Towers Weakened By Planes; Brought Down By Fire

Recommended Areas for Study May Lead to Future Building Code Changes



May 01, 2002, 01:00 ET from American Society of Civil Engineers

    WASHINGTON, May 1 /PRNewswire/ -- Analysis by a team of 25 of the nation's
 leading structural and fire protection engineers suggests that the World Trade
 Center Towers could have remained standing indefinitely if fire had not
 overwhelmed the weakened structures, according to a report presented today at
 a hearing of the House Science Committee.
     That finding is significant, said W. Gene Corley, Ph.D., team lead for the
 ASCE/FEMA Building Performance Study Team, because extreme events of this
 type, resulting in such substantial damage, are generally not considered in
 building design, and the fact that these structures were able to successfully
 withstand such damage is noteworthy.
     Among the significant findings from the World Trade Center Building
 Performance Study: Data Collection, Preliminary Observations and
 Recommendations are:
 
     * Much of the jet fuel on board the hijacked planes that plowed into the
       Towers burned off in fireballs outside the buildings.  Instead of
       causing the fires to burn at extremely high temperatures, as was widely
       speculated, the role of the jet fuel was to ignite other combustible
       materials over several floors simultaneously.  Those fires eventually
       weakened the structural steel, leading to the Towers' collapse.
     * WTC Building 7, which sustained no significant structural damage and
       collapsed on September 11 after burning uncontrolled for seven hours,
       was the first protected steel structure ever known to collapse solely
       due to fire.
     * The team found that some connections between the structural steel beams
       failed in the fires. This was most apparent in WTC 5, where the
       fireproofing did not protect the connections, leading to a partial
       collapse.  The design and construction of WTC 5 is typical of many
       steel-framed high rises.  WTC 5 is the first major collapse caused by
       failure of connections due to fire damage.
 
     "Based on its observations of how the Twin Towers and the surrounding
 buildings performed in the aftermath of the attack, the team recommends that
 the following six items be considered in the design and construction of
 buildings deemed likely targets of terrorist attack.
 
     * Buildings should be designed with sturdy, back-up structural supports to
       bear the weight held by the primary supports when damage to the building
       occurs.
     * Fireproofing needs to adhere under impact and fire-induced steel
       deformation so that the protective coatings remain on the steel and
       provide the intended protection.
     * The connecting structural elements (nuts, rivets and plates) need to be
       analyzed to better understand how they fare under sudden impact and
       fire.
     * When sprinkler systems are a critical part of a building's fire
       protection system, the water supply should be reliable and redundant.
     * Stairwells should be evaluated for multiple alternate routes of escapes
       and strength in order to provide safe and clear evacuation routes when
       the building is damaged.  Transfer floors, stair spacing and locations
       and stairwell resistance to impact should be reviewed as part of the
       evaluation.
     * Fire protection ratings and safety factors for structural transfer
       systems should be evaluated for their adequacy relative to the role of
       transfer systems in building stability.
 
     While the team does not call for immediate changes to existing building
 codes, the team strongly urges continuing study into the collapse of the
 buildings, which could eventually lead to revisions in the building codes.
 The two most significant include a review of current standards for fire
 resistance of connections and a more comprehensive study into the collapse of
 World Trade Center Building 7.
     The National Institute of Standards and Technology is expected to
 spearhead the next round of studies into how the buildings performed.  Their
 work will be completed within 24 months.
     ASCE's Structural Engineering Institute began formation of building
 performance teams within hours of the attack on Sept. 11 as part of its
 Disaster Response Procedure.  The goal of the study is to learn how to make
 buildings safer in the future.  Investigations of this type are commonly
 performed by teams of engineers following other disasters such as earthquakes,
 hurricanes and blasts, and these investigations have frequently formed the
 basis for evolutionary development of our nation's building codes.  At the
 Science Committee hearing, draft legislation is expected to be unveiled
 regarding future investigations into catastrophic building collapses.
     ASCE's Disaster Response Procedure has been in place for approximately 10
 years. The formation of the team to study the collapse of World Trade Center
 Towers marked the fifth time in 2001 that the procedure has been used to
 create study teams.  In addition to the study conducted on the World Trade
 Center complex, ASCE also coordinated a team to assess the performance of the
 Pentagon after the Sept. 11 attack.
     A link to the report and information on ordering printed copies is posted
 at http://www.asce.org.  Interviews with members of the team can be scheduled
 by contacting Norida Torriente, (202)326-5129, or Jane Howell, (202)326-5128.
 
     Founded in 1852, ASCE represents 125,000 civil engineers worldwide and is
 America's oldest national engineering society.  The Society is now celebrating
 its 150th anniversary.
 
