...a standard methodology to reliably predict the potential for complex failures in structural systems subjected to multiple hazards.
NIST also urges that nationally accepted performance standards be developed for conducting wind tunnel testing of prototype structures. According to the Structural Engineering Institute, such a standard is well into development and will be released for public comment by the end of the year.
SEI representatives were present at the briefing. "Our position is that such a humbling event as 9/11 requires the institution and the profession to look at the loads and conditions we do consider [in design] and ask whether we need to broaden the spectrum of those events and conditions to fulfill our responsibility of providing safe buildings to the public," said Jeremy Isenberg, SEI president and president-CEO of Weidlinger Associates Inc.
When asked to define "safe," Jim Harris, SEI board member and head of J.R. Harris & Co., Denver, said, "Safety is not absolute, it is relative and we are examing conditions of how safe is safe enough."
Harris said he finds the study beneficial because it gives the profession more information on how buildings perform in fires not necessarily initiated by a terrorist event. "We think NIST has given us a lot to consider," he said, adding that he thinks NIST "should not have delayed" bringing the findings to the public."
Initially, the report was supposed to be done in two years. NIST had developed its recommendations by the end of last year. Harris also thinks more study will be necessary, and not just by NIST. "Though NIST should not have studied other buildings before releasing this report," he said, other buildings should be studied.
While the investigation into the collapse appears to be "top-notch, nowhere in the sections of the report which I reviewed does NIST define the fire problem which the nation actually faces," says Richard C. Schulte, a fire protection consultant based in Evanston, Ill.
The National Fire Protection Association (NFPA) released a study of high-rise building fires in September 2001. "This study indicates that in the 14-year period between 1985 and 1998 there were a total of 7 fire fatalities in all of the high-rise office buildings throughout the United States," says Schulte.
Statistics collected by NFPA consistently show that more than 60% of the fire fatalities that occur in the U.S. occur in 1- and 2-family dwellings and that 80% of the fire fatalities occur in residential occupancies (homes and apartment buildings), he adds.
NFPA fire statistics also indicate that in a typical year roughly 200 Americans die in fires in commercial (non-residential) buildings, says Schulte. In recent years, the number of fatalities has dwindled to fewer than 100 people.
In May, NFPA released data from a study on fire department personnel fatalities and injuries. Last year, roughly 100 firefighters died in the line of duty. In previous years, two-thirds of the number of firefighter fatalities were volunteer and forestry firefighters. Only between 30 and 40 municipal firefighters die each year in the line of duty. According to NFPA, the principal reason for firefighter fatalities are heart disease, with transportation accidents the second leading cause of firefighter fatalities. The number of firefighters who die due to fire or building collapse is just a handful, Schulte adds.
"NFPA fire statistics show that our nation has never been more fire safe (and firefighters have never been safer), yet the NIST report is written as if fire safety is a major problem in the United States," says Schulte. "As a fire protection engineer with 29 years of experience in the field, I strongly disagree with this conclusion. Since the early 1970's, there has been much progress in the fire safety field. I would hope that the Congressional Science Committee would begin asking NIST for its basis for proposing such radical changes in the fire safety field, particularly in light of the excellent fire safety record of commercial building and, in particular high rise buildings."
NIST urges that performance standards also be developed to estimate wind loads and their effects on tall buildings for use in design, based on wind tunnel testing data and directional wind speed data.
Harris believes some of the recommendations should be applied to existing buildings, especially relating to redundancy in fire suppression systems. Also, importance thresholds for progressive collapse resistance may be different for new and existing buildings, he said. Harris said he does not believe the current stock of buildings is dangerous. He added that NIST did not reveal, in most cases, how it determined their "high-priority needs" that formed the basis of the recommendations.
Under structural integrity, NIST recommends developing and implementing "appropriate" criteria to enhance the performance of tall buildings by limiting how much they sway under lateral load design conditions. "Limiting building sway is a way of ensuring stability," said Sunder.
ACI 318 "Building Code Requirements for Structural Concrete" has had structural integrity requirements since the 1989 version of the code, says David N. Bilow, director, engineered structures at the Portland Cement Association, Skokie, Ill. "ASCE 7 "Minimum Design Loads for Buildings and Other Structures" has included structural integrity requirements for many years and has recently improved the requirements.
According to Bilow, IBC has not adopted the section of ASCE 7 on structural integrity. Therefore, IBC has no provisions for structural integrity for steel, wood and masonry (unless these material design standards have something on it). But there are provisions for concrete because ACI Committee 318 has unilaterally imposed it on the concrete industry.
"As NIST does not have prescriptive nor threshold recommendations, it will be up to the code bodies to develop new requirements for structural integrity, if needed," Bilow says.
Experts wonder whether NIST found any tall buildings that are unstable and how NIST concluded that tall buildings performance "needs" to be improved. "NIST's recommendations have improved on some of their logic from what they published in their findings a few months ago," says Jon D. Magnusson, chairman-CEO of structural-civil engineer Magnusson Klemencic Associates, Seattle Magnusson is a member of the National Fire Protection Associations high-rise building safety advisory committee, which will be meeting with NIST July 12-13 to review the draft report. Magnusson was also a member of the American Society of Civil Engineers-Federal Emergency Management Agencys building performance assessment team that issued the first report on the WTC disaster, in mid-2002.
Magnusson says he agrees with 16 of NISTs 30 recommendations. "The common problem with the other 14 is that there is absolutely no historical data that demonstrates that the changes will actually increase public safety and first responder safety," says Magnusson. "This quite simply makes for an ineffective set of changes. Even worse, for many of these, I can show you how the recommendations could actually reduce safety. As we all work for improvements in public safety, it is critically important that we do not divert the resources of our society from effective strategies to ineffective ones."
NIST is urging the building and fire safety communities to give "immediate and serious consideration" to these recommendations to achieve "appropriate" improvements in the way buildings are "designed, constructed and maintained and used and in evacuation and emergency response procedures."
After issuance of the final report, NIST, as required by the National Construction Safety Team Act, must "conduct or enable or encourage the conduct of appropriate research recommended by the NCST and promote appropriate adoption of the recommendations by the federal government and other agencies and organizations.
The full report is available on wtc.nist.gov.
[ENR requested specific comments on each of the NIST WTC recommendations, issued June 23, from many sources. Please e-mail Nadine_Post@mcgraw-hill.com with any feedback. Any other comments are also welcomed on any part of the NIST report.