Elastoplastic Displacement Spectrum Of Generalized Flag-shaped Hysteretic Model And Its Application

In the displacement-based seismic design method,accurate and reasonable displacement response spectrum are the key to design.The displacement response spectrum are divided into elastic displacement spectrum and elastoplastic displacement spectrum.Compared with the elastic displacement spectrum,the design results based on the elastoplastic displacement spectrum are more accurate.The influencing factors of the elastoplastic displacement spectrum mainly include the magnitude,epicentral distance,site category and types of hysteretic models.At present,the design concept has gradually changed from "seismic resistance" to "seismic absorption",and self-centering structure that can reduce the residual displacement aroused general interest.The hysteretic model of the self-centering structure presents a "flag-shaped" characteristic.As the influence of the hysteretic model on the elastoplastic displacement spectrum cannot be ignored,the elastoplastic displacement spectrum for the self-centering structure needs to be calculated.This paper realized the generalized flag-shaped hysteretic model.The elastoplastic displacement spectrum of this model was normalized by period to reduce the dispersion of the spectrum value.The main research contents are as follows:The "flag-shaped" curve was generalized,and the bilinear hysteretic model can be represented by setting different model parameters.Therefore,the hysteretic model is called the generalized flag-shaped hysteretic model.The elastoplastic displacement spectrum calculation program of the model was compiled.After inputting 102 near-fault pulse-liked ground motions,the constant-ductility displacement spectrum of near-fault ground motions were established,which are related to the normalized period,the post-to-pre-yield stiffness ratio,ductility coefficient,and the energy dissipation coefficient.The results show that the change of post-to-pre-yield stiffness ratio in the interval [0,0.20] has little effect on the spectrum value.The spectrum value first increases and then decreases with normalized period and eventually tends to a constant value.The normalized period corresponding to the maximum value of the spectrum is approximately 1.Increasing the energy consumption coefficient can reduce the displacement,and the efficiency of displacement control for these structures will be better as energy consumption coefficient lies within the range of [0,1].The 269 far-field ground motions were divided into three types of sites,and the constant-ductility displacement spectrum of far-field ground motions related to the site category,the normalized period,the ductility coefficient,and the energy dissipation coefficient,were established.When the normalized period is in the range from 0 to 0.75,the displacement spectra value has a positive correlation with ductility coefficient,after which the correlation between them is opposite.When the value of ductility coefficient is greater than 4,the influence of ductility coefficient on the spectrum value is negligible.After the period is normalized,the spectrum value of the second and third types of sites are relatively close,while the spectrum value of the first and second types of sites have greater differences in the range of a small period.The method of changing a multi-degree-of-freedom system to a single-degreeof-freedom system is introduced.The displacement-based seismic design of a 5-story self-centering braced structure was carried out using elastoplastic displacement spectrum in the article.The design results were input into Open Sees software for finite element simulation.The size relationship between the response of vertex displacement and the design target displacement were compared to verify the accuracy of the design.After completing the above research content,the normalized elastoplastic displacement spectrum in the article can be used to carry out seismic design of various structures of the generalized flag-shaped hysteretic model.