Seismic fragility analysis of deteriorating RC bridge columns with time-variant capacity index

To establish a framework for evaluating the time-variant seismic performance of deteriorated reinforced concrete (RC) structures with uncertainty, offshore RC bridge columns exposed to marine environments are studied in this paper. The uncertainties from the material parameters, corrosion initiation time and earthquake ground motions are taken into account. Due to the different corrosion characteristics in various zones (i.e. the submerged zone, splash and tidal zone, and atmospheric zone) along the column height, corrosion-induced damages in each zone are considered separately, and the geometric mean of the yield displacements of the three zones is used to define the structural capacity (limit state). Meanwhile, the time-variant limit states are determined based on nonlinear static analyses, which reflect the current state of deteriorating RC columns. A total of four cases are studied using the Latin hypercube sampling (LHS) technique based on the probability distributions of the material parameters and corrosion initiation time, including the effects of statistical correlations among the material parameters. The results reveal that the seismic fragility is underestimated by a deterministic numerical model. The uncertainty in the corrosion initiation time influences the seismic fragility less significantly than that in the structural material parameters whether or not anti-corrosion measures are implemented. It is suggested that probabilistic methods should be used for seismic evaluation of deteriorating RC structures to consider the uncertainty involved.

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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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