Dissecting the Collapseds

摘要

The September 11 terrorist attacks on World Trade Center horrified the civilized world. An estimated 2,830 human lives were extinguished by these attacks―the second greatest number of lives ever lost in a single event in the United States. These attacks also resulted in extensive damage to a large number of buildings at the World Trade Center complex and within the vicinity of the complex. In the aftermath of the events, the Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineering (SEI/ASCE)―in association with several other federal agencies and professional organizational―dispatched a team of civil, structural and fire protection engineers to study the structure of the building at the site. These experts in tall building design, steel structure behavior, fire protection engineering, blast effects, and structural investigation were impaneled on a building performance assessment team (BPAT). This BPAT was sponsored by a partnership of FEMA, SEI/ASCE, the state of New York, the New York City Department of Design and Construction, and the Structural Engineers Association of New York. The team was supported by the National Council of Structural Engineers Associations, the National Fire Protection Association, the Society of Fire Protection Engineers, the American Concrete Institute, the American Institute of Steel Construction, the Masonry Society, the Council of Tall Building and Urban Habitat, and the National Institute of Standards and Technology. The BPAT was to review the damage caused by these events, collect available data, develop understanding of the performance of each affected building, determine the causes od observed behavior, and reveal the need for further studies that should be performed. In particular, the team studied the immediate effect of the aircraft impact on each tower, the spread of the following crashes, the reduction of strength caused by the fire, and the mechanism that led to the collapse of each tower. Additionally, the performance of buildings in the immediate vicinity of the towers was studied to determine the effects of damage from falling debris and fires. A draft from the team's report, World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations - a copy of which was obtained by Civil Engineering―was completed in March; the final report is scheduled for release by FEMA on April 30. What follows is essentially a distillation of portions of the draft that focuses on the twin towers.