Development of fragility curves for road bridges exposed to volcanic lahars

Abstract

One of the main volcanic processes affecting roadbridges are lahars, which are flows of water and volcanic materialrunning down the slopes of a volcano and river valleys.Several studies have evidenced the effects of other volcanicprocesses on road infrastructure; however, limited informationis available about the effects of lahars on bridges. Inthis paper, bridge failure models due to lahars are proposedand, based on these, fragility curves are developed. Failuremodels consider the limit state of pier and abutment overturning,and deck sliding caused by lahars. Existing physicalmodels are used to stochastically characterize lahar loads andoverturning momentum on bridges. Monte Carlo simulationsare applied to quantify the probability of bridge failure givenby different lahar depths. Fragility curves of bridges are finallyparameterized by maximum likelihood estimation, assuminga cumulative log-normal distribution. Bridge failuremodels are empirically evaluated using data on 15 bridgesthat were affected by lahars in the last 50 years. Developedmodels suggest that decks fail mainly due to pier and/or abutmentoverturning, rather than deck-sliding forces. Moreover,it is concluded that bridges with piers are more vulnerableto lahars than bridges without piers. Further research is beingconducted to develop an application tool to simulate theeffects of expected lahars on exposed bridges of a road network.