飞机撞击世贸大厦的模拟分析

Abstract

The objective of this report was to analyze the aircraft impacts into each of the World Trade Center (WTC) towers to provide the following:estimates of probable damage to structural systems due to aircraft impact, including exterior walls, floor systems, and interior core columns;estimates of the aircraft fuel dispersal during the impact; estimates of debris damage to the interior tower contents, including partitions and workstations. Thus, this analysis established the initial conditions for the fire dynamics modeling and the thermal-structural response and collapse initiation analysis.

The impact analyses were conducted at various levels of complexity including: the component level, the subassembly level, and the global level to estimate the probable damage to the towers due toaircraft impact. Simplified analyses were also used to support the development of the global finiteelement models. Analysis of uncertainties using the component and subassembly analyses wereconducted to assess the effects of variability associated with various input parameters and identify themost influential parameters that affect the damage estimates using orthogonal factorial design. Based onthe results of the sensitivity analyses, the most influential parameters identified were varied in the globalmodels to provide a range of damage estimates for WTC 1 and WTC 2.

As part of the tower and aircraft models, constitutive relationships describing the actual behavior of thestructures under the dynamic impact conditions of the aircraft were developed based on test results of thetower steels and from the open literature for other materials. Various grades of steels used in the exteriorwalls and core columns of the towers, weldment metal, bolts, reinforced concrete, aircraft materials, andnonstructural contents were considered. The constitutive relationships included high strain-rate effectsand failure criteria for the various materials.

The tower models used in the global impact analyses were developed based on the original WTCdrawings and thestructural databases of the towers developed within the framework of the baselinestructural performance analysis. The tower models included the primary structural components of thetowers in the impact zone, including exterior walls, floor systems, core columns, and connections. Arefined finite element mesh was used for the areas in the path of the aircraft and a coarser mesh was usedelsewhere. The models also included the nonstructural building contents, such as partitions andworkstations, in the path of the aircraft debris.

The Boeing 767 aircraft model was developed based on information gathered from documentary aircraftstructural information, and data from measurements on a Boeing 767 aircraft. The model included the aircraft engines, wings, fuselage, empennage, and landing gear, as well as nonstructural components ofthe aircraft. A detailed analysis was carried out to estimate the fuel distribution in the aircraft wings at the time of impact.

The WTC towers and Boeing 767 aircraft are complex structural systems. In the global model development process, the objective was to include all of the primary structural components and details of both the aircraft and towers. This approach, however, results in very large models. The component and subassembly analyses were used to determine model simplifications to reduce the overall model size while maintaining fidelity in the analysis. Therefore, a series of component impact and subassembly