Research On The Equivalent Linearization Analysis Methods Of Base-isolated RC Frame Structure

Whether the displacement based seismic design method can accurately predict the nonlinear peak displacement response of the structure is the key to the equivalent linearization design of base-isolated structure.The equivalent linearization analysis method can effectively calculate the nonlinear seismic response of the structure based on the response spectrum method,thus speeding up the calculation efficiency and improving the accuracy of the analysis,so as to ensure that the structure has enough safety.In this paper,two RC base-isolated frame structures are taken as the research objects.Firstly,the calculation methods and applicable conditions of five kinds of equivalent parameters of isolation layer are compared.It is revealed that the main factors affecting the accuracy of equivalent calculation results are the calculation methods of equivalent stiffness and equivalent damping ratio;Secondly,based on the equivalent principle that the peak displacement response of SDOF system is consistent,the accuracy evaluation criteria for the equivalent linearization method of isolated structures are established;Finally,for the overall accuracy prediction requirements of equivalent analysis method under different actual seismic waves,the equivalent linearization analysis method based on different types of seismic pseudo acceleration response spectrum is studied with the prediction ability of key seismic peak response indexes of isolated structures as the core goal,Based on the results of 74 non impulse ground motions and 59 impulse ground motions,the accuracy and stability of each equivalent method are evaluated,and the influence of ground motion related characteristic parameters on the equivalent results of response spectrum method is analyzed,The main work and conclusions are as follows:(1)Through the analysis of five representative calculation methods of equivalent parameters of isolation layer,including R-H method,ASD method,JPWRI method,G-Iwan method and Hwang method,the variation of equivalent parameters with displacement ductility coefficient of isolation layer is studied.The results show that the difference of equivalent stiffness ratio of R-H method,JPWRI method and Hwang method is less than 3% when the ductility coefficient is(30～50).However,the ratio difference between G-Iwan method and ASD method is the largest,about 15%.With the ductility coefficient approaching 50,the difference of equivalent damping ratio calculated by R-H method,JPWRI method and Hwang method is obvious,and the maximum is about 10%.(2)Based on the equivalent calculation method under the design response spectrum of the code for seismic isolation,the prediction accuracy of shear force and displacement response index of RC frame base-isolated structure under medium and large earthquakes is evaluated.The results show that the R-H method adopted in Chinese code has the highest prediction accuracy for the displacement response index of isolation layer under medium and large earthquakes,with the error value of(6～9)%,compared with Hwang The(13～19)% advantage of the method is obvious.But for the floor shear force and floor displacement angle response index,the accuracy error of R-H method is(-25～-16)%,and the prediction ability of Hwang method is(-10～-3)%.In addition,the prediction accuracy of Hwang method for the abovementioned response indexes under large earthquakes is relatively high,which is basically within10%.Therefore,in the response spectrum equivalent analysis method,Hwang method will get better results.(3)The prediction accuracy of key seismic response indexes of structures is evaluated based on the equivalent calculation method under the pseudo acceleration response spectrum of non pulse earthquake.Based on the error results of 74 non pulse waves,the influence of the relevant characteristic parameters of ground motion on the equivalent response results is analyzed.The results show that the standard adopted in China The error value of R-H method is(19～26)% compared with that of elastoplastic time history analysis.It has obvious advantages to the stability of prediction of the important index of superstructure failure form,the inter layer displacement.The accuracy error of Hwang method is(16～20)%,only from the calculation accuracy,Hwang method can be improved(4～5)% compared with R-H method;site type is an important factor affecting the critical response accuracy of equivalent linear prediction.The softer the soil,the lower the critical response accuracy of equivalent linear prediction(5～15)%.(4)Evaluate the prediction accuracy of the equivalent calculation method based on the pseudo-acceleration response spectrum of the near-fault pulse-like ground motion.Based on the error results of 59 pulse waves,analyze the influence of ground motion characteristic parameters.The results show that: The R-H method has an error in the prediction accuracy of key structural response indicators under impulse waves,which is basically(15～20)%,which is about 5% higher than that of non-pulse waves.The prediction stability of inter-layer displacement is still the best.The accuracy error of the Hwang method is(11～17)%,an overall increase of about 4%;PGV/PGA,site type,and pulse period are all important factors that affect the accuracy of the key response of equivalent linearization prediction.The PGV/PGA value is increased by 30%,and the overall accuracy of the equivalent linearization prediction of the key response is reduced by about 20%.The softer the soil,the overall accuracy is reduced by about10%.Affected by the pulse period,the key response accuracy of equivalent linearization prediction becomes lower,and the overall accuracy range is(25～30)%.