which required colossal financial investments.

The second is a clash of economic interests of several influential US groups, as well as two states, New Jersey and New York. In addition, the construction of the Center assumed the emergence of new skyscrapers that would exceed the height of the Empire State Building, the pride of the city, the tallest building in the world. The financial groups that controlled this building were not at all eager for the emergence of a formidable competitor.

And only by the beginning of the 60s were all commercial, image and financial issues managed to be settled. The Rockefeller brothers, David and Nelson, played a significant role in this. Using their influence, connections and money, the brothers began to build the World Trade Center in Lower Manhattan.

The entire complex, including the twin towers, was designed by several powerful design companies, but Japanese-American Minoru Yamasaki was chosen as the lead architect, the father of the project.

Before starting work on this project, Yamasaki completed several serious works in different cities of the United States, although he was not one of the most venerable professionals in the country. A proponent of Gothic modernism, strongly influenced by the architecture of Le Corbusier, the Japanese drew attention to the small ancient twin towers in the Italian town of San Gimignano, taking them as a model for his task.

And the master’s task was simple: to create something that would have 5 times more office space than the Empire State Building. After going through several possible options, Yamasaki came to the final one: two slender towers with a square cross-section, shaped like parallelepipeds.

The entire construction process can be divided into the following stages:

• design: 1962 - 1965;
• cleaning and preparing the area for construction - from March to August 1966;
• August 1966 - start of excavation work, excavation of soil for the base of the towers;
• installation of the last load-bearing element of the buildings - December 1970 (North Tower), July 1971 (South Tower);
• grand opening of the complex - April 4, 1974.

At the end of construction, the towers turned out to be the tallest buildings in the world, each with 110 floors. The upper elevation of the South was 415 meters, the North was 2 meters higher, and it was also decorated with an antenna with an elevation of 526.3 meters.

Among other things, the appearance of the towers launched a real race of skyscrapers that began in the world. Looking ahead a little, we can say that on the site of the fallen “candles” the Americans built a new World Trade Center, which is crowned by the tallest building in the Western Hemisphere. However, now it is only the fourth in a cohort of giant buildings.

The unusual face of the Twin Towers

Continuing the analogy we started, we can say that, like people, outstanding buildings also have their own records and unique life events. They are also available at the Yamasaki Towers. Here are some of them:

• During the construction of the buildings, deep 20-meter pits were dug to get to the “bedrock” rock. The earth from the excavations was used for an artificial embankment, on which several buildings of the World Financial Center were subsequently built.
• The design of the towers is based on hundreds of large and small steel pipes, creating a special frame that is resistant to wind and seismic vibrations.
• The façade of the buildings is replete with a huge number of narrow windows, only 56 cm wide. Yamasaki suffered from a fear of heights, and designed the windows so that any person, approaching the window sill, could easily rest against the slopes of the window opening, which would create a special feeling of reliability.

• Each of the towers had 103 elevators, of which 6 were freight. Some passenger elevators were high-speed, some were ordinary. For the transition from the first to the second, platforms on the 44th and 78th floors were used.
• Immediately after the construction of the towers, they received derogatory criticism from the world's leading architects. The city residents didn’t really like the buildings either. But gradually they got used to them and even began to be proud of them. The Eiffel Tower in Paris had approximately the same fate.
• The first attempt to destroy the buildings was made in 1993. Then, in the garage of the North Tower, underground, a truck with more than half a ton of explosives was blown up.

In the end, the terrorists managed to blow up unusual buildings. But, having destroyed them, did they destroy the very idea, the desire of man to conquer, to create something unusual? After all, it is inherent in human nature itself.

