Study On Damage Evolution Mechanism And Vulnerability Based On Endurance Time Method Of Ribbed Arch Aqueduct Under Strong Earthquakes

As one of the main building carriers for water transfer across river valleys for long-distance water transmission and agricultural irrigation,the ferry has an indispensable position in water conservancy projects,which is susceptible to water,temperature,wind,earthquake and other loads during service.In this paper,the damage evolution mechanism and vulnerability study of rib-arch type ferry under strong seismic action are carried out by taking the changgang slope ferry as the research object,and the dynamic response,damage evolution law,failure mode and other performance characteristics of rib-arch type ferry are clarified,and the seismic weak points are revealed.The results of the study can lay the theoretical foundation for the design and reinforcement of the ferry structure and seismic measures.The main research work is as follows:(1)To establish a three-dimensional nonlinear finite element model of the ribbed arch ferry structure with long slope,to introduce a concrete plastic damage intrinsic model,and to carry out research on the dynamic response analysis,damage evolution law and damage mode of the ribbed arch ferry structure under different earthquake intensities.The results show that the peak displacements and accelerations of the structure are larger than those of the linear-elastic model,which is mainly due to the degradation of the structural stiffness due to the plastic damage caused by the continuous action of seismic waves;on the contrary,the peak stresses are smaller than those of the linear-elastic model,which is mainly due to the increase of structural damping and dissipation energy caused by the plastic damage.increase.The response characteristics of dynamic stress and dynamic displacement of the ferry structure increase with the increase of seismic intensity,and the higher the seismic intensity,the more serious the damage characteristics and failure mode of the structure;the serious damage parts of the overall structure of the ferry mainly appear in the upper part of the junction pier,the top of the abdominal arch ring,the rib column in the span and the foot part of the arch,revealing that the damage mechanism of the small abdominal arch,rib column,arch rib and other load-bearing members is mainly shear damage and bending damage.The research results can provide the theoretical basis for the seismic design and reinforcement treatment of similar ferry structures.(2)Based on the clear seismic weakness of the rib-arch type ferry,the displacement ductility ratio and curvature ductility ratio are selected as damage evaluation indexes,and the seismic performance evaluation method of the rib-arch type ferry based on the seismic time duration method is proposed to quantitatively evaluate the damage state of the rib column and arch rib of the ferry.The study shows that the shorter the rib column,the smaller the displacement response;the seismic response curves of the rib column and arch rib can be summarized into three stages: when the seismic time is short,the response curve is approximately linear and the member is in a linear elastic state;as the seismic time increases,the response curve tends to be flat and the member is in a nonlinear transition stage;when the response value of the member increases exponentially,the member is in a nonlinear stage;the seismic time duration is At 20 s,i.e.,when the spectral acceleration reaches 0.9g,the rib column Z1 is slightly damaged,the ribs Z2 and Z3 are moderately damaged,the rib column Z4 is severely damaged,the rib column Z5 is completely damaged,and the arch rib reaches the complete damage,the rib column Z3 reaches the moderate damage earlier than the rib column Z2,and the arch rib reaches the complete damage earlier than the rib column Z5,so the closer the rib column is to the top of the arch,the easier it is to The arch ribs are more likely to be damaged compared with the ribs Z1～Z5.(3)According to the basic principle of vulnerability analysis,the vulnerability analysis method of the rib-arch type ferry based on the seismic time course method is established,and the vulnerability curves of the rib column and arch rib of the ferry based on the seismic time course are obtained,and the vulnerability curves of the system are drawn by combining with the boundary method,forming a more comprehensive vulnerability analysis system of the ribarch type ferry.The study shows that: the vulnerability of the rib column is greater as it is closer to the middle of the span,and the vulnerability of the arch rib is greater than the vulnerability of the rib column Z1～Z5;the vulnerability of the ferry system is greater than the vulnerability of the members,and it is imperfect to evaluate the whole structure by considering the vulnerability of the members only,and the vulnerability analysis of the whole system is needed;the width of the upper and lower boundaries of the vulnerability curves drawn by the second-order boundary method under different damage states is reduced by more than 80% compared with the first-order boundary method This is mainly due to the fact that the second-order method takes into account the correlation between the components and can predict the vulnerability of the ferry system more accurately.Based on the vulnerability curves drawn by the second-order boundary method,the probability of minor and moderate damage of the ferry system reaches99.9%,the probability of severe damage is 39.49%-44.33%,and the probability of complete damage is 11.26%-12.56%,which shows that the seismic performance of the ribbed arch ferry is good.The research results and analysis methods can provide new analytical ideas for the evaluation of seismic performance of ribbed arch aqueduct.