The effects of explosive blast load variability on safety hazard and damage risks for monolithic window glazing Michael D. Netherton * , Mark G. Stewart Centre for Infrastructure Performance and Reliability, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia article info Article history: Received 8 April 2008 Accepted 11 February 2009 Available online 27 May 2009 Keywords: Safety hazards Security risks Glazing Structural reliability Explosive blast abstract Although the modelling of built infrastructure subject to blast loading has been well developed, considerable uncertainty remains with respect to explosive loading parameters and structural response. This paper focuses on facade glazing – as this poses significant safety hazards when affected by explosive blast loads. A structural reliability analysis is used to calculate probabilities of glazing damage and safety hazards conditional on given threat scenarios. The analysis considers the variability of explosive blast loading; in particular, from variations in explosive weight, explosion effects in terms of pressure, stand- off distance, inherent blast load variability and model error. Uncertainties in structural response (including the variability in glazing stress limits, situational geometry, fragment drag coefficients and modelling error) are then considered in the analysis. This allows the prediction of likelihood and extent of damage and casualties. It was found that damage and safety hazard risks are very sensitive to the accuracy of the blast loading prediction model and the inherent variability of blast loading. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction A favoured method of attack to infrastructure is via Vehicle Borne Improvised Explosive Devices (VBIEDs) detonated within urban environments. The use of terrorist-style explosive blast loads within urban environments typically aims to maximise disruption, damage or destruction to infrastructure, public systems or people. Military planners, on the other hand, try to minimise collateral damage that may occur as a result of ordnance delivered into areas where civilian infrastructure and military targets are in close proximity, which tends to also occur in complex urban environs. Thus, for these and many other scenarios the quantification of infrastructure related safety hazards and damage risks will be of significant interest to decision makers in civil defence, the military and elsewhere. With the exception of extraordinarily large blasts, experience in the United Kingdom [1] and elsewhere, shows that terrorist-style blast loadings cause little structural damage to moment resisting reinforced concrete or steel framed buildings designed to modern codes. Most damage occurs to building facades (see Fig. 1), partic- ularly glazed areas, causing high casualties and significant damage to building interiors. For example, window damage and glass related injuries occurred up to 1.6 km from ‘ground zero’ of the 1995 Oklahoma city bombing [2]. Clearly, in urban environs, a very large number of buildings can be affected by a medium to large explosive charge. It follows that the effects of explosive blast loading on building facades are worthy of detailed analysis, and for glass facades in particular. Nearly all current explosive blast modelling techniques are deterministic, for example, given an explosive weight and range, does a particular element of a building survive the shock wave or not? One tool that is often used in the deterministic prediction of glazing safety hazards is HazL [3]. This software and other design tools and specifications are also likely to be conservative (i.e. provide an upper bound value of damage or safety hazard). This may be appropriate for risk screening or preliminary hazard anal- yses, but they often fail to reflect degrees of uncertainty associated with many aspects of threats and vulnerabilities and the degree of conservatism in predictions is not known. For example, there may be considerable variability in the weight of explosive, the range to the intended target, the energetic output of the explosive (in terms of either peak pressure or impulse), the vulnerability of any element affected, trajectory path of debris, and so on. A favoured method for dealing with such uncertainties is probabilistic risk assessment where quantitative advice can be provided to decision makers in the form of probabilities of damage or safety hazard. Information derived using probability and structural reliability * Corresponding author. Graduate Research Student, Centre for Infrastructure Performance and Reliability, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia. Tel.: þ61 2 49215401 fax: þ61 2 49216991. E-mail address: michael.netherton@newcastle.edu.au (M.D. Netherton). Contents lists available at ScienceDirect International Journal of Impact Engineering journal homepage: www.elsevier.com/locate/ijimpeng 0734-743X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijimpeng.2009.02.009 International Journal of Impact Engineering 36 (2009) 1346–1354