And, perhaps, the daring Frenchman Philippe Petit said this very well, who in August 1974 managed to walk 8 times in a row (!) on a rope stretched between two towers, while dancing and even lying down: “Lying on the rope, I saw very close above you is a seagull. And I remembered the myth of Prometheus. Here, at this height, I invaded her space, proving that a person can be compared with a bird ... "

Finite element model of the World Trade Center floor to evaluate the building's structural system

The dimensions of the structure in plan are 63.4x63.4 m, the rigidity cores are 26.8x42.1 m. The WTC towers were designed as a “pipe-in-pipe” (stem structural design) in order to create a continuous space on the floors, not divided 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 (stiffness 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 staircases passed through the rigidity core, leaving large free space between the core and the perimeter of the tower to accommodate offices.

The floor structure consisted of 10 cm of lightweight concrete laid on permanent formwork made of profiled decking. The corrugated sheeting was laid on secondary (auxiliary) trusses (beams), supported by the main trusses, transmitting 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 lintels connecting the peripheral columns at the level of each floor, and from the inside to the central columns. The floor was secured through elastic dampers designed to reduce the impact of building vibrations on the people working in it.

This truss system allowed optimized load redistribution of the floor diaphragms between the perimeter and core with improved performance between various materials flexible steel and rigid concrete allowing the moment structure to transfer influence into compression on the core, which also mainly supported the transmission tower.

The towers also included an "outrigger 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 increase the overall stability of the building, and also to support the antenna spire, which was installed on only one of the towers. NIST found that this design played a role key role in the sequence of events leading to the complete destruction of the towers.

Possibility of resisting fire and aircraft hits

Like all modern high-rise buildings, the WTC towers were designed and built to withstand a normal fire. Many fire safety features were incorporated during the design and construction phase, and others were added after a 1975 fire that consumed six floors before being contained and extinguished. Tests carried out before the disaster showed that the steel structures of the towers met or even exceeded current fire resistance requirements.

The structural engineers who designed the World Trade Center considered the possibility that a plane could collide 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 the skyscraper at 40 Wall Street, and another plane came close to another collision with the Empire State Building.

NIST stated that “American Building Standards do not include requirements for the stability of buildings when struck by an aircraft. … and thus buildings are not designed to withstand the impact of a fully fueled commercial airliner.” , nevertheless, the designers and architects of the World Trade Center discussed this problem and recognized its importance. Leslie Robertson, one of the chief engineers of the World Trade Center, recalled that the scenario considered was that a Boeing 707 jet would hit the building, 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 carried out an analysis that showed that the biggest problem if the WTC towers collided with a Boeing 707 would be that all the plane's fuel would end up inside the building and lead to a "terrible fire." and many casualties, but the building itself will remain standing. FEMA wrote that the World Trade Center buildings were built to withstand a collision with a Boeing 707 jet airliner, which weighs 119 tons and has a speed of about 290 km/h, much less in weight and speed than the aircraft used in the September 11 attacks.

NIST found in the archives a three-page report summarizing research 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 NIST experts noted, “the 1964 study did not model the effect of a fire caused by jet fuel spraying into a building.” NIST also noted that in the absence of initial calculations used to model the situation, further comment on this topic would be largely “speculation.” Another document found by NIST was a calculation of the period of oscillation of a building if a plane were to hit the 80th floor of the World Trade Center tower, but it made no assumptions about the fate of the building after the impact. A property risk assessment report prepared for Silverstain Properties considered the possibility of an aircraft hitting the World Trade Center towers as unlikely but possible. The report's authors cited WTC structural engineers who said the towers should have withstood a collision with a large passenger plane, but burning fuel flowing from the plane to ground level would have damaged the building's skin. Some documents related to the analysis of the scenario of an aircraft hitting the towers were 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 flew two Boeing 767 jet airliners, 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, and carries on board from 62 tons (-200) to 91 tons (-200ER) of aviation fuel. The planes crashed into the towers at very high speed. Flight 11 was traveling at approximately 700 km/h when it struck the north tower; Flight 175 crashed into Southern at a speed of about 870 km/h. In addition to the fact that the hits caused severe damage to the supporting columns, they caused the explosion of approximately 38 tons of aviation fuel in each tower, which led to the almost immediate spread of a large fire on several floors containing office furniture, paper, carpeting, books, and other flammable materials. The shock wave from hitting the north tower spread down to the first floor, along at least one high-speed elevator shaft, and broke glass on the first floor, causing injuries to several people.

