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e. An intelligence quotient ( IQ) is a total score derived from a set of standardised tests or subtests designed to assess human intelligence. [1] The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests at University of Breslau he advocated ...
Dwight D. Eisenhower. Dwight David Eisenhower ( / ˈaɪzənhaʊ.ər / EYE-zən-how-ər; born David Dwight Eisenhower; October 14, 1890 – March 28, 1969), nicknamed Ike, was an American military officer and statesman who served as the 34th president of the United States from 1953 to 1961. During World War II, he was Supreme Commander of the ...
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George Catlett Marshall Jr. GCB (31 December 1880 – 16 October 1959) was an American army officer and statesman. He rose through the United States Army to become Chief of Staff of the U.S. Army under Presidents Franklin D. Roosevelt and Harry S. Truman, then served as Secretary of State and Secretary of Defense under Truman.[3] Winston ...
- Background
- The Two Crashes
- Collapse of The Towers
- Building 7 Collapse
- Other Buildings
- Investigations
- Aftermath
- External Links
When they opened in 1973, the Twin Towers were the tallest buildings in the world. At the time of the attacks only the Petronas Towers in Kuala Lumpur, Malaysia and the Willis Tower (known then as the Sears Tower) in Chicago were taller. Built with a novel "framed tube" design that maximized interior space, the towers had a high strength-to-weight ...
Aircraft impacts and resultant fires
During the September 11 attacks, four teams of al-Qaeda terrorists hijacked four different jetliners. Two of these jetliners, American Airlines Flight 11 and United Airlines Flight 175, both Boeing 767s, were hijacked after takeoff from Boston's Logan International Airport. In its final moments, American Airlines Flight 11 flew south over Manhattan and crashed at roughly 440 mph (710 km/h) into the northern facade of the North Tower (WTC 1) at 8:46 a.m., hitting the 93rd through 99th floors....
Emergency response and evacuation
Almost all the deaths in the Twin Towers occurred in the zones above the points of aircraft impact. As the North Tower had been struck almost directly midway into the structure, the three main stairways (A, B, and C) in the tower core were all damaged or blocked by debris preventing escape to lower floors. In the South Tower, the impact was east of center to the central section of the tower and close to the southeast corner, resulting in stairway A in the northwest portion of the central core...
The destruction of the Twin Towers has been called "the most infamous paradigm" of progressive collapse. Each collapse began with the local failure of the vertical load-bearing components of the floors that were hit by the planes and progressed to encompass the whole of the structure. Structural components were severed, releasing gravitational ener...
As the North Tower collapsed, heavy debris hit 7 World Trade Center, causing damage to the south face of the building and starting fires that continued to burn throughout the afternoon. Structural damage occurred to the southwest corner between Floors 7 and 17 and on the south facade between Floor 44 and the roof; other possible structural damage i...
Many of the surrounding buildings were also either damaged or destroyed as the towers fell. 5 WTC endured a large fire and a partial collapse of its steel structure and was torn down. Other buildings destroyed include St. Nicholas Greek Orthodox Church, Marriott World Trade Center (Marriott Hotel 3 WTC), South Plaza (4 WTC), and U.S. Customs (6 WTC...
Initial opinions and analysis
In the immediate aftermath of the attacks, numerous structural engineers and experts spoke to the media, describing what they thought caused the towers to collapse. Abolhassan Astaneh-Asl, a structural engineering professor at the University of California at Berkeley, explained that the high temperatures in the fires weakened the steel beams and columns, causing them to become "soft and mushy", and eventually they were unable to support the structure above. Astaneh-Asl also suggested that the...
FEMA building performance study
FEMA suggested that fires in conjunction with damage resulting from the aircraft impacts were the key to the collapse of the towers. Thomas Eagar, Professor of Materials Engineering and Engineering Systems at MIT, described the fires as "the most misunderstood part of the WTC collapse". This is because the fires were originally said to have "melted" the floors and columns. Jet fuel is essentially kerosene and would have served mainly to ignite very large, but not unusually hot, hydrocarbon fi...
NIST report
After the FEMA report had been published, and following pressure from technical experts, industry leaders and families of victims, the Commerce Department's National Institute of Standards and Technology conducted a three-year, $16 million investigation into the structural failure and progressive collapse of several WTC complex structures. The study included in-house technical expertise, along with assistance from several outside private institutions, including the Structural Engineering Inst...
Cleanup
The cleanup was a massive operation coordinated by the City of New York Department of Design and Construction. On September 22, a preliminary cleanup plan was delivered by Controlled Demolition, Inc. (CDI) of Phoenix, Maryland. Costing hundreds of millions of dollars, it involved round-the-clock operations with many contractors and subcontractors. By early November, with a third of the debris removed, officials began to reduce the number of firefighters and police officers assigned to recover...
Health effects
The collapse of the World Trade Center produced enormous clouds of dust that covered Manhattan for days. On September 18, 2001, the United States Environmental Protection Agency (EPA) assured the public that the air in Manhattan was "safe to breathe". In 2003 the EPA's inspector general found that the agency did not at that time have sufficient data to make such a statement. Dust from the collapse seriously reduced air quality and is likely the cause of many respiratory illnesses in lower Man...
World Trade Center – Some Engineering Aspects Archived March 6, 2012, at the Wayback MachineEarly suggestion by University of Sydney engineering instructor about how the towers might have collapsed.129,000–226,000. On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki. The bombings killed between 129,000 and 226,000 people, most of whom were civilians, and remain the only use of nuclear weapons in an armed conflict. Japan surrendered to the Allies on 15 August, six days ...
Douglas MacArthur (26 January 1880 – 5 April 1964) was an American military leader who served as General of the Army for the United States, as well as a field marshal to the Philippine Army.He served with distinction in World War I, was Chief of Staff of the United States Army during the 1930s and played a prominent role in the Pacific theater during World War II.
