Probabilistic seismic risk forecasting of aging bridge networks

Bridges are the most vulnerable elements in transport systems, and they may undergo structural prob- lems due to environmental conditions and natural disasters. Governmental agencies and owning compa- nies must therefore plan maintenance and retrofit interventions rationally, to avoid potential severe network disruptions. With reference to seismic risk, several studies on the risk assessment of bridge networks, and on aging as one of the main factors affecting the seismic vulnerability of existing bridges, have recently also been reported. In these contributions, the seismic fragility of bridges is considered as a time-dependent parameter, whereas seismic hazard and financial exposure are described according to classic stationary assumptions. The present study proposes an innovative, comprehensive and fully time-dependent probabilistic seismic risk framework, to evaluate the expected average annual loss for stocks of deteriorating bridge structures. This framework is illustrated in a case study of 500 bridges and the results are critically discussed.