Building a Terror-Proof Skyscraper: Experts Debate Feasibility, Options
📅 Wed September 25, 2002 - Northeast Edition
Ground Zero, the 16-acre site of the destroyed World Trade Center buildings, is now bare brown earth, at a level seven stories down from the surrounding skyscrapers and streets. But it is a place of great hope, symbolized not only by the visit of President Bush on Sept. 11, to encourage grieving relatives of the lost, but also by plans for construction of a future new Lower Manhattan.
The new feeling was especially evident on the anniversary. Last year, the President spoke with tired construction workers and firemen, pledging to finish a terrible task.
This year, at the fully excavated site, he embraced, and talked with, person after person among hundreds of relatives who stood around flowers and cards in a circular memorial area near the center of the area. He joined with them in singing “America the Beautiful.”
“Last year was a time for grieving,” said the mother of 35-year-old Christopher “Buddha” Clark, a financial executive who disappeared in the South Tower. “This year is a time for celebrating his life.” Bush had kissed her after she reached a large card with his picture to him with the words: “Here’s my boy!”
There were smiles as well as tears. A young African American boy, whose uncle, a fireman, had died while helping a paraplegic individual descend from the North Tower, reached a memorial card out to the President. When Bush started to sign it, the boy called out: “Keep it!” Bush grinned appreciatively and stuck the card inside his coat.
Ground Zero now symbolizes the future potential as well as a past tragedy. Proposals now envisage new “terrorist-resistant” World Trade Center (WTC) towers, even taller than the Twin Towers destroyed on Sept. 11, 2001. As many as three new towers may rise like beacons of freedom near the hallowed space — once twisted steel and smoking ashes — where 2,802 people died.
Leading U.S. engineers, interviewed by Construction Equipment Guide (CEG), declare that new towers, incorporating improvements learned from an extensive, still-continuing investigation of the 9/11 disaster, could be inviting, functional and relatively safe in terms of escaping from another attack.
The new buildings, rising Phoenix-like near where the old ones stood (but preserving their exact location for memorial purposes) could even follow the same basic design — vertical “pinstripe” exterior support columns connected to thin steel horizontal trusses beneath each floor, and further support from a central core of thick steel columns.
“Sure, it [constructing taller new buildings with many elements of the original design] could be considered,” said Dr. Gene Corley, senior vice president of Construction Technology Laboratories Inc., Skokie, IL, who directed the original six-month engineering investigation into the performance of the WTC buildings on 9/11. “Our report points out that the towers really did amazingly well. The terrorist aircraft didn’t bring the buildings down; it was the fire which followed. It was proven that you could take out two thirds of the columns in a tower and the building would still stand.
“My personal belief since the day this happened is that we should build even taller towers very much like the old ones. I wouldn’t give the terrorists the satisfaction of [my] saying that they will have won if we don’t, but I think rebuilding even larger towers is very appropriate.”
Corley said the following design features would make the new WTC more resistant to terrorist attack:
• Better location of stairwells for escape;
• Enclosures around stairwells should contain better fire-resistant materials that would not break loose after impact; and
• Increased fireproofing throughout the buildings allowing individuals to survive.
“My personal belief is that there should be enough fireproofing so the buildings could survive a complete burnout without collapsing,” Corley told CEG. “If the buildings hadn’t collapsed, we wouldn’t be going to funerals of 300 or 400 rescue workers.”
Corley directed a building performance study, completed on May 1, whose sponsors included the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers (ASCE).
The study concluded that impacts of the two aircraft knocked off the fireproof (mineral wool) material that had been sprayed on the lightweight gypsum board around the stairwells of the towers, and on the thin steel horizontal trusses supporting the floors.
“One of our major conclusions is that, if a building comes under a terrorist attack, the fireproofing material needs to stick on better,” he said. “Such materials are available now. Their costs are still unreasonably high but would come down as they are used more extensively. Effective fireproofing gives time to escape. There could even be fireproof shelters to protect those who are trapped.”
Corley said it’s “very debatable” whether the floor trusses, which softened and bent in the extreme heat of the fires, snapping away from the exterior columns, do a worse or better job than other systems.
“There are older buildings out there that people think would do extremely well which actually might do worse under similar conditions,” he said. “It’s not really a question of trusses versus [heavier] steel beams as how a specific building is put together.”
New towers also would incorporate redundant connections between horizontal and vertical supports. These would meet new fire-resistance standards that are expected to be adopted. Corley said the study indicated that connections were not a major factor in the collapse of the towers, but was a major factor in the collapse of Buildings 5 and 7.
Who Would Occupy?
Incorporating a wide range of improvements learned from 9/11, new towers would have to be useful, inviting and terrorist-resistant, Corley said, adding: “You still need to have something which people want to go into. A bunker structure like the NORAD [North American Air Defense] structure in Cheyenne, WY, obviously wouldn’t be very useful as an office building. Structures designed so planes would bounce off them are also wishful thinking. No one would occupy them because they would have no windows.”