Fire

The lightweight design of the towers and the absence of solid walls and ceilings led to the fact that aviation fuel spread in a sufficiently wide range. large volume buildings, leading to multiple fires on several floors close to the aircraft's impact areas. The aviation fuel itself burned out within a few minutes, but the combustible materials in the building itself kept the fires burning intensely for another hour or an hour and a half. It is possible that if more traditional structures had been in the path of the aircraft, the fires would not have been so centralized and intense - aircraft debris and aviation fuel could have remained primarily in the peripheral area of ​​the building, rather than penetrating directly to its central part. In this case, the towers would probably have survived, or in any case, would have stood significantly longer.

Development of the situation

• 9:52 - A 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 helicopter reports that the south tower is falling.

Helicopters also reported the development of the situation with the north tower of the World Trade Center.

• 10:20 - Fire Department helicopter reports that the upper floors of the north tower may be unstable.

• 10:21 - it is reported that the south-eastern 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 north tower may collapse at any minute.

• 10:28 am - The fire department receives a report that the north tower has collapsed.

Overloaded dispatchers and poor communications meant that New York City's fire and police departments were having trouble communicating in a timely manner, both with their departments and with each other. As a result, the fire brigades located in the towers did not receive orders to evacuate and 343 firefighters died when the buildings collapsed.

WTC towers collapse

The south tower collapsed at 9:59 a.m., 56 minutes after impact. The north tower stood until 10:28, 102 minutes after the plane 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 onto the lower floors. Both towers fell almost vertically, although there was a significant deviation from the vertical of the top of the south 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 found that because the planes hit the towers in different ways, the process of destruction of the north and south towers was also slightly different, although it was generally the same in both cases. After being hit by the planes, the internal power columns were seriously damaged, although the external columns suffered relatively little damage. This caused a serious redistribution of the load between them. The upper power structure of the towers played a significant role in this redistribution.

Aircraft that struck buildings stripped fire-resistant coatings from large portions of steel structures, exposing them to direct fire. In the 102 minutes preceding the collapse of the north tower, the temperature of the fire, although well below the melting point of the metal, had reached a sufficient magnitude to cause the weakening of the strength columns in the center of the building, which began to deform and bend under the weight of the upper floors. The NIST report describes this situation as follows:

A similar situation occurred 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 floors on the damaged floors to settle and placing significant stress on the peripheral columns towards the interior of the building.

At 9:59, 56 minutes after impact, the settling floor caused severe inward bending of the outer columns on the east side of the south tower, the upper load structure transferred this bending force to the central columns, causing them to collapse and begin the collapse of the building, the top of the tower in the process deviated towards the damaged wall. At 10:28 a.m., the south wall of the north tower buckled, causing approximately the same sequence of events. As a result of the subsequent collapse of the upper floors, the complete destruction of the towers became inevitable, due to huge weight that part of the buildings that were located above the damage zone.

The reason that the northern tower stood longer than the southern one was a combination of the following three factors: the area where the aircraft hit the northern tower was higher (and the weight of the upper part of the building, accordingly, less), the speed of the aircraft that hit the tower was lower, in addition, the aircraft hit floors whose fire protection has previously been partially improved.

The theory of complete progressive collapse

Ruins of the South Tower (right) and North Tower (left), as well as other World Trade Center buildings

A huge cloud of dust obscured the collapsing towers, making it impossible to determine the exact duration of the destruction based on visual evidence.

Because the NIST report focuses primarily on the mechanisms of the initial collapse, it does not address the subsequent complete collapse of both WTC towers. Initial tests the collapse was explained by the fact that the kinetic energy of the falling upper floors was much greater than what the interfloor ceilings could withstand, which also collapsed, adding kinetic energy to the falling building. This scenario was repeated with increasing speed until the towers were completely destroyed. Although this is the most widely accepted view among civil engineers, it has been criticized for not taking into account the resistance of the underlying structures, which should have slowed, or even stopped, the collapse of the towers.

