Seismic Fragility Analysis Of Concrete Dam Based On Endurance Time Analysis Method

With the development of society and economy,water conservancy industry in China is booming.As an indispensable part of hydraulic engineering,concrete high dam plays an extremely important role in power generation,flood control,irrigation and shipping.In this paper,the most common type of dam-concrete gravity dam is studied,and the dynamic response and damage distribution characteristics of Koyna concrete gravity dam under strong earthquake are analyzed.For different damage failure states,the evaluation indices that can reflect the failure degree of dam body are proposed,and the seismic performance and fragility analysis of concrete dam under different ground motions are studied.This paper mainly does the following aspects:(1)On the basis of the traditional time history analysis,a new method for evaluating the seismic performance of dam-endurance time method is proposed.A new acceleration time history curve-the endurance time history acceleration curve was developed and synthesized and applied to Koyna concrete gravity dam.The basic concept of endurance time analysis method is introduced in detail,the process of synthesis optimization of endurance time acceleration curve is described,and then,the effective loading method of earthquake ground motion is realized.(2)Based on endurance time method,the damage index analysis method is proposed,and the damage evaluation index-response spectral difference area,which can macroscopically describe damage expansion of the dam body,is established.The spectrum curve of Koyna concrete gravity dam under excitation with the change of peak acceleration is obtained by means of the harmonic response and endurance time analysis method.The corresponding spectral difference area is calculated,and an effective index is found to evaluate the damage condition of the dam body,and the reliability of the index is verified.(3)Combined with endurance time method and pushover analysis method,the POA-ETA method is proposed which is used to seismic performance evaluation.In this paper,the basic theory and implementation of the key steps of POA-ETA method is elaborated.Koyna concrete gravity dam finite element model is established,and the seismic acceleration curve was used as the dam base time history input to simulate dynamic response under different intensities.The relative displacement and acceleration are converted into spectral displacement and spectral acceleration under the first mode.The pushover analysis method is adopted to establish the capacity spectrum curve and the demand curve,and define different failure criteria.The performance points under different failure criteria are solved repeatedly and the seismic performance evaluation of POA-ETA method under different failure criteria is realized.(4)Based on the basic theory of seismic vulnerability,a vulnerability analysis method based on ETA method is proposed.Considering the influence of the randomness of ground motion,20 sets of bidirectional time history acceleration curves were generated,and applied to Koyna dam to explore the impact of different ground motions and different peak accelerations on dam response.By defining the failure criteria of the structure,the relationship between the vulnerability and the engineering demand parameters under different failure criteria is established,and then the damage degree and vulnerability of the structure are evaluated.