| The use of high strength steel in steel structures is one of the most important trends in the development of steel structure.It is verified that the mechanical properties,environmental efficiency and economic efficiency of steel structure are improved with higher steel grade.High strength steel(HSS)mainly refers to steel with yield strength no less than 420 MPa,and structural steel with yield strength no less than 690 MPa is also called ultra-high strength steel(UHSS).China already have the technical reserves and industrial foundation to promote the application of high-strength steel structure.However,the application of high-strength steel structure is very limited in China’s newly-built structure.The main reason is that the high strength steel structures have poor energy-dissipation capacity and low lateral stiffness,which have detrimental effects on the seismic behavior.Buckling restrained brace(BRB)is a kind of high-performance energy dissipation brace,which has similar tensile and compressive properties,stable strengthening performance,high lateral stiffness,and excellent energy dissipation capacity.High strength steel frame with buckling restrained brace(HSSF-BRB)is an efficient dual system for seismic application.It can make up for the poor energy dissipation capacity and insufficient lateral stiffness of high-strength steel frame(HSSF-BRB)through combined effect and reduce the seismic response of HSSF.In this paper,the seismic performance of HSSF-BRB is systematically studied,which provides theoretical basis and practical design method for the practical application of HSSF-BRB and promotes the application of high-strength steel structure in China’s construction engineering.(1)The quasi-static tests are carried out for two HSSF-BRB substructure specimens.The design procedure,material properties,loading scheme and measurement scheme are introduced in detail.The main observations such as plastic deformation,local buckling,local flange fracture and complete flange fracture are observed.The overall ductile deformation and failure mode of the structure are revealed.(2)The hysteretic behavior,internal force,BRB displacement loss,bearing capacity degradation,stiffness degradation,plastic deformation,energy dissipation capacity and ductility of HSSF-BRB specimens are studied in detail.The horizontal deformation and failure process of the structure is divided into three typical stages,and corresponding design suggestions are put forward according to the performance characteristics of each stage.(3)The seismic performance of HSSF-BRB structure is studied using nonlinear static finite element analysis.The finite element model was established using the appropriate element type and constitutive material property model.The correctness of the finite element model was verified by comparing the numerical simulation results with experimental results.The failure mechanism was reviewed by the evolution process of yield state.Parameters analysis was carried out on the correlation between the design parameters(i.e.strength grade of steel frame,stiffness ratio and axial compression ratio of column)and the seismic performance(i.e.yield drift ratio of BRB,yield drift ratio of steel frame,ductility,overstrength ratio and strength reduction factor).(4)The seismic response of multistory HSSF-BRB was studied based on the finite element time-history analysis.Under the same design conditions,three-story steel frames were designed using steels with different grade.Based on the design response spectra of 8 degree(0.2g)area in China,five strong earthquake records was adjusted and used as input seismic waves.The maximum value of inter-story drift ratio,the cumulative plastic deformation of BRB and the total input energy of earthquake are obtained.The range of effective stiffness ratio for frames with different strength grade is proposed.(5)The mechanical properties of the HSSF-BRB were simplified as a trilinear force-displacement relation.Based on the simplified model,the theoretical formulas of equivalent damping ratio and strength reduction factor were derived,and the theoretical values are compared with the test data or the results of finite element method.The error sources were analyzed,and the correction suggestions were put forward.The effects of stiffness ratio and targe inter-story drift ratio on the equivalent damping ratio and strength reduction factor were studied.(6)Based on the seismic behavior and design objectives of the HSSF-BRB,a performance-based design method based on the maximum inter-story drift was proposed.The design steps and process are described,and the design process is illustrated in detail with an example. |
