Progressive Collapse Behavior Of Planar Steel Frame With Composite Beam

The progressive collapse of buildings would result in significant casualties and property loss. Hence the study on the progressive collapse resistance of structures has drawn more attentions among researchers and engineers. Once the vertical load-resisting component in structure is damaged, the beams and joints above the damaged component would carry the vertical loads through “catenary action”. The joints with high moment-resistance and good ductility play an important role in the formation of catenary action and redistribution of internal load. Normally, the joints under service loads sustain hogging moment. Tensile loads would appear in the beams due to catenary action under column loss. Hence the joint would sustain bending moments combined with tension. The behavior of the joints under the combination of moment and tension is a key factor in the design of preventing progressive collapse.Previous studies were mainly focused on steel structures or reinforced concrete structures. Fewer attentions were paid to steel-concrete composite structures. Although some studies were conducted recently to investigate the performance of the connection under the scenario of column loss, only the beam-to-column connections were tested within a simplified boundary condition. Specially, the combination of bending moment and tension is rarely considered in the study of composite joint. In this paper, the experimental study and theoretical analysis have been carried on the progressive collapse behavior of planar steel frame with composite beam and the moment-tension performance of composite joint. The main research is listed as followed:(1) Two1-storey4-bay planar steel frame with composite beam were tested under the loss of middle column. The influence of fully welded rigid connection and flush endplate semi-rigid connection on the progressive collapse resistance of structures was considered in the test. The measurement included the vertical load and displacement of the loss column head, the horizontal displacement of frame column and the strains at the beam ends and the mid-span. The transfer mechanism of tension and moment in the loading process was achieved. The influence of beam-to-column connection configuration on the behavior of composite frame under column loss was also analyzed.(2) Ten tests of composite joints were conducted. Two joint types of rigid connection and semi-rigid connection and three load conditions of pure bending, bending combined with tension and pure tension were employed. The moment- rotation relationship curves, moment-tension relationship curves and tension-displacement relationship curves were drawn in the test. The strain distribution and development at the beam ends and the deformation of joints in loading process were also captured. Based on the test results, a moment-tension relationship formula for composite joints was proposed and the mechanism of composite joints in the collapse process was studied.(3) Finite element models for planar steel frame with composite beam were developed by using the software ABAQUS. For semi-rigid composite frame, the mixed-element method was considered and the material fracture was also considered. The influence of height of steel beam, depth of concrete slab, rebar ratio and connection rigidity on the performance of composite frame under column loss was studied by using the FE models. A mechanical model for planar steel frame with composite beam under column loss and an arch action model were proposed. The load-deformation formulae corresponding to the mechanical model and arch action model were also derived.(4) Finite element models for3-storey and9-storey planar steel frame with composite beam were developed. Based on the models, the dynamic column removal analysis was conducted. The dynamic response of the structure under different column losses was studied. The affected area under column loss and the influence of connection behavior were certified. A simplified model for analyzing progressive resistance of multi-storey was suggested.