7 WTC building collapse

FEMA's initial study was inconclusive, and the collapse of 7 WTC was not included in the final NIST report released in September 2005. Except for the letter published Metallurgical Journal, which suggested that the building's steel frame could have melted in a fire, no other studies of this issue have been scientific journals was not published. The 7 WTC crash was investigated separately from the 1 WTC and 2 WTC crashes, and in June 2004, NIST released a working report that contained several hypotheses about what happened. One hypothesis was the destruction of one of the building's critical support columns, caused by fire or large debris from falling towers, leading to "disproportionate collapse of the entire structure."

NIST diagram showing the bending of Column 79 (outlined in orange) that began the progressive collapse of the building.

The order of destruction of 7 WTC in the diagram from the 2004 NIST preliminary report. Column 79 is marked with a circle in the center of the red zone.

NIST's 7 WTC fall model. In the first part of the video, columns 81, 80 and 79 are depicted from left to right.

On November 20, 2008, NIST published the final report on the fall of 7 WTC. The NIST report cited fire as the main cause of destruction, along with a lack of water for firefighters and the automatic fire suppression system to fight the fire. NIST reconstructs the sequence of events as follows: At 10:28 a.m., debris from the falling 1 WTC caused damage to the nearby 7 WTC. Fires also broke out, likely from burning debris from 1 WTC. Firefighters immediately arrived at 7 WTC, 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 water supply system, destroyed as a result of the falls of towers 1 WTC and 2 WTC. New York City Fire Department ( English), fearing for the lives of firefighters in the event of the destruction of 7 WTC, at 14:30 he recalled the firefighters and stopped fighting 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 beams heated to approximately 400 °C around column 79 in the eastern part of the building in the area of ​​the 13-14th floor led to the failure of the fire-weakened floors adjacent to column 79 from the 13th to the 5th floor. The destruction of the floors deprived column 79 of horizontal support, and it began to bend, which was the immediate cause of the complete destruction of the building within a few seconds. The bending of column 79 led to the transfer of the load to columns 80 and 81, which also began to bend, as a result of which all the floors associated with these columns were destroyed up to the top of the building. The falling floors destroyed truss 2, which led to the fall of columns 77, 78 and 76. As a result of the increased load transferred from the bent columns, the falling of fragments of the floors from above, and the lack of horizontal support from the destroyed floors, all internal columns from east to west began to bend sequentially. Following this, in the area of ​​floors 7-14, the outer columns began to bend, to which the load was transferred from the lowered inner columns and the center, and all floors above the bent columns began to fall down as a single whole, which completed the final destruction of the building at 17:20.

Some authors criticized the city authorities' decision to locate the 7 WTC headquarters on the 23rd floor Office of Emergency Situations(English) Office of Emergency Management ). It was believed that this could have been a significant factor in the destruction of the building. Particularly noted was the placement of large diesel fuel tanks in the building, 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 Management was a contributing factor to the poor communication between various agencies and the loss of control over the situation. The main cause of the building's destruction was fire; damage from debris from the falling 1 WTC accelerated the fall of the building, but NIST calculations showed that 7 WTC would have collapsed from an uncontrolled fire alone.

Progress of investigations

First reaction

The destruction of the World Trade Center towers came as a surprise to construction engineers. “Before September 11,” the magazine wrote New Civil Engineer“We quite sincerely could not imagine that a structure of such a scale could suffer such a fate.” Although the damage from the aircraft was severe, it only affected a few floors of each building. The challenge for engineers was to figure out how such local damage caused the complete progressive collapse of three of the world's largest buildings. In an October 2001 BBC interview, English architect Bob Halvorson aptly predicted that there would be much "debate about whether the World Trade Center could have collapsed the way it did." A full analysis would include architectural and structural plans of the World Trade Center, witness testimony, videos of the destruction, debris survey data, etc. Underscoring the complexity of the task, Halvorson said the destruction of the World Trade Center towers is "far beyond the realm of normal experience."

