Project Description

Subway system is one of the main targets of terrorist attacks. Among the various schemes that terrorists may turn to, bombing is one of their prime options, examples of which include the 1995 attack on Paris subway and the 2005 attack on the London subway. Explosion inside a subway structure could threat the nearby people’s lives; it could also severely damage the subway structure and cause further loss of lives and properties. The importance of this issue was addressed by the Blue Ribbon Panel on Bridge and Tunnel Security in their 2003 report but the method to evaluate the structure integrity of existing subways and the guideline to design new underground structures taking into account the internal blast loading still need to be developed. Specifically in New York City, the threat of terrorist attacks on subway system has intensified over the years yet how the existing subway structures would response under internal blasting is still not clear; and how to consider such events in the structural design of the new Second Avenue Subway is also not resolved.

In order to develop a reliable method for evaluation and design, it is necessary to investigate the dynamic response and the damage mechanism of subway structures under internal blast loading. However, very limited related studies can be found in this field. This is due to, first of all, the negligence of the issue in the days when threats of terrorist attack were not as severe, and secondly, the very complicated characteristics of the problem, which includes coupled fluid-structure interaction, dynamic soil/rock-structure interactions, structure damage, nonlinear response of soil or rock, and three-dimensional effects. Considering this complexity, small-scale experiments or analytical analyses generally cannot reveal the true mechanism; instead, carefully-designed, sophisticated dynamic numerical method has the potential to accomplish the task. There exist few dynamic analyses on the responses of underground structures subject to internal blast loading, but the nonlinearity and plasticity of geomaterials, as well as the dynamic and nonlinear interactions between the structure and the surrounding medium, were generally over-simplified; more importantly, no investigation considering the geological condition and subway structures in New York City has ever been endeavored.

In this study, nonlinear dynamic Finite Element analyses on the responses of subway structures subject to internal blast loading will be carried out using ABAQUS. At this stage, the focus will be placed on dynamic soil/rock-structure interactions, structure damage, nonlinear response of soil or rock, and three-dimensional effects. The increases in materials’ stiffness and strength due to rapid loading will also be considered. The fluid-structure interaction will be simplified in the present stage of study. The blast will be applied to the subway structure as impulse loading at appropriate locations using existing solutions of explosion problems. The analyses will use typical subway tunnels in New York City as objects and take into account the geological condition of New York City. The coupled fluid-structure interaction, the guidelines to evaluate the structure integrity of existing subways and those to design new underground structures will be investigated in the later stage of investigation.

The present study can serve as a corner stone for the resistance evaluation and design of New York Subway structures subject to possible terrorist attack using explosives.