Pseudo-dynamic Experiments And Numerical Analysis Of CFDST Composite Joints With Blind Bolts

Concrete-filled double shin steel tubular(CFDST)column is a novel structural member formed by pouring concrete between two layers of concentric steel tubes.It has the characteristics of developed cross section,large bending rigidity,good anti-seismic performance and fire resistance.The self-weight of CFDST column is lighter than solid concrete-filled steel tubular(CFST)column with the same cross section.For the cross section of inner and outer steel tubes is various,the CFDST column can be formed into different cross section type,which enhance the flexibility in practical engineering.So far,there are many experimental and theoretical researches on the mechanical properties of CFDST column members,but the related study of beam-column joints is still limited.High strength blind bolted end plate connections to beam and column exhibit typical semi-rigid behavior and have better seismic performance and ductility compared with full rigid joints.Moreover,beam-column joints using blind bolts avoied the limitations of ordinary high-strength bolts when used in closed section,so it has good prospects in engineering application.However,the experimental research and theoretical analysis on the high strength blin d bolted end plate joints to CFDST column and steel beam are rare.To investigate the seismic performance and dynamic response of the novel joints to CFDST column and steel beam under earthquake,seven specimens were exposed to pseudo dynamic loads.And the nonlinear time history analysis of the joints and frame were also conducted through finite element analysis model based on OpenSees progress.The study of this paper were supposed to provide experimental and theoretical supports for the development of th e type joints in practical engineering.The main work of this paper is summarized as follows:(1)With EI Centro earthquake wave as the simulated seismic excitation input of pseudo dynamic test,five CFDST column-to-steel beam joints connected by blind bolts and endplates were supposed to pseudo-dynamic tests.The failure modes and dynamic response of the joints were studied.Seismic performance in terms of hysteretic performance,ductility and energy dissipation,et al were analyzed in detail.Moreover,the influence of the column section type and hollow ratio on seismic behavior of the joints were discussed as well.(2)With EI Centro earthquake wave as the simulated seismic excitation input of pseudo dynamic test,two CFDST column-to steel-concrete composite beam joints connected by blind bolts and endplates were supposed to pseudodynamic tests.The failure modes and dynamic response of the joints were studied.Seismic performance in terms of hysteretic performance,ductility and energy dissipation,et al were analyzed in detail.Meanwhile,the influence of the column section type and steel truss-concrete composite slab on seismic behavior of the joints were also discussed.(3)The FE analysis model of CFDST column-to-beam joints with blind bolts were established through OpenSees progress.The zero-length spring elements were used to simulate the performance of high strength blind blots.The displacement time history curves,load-displacement relationship curves and shkelen curves of the load-displacement relationship under EI-Centro earthquake wave were recorded and analyzed.The accuracy of this model was evaluated by comparing the simulated results with the experimental dat a.(4)The FE analysis model of CFDST column-to-beam joints with blind bolts were established through OpenSees progress.With column section type and frequency character of ground motion as study parameters,the elastic time history analysis under frequently occurred earthquake and elastoplastic time history analysis under rare earthquake of the frame were studied.