Risk of progressive collapse of buildings from terrorist attacks: are the benefits of protection worth the cost?

The paper describes a probabilistic risk assessment model to identify the risks associated with vehicle-borne improvised explosive device (VBIED) attacks to large federal government buildings in the United States. Probability of terrorist threat, hazard, damage, fatality, and economic and social loss for progressive collapse are modeled as stochastic variables. It was found that the existing annual fatality risk for building occupants is lower than acceptable risk criteria, and that progressive collapse is an exceedingly rare event in Western countries. A performance-based design using cost-benefit analysis of U.S. design provisions to mitigate against progressive collapse showed that these design measures only becomes cost-effective when the threat likelihood is a very high 1 in 1,000 per building per year. However, such provisions are more likely to be cost-effective in regions of high seismicity due to a lower cost premium