| Because of its simple structure,strong adaptability and low cost,the concrete-faced rockfill dams(CFRDs)are favored by engineers and become one of the first choice in dam construction.With the accumulation of more than 40 years of dam building experience,the improvement of dam building technology and the rise of design level,the height of CFRDs is also increasing.Now,the height of CFRDs in planning,design and under construction has reached more than 250 m,and some of the high dams are located in the southwest strong earthquake-prone regions of China.Once these high dams break due to strong earthquake and the secondary disasters caused by dam-break,it will cause disastrous consequences.Therefore,great attention should be paid to the seismic safety of high CFRDs.With the development of earthquake research,people gradually realize that earthquakes always occur in the form of seismic sequences,which makes the dam may suffer the damage of the aftershock again after the mainshock.It aggravates the damage degree of the dam and seriously threatens the seismic safety of the dam.Therefore,it is very important to consider the aftershock effect in the seismic design and safety evaluation of high CFRDs.However,in the current seismic design code and seismic performance research of high CFRDs,only the mainshock is considered,and the additional damage of the aftershock to the dam is ignored.And the traditional deterministic analysis method is often used in the seismic safety evaluation of high CFRDs.It can't meet people's needs for performance-based seismic analysis of structures.To solve the above problem,a 200-m-high 2D CFRD model is established as the research object in this paper.The influence of the aftershock on the dynamic response of high CFRDs is analyzed from three aspects: dam deformation,dam slope stability and face slab safety based on elastoplastic analysis.The fragility analysis method is used to evaluate the influence of the aftershock on the seismic performance of CFRDs from the perspective of probability.The main contents of this paper are as follows:(1)Taking 24 as-recorded mainshock-aftershock sequences as seismic input.Considering three calculation conditions: single mainshock,single aftershock and seismic sequence,The deformation of the dam body,the stability of the dam slope and the safety of the face slab of the high CFRDs under three conditions are compared,which reveals the potential damage ability of the aftershock on the high CFRDs.The research shows that the aftershock will further aggravate the damage degree of the dam which has subjected to the mainshock,and the single mainshock cause more serious damage to the dam than the single aftershock.(2)First of all,20 as-recorded seismic sequences are selected from the seismic database,and then the mainshock-aftershock sequences are generated by the single parameter and multi parameters artificial seismic sequence construction methods respectively.The dynamic response of high CFRDs under the action of these two kinds of artificial seismic sequences and as-recorded seismic sequences are compared,so as to provide some reference and experience to select seismic sequences for the study of the dynamic response of high CFRDs subjected to seismic sequences in the future.(3)The relative intensity of aftershock is introduced.Considering the relative intensity of aftershock 0.5,0.7,0.9 and 1.0,a series of nonlinear dynamic time history analysis results are used to select the engineering demand parameter that can best reflect the cumulative damage effect of the aftershock on the high CFRDs.The damage effect of the aftershocks on the high CFRDs is studied by using the fragility analysis method based on the vertical deformation of dam body and damage index DI of the face slab.The results show that aftershocks will increase the probability of the dam reaching the limit state,and the probability increases with the increase of aftershock intensity. |
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