Research On The Lateral Load Pattern For Pushover Analysis Of Asymmetric-plan Structures

Pushover analysis method has been used as one of the principle tool for seismic estimation of structures for a long time.Currently,the structural schemes with irregular plans are widely used in architectural design,and such structure forms is vulnerable to be damaged with torsional brittle failure under earthquake excitations.Reasonable selection of the lateral load pattern for Pushover analysis is particularly important.If the conventional load pattern is directly applied to Pushover analysis of asymmetric-plan buildings,it will lead to evident errors.In this paper,a new lateral load pattern for Pushover analysis of asymmetric-plan structures is proposed.Additionally,taking three practical irregular multistory RC buildings as examples,the applicability and accuracy of the proposed pattern are also discussed.The main research work and related results are as follows:Firstly,the application limitation of the conventional lateral load pattern in the seismic evaluation of irregular structures is discussed.Based on the seismic response characteristics and dynamic analysis of torsion-irregular buildings,a mathematical formula for spatially distributed lateral load is proposed.The formula introduces lateral load adjustment and distribution coefficients,and the translational-torsional coupling effect of asymmetric-plan structures has been taken into consideration,so as to simulate the practical inertial force distribution of each story in the buildings under ground motions to the greatest extent.According to Chinese structural design code,three typical RC buildings with irregular plans are designed by PKPM software,and the verification work is performed in the SAP2000 program.Based on the torsion effect parameters(eccentricity ratio,inter-story torsion angle)of each structure,the spatial distribution load patterns corresponding to three buildings are eventually obtained.For each example,five suitable ground motion records are selected for analyses.Time history analysis(including IDA analysis),Pushover analysis with three conventional lateral load pattern and proposed pattern are all calculated by SAP2000 program.The difference between the results of three irregular structures under nonlinear time history analysis and Pushover analysis is investigated.Taking structural deformation index as the comparison object,from the perspective of inter-story displacement,the error rate obtained by Pushover analysis is less than 5%compared with the average results of time history analysis,while several conventional load patterns recommended by FEMA show remarkable errors.From the perspective of inter-story torsion,it can be seen that the average torsional angle curve of time history is basically consistent with the inter-story torsional angle curve obtained from the proposed load pattern.From the perspective of the capacity curve,the IDA curves of the structures in the linear elastic stage is completely consistent with the Pushover curves.From the perspective of the plastic hinges,the positions and states of hinges are concentrated in the weak part of the middle floor and the floor number is approximately the same.The structural yield order predicted by two nonlinear analyses is relatively close.The results show that the proposed method of the spatial lateral distribution pattern can reflect the torsion effect on asymmetric-plan structures.Compared with the conventional Pushover method,the former can reflect more detailed and accurate results.The obtained seismic performance verifies the applicability and accuracy of the proposed lateral load pattern in this paper.