Research credibility

Immediately after the disaster, there was a situation of uncertainty as to who had sufficient authority to conduct an official investigation. Contrary to the practice found in air crash investigations, clear procedures for investigating building collapses simply did not exist.

A short time after the disaster at the base Institute of Civil 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 Construction(English) American Institute of Steel Construction ), American Concrete Institute(English) American Concrete Institute ), National Fire Protection Association and Fire Protection Engineering Society(English) Society of Fire Protection Engineers ) . ASCE also invited the Federal Emergency Management Agency (FEMA) to join the work of this group, which later received joint ASCE-FEMA control. This investigation was subsequently criticized by American engineers and lawyers, however, the authority of the above-mentioned organizations was sufficient to conduct the investigation and to provide access to the disaster site for the group's experts. One of the most poignant aspects of the investigation was that clearing the disaster site actually led to the destruction of the remaining components of the building. Indeed, when NIST published its final report, it noted a “lack of physical evidence” as one of the main problems of the investigation. Only a fraction of a percent of the building's remains remained available for investigation after the clearance work was completed, with a total of 236 individual steel fragments recovered.

FEMA released its report in May 2002. Although NIST had already announced 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 to create a new group under 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 World Trade Center towers, called the "stack of pancakes" theory. pancake theory). This theory was defended by Thomas Iga and was 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 on the floor below, placing loads on its structure that it was not designed for. Some individual publications have proposed other sets of factors that caused the collapse of the towers, but overall this theory has been accepted by most.

Fires remained the main key factor in this theory. Thomas Iga, a professor of materials science at MIT, described the fires as "the most baffling part of the collapse of the World Trade Center towers." Although the fires were initially thought to have "melted" the steel structures, Iga stated that "the temperatures of the fires in the WTC towers were unusually high, but still certainly not sufficient to cause melting or severe softening of the steel." Aviation kerosene combustion typically results in extensive fires, but these fires do not have very high temperature. This led Iga, FEMA and other researchers to believe that there was a weak point, and this point was identified as the floor anchorage to the building's supporting structure. 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 fasteners 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, bending the columns inward.

At temperatures above 400-500 °C there is a sharp decrease in the tensile strength and plasticity limit (3-4 times), at 600 °C they are close to zero and load bearing capacity steel is running out.

NIST report

Organization of the study

As a result of mounting pressure from experts, construction industry leaders and family members following the release of the FEMA report, National Institute Standards and Technologies The Commerce Department's NIST conducted a three-year, $24 million investigation into the destruction and collapse of the World Trade Center towers. The research included a series of experiments, in addition, leading specialists 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

The NIST study's scope was limited to examining the "sequence of events from the moment the aircraft was hit until the collapse of each tower began" and also included "a small analysis of the structural behavior of the tower structure once the conditions for its failure had been reached and collapse was imminent." Like many other engineers working on this issue, NIST experts focused on aircraft hits on towers, simulating the effects of hits such as structural failure, fire spread, etc. in a very high degree of detail. NIST has developed several very high-detail models of various building components, such as floor-supporting lintels, and entire buildings have also been modeled, but at a lower level of detail. These models were static, or quasi-static, and included deformation simulations, but did not include simulations of the movement of structural elements after they were separated from each other. Thus, NIST models are useful for understanding why towers begin to collapse, but 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 the fires alone, even without taking into account the destructive effects of aircraft strikes, were enough to completely destroy the WTC towers. In their opinion, the design of the towers made them uniquely vulnerable to large fires covering several floors at once. When the NIST report was released, Barbara Lane and the English engineering company Arup criticized its conclusion that the destruction caused by aircraft hits was a necessary factor for the collapse of buildings .

Criticism

Some engineers have offered insight into how the towers collapse by developing animated collapse sequences based on dynamic computer models and comparing the resulting results with video footage of the disaster site. In October 2005, the magazine New Civil Engineer relative to a 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 to correct models of tower collapses and bring those models into full agreement with observed events.

