Model Pushover Analysis Method On Mid-Rise Lightweight Steel Composite Shear Wall Structure

Lightweight steel composite shear wall structure has the following excellent performances,such as the standardization of component production process,convenience of construction,environment-protection and so on.Considering all the aforementioned advantages,such new type of structural system meets the requirements of house industrialization,whose application would help to accelerate the pace of urbanization in China.It is a key problem to analyze the seismic performance of the whole structure when extending the application of low-rise CFS structure to mid-rise building.With the proposal and application of performance-based seismic design,the modal pushover analysis(MPA)method considers the influence of higher order modes,this method is regarded as a hot spot of valuating the seismic behavior of structures.The research group of Prof.Ye has completed the full scale lateral performance test of shear wall specimens which are used in the mid-rise lightweight steel structure.To facilitate the calculation,the wall was simplified reasonably.On the basis of preliminary work,the computing model of 5-story light steel structure was established.The MPA method was used to evaluate the elastic-plastic response under rare earthquakes and collapse margin of structures.The regular structure can be simplified as two-dimensional plane model for analysis.The 5-story plane building of light steel regular structure was modeled on the platform of OpenSEES.After that,the model pushover analysis was carried out and the capacity curve was simplified reasonably to determine the yield parameters of the model.To solve the target displacement subjected to eight-degree rare earthquake,equivalent linearization method and Ry-?-T model were adopted respectively to establish inelastic demand spectrum and displacement coefficient method.At the same time,the nonlinear time-history analysis was carried out subjected to 10 seismic waves which were selected by the method of double frequency wave.The average displacement of time-history analysis was taken as the accurate value.The displacement error of the building obtained by the three methods was not more than 16%,which demonstrates the MPA method was a conservative approach.In addition,the error of maximum story drift angle was not more than 10%.Earthquake can trigger torsion vibration of the irregular light steel structure.The 5 layer space truss torsion model of lightweight steel structure was modeled which adopted the rigid-floor hypothesis.Three methods,such as equivalent linearization method,Ry-?-T demand spectrum method and displacement coefficient method were used to solve the target displacement subjected to the one-way horizontal seismic action of eight degree rare earthquakes.The top drifts by the three methods were close.Among them,the results of displacement coefficient method were relatively conservative.In addition,the inelastic response spectrum method based on the Ry-?-T model was used to solve the elastic-plastic response of the structure subjected to the bidirectional horizontal earthquake.Compared with the results of nonlinear time history analysis,The MPA method can be used to evaluate the results of the elastic-plastic deformation when the three-dimensional lightweight steel building subjected to the action of one-way or bidirectional horizontal earthquake.The displacement error of the floor of the structure was less than 9%under the excitation of the one-way horizontal earthquake and the displacement error was less than 15%under the excitation of bidirectional horizontal;However,the defects of MPA method was that it underestimated the maximum story drift angle and the floor torsion angle.The incremental dynamic analysis(IDA)method suggested in ATC-63 report requires a large amount of time history analyses in determining a structural collapse margin ratio(CMR).It is computationally inefficient.A practical method proposed herein to evaluate CMR was based on the model pushover analysis procedures.The collapse point of each capacity curve was determined by ultimate displacement.Inelastic demand spectrums were generated from the response spectra of the motions reduced by the Ry-?-T model.Combining the collapse point and inelastic demand spectrum,the collapse intensity index of all selected strong ground motions were determined.The collapse margin ratio(CMR)was calculated by plotting the collapse fragility curve.20 far-field seismic waves recommended in the ATC-63 report were chosen to do the CMR of the light,weight steel building,the result the results obtained through MPA and IDA methods had few discrepancies,the difference was only 8.71%,and the result of MPA was conservative.Besides the method based on the design response spectrum of MPA to solve the collapse margin ratio has good accuracy,and the difference compared with the results based on IDA solution is 1.82%.This method has the high calculation efficiency,which will be helpful to introduce the CMR into the engineering field.The light steel structure has the characteristics of light weight,large stiffness,short natural period.The results of nonlinear analysis showed that the light steel structure has a good seismic performance,and can meet the seismic fortification objects that the structure does not collapse under strong earthquake.