| Large-scale converter station valve hall structure is one of key structures of lifeline engineering,but researches already show that inevitable damage and malfunction happened under strong earthquakes.Function failure caused by the destruction of valve hall structures will lead to significant economic losses and serious social impact.Though seismic design based on seismic fortification specified by the codes is suitable for the level of safety of life,but not sufficient to guarantee seismic resilience of lifeline engineering after earthquakes.Hence,appropriate measures should be taken to improve the earthquake resilience and ensure continuous operation of valve hall structure,therefore,reduce economic losses caused by function cessation.Seismic isolation is a promising technique to decrease earthquake energy input and structural damage with many successful engineering applications.However,whether seismic isolation is effective to improve seismic behavior of valve hall structure remains unknown.Meanwhile,as seismic isolation tends to increase initial investments of construction project,whether or not it is economical during life span to improve the earthquake resilience by adding investment is still needed to study.Therefore,a large-scale converter station valve hall structure with suspended equipment was selected to be renovated using seismic isolation.Model analysis and elastic-plastic time history analysis were proceed by using Nonlinear FEM software,ETABS and Perform-3D,to study seismic performances of original valve hall structure and isolated valve hall structure,including dynamic characteristics,structural responses,energy dissipating component damages and structural fragility.Based on a large number of elastic-plastic time history analysis,life cycle cost analysis of original valve hall structure and isolated valve hall structure taking seismic loss into account was conducted.The main work and conclusions are as follow:(1)A large-scale converter station valve hall structure with suspended equipment was selected to be renovated using seismic isolation and seismic performance of original valve hall structrue and isolated valve hall structure were studied.Firstly,base isolation design of valve hall was conducted and performance goals of the valve hall structure,a lifeline engineering,was defined according to relevant codes.After verifying the FEM model of the structure,two FEM models of original valve hall structure and isolated valve hall structure were built,and model analysis and elastic-plastic time history analysis were proceed to compare seismic performances of two structures,including dynamic characteristics,structural responses,energy dissipating and component damages.Results showed that the natural vibration period is extended from 0.954 s to 1.956 s and the second mode translated from torsion into translation after the valve hall structure was isolated.Under strong earthquake in 7 degree(0.15g),compared with seismic responses of original valve hall structure,base shear reduces by 79% maximally,peak acceleration of suspension valve decreases by 78%,seismic forces on the roof caused by suspension valves are 44% lower,the maximum top displacement angle of superstructure is 78% smaller and the damage states of 89% of shear walls change from medium damage level to mild damage level,as the maximum compressive strain of concrete reduces by 55% and tensile strain of reinforcing bars decreases by 58% after the valve structure was isolated.More than half of the earthquake energy was dissipated by isolation bearings.Hence,base isolation technology can effectively control damages of the structure,keep the superstructure in elastic state,dramatically improve the seismic resilience of the large-scale valve hall structure under strong earthquake.(2)For the insufficient of seismic force calculating method of suspension equipment in valve hall structure design,a simplified method of calculating seismic force caused by suspension equipment for isolated valve hall structure was presented.Based on simplified method of calculating seismic forces caused by suspension equipments for original valve hall structure presented by our research group before,a simplified formulas of computing seismic forces caused by suspension equipment for isolated valve hall structure was obtained through coefficient adjustment.Earthquake induced forces by suspension equipment in isolated valve hall structure can be obtained by the proposed simplified calculation method,according to different seismic performance levels,site classification of design earthquake.(3)Seismic fragility analysis is an effective method in seismic performance evaluating of valve hall structure.Seismic fragility analysis of original valve hall structure and isolated valve hall structure was conducted with suitable ground motion intensity parameter in this paper.100 natural earthquake records were selected from PEER as input earthquake waves and a large number of elastic-plastic time history analysis were carried out.Function relationship between engineering demand parameter(EDP)and ground motion parameter were fitted based on analysis results.SA1,PGV,PGA,M and R were chosen as ground motion intensity parameters in structural fragility analysis according to correlation,efficiency,practicality and proficiency.Structural fragility analysis of original valve hall structure and isolated valve hall structure were compared.Analysis results indicated that,under strong earthquake in 7 degree(0.15g),exceedance probability of serious damage level of original valve hall structure with SA1-M,PGV-M,PGA-M,SA1-R,PGV-R and PGA-R selected as ground motion intensity parameter respectively are 8%,22.9%,33.66%,28.36%,25.8% and 16.25%,while the corresponding results for isolated valve hall structure drop to 0.15%,0.06%,16%,0.07%,0.35% and 1.8%.Seismic isolation significantly decrease the exceedance probability of each damage level of valve hall structure.(4)Life cycle cost analysis is able to study the effect of seismic isolation on life cycle cost of valve hall structure.In this paper,initial investment,maintenance cost and seismic loss of original valve hall structure and isolated valve hall structure were calculated and life cycle cost of two structures were studied.Based on a large number of elastic-plastic time history analysis results,component fragility curves against top displacement angle of original valve hall structure and isolated valve hall structure were calculated and compared using method proposed by FEMA-P58.Seismic losses of original valve hall structure and isolated valve hall structure were calculated using FEMA-P58 seismic loss prediction method.Then,lift cycle cost of two structures including initial investment,maintenance cost and seismic loss were computed.Component fragility results indicated that,given the same earthquake motion,the exceedance probability of each damage level of structural component of isolated valve hall structure is significantly less than that of original valve hall structure,such as,under strong earthquake in 7 degree(0.15g),the exceedance probability of serious damgde level of shear wall drops to 1.7% from 43% after isolated,since deformation responses were concentrated in isolation storey and the top displacement angle of superstructure was decreased visibly after isolated.Lift cycle cost analysis manifested that,lift cycle cost of original valve hall structure and isolated valve hall structure respectively are 15.303 millions yuan and 10.633 millions yuan.Isolated valve hall structure cost 4.67 millions yuan less than original valve hall structure,which means that,from the aspect of life cycle cost,isolated valve hall structure is more economical than original valve hall structure. |
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