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Aircraft Impact Damage

The “post-September 11” structural engineer, while feeling the remorse and confusion that every other American has dealt with, is also privileged with the immense education an analysis of the WTC collapse can provide. A newly found understanding for impact dynamics and failure of very large systems, as well as a comprehensive grasp of the brevity accompanying safety considerations in construction projects, will be present in industrial practice from now on. The research into the World Trade Center Towers collapse following the initial factgathering phase is now beginning the more ambitious tasks of reconstructing various stages of the damage and destruction of the Twin Towers. Currently, or at least as current as this paper, the FEMA/ASCE team has just released their report, [1], and an independent investigation is being conducted by the National Science Foundation study group. Preparations are also underway to launch a new program aimed at a producing a detailed simulation of the aircraft impact damage, fire damage, and the total collapse of the buildings. This work is led and coordinated by the National Institute of Standards and Technology. This article was completed prior to the public release of the FEMA/ASCE report, therefore only the generally accessible information from the media and literature were used in the analysis. The facts documenting the first phase of the main objective of the present research is to predict the amount of internal structural damage that occurred within the Towers upon the aircraft impact and that was hardly visible from the outside. Attention is focused on three main structural components of the Towers, i.e., a lattice of exterior colu mns, complex floor truss assemblies, and the core load-bearing structure. A thorough understanding of failure mechanisms and the extent of damage done when a high speed aircraft impacts a largescale structural system is a prerequisite for undertaking the next stage of the analysis, which is the weakening effect of fire and finally the self-distracting implosion of both Towers. The airplane itself, built as an assemblage of ring and stringer-stiffened panels, was also subjected