Abstract:
This report presents the global structural analysis of World Trade Center Building 7 (WTC 7) in response to fire-induced damage and debris impact following the collapse of the nearby Twin Towers on September 11, 2001. Conducted as part of the National Institute of Standards and Technology (NIST) investigation into the WTC disaster, the study aims to determine the sequence of structural failures leading to the building’s global collapse.
A comprehensive finite element model of WTC 7 was developed using original structural and fabrication drawings to capture the primary load-bearing components, including exterior and core columns, floor framing elements, and transfer trusses. The model incorporated thermally dependent material properties to simulate the progressive weakening of structural members due to fire exposure. Various failure scenarios were examined, including local component failures, load redistribution effects, and progressive collapse mechanisms.
The analysis demonstrated that fire-induced thermal expansion and column instability were the primary contributors to the initiation of collapse. The study also compared simulated structural responses with available photographic and video evidence to validate the modeled collapse sequence. The findings provide critical insights into progressive structural failure in high-rise buildings subjected to extreme conditions and offer recommendations for improving fire safety and structural integrity in future building designs.
