PULLMAN, Wash. — Preventing the tragedy of the collapse of the World Trade Center towers rests with improving airline security, not with designing skyscrapers to withstand jetliner crashes, said Jon Magnusson, the chairman and chief executive of the firm that oversaw the structural engineering for the center during its construction in the 1960s.
“We would have to repeal the laws of physics to design a building that could withstand a crash (from a large jetliner),” he told an audience of several hundred at an afternoon lecture at Washington State University Thursday (May 2). Magnusson was the WSU’s College of Engineering and Architecture Lanning Distinguished Lecturer.
Magnusson said the towers’ superior construction allowed it to withstand the initial impact of two jetliners long enough for thousands to escape.
“Ninety-nine percent of buildings would have collapsed immediately,” he said.
Magnusson, who recently finished serving on a federal panel that examined the towers’ construction, said a combination of factors caused by the impact and the resulting fire caused the collapse.
During the Sept. 11 attack, the first plane hit the trade center’s north tower between the 94th and 99th floors. The next plane hit the south tower between the 78th and 84th floors about 11 minutes later. The south tower fell 56 minutes, 10 seconds after impact. The north tower fell about six minutes later.
While engineers can design buildings to withstand gravity, earthquakes and wind, it is impossible to control the complex and devastating chain of reactions that occur when a large jetliner punches a colossal hole in a building, he said.
The impact of each plane immediately stripped away a protective fire-resistant coating sprayed on the steel support columns. Nearly two-thirds of the support columns were initially destroyed.
Sprinklers – that likely had their water source cut off by the impact – could never deliver enough water fast enough to control the fire. While most of the 10,000 gallons of jet fuel each plane was carrying were immediately consumed in massive fireballs, the remainder flowed across floors and down elevator shafts, setting ablaze debris.
The fire, which reached temperatures of 2,000 degrees, weakened the buildings’ steel framework. Upper floors collapsed onto lower floors, which could not withstand the weight.
“The fact the (towers) withstood the impact of two 767s gave the public false expectations about what to expect when a high-rise building is hit,” Magnusson said.
The towers stood as long as they did because of a unique design that included closely spaced support columns. Most architects prefer fewer columns, but the towers’ architect was afraid of heights and wanted to create a feeling that one could not fall between the columns.
Some have wondered why the towers collapsed while the Empire State Building withstood the crash of a B-25 twin-engine bomber in 1945. A jetliner weighing some 275,00 pounds and carrying thousands of gallons of highly flammable fuel is not comparable to a two-propeller, 20,000-pound plane, Magnusson said.
“What hit the Empire State Building was an insect,” he said.
There are planes flying now that are many times larger than the jetliners that hit the towers, Magnusson said. Rather than trying to build a jetliner-proof building, he said society should put resources toward making sure a plane never hits a building.
A change in attitude about how to handle terrorists may already be the answer, rather than “taking away nail clippers.”
Before Sept. 11, airline crews and passengers were encouraged to remain passive during a terrorist takeover. “Now, if someone stands up and says ‘nobody move,’ that’s the signal to attack,” Magnusson said of passengers’ reactions.
“It’s not about tall buildings. If we can’t control airports, our problem is much bigger than airplanes.”
Magnusson’s 120-person firm, Skilling Ward Magnusson Barkshire, is based in Seattle The firm has completed projects in 27 countries and 43 states, and Magnusson was recently named “Engineer of the Year” by the American Council of Engineering Companies of Washington. He was the principal structural engineer for a number of important projects in Seattle including the Key Arena, Safeco Field, the new Seahawks stadium and the Seattle Central Library.
The annual Lanning lecture was established in 1988 by WSU alumnus Jack Dillon in honor of his wife, the late Frances Lanning Dillon. Jack Dillon is a retired engineer and rear admiral in the Civil Engineer Corps of the U.S. Navy.