June 24, 2005
Industry groups are joining forces to
review recommendations for changes to structural and life-safety
systems for tall buildings proposed by the National Institute
of Standards and Technology as part of its $16-million World
Trade Center Investigation. The recommendations, released
June 23 for public comment, will form the basis of a debate
on how future tall buildings will be designed and constructed
and how building codes may evolve.
The National Council of Structural Engineers Associations,
the American Institute of Architects and the Council on Tall
Buildings and Urban Habitat are forming a joint a panel to
review the draft report and provide an "official"
opinion on the part of the profession. In addition, the Association
of Major City/County Building Officials has announced it will
review the draft and provide NIST with formal comments from
the nations largest cities and counties.
Claude Cooper, AMCBO chairman and Richmond, Va., building
official, said in a statement: AMCBO members are "gratified
that this report reinforces the fact that tall buildings involved
in the disaster were built safely and, for the most part,
performed as they were designed.
"AMCBO is pleased NIST has offered
from their research for us to consider regarding the design,
construction and operation of tall and iconic buildings,"
he said. "Our comments will include possible coordination
of major city/county support for suggested code changes found
in that report."
In additional to Richmond, some AMCBO members are New York,
Chicago, Los Angeles, Detroit, Milwaukee, Denver, St. Louis
In the design arena, NIST is calling for changes to building
standards, codes and practices, especially for structural
and life safety system design and emergency evacuation of
buildings. Specific recommendations concern stairs, elevators,
fireproofing of structural steel, and structural integrity
to reduce chances of progressive collapse in high-rise buildings
during disaster situations.
Of particular concern at the World Trade Center was that
6% of the people who evacuated the two towersrepresenting
about 1,000 individuals were physically challenged.
"It appears that building commissioners need to consider
ways to better accommodate the needs of these people,"
Stephen S. Szoke, director of codes and standards for the
Portland Cement Association, Skokie, Ill., says that many
of NISTs proposals have already been discussed by professional
organizations and other bodies but has been rejected, often
because available "data" did not indicate a need
for a change. He does not expect the NIST recommendations
to further the push for changes in model codes.
"Most of the recommendations that relate to technical
provisions of building codes have been discussed in the model
code development arenas for the past several decades, including
during the development and subsequent changes to the first
edition of the International Code Councils International
Building Code and National Fire Protection Association Building
Construction and Safety Code, NFPA 5000," says Szoke
"The Portland Cement Association and its allies in the
cement-based product industries have initiated many of these
discussions via code change proposals. Such proposals have
attempted to strengthen code provisions by increasing the
required fire resistance rating of the structural frame, eliminating
sprinkler trade-offs and improving compartmentation by increasing
the required fire resistance rating and/or requiring fire
resistance rated barriers where codes presently do not require
rated walls. Specific emphasis on required fire resistance
rating has been related to exit stairway walls, by modifying
the hose stream test of American Society for Testing and Materials
E 119 Standard Test Methods for Fire Tests of Building Construction
and, Materials to require a more rigorous test.
" Almost all of these proposals have been disapproved,"
he says. "The reason generally cited for their disapproval
is that fire data does not indicate a need for the change.
While PCA and our allied industry groups support many of NISTs
recommendations, based on our experience over the past several
decades, we do not anticipate any significant changes will
be made in our model codes as a result of the NIST study."
NISTs recommendations are a result of studying only
the behavior of occupants, emergency responders and the twin
110-story towers after the terrorist attacks on Sept. 11,
2001. But it is basing its recommendations on its findings
related to procedures and practices commonly used for buildings
under normal conditions, said S. Shyam Sunder, a NIST deputy
director and the lead investigator in the three-year WTC study.
Sunders remarks were made during a media briefing June
23, in New York City.
Sunder said NIST did not study any other commercial buildings
or any other emergency scenarios in forming its recommendations.
He did, however, say the "tragic consequences" of
the Sept. 11 attacks were "directly attributable to the
fact that terrorists flew large, jet-fuel-laden commercial
airliners into the WTC towers." He also said that "buildings
for use by the general population are not designed to withstand
aircraft attacks" and that "building codes do not
require building designs to consider aircraft impact."
In earlier briefings, Sunder made it clear that the twin
towers performed well on 9/11 and that the fact that they
did not collapse on impact of the jetliners is a tribute to
their structural redundancy, which saved thousands of lives.
Still, he said "public officials and building owners
will need to determine appropriate performance requirements
for buildings that are at higher risk due to their iconic
status, critical function or design."
The public comment period will end at the end of the business
on Aug. 4, Eastern Daylight Time.. NIST is holding a conference
to discuss putting its recommendations into practice on Sept.
13-15, in Gaithersburg, Md. The final WTC report will be issued
The NIST report on Seven WTC, which collapsed on 9/11 after
burning unattended for about five hours, will be released
in draft form in October and final form in December.
Sunder said NIST believes its recommendations are realistic
and achievable within "a reasonable period" of time
and that implementation of the recommendations would make
buildings, occupants and emergency responders safer in future
The recommendations do not prescribe specific threshold levels.
Sunder says this is not the responsibility of NIST.
The recommendations that relate to "increased"
structural integrity are that progressive collapse should
be prevented in buildings through development and nationwide
adoption of consensus standards and code provisions, with
tools and guidelines needed for their use in practice. NIST
recommends developing 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
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,"
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),
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,
"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
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
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
The full report is available on wtc.nist.gov.