Seismic Fragility Analysis Of The Aqueduct Structure Under Multi-support Earthquake Excitations

Aqueduct is one of the key buildings in the construction of the national water network,and is a pivotal project in the realisation of water resources deployment.In recent years,the construction of large-scale aqueducts has been on the rise,and their safety under seismic action has gradually attracted the attention of the academic and engineering communities.In order to ensure the smooth construction of the national water network,it is urgent to deeply study the seismic performance of large-scale aqueduct.At present,the seismic analysis of aqueduct structure generally adopts the ground motion input method of uniform excitation.However,for large aqueduct,due to the influence of space specificity,the seismic excitation received by each support point is not consistent,still using consistent excitation will cause a large error in the analysis results,the multi-point excitation input is more in line with the actual situation.At the same time,in order to accurately predict the probability of damage at all levels of the aqueduct structure under different levels of seismic action,a seismic vulnerability analysis based on vulnerability curves was carried out for the aqueduct structure,providing a reliable basis for the safety assessment of the aqueduct structure.At present,no one at home and abroad has carried out the vulnerability analysis of large aqueduct structure under multi-point seismic excitation,so this paper takes a large aqueduct in the central Yunnan water diversion project as the research object,and applies the combination of multi-point excitation and vulnerability analysis to the aqueduct structure.A MATLAB program was written to synthesize artificially seismic waves considering multi-point excitations.In order to take into account the ground shaking uncertainty,In order to consider the uncertainty of ground motion,the program is generated by the random combination of three coherent function models,three phase difference spectrum models and three apparent wave velocities.Then 10 programs are selected randomly and 100 groups of multipoint excitation ground motions are generated according to the designed response spectrum considering the traveling wave effect and coherent effect.Finally,an example is given to verify the rationality of the synthesized multipoint excitation ground motion from waveform,coherence and response spectrum,and it is pointed out that multiple iterations are needed to ensure the accuracy of the conversion of response spectrum and power spectrum by integrating method.Taking a large aqueduct as the research object,a three-dimensional finite element model of large aqueduct structure was established with ANSYS,and the uncertainty of model parameters was considered by Latin hypercube sampling method.Finally,10 groups of finite element models were selected.The input of multi-point ground motion cannot be realized directly in ANSYS,so several multi-point excitation calculation methods are derived in detail,and the traditional large mass method is modified,and the modified acceleration time history is equivalent to transform the time history into the longitudinal input of the mass point.The uncertainty of model parameters and the uncertainty of the ground motion parameters model are considered comprehensively.The seismic response analysis was carried out on 1000 sample models,and the most suitable ground vibration strength index was selected from 8commonly used ground vibration strength indexes,and then suitable damage indexes were selected to construct the fragility curves of each support,each channel pier and the ferry system under consistent and multi-point excitation.The final comparative analysis reveals that the bearings are the most vulnerable components of the ferry structure,and the vulnerability of the system is greater than that of the individual components.The vulnerability of the system under multi-point excitation is greater than under unanimous excitation,with the largest difference being the probability of overtopping under severe damage,which is nearly 42.2%.The multi-point excitation vulnerability analysis of aqueduct structure equipped with high damping rubber bearing and common bearing was carried out to explore the influence of vibration reduction and isolation bearing on multi-point seismic excitation and seismic performance of aqueduct structure.The results show that the high damping rubber bearing can effectively reduce the vulnerability of aqueduct structure,and the greatest reduction is the exceedence probability of the intermediate failure state,about 60%.