Though he personally favors following the original design, Corley said other concepts also could be considered for new towers. These include designs used in earthquake areas and column-and-beam structures similar to the Bankers Trust Building next to the South Tower.
“Bankers Trust [next to the South Tower] took terrific heat but remained standing,” he said. “The damage was isolated to locations where debris hit.”
The entire Bankers Trust, overlooking the Ground Zero cavity, now stands beneath a black cover while work continues on restoring the building. The cover holds a large U.S. flag and messages such as “The human spirit is not measured by the size of the cut, but the size of the heart.” and “We will never forget them. We will never forget you.” Blown-out areas still scar the top of other buildings on the edge of the site.
Steve Solomon, a spokesperson for developer Larry Silverstein, who holds a 99-year lease on the WTC site, said that he doesn’t think people would want to rent space in new towers as high as the old ones.
“The question is one of marketing effectiveness,” he told CEG. “I don’t think many tenants would choose to lease space in another 110-story building.”
Corley commented, “Our first line of defense is keeping resources out of the hands of terrorists. Aircraft on the drawing boards are essentially three times as large as the 767s, which hit the towers. Given access to aircraft and explosives, there’s always a way to destroy something that has been built. There’s no such thing as ’terror-proof,’ any more than earthquake-proof, fire-proof or anything else, but you can make buildings terror-resistant.”
Guy Nordenson and Associates, a structural engineering firm in Manhattan, has proposed three “resilient” towers that would twist to resist wind and would absorb impact shock (see illustration).
The towers — 2,000, 1,500 and 1,250 ft. high (609.6, 457.2 and 381 m) respectively — include a concrete cylinder central “mast” with solid “outriggers,” perpendicular to the mast, extending, like a horizontal spreader on a sailboat, to a lattice-steel exterior. The curving design allows the structure to swing at different frequencies to counteract the vortices of wind, which would form behind the building. The riggers, at different levels, strengthen the structure to resist or prevent progressive collapse like that which happened on 9/11.
The top 500 ft. of the 2,000-ft. building would be an open-air structure including such elements as observation levels and broadcast towers.
“The whole building kind of rotates as it goes up,” Dieter Janssen, an architect with the firm, told CEG.
Room for Memorial
Proposals for new towers preserve the Ground Zero “footprint” of the towers.
One published plan, for instance, would place one new tower on the southeast corner of the original 16-acre site, with the other nearby, just outside the site.
What type of memorial will be built? This is a topic of intense discussion but few doubt there will be one.
“There is no doubt there will be enough room for a memorial,” said Solomon.
The Lower Manhattan Development Corporation (LMDC), a joint city/state body supervising the rebuilding of Ground Zero and the financial district, said it hopes to select a memorial design from an international competition by the end of next year.
Maya Lin, who designed the Vietnam Veterans Memorial Wall in Washington, D.C., has made several proposals, including luminous “light towers” forming a “candelabra” encircling the site. She also has proposed a memorial on a new artificial island in the Hudson River, which would be connected to the WTC area by a tree-lined promenade.
A wide range of other proposals includes reflecting pools at the site of the original towers.
Maybe the most moving memorial would be a letter that is on display in the “Family Room” for relatives overlooking the entire Ground Zero from the 20th floor of One Liberty Plaza. The letter, in loving memory of Andrew Joseph Bailey, is as follows:
Hi, this is Veronica talking
I MISS you a lot. My life has changed now since you are gone
Oh! Can I ask you a question?
Did you forget my age yet? Guess what. My birthday is coming. It is April 2, 1993
Yours is coming too. It is on April 20, 1976
The 9/11 tragedy has brought forth many stimulating new ideas for rebuilding the entire Lower Manhattan area as part of a resilient city. A proposal by Frederic Schwartz, an architect who worked on the Westway Project in the 1970s, would cover the six-lane West Street, creating a new corridor that would add more than 16 acres of developable land, worth more than $2 billion, to the area near Ground Zero.
New buildings along the promenade would include pioneering-design offices, apartments and hotels. One of the biggest benefits: the corridor would integrate Battery Park City with the financial district in Lower Manhattan, accelerating the development, which was one of the purposes of building the trade center.
Ideas also include converting much of Ground Zero into a new center of activity. This could include a transit interchange with curved wave-like pedestrian ramps, lined with shops and cafes, both above and below ground, plus moving walkways; a cultural center for music, dance and theater; and an educational facility focusing on critical subjects such as world religions and urban problems.
But perhaps the brightest hope lies in the hearts of the people of New York and their resilient spirit, “You knocked down two towers; we’ll build three new ones even better.”