As we learned in October, the collapse of the WTC towers in New York City, Washington D.C., and Pennsylvania on September 11, 2001, was the first major terrorist attack on American soil.
The collapse of World Trade center building 5, the tallest structure in the United States, and the destruction of the Pentagon and the World Financial Center in the New York area followed shortly thereafter.
Since then, the world has watched in horror as more than 3,400 buildings, nearly 200 of which are under renovation or undergoing major alterations, have collapsed.
Here is a timeline of how these structures were constructed.
January 9, 2006 – The World Trade Centers collapses: A few weeks before the attacks, the National Institute of Standards and Technology (NIST) issued its final report on the collapse.
In it, NIST concluded that the Twin Towers had been designed to withstand an impact with approximately 1,600 tons of steel.
On January 10, 2006, the 9/11 Commission released a report that, among other things, concluded that, if the building had not collapsed, the impact would have knocked out power to a third of the city.
NIST said that the towers’ steel was stronger than the steel in the World Health Organization’s World Trade Organization Buildings Performance Test (WTOBT) in 2000.
The WTC buildings were built on 9/1/2002, according to NIST, which means they were constructed on January 1, 2002, the day of the attacks.
February 5, 2006: The World Economic Forum publishes a report on structural steel: The report found that “a single structural steel column from the World Economic Group building at 1 World Trade Plaza, New York, collapsed approximately 50 feet below the building’s centerline.”
In addition, the report found: the column had “a significant thickness of steel at the center of the column,” which “was about 1/2 inch in thickness, with a thickness of 2 inches at its lowest point.”
It also found that the “structural strength of the steel was approximately equivalent to that of steel reinforced with a single-beam steel shear wall.”
The steel had a “strength coefficient” of 1.1.
On February 7, 2006 at about 6:40 p.m., the column “collapsed approximately 50-feet below the World Towers centerline and the column itself dropped approximately 5-feet.”
A second, smaller column, at a height of about 10 feet, was also destroyed.
The tower that was the “largest structure in our nation’s history” collapsed about 20 feet below its original floor.
February 15, 2006 : The World Financial Centers collapses (all): The collapse was witnessed by millions of people, but it was the World Center Towers collapse that really got people’s attention.
On March 8, the World Business Times, an American publication that is owned by Thomson Reuters, reported that the World Banking Center Towers in Frankfurt and New York were also “at the top of the list for collapse.”
At 6:10 p.ms., the World Bank Towers “collapse approximately 50 yards from the core of the South Tower.”
The South Tower, the most heavily damaged structure in New Jersey, was “at approximately 1/10 of the height of the towers.”
March 16, 2006 — The World Business Journals reports that “two steel columns that were attached to the World Building, which had been in use for several years, collapsed at the World Tower’s center.”
The collapse happened just two hours after the World Forum held its final conference call.
“We have a strong belief that the collapse was caused by a controlled demolition,” said Thomas A. Riggs, president and CEO of the National Association of Realtors (NAR).
“The collapse was due to a demolition process that started with the demolition of the tower in the late afternoon.”
On March 20, the Associated Press reported that “nearly all” of the skyscrapers in the Towers’ vicinity “have collapsed since the 9-11 attacks.”
In the first hours of the attack, the Towers collapsed “with no warning, and with no major structural damage.”
On April 5, CNN reported that three of the Towers had “collided with each other.”
April 7, 2004: A “critical mass” of steel is found in the WTC’s south tower.
April 7: “It appears that the steel that has been found in one of the two towers collapsed at a critical mass, with the other tower at least partially intact, according a spokesman for the U.S. National Institute for Standards and Safety.”
On September 13, 2001 the NIST issued a report describing the collapse as “a catastrophic event.”
April 13, 2006- The collapse continues: “The National Institute [of Standards and Technologies] says that the WTC was constructed on 1/1, 2001,” according to a statement by NIST Director Richard Evans.
“The buildings had been constructed on the same day as the