"We don't really need solutions looking for a problem," said Jon D. Magnusson, chairman and CEO of structural engineer Skilling Ward Magnusson Barkshire Inc., Seattle, at the National Workshop on Prevention of Progressive Collapse, July 10-12, in Rosemont, Ill.
The meeting of 60 practitioners, researchers, academics and government agency representatives was organized by the Multihazard Mitigation Council of the National Institute of Building Sciences, Washington, D.C., at the request of the National Institute of Standards and Technology, Gaithersburg, Md. "This workshop serves as a benchmark" to assess resources needed to develop standards for new and existing commercial and residential buildings, said H.S. Lew, NIST senior research engineer and workshop coordinator.
Lew expects NIST to issue a final action plan by the end of September, followed next year by a best-practices document based on existing knowledge. Code development could take four to five years, said Lew. Participants estimated the cost of code development at a minimum of $9 million.
Lew defines progressive collapse as "a catastrophic partial or total failure that is disproportionate to local failure due to an initiating event." The chain reaction can propagate vertically or horizontally.
The genesis of the meeting was a Sept. 10, 2001, MMC workshop that looked at the applicability of seismic rehabilitation technologies to mitigating progressive collapse in the event of the loss of primary load-carrying elements through blast or other triggers. The MMC steering committee concluded a national plan was needed. Sept. 11 then "highlighted the urgency of further exploring the subject...to protect the national interest," stated the current workshop invitation letter from NIBS.
Not everyone agrees. William J. Faschan, a partner at structural engineer Leslie E. Robertson Associates, New York City, questioned whether there is a "societal need" for the initiative.
Bruce R. Ellingwood, chair of civil engineering at the Georgia Institute of Technology, Atlanta, thinks research will answer the question. "It's not all that obvious to me that we don't need to do anything," he said.
General mitigation strategies include designing a system to retard progressive collapse after a triggering event; to provide structural redundancy through methods including alternate load path design; and to harden pivotal structural elements.
Building performance could be improved through standards development without adding much to cost, especially when taking a multihazard mitigation or balanced approach to design, said W. Gene Corley, senior vice president, Construction Technology Laboratories, Skokie, Ill.
Designing against earthquake, blast, fire and wind is less costly than looking at each hazard in a "stovepipe way, which is what most codes do," agreed S. Shyam Sunder, chief of the materials and construction research division of NIST's Building and Fire Research Laboratory.
Many agreed there is a need to develop a hierarchy of risk for building types, occupancies and locations. "We don't want to apply progressive collapse design to every building," said Sunder.
There was consensus on one thing: By definition, the World Trade Center towers did not collapse progressively because the response was proportionate to the triggering event. Regardless, most agreed that 9/11 opened a window of opportunity for research into hazard mitigation. "We all probably wouldn't be here [at the workshop] were it not for 9/11," said Ellingwood.esign professionals gathered recently to help develop a "national action plan" on the prevention of progressive collapse in buildings called into question the very premise of the initiative, saying the sponsoring organizations had neglected to first demonstrate a need for action or identify the hazard.