World Trade
Center Building Performance Study:
Data Collection, Preliminary Observations, and Recommendations
FEMA 403 • September 2002 • Second Printing
On
the morning of September 11, 2001, two hijacked commercial jetliners were
deliberately flown into the two towers of the World Trade Center (WTC).
The first plane crashed into the north face of the north tower (WTC 1) at
8:46 a.m. The second plane crashed into the south face of the south tower
(WTC 2) at 9:03 a.m. The structural damage to each tower caused by the aircraft
impact, combined with the ensuing fires, resulted in the total collapse
of each building. As the towers collapsed, massive debris clouds consisting
of crushed and broken building components fell onto and blew into surrounding
structures, causing extensive collateral damage and, in some cases, igniting
fires and causing additional collapses. In total, 10 major buildings experienced
partial or total collapse, and approximately 30 million square feet of commercial
office space was removed from service, of which 12 million belonged to the
WTC Complex.
Following the WTC attack, the Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), in association with New York City and several other Federal agencies and professional organizations, deployed a Building Performance Study Team consisting of civil, structural, and fire protection engineers to study the performance of buildings at the WTC site.
The purpose of the study was to examine building damage, collect data,
develop an understanding of the response of each affected building, identify
the causes of observed building performance, and identify studies that
should be performed. The immediate effects of the aircraft impacts on
the towers, the spread of fires following the crashes, the fire-induced
reduction of structural strength, and the mechanism that led to the collapse
of each tower were studied. Additionally, the team studied the performance
of buildings in the immediate vicinity of the towers to determine the
effects of damage from falling debris and fires. From its observations
and findings, the team developed recommendations for more 
detailed
engineering studies with the goals of completing the assessments and producing
improved guidance and tools for building design and performance evaluation.
The results of the study are presented in World Trade Center Building
Performance Study: Data Collection, Preliminary Observations, and Recommendations
(FEMA 403). An electronic version of the report, in the form of Adobe
Portable Document Format ® (PDF) files is contained on
this CD-ROM. The report consists of an Executive Summary, eight chapters,
and nine appendixes, which can be accessed directly with the links that
appear along the top of this page. A link to the report Table
of Contents is also provided. From the Table of Contents, you can
jump to any chapter, section, subsection, figure, or table in the report.
Executive Summary – Background of the event and summary of major observations and conclusions.
Chapter 1: Introduction – Purpose and scope of the study, description of the WTC site, summary of events, response of the engineering community, and overview of building codes and fire standards as they relate to the performance of the WTC buildings.
Chapter 2: WTC 1 and WTC 2 – Design and construction of the WTC towers, including structural, fire protection, emergency egress, and emergency power systems, and the response of each tower to the impact and fire damage.
Chapter 3: WTC 3 – Design and construction of WTC building 3, the 1993 car bomb attack, and the evacuation and performance of the building after the September 11 attacks.
Chapter 4: WTC 4, 5, and 6 – Structural and fire protection features of the three buildings, loads placed on the buildings by fire and debris impact, and analysis of building performance, including collapse mechanisms.
Chapter 5: WTC 7 – Design and construction of WTC building 7, fire protection systems, building loads, timeline of events, and potential collapse mechanisms and sequences.
Chapter 6: Bankers Trust Building – Building description, structural and architectural damage caused by debris impact, and computer model analysis of the building performance.
Chapter 7: Peripheral Buildings – Damage to the Winter Garden, World Financial Center (WFC) building 3, the Verizon building, One Liberty Plaza, and the buildings at 30 West Broadway, 130 Cedar Street, 90 West Street, and 45 Park Place.
Chapter 8: Observations, Findings, and Recommendations – Observations, findings, and recommendations regarding the overall study, the individual buildings studied, and issues for future study.
Appendix A: Overview of Fire Protection in Buildings – Fire behavior, structural response to fire, and life safety considerations.
Appendix B: Structural Steel and Steel Connections – Mechanical properties of structural steel and connection capacities in WTC 1, 2, and 5.
Appendix C: Limited Metallurgical Examination – Results of laboratory analyses of steel samples from WTC 7, and WTC 1 or WTC 2.
Appendix D: Steel Data Collection – Collection of samples from steel pieces delivered to salvage yards, including a detailed spreadsheet that documents the samples collected.
Appendix E: Aircraft Information – General specifications for the Boeing 767-200ER aircraft.
Appendix F: Structural Engineers Emergency Response Plan – List of criteria, taken from the Structural Engineers Association of New York (SEAoNY) Structural Engineering Emergency Response Plan (SEERP), for the development of emergency response plans for natural and manmade disaster events.
Appendix G: Acknowledgments – Individuals and organizations who contributed to the WTC Building Performance Study.