Other buildings

Parts of the outer wall of the north tower opposite the remains of the 6 WTC building, which received very serious damage as a result of the fall of the north tower. In the upper right corner are the remains of the 7 WTC building.

On September 11, 2001, the entire World Trade Center complex and the small Greek Orthodox 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 disaster site

The huge pile of rubble at the World Trade Center site continued to burn and smolder for another three months, with attempts to control the fire unsuccessful until a significant amount of debris and debris had been removed. The clearance was a very large-scale operation, coordinated by the Department of Construction (DDC). A preliminary clearing plan was prepared on September 22 by Controlled Demolition Inc. (CDI) from Phoenix. Mark Lozo, president of CDI, particularly emphasized the importance of protecting the clay wall (or "bathtub") that protected the WTC foundation from being flooded by the waters of the Hudson. 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 cleared, the city government began reducing the involvement of police and firefighters in the cleanup as they searched for the remains of the dead, and shifted priorities to trash removal. This caused objections from firefighters. As of 2007, demolition of some of the buildings surrounding the WTC was ongoing, while construction of the WTC replacement, memorial complex, and Freedom Tower continued.

Controlled demolition versions

There is a theory that the WTC towers could have been destroyed as a result of a planned, controlled demolition, and not as a result of being hit by aircraft. 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 look for explosive residues of any kind in the debris 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 residue 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 explosive that could destroy Column 79 would produce a noise of 130-140 decibels at a distance of 1 km from 7 WTC, but such noise was not noticed by either sound recording equipment or witnesses. This theory has become a prominent part of most of all the "conspiracy theories" that arose as a result of the events of September 11.

Notes

1. Relatives gather at ground zero to mark 9/11, The Associated Press/MSNBC(September 9, 2007). Retrieved November 3, 2007.
2. 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.
3. Hamburger, Ronald, et al.(pdf). Federal Emergency Management Agency. Archived
4. 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.
5. Chapter 1 // . - NIST. - P. p. 6.
6. National Construction Safety Team Final Report on the Collapse of the World Trade Center Towers. - NIST.
7. Barrett, Devlin Steel type in WTC met standards, group says. The Boston Globe. Associated Press (2003). Retrieved May 2, 2006.
8. Glanz, James and Eric Lipton. The Height of Ambition (English) , The New York Times(8 September 2002).
9. Adam Long. PILOT LOST IN FOG; SCENE OF PLANE CRASH LAST NIGHT AIRPLANE CRASHES INTO SKYSCRAPER Ceiling Reduced by Fog, The New York Times(24 May 1946).
10. (pdf). NIST NCSTAR 1-1 Pages 70-71 Archived
11. Leslie E. Robertson. Reflections on the World Trade Center (English) // The Bridge. - National Academy of Engineering, 2002. - Vol. 32. - No. 1. Archived from the original on February 28, 2010.
12. Fahim Sadek. NIST NCSTAR 1-2. Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers. - NIST, September 2005. - pp. 3-5, 308.
13. Nalder, Eric. (English) The Seattle Times (27-02-1993).
14. Ronald Hamburger, et al. World Trade Center Building Performance Study. - Federal Emergency Management Agency. - P. 1-17.
15. 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.
16. 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.
17. 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.
18. Jane's All the World's Aircraft Boeing 767. Jane's (2001). Retrieved August 19, 2007.
19. Field, Andy A Look Inside a Radical New Theory of the WTC Collapse. Fire/Rescue News (2004). Retrieved July 28, 2006.
20. 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
21. Wilkinson, Tim World Trade Center - Some Engineering Aspects (2006). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
22. 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.
23. McKinsey Report - Emergency Medical Service response. FDNY/McKinsey & Company (August 9, 2002). Archived from the original on August 26, 2011. Retrieved July 12, 2007.
24. McKinsey Report - NYPD (August 19, 2002). (inaccessible link - story) Retrieved July 10, 2007.
25. NY Firefighters attack Giuliani. BBC News, July 12, 2007 http://news.bbc.co.uk/2/hi/americas/6294198.stm
26. 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.
27. Bažant, Zdeněk P.; Mathieu Verdure (March 2007). "Mechanics of Progressive Collapse: Learning from the 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.
28. 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.
29. Hayden, Peter WTC: This Is Their Story. Firehouse Magazine (April 2002). (inaccessible link - story)
30. 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.
31. Barnett, J.R.; R.R. Biederman, R.D. Sisson Jr. An Initial Microstructural Analysis of A36 Steel from WTC Building 7. Feature: Letter. The Journal of Materials (2001). Archived from the original on March 4, 2012. Retrieved May 12, 2006.
32. 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.
33. 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.
34. 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.
35. 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. - pp. 119-120.
36. 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.
37. Barrett Wayne Grand Illusion: The Untold Story of Rudy Giuliani and 9/11. - Harper Collins. - ISBN 0-06-053660-8
38. Replying to Giuliani
39. Oliver, Anthony Lasting lessons of WTC. New Civil Engineer (June 30, 2005). (inaccessible link - story) Retrieved July 28, 2006.
40. Whitehouse, David WTC collapse forces skyscraper rethink. BBC News (2001). Archived from the original on March 4, 2012. Retrieved July 28, 2006.
41. Snell, Jack. "The Proposed National Construction Safety Team Act." NIST Building and Fire Research Laboratory. 2002.
42. Experts Debate Future of the Skyscraper in Wake of Disaster, Engineering News-Record(September 24, 2001).
43. Glanz, James and Eric Lipton. “Nation Challenged: The Towers; Experts Urging Broader Inquiry In Towers" Fall". New York Times December 25,
44. Dwyer, Jim. "Investigating 9/11: An Unimaginable Calamity, Still Largely Unexamined." New York Times. September 11,
45. NIST. "NIST's Responsibilities Under the National Construction Safety Team Act"
46. Thomas Egar. The Collapse: An Engineer's Perspective. Nova (2002). (inaccessible link - story) Retrieved July 28, 2006.
47. 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.
48. Clifton, G. Charles Collapse of the World Trade Center Towers (pdf) (2002). (inaccessible link - story) Retrieved July 28, 2006.

