Quantifying system vulnerability as a performance measure for systems investment evaluation and decision-making

Civil engineering systems are vulnerable to natural and man-made threats. In recent years, agencies are paying increased attention to investments that are geared towards reducing system vulnerability. For purposes of analyzing the effectiveness of such investments and also for vulnerability monitoring, a procedure is needed to quantify the level of system vulnerability at any time. This paper identifies vulnerability types and presents a general procedure for establishing system vulnerability. The procedure quantitatively assesses the threat likelihood and consequence. Threat likelihood is expressed as a function of the system environment (threat type); and consequence, is expressed as a function of the system attributes. Specifically, the consequence of failure due to the threat is evaluated on the basis of possible failure modes and the extent of public exposure in the event of failure. Public exposure, a function of the occupancy (or traffic) and the class of the system, reflects the effect of system failure on users and the surrounding community.