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World Trade Center - Structural Engineering Investigation

Lead structural engineer for investigation that determined that the collapse of one WTC tower did not cause or contribute to the collapse of the other.

An investigation of the collapses of the World Trade Center towers was performed by a pre-eminent group of engineering firms led by Weidlinger Associates. The study, conducted on behalf of the attorneys for Silverstein Properties, Inc., is the most comprehensive study to date of why the Twin Towers stood for as long as they did and why they ultimately collapsed. The results of the study were released to the National Institute of Standards and Technology, the federal agency charged with conducting an in-depth investigation of the causes of the collapses. The study established that the strength and redundancy of the superstructure of the towers initially allowed them to withstand the high-speed impact of the Boeing 767s and that the subsequent collapses were initiated separately by a combination of immediate damage from the impact of the airliners and the resulting fires on the floors that were struck.

Based on analysis of the available data, including original structural engineering plans and thousands of photos and dozens of videos, and the use of advanced computer modeling and fire evaluation techniques, the engineering team was able to recreate the condition of the towers at various critical points in time from impact to collapse. Using FLEX software, developed in-house for the Department of Defense for analysis of structures undergoing large deformations under extreme loads, Weidlinger engineers developed sophisticated computer models to analyze events on the impacted floors. The results established the extent of damage in the tower cores due to the airplane impacts, the subsequent effects of fires on the structural capacity of the columns, the resultant load redistribution, and the ultimate failure mechanisms at the point of collapse of each tower. To establish a baseline for the structures prior to September 11, 2001, the engineers studied the original design documents, as well as inspection records, and quantified the structural performance. These studies established that the structures were well designed and extremely resilient and robust. They had been maintained to a standard that exceeded customary practice in high-rise office buildings.

Completion Date: 2004
Location: New York, New York
Owner or Client: Silverstein Properties
Prime Consultant(s): WAI Prime; Wachtell Lipton Rosen & Katz

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