Three-dimensional Effect Study Of Steel Frame-Composite Floor Structures Against Progressive Collapse Under An Internal-column-removal Scenario

Since the collapse of the World Trade Centre towers in 911 events,an increasing number of researchers and engineers in the world pay attention to the structural resistance to progressive collapse under accidental load.In past decades,the performance of reinforced concrete(RC)frames in resisting progressive collapse has been numerously conducted.However,in spite of the widely use in High-rise Buildings,limited research works are conducted about the performance of Steel frame-composite floor structure against progressive collapse,especially the three dimensional(3D)effect considering the influence of composite slab.After the removal of internal column,the span of girder and beam adjacent the column expands two times,as a result,the load path and force mechanism change.At small deformation stage,the arch action and bend mechanism play the key role,while catenary action and tensile membrane action carry the main load at large deformation stage.Aspect ratios of slab,thickness of slab and decking profile,composite action and performance of connections are regarded as the essential factors influencing the behavior of 3D composite floor system against progressive collapse.Experimental studies demand much time and labor,so a 3D finite element(FE)model is established to investigate the influence of various factors on performance of structure against progressive collapse through parameter analysis and nonlinear dynamic analysis after validation by test results.The main contents of the paper are summarized as follows:(1)An experimental study of 3D steel frame-composite structure with displacement-control load method are introduced for the verification of FE model.The component-based joint models are created in the component method introduced in Eurocode3,and the properties of equivalent spring in the model are obtained in experimental method,which will be used in the 3d FE models.(2)The component-based joint models are created in the component method introduced in Eurocode3,and the properties of equivalent spring in the model are obtained in experimental method,which will be used in the 3d FE models.Finite element models of 3d steel frame-composite structures are established in the common software ABAQUS,and the results in terms of the load-displacement response,failure mode and failure process are comprehensively compared with the experimental results.Eventually the effectiveness and reliability are validated.(3)After validation,the FE models are conducted to widely parameter studies influencing the behavior of 3D composite floor system against progressive collapse,involving aspect ratios of slab,thickness of slab and decking profile,composite action and performance of connections.(4)A direct nonlinear dynamic analysis is conducted and the result is found in good agreement with Izzuddin’s simplified method.Both results indicate the dynamic increasing factor(DIF)in GSA is conservative.So factor 1.5 is recommended as DIF in terms of force and 3 is recommended as DIF in terms of displacement in this paper.