In recent years,assessing and managing hazard risks to infrastructure system has become a high profile matter of infrastructure managers as a results of the need of our society to have proactive responses to natural disasters.(Taylor et al.2006; Biringer et al.2013).Significant works have been archived,especially in the application of probabilistic methods to model the occurrences of hazard events and the expected impacts incurred (Castelli & Scavia 2008; Korup & Clague 2009).In civil engineering,one of the popular methodologies that is used to estimate the expected risks associated with failure of infrastructure objects due to hazard risks is the method of using fragility curves (Karim & Yamazaki 2001; Graf et al.2009).