World Trade Center Construction

In order to understand how the World Trade Center collapsed we need to understand their structure. To save money and maximize floor space the two towers were built with a tube structure instead of the more common lattice structure. The tube structure was economically favorable because the structure required half the amount of steel compared to the lattice structure and created more floor space (one acre for every floor) without compromising the strength of the structure. This design also makes the building more resistant to strong winds. This was particularly important in New York City where winds created more lateral load on the building than seismic activity. The World Trade Center was built to sustain thirteen thousand tons of wind. The
A little after noon, during the lunch break, a van containing a bomb parked in the parking garage under the North tower. The van was located under the perimeter wall. The attack was supposed to destroy that portion of the base of the North tower and cause it to fall onto the South tower destroying them both. If successful the attack would have killed as estimated forty thousand people. Thankfully the terrorists underestimated the strength of the building and the bomb only destroyed part of the parking garage killing six and injuring one thousand and forty two people. The core acted as a chimney and sucked smoke up into the higher
on September 11, 2001. A Boeing 767 filled with fuel for a transatlantic flight flying at four hundred miles per hour hit the tower straight on. The increased speed and mass created more kinetic energy than the building was originally designed to handle. Despite not being built to withstand such force the building remained standing for an hour and forty two minutes until finally collapsing at 10:28 a.m. when the core failed. The plane hit floors ninety three through ninety eight demolishing the core and cutting off any escape route for the people on the floors above the crash. The fuel from the plane fed fires that heated the steel frame of the building. While the fire was nowhere near hot enough to melt steel it did cause the steel to soften and be distorted. This caused the floor to sag and eventually give way and the upper floors slammed into the lower ones causing the tower to collapse straight