Time-Varying Seismic Fragility Analysis of Offshore Bridges with Continuous Rigid-Frame Girder under Main Aftershock Sequences

For offshore bridges, the most prominent problem in the whole life cycle is that it is in an earthquake prone zone and an offshore corrosion environment at the same time. A nonlinear dynamic analysis model is set up for an offshore multispan and continuous rigid frame bridge based on the OpenSEES platform. The fragility surface of the bridge pier, bearing, bridge platform, and system are established by selecting a reasonable damage constitutive model of the material durability and a damage index analysis that studies the damage of the bridge durability to time-varying seismic fragility of bridge components and the system of the whole life cycle in offshore environment. The results show that the durability damage will lead to a constant decline in seismic capacity of the pier and an increase of the seismic demand under earthquake action as well as the probability to reach the ultimate failure state; compared to high piers, a low pier is more vulnerable to the offshore corrosion environment; the seismic fragility of bridge platform is higher than that of simply bearing; and the influence of offshore corrosion on environment is relatively large. With the prolongation of service period, the effect of durability damage on the seismic fragility of bridge system cannot be ignored in the coastal environment and it is necessary to make a reasonable evaluation on the seismic fragility of bridge structure during the whole life period.

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Comparison of steel frames with RWS and WFP beam-to-column connections through seismic fragility analysis

Advances in Structural Engineering ◽

10.1177/1369433220977284 ◽

2020 ◽

pp. 136943322097728

Author(s):

Haoran Yu ◽

Weibin Li

Keyword(s):

Limit State ◽

Pushover Analysis ◽

Steel Frames ◽

Fragility Analysis ◽

Structural Safety ◽

Seismic Fragility ◽

Fe Modelling ◽

Collapse Resistance ◽

Seismic Collapse ◽

Probabilistic Seismic Demand

Reduced web section (RWS) connections and welded flange plate (WFP) connections can both effectively improve the seismic performance of a structure by moving plastic hinges to a predetermined location away from the column face. In this paper, two kinds of steel frames—with RWS connections and WFP connections—as well as different frames with welded unreinforced flange connections were studied through seismic fragility analysis. The numerical simulation was conducted by using multiscale FE modelling. Based on the incremental dynamic analysis and pushover analysis methods, probabilistic seismic demand analysis and seismic capability analysis were carried out, respectively. Finally, combined with the above analysis results, probabilistic seismic fragility analysis was conducted on the frame models. The results showed that the RWS connection and WFP connection (without double plates) have little influence on reducing the maximum inter-storey drift ratio under earthquake action. RWS connections slightly reduce the seismic capability in non-collapse stages and improve the seismic collapse resistance of a structure, which exhibits good structural ductility. WFP connections can comprehensively improve the seismic capability of a structure, but the seismic collapse resistance is worse than that of RWS connections when the structure has a large number of storeys. The frame with WFP connections has a lower failure probability at every seismic limit state, while the frame with RWS connections sacrifices some of its structural safety in non-collapse stages to reduce the collapse probability.

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