Modeling Methodologies for Assessment of Aircraft Impact Damage to the World Trade Center Towers

The Federal Building and Fire Safety Investigation of the World Trade Center Disaster was recently completed by the National Institute of Standards and Technology (NIST). A critical component of the investigation was to analyze the aircraft impacts into the World Trade Center (WTC) towers to evaluate the impact-induced damage to the towers. This impact damage established initial conditions for the fire dynamics modeling, thermal-structural response, and collapse initiation analyses performed as part of the NIST investigation into the collapse of the WTC towers. This paper presents the development of the WTC tower and aircraft models and associated analysis methodologies used to simulate the aircraft impact response. The analyses performed span the range from laboratory-scale material testing up to the global aircraft impact response of the WTC towers. Simulations were performed at various levels of refinement. Component analyses were performed using small portions of the aircraft and tower. In these analyses, components were modeled with a fine resolution to investigate the details of the initial impact and breakup behavior. Results from the component analyses were used to develop the simulation techniques required for the global analysis of the aircraft impacts. The global impact simulation techniques were aimed at reducing the overall global model size while maintaining fidelity in the impact response. The accuracy of the calculated aircraft impact damage was evaluated by comparison with observed impact damage to the towers.