Building: North Tower of the World Trade Center
Location: New York, NY
Years of completion: 1973
Year of failure: 1993
Type: Terrorist attack
Architect: Minoru Yamasaki
Structural Engineer: John Skilling and Leslie E. Robertson
Construction Firm: Tishman Realty & Construction
Seven suspects organized and bombed the World Trade Center on February 26, 1993. The 1,200 lb. bomb was said to have been in a truck on the ground level parking garage of the North Tower [a][b]. The goal of the terrorists was to bomb the South Tower so that the failing debris would knock down the South Tower, luckily this was not a success [c].
The effects of the blast were quiet severe. On the ground level, where the bomb was detonated, a large crater approximately 130 feet by 150 feet was opened, causing reinforced concrete and debris to fall to the below level garages. 9 steel columns were damaged leaving them without lateral support. Several walls collapsed and nearby elevator shafts, stairways and enclosures were damaged. Mechanical, electrical, and plumbing systems were all ruined on the ground level and the four levels below [d]. A full diagram of damages can be seen in figure 1 above.
On the level above the explosion, approximately a 5,000 sf hole was opened, along with damage to many walls and elevators. On this level, seven steel columns were destroyed leaving almost no lateral support. On the second and third levels above the explosion, a large section of concrete was cracked and shifted. A wall of glass windows blown out between the tower and a nearby hotel, allowing large amounts of smoke to pass through [d].
The structural failures occurred because concrete fell placing heavier loads on levels below. Fire and the bursting of several pipes caused excessive heat to materials of the columns, beam, and walls. Luckily, the building was able to be repaired. Six people died during this terrorist attack, and over 1,000 were wounded. Higher safety regulations were put in place concerning terrorist precautions and evacuation protocol [e].