Wind-Induced Fragility Assessment of Large-Span Continuous Girder Bridges under Construction in Cold Regions

In this work, finite-element models of four typical bridge construction stages were established via OpenSees (version 3.4.0) software using the Tonghe Songhua River Highway Bridge as a case study, and the OpenSees model was compared with a Midas Civil 2022 (version 1.1) model to verify its accuracy. The effect of air density at low temperatures in cold regions was considered with an autoregressive model and linear filtering method, and a girder was simulated by incorporating the von Karman wind spectrum to obtain the dynamic response at the bridge height under a fluctuating wind velocity at four construction stages via nonlinear dynamic analysis with OpenSees. Finally, a wind-induced fragility model of the bridge was established, and the exceeding probability curves of the bridge with different damage levels in four typical construction stages were plotted. Fragility curves in the maximum cantilever state at four temperatures were also established. The fragility curve analysis revealed that there is a small probability of damage during the construction stage of the bridge with a 100-year return period wind speed, and the larger the cantilever, the greater the probability of bridge damage from pulsating wind at the same wind speed. Therefore, the construction schedule should be adjusted to prevent the bridge from experiencing downtime in winter in a severely cantilevered state.