Investigations of WTC twin towers, Pentagon continue

August 11, 2010

An American Society of Civil Engineers (ASCE)-sponsored assessment of the performance of the World Trade Center (WTC) towers and the Pentagon in the wake of the Sept. 11 terrorist attacks is continuing.

The investigation is headed by W. Gene Corley, senior vice president of Skokie, Ill.-based Construction Technology Laboratories. Corley was also the principal investigator for an ASCE-sponsored study of the 1995 bombing of the Murrah Federal Building in Oklahoma City. Many of the members of that team have been reassembled.

Separate teams are studying the World Trade Center and the Pentagon. Each team consists of seven to 10 members and includes structural engineers as well as experts in blast and fire protection.

Corley said late last month that investigators are still waiting for material to be removed from the WTC site.

Paul Mlakar of the Army Corps of Engineers Vicksburg, Miss., research center made an initial visit to the Pentagon within days of the attack. His team returned in early October and collected probably all the information it will need.

Mlakar will lead the data reduction and report preparation functions for the Pentagon study. William Baker of Skidmore, Owings & Merrill's Chicago office will serve in a similar capacity for the WTC investigation.

Preliminary reports on both sites are expected to be released in about six months, if the investigations are not delayed by the criminal investigation proceedings. A more detailed report on WTC is expected to take about 18 months. It has not been determined whether a second report will be issued on the Pentagon.

Investigators will have access to several computer programs and may use a single program or a combination of programs to analyze factors such as impact, fire or stability. Their reports will include calculations of the cost of recommendations that result from their studies, if funding can be obtained for this purpose.

'We have ideas about things we need to look into in detail, but at this point we have not arrived at any conclusions,' Corley says. 'It would be an overstatement to say we think a collapse from the impact of all aircraft could be prevented.' He noted that the planes that struck the WTC towers were larger than a 707, not as big as a 747 - and about one-third the size of a jetliner currently being developed by Airbus.

Corley says that if the fires could have been put out, it is reasonable to believe that neither of the Trade Center towers would have collapsed. He adds that investigators anticipate they will find things that could have been done to the towers that might have extended the time until they collapsed. He emphasizes that 25,000 people are thought to have escaped, and speculates that another 5,000 might have been saved if the collapses had been delayed.

Chalk marks to yield clues

Pieces of the towers still bear chalk marks that were used for the steel erection, so it will be possible to determine the locations of pieces that are not badly burned.

All team members are currently working on a pro bono basis, although ASCE is paying out-of-pocket costs.

Salary-related expenses are expected to be upwards of $500,000, with substantial additional costs for data acquisition and computer simulations.

Investigators are working with the Federal Emergency Management Agency at the World Trade Center and with the Military District of Washington and Army Corps of Engineers at the Pentagon.

The reports will be officially presented to ASCE. Cooperating organizations include the American Institute of Steel Construction, American Concrete Institute, National Council of Structural Engineers Organizations and the National Fire Protection Association.

Task force recommendations

Meanwhile, a 24-member task force of the Council on Tall Buildings and Urban Habitat that met in Chicago last month concluded that steps can be taken to enhance emergency performance of buildings. These include egress strategies, redundant building systems, integrated control systems, performance-based design, education and research.

The task force says it is unlikely that a single answer will apply to exit and evacuation procedures for every building and every situation. But it plans to develop updated standards that contain varied approaches to egress. Building systems should have multiple sources and independent distribution routes to withstand disruptions. Numerous systems inside and outside of a building, if integrated, could provide on-site and remote information about the building and its occupants to the appropriate authorities.

Added functions

The task force is exploring the potential of adding the function of performance-based design of buildings so those involved in designing, constructing and operating them can match the overall design with the purpose.

Noting that safety procedures are regularly explained on airplanes and in facilities such as schools, the task force plans to develop guidelines to better educate building management on safety procedures, decision-making and communicating during an emergency. It also will recommend research aimed at improving overall building safety.

         
 

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