Abstract:
This report presents a comprehensive analysis of the baseline structural performance and aircraft impact damage of the World Trade Center Towers as part of the National Institute of Standards and Technology (NIST) investigation into the September 11, 2001 attacks. The study is divided into two key tasks: (1) the establishment of reference structural models to assess the towers’ original design and performance under gravity and wind loads, and (2) the estimation of aircraft impact damage to define initial conditions for subsequent fire dynamics and collapse initiation analysis.
The first task examines the original structural integrity of the towers, evaluating factors such as story drift, floor deflections, demand-to-capacity ratios, and load distribution in primary structural components. Wind loads are analyzed based on both the original design estimates and modern wind tunnel studies, providing insight into reserve capacity and the ability to withstand unexpected events like major fires or impact damage.
The second task focuses on the impact of the aircraft on the towers, using finite element simulations and computational modeling to assess structural response, localized failures, and debris dispersion. The study includes analyses of fuel dispersion, fireproofing damage, and the progressive weakening of structural elements. Additional component and subassembly impact analyses were performed to refine the global impact model, addressing factors such as aircraft speed, trajectory, and material interactions.
Findings from this research contribute to a greater understanding of high-rise structural behavior under extreme conditions and offer insights for improving building safety standards to mitigate future risks from impact, fire, and progressive collapse scenarios.
