Seismic Fragility Analysis Of High Arch Dams

To reasonably explore the abundant water resources in western China,many high concrete arch dams with height over 200 meters have been build or planed during last two decades.It is a key issue to ensure the seismic safety of these high arch dams.With the improvement of seismic demands,aleatory and epistemic uncertainties have been considered in the seismic design of structures.Seismic fraglity analysis may take into account those uncertainties,and thus has been applied to various structural types.This study focuses on the seismic fragility analysis of high arch dams.The main research achievements are summarized as follows.(1)The parametric analysis of the seismic response of arch dams is implemented considering different foundation models and artificial earthquake accelerogrms.Firstly,the parametric analysis on the truncated size,material damping and non-uniformity of the foundation are analyzed comprehensively.Based on the analysis results,it is suggested to ignore the foundaton damping,consider the non-uniformity,and truncate foundation with the size as two times the dam height.Subsequently,the uncertainty of artificial synthesized earthquake accelerograms is studied,and the rationality of using artificial synthesized earthquake records in the seismic fragili ty analysis of high arch dams is verified.(2)Since the seismic fragility analysis of high arch dams is time-consuming,a spectrum-based earthquake record truncation method is proposed based on statistic analysis of a large number of actual earthquake rec ords.By considering the structural characteristics of high arch dams,the proposed truncation method may ensure analysis accuracy and improve the calculation efficiency comprared with the exising methods.(3)Cloud Analysis(CLA),Multiple Strip Analysis(MSA)and Incremental Dynamic Analysis(IDA)methods are used for the fragility analysis of high arch dams.By a comprehensive comparison,it is found that both CLA and IDA have some limitations,and MSA has the highest reliability.Based on the MSA method,the demand level in the fragility analysis is suggested.The effect of material uncertainty and the optimal Intensity Measure(IM)suitable for high arch dams are further studied.It is demonstrated that the material uncertainty affects only the standard deviation of the seismic fragility functions,and the IMs based on the spectral acceleration have better correlation on the dynamic response of high arch dams.(4)The decrease ratio of the fundamental natural frequency of high arch dams is proposed as a new Engineering Demand Parameter(EDP).It is shown that the decrease in the fundamental natural frequency has a linear correlation with the damage of the dam body,and can represent the structural characteristic change of high arch dams.Based on this new EDP,three limit states are defined for high arch dams,and the corresponding seismic fragility curves are generated.(5)Based on the mainshock-aftershock sequences,which are constructed using the Endurance Time Analysis method(ETA),the variation of t he seismic capability of high arch dams is studied for the case that the dam is damaged by the mainshock.The concept of seismic capability loss is proposed for arch dams.As expected,the seismic capability decreases with an increase in the mainshock intensity.By combining with the seismic fragility,the loss curve of the seismic capability can be achieved,which can provide a new perspective for the the seismic design and post-earthquake safety evaluation of arch dams.