Given the time period the WTC was constructed, the engineers made calculations based on aircraft like the Boeing 707, with the assumption that the aircraft would be impacting the towers due to some sort of pilot error or navigational issue (like the B-25 which flew into the Empire State building in 1945.
Empire State Building after the crash
Boeing 707’s
WTC under construction
So the worst case scenario they designed for was a slow moving, off course 707 attempting to land at one of New York’s airports. The assumptions made in the 1960s prior to construction were reasonable at the time, and also passed analysis using mathematical and computer modelling available to the engineers of the day.
In 2001, the towers faced something quite different . Larger and heavier aircraft, fully fuelled for a transcontinental flight were deliberately flown into the towers at high speed, far exceeding the parameters the engineers used 30 years before. Even then, the towers withstood the impacts pf the airplanes, and only collapsed as the steel supporting beams gradually lost their strength due to the prolonged exposure to the burning jet fuel and debris.
Aircraft becoming kamikaze weapons
Prolonged exposure to the heat of the fire caused the beams to weaken
No longer able to support the weight of the structure above them, the beams buckled and collapsed
So the towers were dealing with a scenario the engineers had never considered, and indeed was inconceivable at the time, and for many years thereafter. The alarm should have sounded when Islamists attempted to destroy the tower by placing a bomb in a van and detonating it in the underground parking garage in 1993, but even then, an attack of the scale and magnitude of 9/11 was never contemplated. The towers held up against the impact, and remained standing long enough for many people to escape - the engineers can be commended for that.
No comments:
Post a Comment