On September 11, 2013, the United States pays tribute to the victims of the 2001 terrorist attack, when suicide bombers on two hijacked planes attacked the World Trade Center towers in New York and the Pentagon building in Washington, the third plane, the crew and passengers of which tried to neutralize the terrorists, crashed in Pennsylvania.

According to official data, 2977 people died. More than half were never identified. It took 9 months to clear the rubble. So many bone and tissue fragments were found at the site of the terrorist attack that the number of bodies may be much higher than the official one. Relatives of the victims complained that the remains could have been taken along with the garbage to a landfill.

Photographer Gulnara Samoilova witnessed the terrorist attack and took unique photographs.

The first thing the woman did was throw herself on the ground behind the nearest parked car. "The dust was very prickly. Darkness fell. I began to choke, thinking that I was buried alive. Then he called out to me unfamiliar voice: "Are you okay?" Only then did I realize that I had survived,” the woman recalls. And then she immediately took out the camera again, reloaded the film, changed the lens and started shooting.

"The dust was very prickly. Darkness set in. I began to choke, thinking I was buried alive" - ​​AP eyewitness

The site where the twin towers of the World Trade Center collapsed on the morning of September 11, 2001 takes on new shape only 12 years after the tragedy, but the development project, which includes five new skyscrapers, a 9/11 memorial and a museum, a transport terminal and a concert hall, is still has not yet been completed. This is what it looks like now:

For the second year in a row, politicians did not make speeches at the ceremony. The roll call of the names of the dead and the minutes of silence marking the timing of the tragedy are preserved in the memorial ritual of New York. In the evening, two giant rays of light will rise over the city, representing the destroyed twin towers. They will be visible from 50 kilometers away.

Since 2002, September 11 has been celebrated in the United States as Patriot's Day, and since 2009, the day has also become a national day of service and remembrance.