Engineers had to consider every peril they could imagine when they designed the World Trade Center three decades ago because, at the time, the twin towers were of unprecedented size for structures made of steel and glass.
"We looked at every possible thing we could think of that could happen to the buildings, even to the extent of an airplane hitting the side," said John Skilling, head structural engineer. "However, back in those days people didn't think about terrorists very much."
Skilling, based in Seattle, is among the world's top structural engineers. He is responsible for much of Seattle's downtown skyline and for several of the world's tallest structures, including the Trade Center.
Concerned because of a case where an airplane hit the Empire State Building, Skilling's people did an analysis that showed the towers would withstand the impact of a Boeing 707.
"Our analysis indicated the biggest problem would be the fact that all the fuel (from the airplane) would dump into the building. There would be a horrendous fire. A lot of people would be killed," he said. "The building structure would still be there."
Skilling - a recognized expert in tall buildings - doesn't think a single 200-pound car bomb would topple or do major structural damage to a Trade Center tower. The supporting columns are closely spaced and even if several were disabled, the others would carry the load.
"However," he added, "I'm not saying that properly applied explosives - shaped explosives - of that magnitude could not do a tremendous amount of damage."
He took note of the fact that smoke and fire spread throughout the building yesterday. He said that is possibly because the pressurizing system that stops the spread of smoke didn't work when the electric power went off. Skilling, 72, was not involved in the design of the building mechanics.
Although Skilling is not an explosives expert, he says there are people who do know enough about building demolition to bring a structure like the Trade Center down.
They should of wrapped the structural columns in paper passports since you know... they are apparently jet fuel fire resistant.
NYC WTC 'designed to withstand multiple airliner impacts' Frank De Martini construction boss
Nov 22, 2008
Frank De Martini WTC architect explains it would resist jetliner impacts
At the time the Twin Towers were built, the design approach of moving the support columns to the perimeter and the core, thereby creating large expanses of unobstructed floor space, was relatively new, and unique for a skyscraper. However, that approach is commonplace in contemporary skyscrapers. Frank Demartini's Statement
Frank A. Demartini, on-site construction manager for the World Trade Center, spoke of the resilience of the towers in an interview recorded on January 25, 2001.
The building was designed to have a fully loaded 707 crash into it. That was the largest plane at the time. I believe that the building probably could sustain multiple impacts of jetliners because this structure is like the mosquito netting on your screen door -- this intense grid -- and the jet plane is just a pencil puncturing that screen netting. It really does nothing to the screen netting.
Demartini, who had an office on the 88th floor of the North Tower, has been missing since the 9/11/01 attack, having remained in the North Tower to assist in the evacuation. 6 Demartini had first worked at World Trade Center when Leslie E. Robertson Associates hired him to assess damage from the truck bombing in 1993. LINK Like All Skyscrapers, the Twin Towers Were Over-Engineered
One aspect of engineering that is not widely understood is that structures are over-engineered as a matter of standard practice. 7 Steel structures like bridges and buildings are typically designed to withstand five times anticipated static loads and 3 times anticipated dynamic loads. The anticipated loads are the largest ones expected during the life of the structure, like the worst hurricane or earthquake occurring while the floors are packed with standing-room-only crowds. Given that September 11th was not a windy day, and that there were not throngs of people in the upper floors, the critical load ratio was probably well over 10, meaning that more than nine-tenths of the columns at the same level would have to fail before the weight of the top could have overcome the support capacity of the remaining columns.
There is evidence that the Twin Towers were designed with an even greater measure of reserve strength than typical large buildings. According to the 1964 white paper cited above, a Tower would still be able to withstand a 100-mile-per-hour wind after all the perimeter columns on one face and some of the columns on each adjacent face had been cut. 8 Also, John Skilling is cited by the Engineering News Record for the claim that "live loads on these [perimeter] columns can be increased more than 2000% before failure occurs."
The most recent example of a spectacular skyscraper fire was the burning of the Hotel Mandarin Oriental starting on February 9, 2009. The nearly completed 520-foot-tall skyscraper in Beijing caught fire around 8:00 pm, was engulfed within 20 minutes, and burned for at least 3 hours until midnight. Despite the fact that the fire extended across all of the floors for a period of time and burned out of control for hours, no large portion of the structure collapsed.
It is tempting to draw parallels between this spectacle and the destruction of WTC 1, 2, and 7 because of the stark opposites: on 9/11/01, three skyscrapers were transformed into piles of rubble primarily as a consequence, supposedly, of fires -- fires spanning small fractions of each building; and on 2/09/09, a skyscraper remained intact after burning like a torch for hours. However such parallels may be limited by major structural differences between the buildings in the two cases -- one being that the Hotel Mandarin Oriental, designed by the famous Dutch architect Rem Koolhaas, had a full-height interior atrium, and thus had the hollowness that the 9-11 Commission deceptively attempted to attribute to the Twin Towers. 10
Perhaps the relevance of the Mandarin fire to the events of 9/11/2001 is more symbolic than forensic. The Mandarin fire is examined more fully here.
On February 9, 2009, in the middle of the Lunar New Year, the distinctive 40-story Mandarin Oriental hotel in Beijing's Television Cultural Centre (TVCC) erupted in sparks and flames that consumed the building from top to bottom in an intense fire lasing for several hours. Blamed on a ground-based fireworks display gone afoul or illegal fireworks operations inside of the building, the fire started around the tower's top and proceded downward around the tower's sides while fireworks continued to burst dramatically above the blaze. 1
Skyscraper-Turned-Torch Remains Standing
The spectacular torching of the Mandarin tower further underscores the anomalous nature of the official explanation of the total collapse of the Twin Towers and WTC 7 -- an explanation that primarily blames fires for causing the "global collapse" of those structures. It is yet another example of a severe fire that failed to induce even the partial collapse of a skyscraper. Although less similar to the WTC towers than other skyscrapers ravaged by fires, the Mandarin tower is notable for the magnitude of the fire it withstood -- a fire that dwarfed the fires that preceded the "collapses" of each of the the WTC skyscrapers.
Coming exactly 2711 days after 9/11/2001, the burning of the Hotel Mandarin Oriental, which was unoccupied pending its completion, killed one firefighter.