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                http://tbutton.prnewswire.com/prn/11690X12388256
 
 

SOURCE American Society of Civil Engineers
    WASHINGTON, May 1 /PRNewswire/ -- Analysis by a team of 25 of the nation's
 leading structural and fire protection engineers suggests that the World Trade
 Center Towers could have remained standing indefinitely if fire had not
 overwhelmed the weakened structures, according to a report presented today at
 a hearing of the House Science Committee.
     That finding is significant, said W. Gene Corley, Ph.D., team lead for the
 ASCE/FEMA Building Performance Study Team, because extreme events of this
 type, resulting in such substantial damage, are generally not considered in
 building design, and the fact that these structures were able to successfully
 withstand such damage is noteworthy.
     Among the significant findings from the World Trade Center Building
 Performance Study: Data Collection, Preliminary Observations and
 Recommendations are:
 
     * Much of the jet fuel on board the hijacked planes that plowed into the
       Towers burned off in fireballs outside the buildings.  Instead of
       causing the fires to burn at extremely high temperatures, as was widely
       speculated, the role of the jet fuel was to ignite other combustible
       materials over several floors simultaneously.  Those fires eventually
       weakened the structural steel, leading to the Towers' collapse.
     * WTC Building 7, which sustained no significant structural damage and
       collapsed on September 11 after burning uncontrolled for seven hours,
       was the first protected steel structure ever known to collapse solely
       due to fire.
     * The team found that some connections between the structural steel beams
       failed in the fires. This was most apparent in WTC 5, where the
       fireproofing did not protect the connections, leading to a partial
       collapse.  The design and construction of WTC 5 is typical of many
       steel-framed high rises.  WTC 5 is the first major collapse caused by
       failure of connections due to fire damage.
 
     "Based on its observations of how the Twin Towers and the surrounding
 buildings performed in the aftermath of the attack, the team recommends that
 the following six items be considered in the design and construction of
 buildings deemed likely targets of terrorist attack.
 
     * Buildings should be designed with sturdy, back-up structural supports to
       bear the weight held by the primary supports when damage to the building
       occurs.
     * Fireproofing needs to adhere under impact and fire-induced steel
       deformation so that the protective coatings remain on the steel and
       provide the intended protection.
     * The connecting structural elements (nuts, rivets and plates) need to be
       analyzed to better understand how they fare under sudden impact and
       fire.
     * When sprinkler systems are a critical part of a building's fire
       protection system, the water supply should be reliable and redundant.
     * Stairwells should be evaluated for multiple alternate routes of escapes
       and strength in order to provide safe and clear evacuation routes when
       the building is damaged.  Transfer floors, stair spacing and locations
       and stairwell resistance to impact should be reviewed as part of the
       evaluation.
     * Fire protection ratings and safety factors for structural transfer
       systems should be evaluated for their adequacy relative to the role of
       transfer systems in building stability.
 
     While the team does not call for immediate changes to existing building
 codes, the team strongly urges continuing study into the collapse of the
 buildings, which could eventually lead to revisions in the building codes.
 The two most significant include a review of current standards for fire
 resistance of connections and a more comprehensive study into the collapse of
 World Trade Center Building 7.
     The National Institute of Standards and Technology is expected to
 spearhead the next round of studies into how the buildings performed.  Their
 work will be completed within 24 months.
     ASCE's Structural Engineering Institute began formation of building
 performance teams within hours of the attack on Sept. 11 as part of its
 Disaster Response Procedure.  The goal of the study is to learn how to make
 buildings safer in the future.  Investigations of this type are commonly
 performed by teams of engineers following other disasters such as earthquakes,
 hurricanes and blasts, and these investigations have frequently formed the
 basis for evolutionary development of our nation's building codes.  At the
 Science Committee hearing, draft legislation is expected to be unveiled
 regarding future investigations into catastrophic building collapses.
     ASCE's Disaster Response Procedure has been in place for approximately 10
 years. The formation of the team to study the collapse of World Trade Center
 Towers marked the fifth time in 2001 that the procedure has been used to
 create study teams.  In addition to the study conducted on the World Trade
 Center complex, ASCE also coordinated a team to assess the performance of the
 Pentagon after the Sept. 11 attack.
     A link to the report and information on ordering printed copies is posted
 at http://www.asce.org.  Interviews with members of the team can be scheduled
 by contacting Norida Torriente, (202)326-5129, or Jane Howell, (202)326-5128.
 
     Founded in 1852, ASCE represents 125,000 civil engineers worldwide and is
 America's oldest national engineering society.  The Society is now celebrating
 its 150th anniversary.
 
                     MAKE YOUR OPINION COUNT -  Click Here
                http://tbutton.prnewswire.com/prn/11690X12388256
 
 SOURCE  American Society of Civil Engineers