Volume 38, Issue 1, January 2003
Investigation of Collapse Begins
Engineers now are studying the towers to determine exactly when and how the 110-story twin structures collapsed.
The federal investigation is being conducted at an undisclosed location where a group of 23 engineers has met to watch the video of the collapse hundreds of times in an effort to resolve some of the unanswered questions from September 11, and to prepare for future disasters.
The engineers hope to determine whether the core columns fell first, dragging each floor with them as they fell, or if the exterior columns pulled inward, giving in to floor joists weakened by raging fires.
The towers were built to withstand the impact of a Boeing 707 when they were completed 30 years ago—but not one filled with fuel.
They were designed in a tubular shape with a load-bearing interior core and perimeter walls of glass and 62 steel columns per side with no other vertical support. While the design opened up more floor space, some engineers suspect it was more vulnerable than most buildings of its type.
The Federal Emergency Management Agency is financing the investigation, which is expected to cost about $600,000.
In other news, two representatives of the National Fire Protection Association (NFPA), Robert E. Solomon, P.E., a fire protection engineer and Robert F. Duval, a senior fire investigator, are each serving on special panels that examine the World Trade Center's collapse.
Solomon is a member of the special task force on the Future of Tall Buildings, which was formed by the Council on Tall Buildings and Urban Habitat (CTBUH). Duval is serving on the Federal Emergency Management Agency's Building Performance Assessment Team (BPAT) for the World Trade Center.
According to NFPA, the CTBUH group is focusing on new strategies that may be considered in tall-building design, such as egress and performance-based design. The hope is to increase the performance of tall buildings.
The BPAT group is examining the performance of the towers, as well as the surrounding buildings.
Expert studies have concluded that even if the towers hadn't collapsed, it would have been difficult, even impossible, to rescue stranded victims from upper floors because of the design of exit stairwells and the blocked exits that
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