Researchers at Purdue University have created a state-of-the-art animation depicting the structural damage which occurred as a result of the Boeing 767 airliner crashing into the North Tower on 9/11. This animation clip is narrated with a description of what is taking place as the crash unfolds.
The simulation found that the airplane's metal skin peeled away shortly after impact and shows how the titanium jet engine shafts flew through the building like bullets.
As with an earlier simulation developed by this team that examined the 9/11 attack on the Pentagon, the World Trade Center simulation showed that it was the weight of the 10,000 gallons of fuel more than anything else that caused the damage.
"It is the weight, the kinetic energy of the fuel that causes much of the damage in these events," Hoffmann says. "If it weren't for the subsequent fire, the structural damage might be almost the same if the planes had been filled with water instead of fuel."
Click on the "play" button in the lower left-hand corner to play the video.
Mete Sozen, Purdue's Kettlehut Distinguished Professor of Structural Engineering and a principal investigator on the simulation project, says the researchers worked for years and used the best computing resources available to recreate the event.
"To estimate the serious damage to the World Trade Center core columns, we assembled a detailed numerical model of the impacting aircraft as well as a detailed numerical model of the top 20 stories of the building," Sozen says. "We then used weeks of supercomputer time over a number of years to simulate the event in many credible angles of impact of the aircraft."
Sozen says the actual damage to the building's facade that was observed was identical to the damage shown by the numerical simulation.
"We calibrated our calculations using data from experiments we had conducted to evaluate the energy imparted from fluid moving at high speed to solid targets," he says. "We concluded that the damage map we calculated for our numerical model of the building would correspond closely to the actual extent of the damage."
The simulation represented the plane and its mass as a mesh of hundreds of thousands of "finite elements," or small squares containing specific physical characteristics. In the visualization, these scientific data points are used to show how airplane components swept through the building and out through the other side as the fuel ignited.
"The aircraft moved through the building as if it were a hot and fast lava flow," Sozen says. "Consequently, much of the fireproofing insulation was ripped off the structure. Even if all of the columns and girders had survived the impact - an unlikely event - the structure would fail as the result of a buckling of the columns. The heat from an ordinary office fire would suffice to soften and weaken the unprotected steel. Evaluation of the effects of the fire on the core column structure, with the insulation removed by the impact, showed that collapse would follow whatever the number of columns cut at the time of the impact."
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