Fragility surfaces for multi-hazard analysis of suspension bridges under earthquakes and microbursts

The flexible nature of long-span suspension bridges increases their vulnerability to dynamic excitations such as winds and earthquakes. Non-stationary and transient wind events such as microbursts have the potential to create even more damage to these flexible structures. The problem becomes even more apparent when a structure is expected to undergo multiple extreme events. This paper aims to present a multi-hazard framework that assesses the vulnerability of a suspension bridge to earthquake and extreme wind events. For this purpose, specific damage states for wind and earthquake have been defined. Then, fragility curves and surfaces are generated to estimate the exceedance probability of different damage states throughout the structure as it undergoes multiple extreme events. The probability convolution theory is then used to assess the annual probability of failure considering the likelihood of occurrence of damage and likelihood of occurrence of each of the extreme events. The proposed framework will provide a meaningful procedure to calculate and communicate the risks from multiple extreme events on suspension bridges.