Seismic Design And Evaluation Method For BRBF Based On The Energy Dissipation-ductility Demand Model

The existing braced frame structures in China were built at an early age and there may be some potential safety hazards.A large number of this kind of structures have suffered from different levels of damage after the earthquakes so it is necessary to retrofit the conventional braced frame structures.The conventional retrofit methods include enlarging the section area of members or taking construction measures.Although bearing capacity of structures can be improved by these methods,the damage may increase in earthquakes.The bulking of braces can be avoided in BRBs and the seismic energy can be dissipated by yielding of BRBs under earthquakes so the problems in structural retrofit can be solved by substituting conventional braces by BRBs and it is convenient for structural retrofit after earthquakes.However,the structure will become an energy dissipation system after substitute and the design method is totally different from original structure.Taking response of structures as the energy input and dissipate process of earthquakes,the energy input by earthquakes can be estimated and the response can be derived by estimating equivalent energy consumption of structures.Meanwhile,BRBF is a kind of structures with good ductility so the ductility demand can be regarded as evaluation criterion for seismic performance.In this paper,a seismic design and performance evaluation method for BRBF was proposed by establishing relationship of BRBF equivalent energy consumption and ductility demand.Stiffness ratio and strength ratio were introduced to reveal basic mechanical relationship of frames and braces in design and retrofit of BRBF.The relationship of equivalent energy consumption(E)and ductility demand(μ)(E-μ model)is derived by analyzing ductility demand of two kinds of structures under different parameter cases.In this paper,a seismic design and performance evaluation method for BRBF based on the E-μ model was proposed based on the E-μ model.In this method,the ductility of multistory structures can be evaluated by SDOF systems derived from Pushover analysis so that the iteration and nolinear time history analysis process can be simplified.Finally,a 6-story braced-frame structure case study building was retrofitted by this method the result showed that the method proposed in this paper is accurate and appropriate in design.