Terrorism Risks and Blast Damage to Built Infrastructure Mark G. Stewart 1 ; Michael D. Netherton 2 ; and David V. Rosowsky 3 Abstract: There is increasing interest in the use of risk management techniques for assessing vulnerability of built infrastructure to the “new” man-made hazard of terrorism. As such, the various uncertainties and risks associated with terrorism must be quantified and then used as the basis for assessing the viability and relative benefits of different mitigation measures, such as the use of blast-resistant technologies and other protective measures. In this paper, a probabilistic risk assessment procedure is developed to predict risks of damage arising from blast damage to built infrastructure. Issues related to risk assessment, including the concept of “risk transfer” and compari- sons with natural hazards, are also discussed. To illustrate the concepts described, a preliminary reliability analysis is conducted, where fragility and blast reliability curves are developed for common glazing systems subject to explosive blast. The probabilistic analyses include the uncertainties associated with blast modeling, glazing response, and glazing failure criteria, and these are used to assess the effectiveness of various glazing systems. DOI: 10.1061/ASCE1527-698820067:3114 CE Database subject headings: Risk management; Blasting; Infrastructure; Decision making; Benefit cost ratio; Terrorism. Introduction Following the devastation of the World Trade Center on Septem- ber 11, 2001, the Bali bombing on October 12, 2002, and the bombing of the Australian Embassy in Jakarta on September 9, 2004, and other similar events worldwide, there has been renewed emphasis in the United States, the United Kingdom, Australia, and elsewhere on designing and retrofitting critical infrastructure to resist blast damage. Critical infrastructure may include built infrastructure such as buildings, bridges, power plants, pipelines, water supply systems, dams, and chemical process facilities as well as such “cyber” systems as safety-critical software, commu- nication, and intelligence technology IT software essential to the operation of many aspects of society. Built infrastructure, particu- larly buildings, has been the frequent target for terrorism and, as such, is the focus of the present paper. The present paper focuses on structural and load-capacity systems, as they share character- istics similar to most built infrastructure—namely, variability of loads and system response, failure is a low probability/high con- sequence event, and decisions made with incomplete information. Experience in the United Kingdom shows that intense blast loadings cause little structural damage to reinforced concrete RC or steel framed buildings designed to modern codes. Most damage occurs to the building facade, particularly glazed areas Smith and Rose 2002. Blast entering buildings can cause sig- nificant damage to building interiors, resulting in disruption to the working environment and building services sustaining that envi- ronment. Clearly, maintaining the integrity of the building enve- lope will reduce hazards to building occupants. The effect of glazing failure on interior damage can be reduced by antishatter film and bomb blast net curtains, while window strength can be increased by use of toughened or laminated glazing systems Mays and Smith 1995; Norville and Conrath 2001. Wall strength can be improved by additional reinforcement, additional supports, geotextiles, energy absorbing restraints, internal con- crete skins, composite materials, etc. Naturally, the most effective countermeasure is to keep the source of blast loading as far as possible from a building. This is not to say, though, that blast loadings cannot cause severe structural damage, such as that experienced by the Murrah Building in Oklahoma City on April 19, 1995. However, in this case, partial collapse of the building was caused by disintegration of a critical column, causing progressive collapse. If the building had been designed as a special moment frame for earthquake design, then loss of floor area would have been reduced by be- tween 50 and 80% Corley et al. 1998. Damage to the Pentagon on September 11, 2001, was contained by its resilience to pro- gressive collapse, namely, its continuity, redundancy, and energy- absorbing capacity ASCE 2003. There is therefore renewed interest in progressive collapse provisions Nair 2004, many of which were incorporated into many design codes following the Ronan Point collapse in 1968. Hence, with the exception of ex- traordinarily large blasts, a moment resisting RC or structural steel frame designed and detailed for alternative load paths should provide sufficient structural resistance to prevent collapse. The threat of terrorism may be high in some countries. How- ever, given the very high number of buildings, bridges, pipelines, and other built infrastructure in any one country, the threat to an individual building, bridge, pipeline, etc., is low. On the other 1 Professor, Centre for Infrastructure Performance and Reliability, School of Engineering, Univ. of Newcastle, Callaghan, NSW, 2308, Australia corresponding author. E-mail: mark.stewart@ newcastle.edu.au 2 Graduate Student, Centre for Infrastructure Performance and Reliability, School of Engineering, Univ. of Newcastle, Callaghan, NSW, 2308, Australia. 3 A. P. and Florence Wiley Chair Professor and Dept. Head, Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843-3136. Note. Discussion open until January 1, 2007. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and pos- sible publication on April 7, 2005; approved on October 25, 2005. This paper is part of the Natural Hazards Review, Vol. 7, No. 3, August 1, 2006. ©ASCE, ISSN 1527-6988/2006/3-114–122/$25.00. 114 / NATURAL HAZARDS REVIEW © ASCE / AUGUST 2006 Downloaded 07 Feb 2010 to 140.254.17.119. Redistribution subject to ASCE license or copyright; see http://pubs.asce.org/copyright