The aircraft impact and progressive collapse of the World Trade Center (WTC) towers, an unprecedented building disaster, pointed out that peculiar external loads and phenomena, which are not considered in building designs and about which little technical information is available, can lead to the total collapse of buildings and the loss of many lives. It may be impractical to adopt building codes that demand structural capabilities to resist such loads and phenomena. However, we should have in-depth technical knowledge about them in order to minimize fatalities and structural damage. Due to the nature of the problem, numerical simulation with dynamic schemes and global analytical models is considered to be an effective means of clarifying actual phenomena. However, if we try to conduct dynamic analyses of full-model large-scale structures like the WTC towers, calculation cost usually becomes a bottleneck. Therefore, a highly accurate numerical code with a very low calculation cost is strongly desired.
The objective of this study is to develop a dynamic finite element code that can effectively cope with strong nonlinearities and discontinuities common in impact collapse problems, and whose calculation cost is sufficiently low to enable dynamic analyses of full-model large-scale structures. The Adaptively Shifted Integration (ASI) technique for the linear Timoshenko beam element is modified to an ASI-Gauss technique, to further reduce calculation cost. Algorithms considering member fracture and elemental contact are also modified. An impact collapse analysis is conducted using a full-scale finite element model to simulate the aircraft impact with the World Trade Center South Tower (WTC2), and the analytical results are compared with the observed data. The results show a clear resemblance. Moreover, the propagation of shock waves through the whole structure and the instantaneous redistribution of stresses, which may have caused some damages to structurally important parts, are observed.