Progressive Collapse Resistance Of Composite Frame With Concrete-Filled Steel Tubular Column And Fabricated Connection

Progressive collapse is a kind of low-probability and high-risk accident that can cause tragic consequences.Therefore,the progressive collapse resistance of structures should be urgently investigated.Currently,studies on the progressive collapse resistance are mainly based on the alternate load path method(ALP method).More systematic studies have been carried out on reinforced concrete(RC)structures and steel structures,but few studies focuses on concrete-filled steel tubular(CFST)structures.Accordingly,a series of studies on the progressive collapse resistance of composite joint and frame with CFST column and fabricated connection were performed,focusing on the following issues.(1).A total of six CFST column-composite beam fabricated joints were tested.The types of fabricated connections and shear connectors were compared to investigate the failure mode,vertical resistance,and rotation capacity.Subsequently,the force transfer mechanism was investigated based on the bending moment and axial force of steel beams as well as the contribution ratio of each component to vertical resistance.Besides,the nonlinear parameters of progressive collapse resistance of the tested specimens were compared with various criteria.(2).On the basis of the experimental results,progressive collapse analyses of CFST column-composite beam fabricated joints under static,dynamic,and impact loads were carried out by finite element(FE)simulations.In the static analysis,the failure mode and resistance mechanism were investigated.Meanwhile,the effects of RC slab,shear connector,positive and negative bending moment scenarios were studied.For the dynamic analysis,the displacementtime curve,dynamic resistance,and DIFs were discussed,respectively.Moreover,a FE simulation of fabricated composite joints subjected to an impact load was developed to compare the bearing capacity of joints under impact and static loads.The effects of varying impact energies on the impact force,resistance distribution,and energy absorption were discussed,as well as the DIFs based on force,displacement,and energy.(3).A total of four two-story three-span composite frames with CFST column were tested to study the progressive collapse resistance of composite frames under a penultimate columnloss scenario.Subsequently,the effects of connection and RC slab on the failure modes and vertical resistance were investigated.The internal force transmission path of the beams and columns in directly affected region(DAR)under an asymmetric boundary constraint was discussed.Furthermore,the dynamic response and DIFs were analytically estimated by energy balanced(EB)method and compared with the recommended values in relevant criteria.(4).A simplified multi-scale FE simulation method was proposed,significantly increasing the computing efficiency and accuracy.Subsequently,the progressive collapse resistance of plane and spatial frames with CFST column and composite beam was numerically studied.For the FE models of plane frames,the effects of column-loss scenarios and number of stories were compared and analyzed.Moreover,two improvement alternatives were proposed to enhance the capacity of composite frames to resist progressive collapse.On the other hand,the progressive collapse resistance of the one-story 2×1 span CFST column-steel beam-RC slab substructure was investigated to compare the corner column-,penultimate column-,and side column-loss scenarios.Finally,the effects of boundary constraint,loading method,number of stories,RC slab,shear wall,and steel brace on the performance of spatial frame were discussed.