Assessment of risk reduction strategies for terrorist attacks on structures

Attacks on infrastructure have been a common feature of terrorism over many decades. The weapon of choice is often a Vehicle-Borne Improvised Explosive Device (VBIED) or a person-borne or other type of IED. The consequences of a successful attack in terms of casualties, physical damage, and other direct and indirect costs including societal costs can be catastrophic. Protectives and other risk reduction measures can ameliorate the threat likelihood, vulnerability or consequences. There is a need for a rational approach to deciding how best to protect infrastructure, and what not to protect. Hence, this paper describes a probabilistic risk assessment for the protection of infrastructure from explosive attacks. This includes a description of terrorist threats and hazards, vulnerability assessment including progressive or disproportionate collapse, and consequences assessment. Illustrative examples of the decision analysis consider the optimal risk reduction and design strategies for bridges and the progressive collapse of buildings.