The Performance Of Three-dimensional Steel Frame-composite Floor System Adopted Endplate Connections Against Progressive Collapse Under Exterior Column Loss Scenario

After the collapse of Ronan Point apartment in 1968,the collapse of Murrah Federal Building in the USA.in 1995 and the collapse of Twin towers of the World Trade Center in 2009,the progressive collapse of building structures has been a course for concern of academic researchers all around the world.At the same time,with the rise and development of assembly structures in China,composite structures are adopted in a mass of high-rise and large-span buildings.As a typical composite structure form,steel frame-profiled decking with reinforced concrete composite slab is applied in practical projects in a large range.However,experimental studies on this kind of structure against progressive collapse are relatively few.Among these few experimental tests,two-dimensional tests occupied a large part,and some references indicated that three-dimensional effect played a crucial role in the structural performance against progressive collapse.Therefore,it is necessary to carry out relevant experimental research to provide reference for theoretical analysis,finite element analysis and engineering application.With financial support of ‘Design theory and engineering application of disaster prevention and mitigation for steel structure system'(Ministry of Science and Technology of the People's Republic of China,2016yfc0701203),in this thesis,the progressive collapse resistance of this kind of composite structure under the failure of exterior column will be studied in detail by the method of experimental test.In the composite frame,endplate connections are applied to connect the columns and the main beams,while the bolted angle connections are adopted to connect the secondary beams and the columns.Besides,the shear studs are used to connect the composite slab and the steel frame.Meanwhile,the load-transferring path and the load-transferring mechanism of the composite frame under exterior column loss scenario are analyzed in detail in this thesis.And also,the bending action,the catenary action and the tensile membrane action of the whole frame at different stages are analyzed.After that,component method is utilized to study the mechanical performance of the connections in the frame.And the composite action of the floor and the steel frame is researched in experimental way,whose results are expected to provide evidence to the further study.Through this experiment,the following vital conclusions are summarised:(1)The three-dimensional steel frame-composite floor system has good performance to resist progressive collapse,and stages of the loading-displacement curve are divided obviously.(2)When designing the frame system under exterior column loss scenario by alternative load path method,bending action should be mainly considered,catenary action should not be taken into consideration and tensile membrane action improving the load bearing capacity of the system should be calculated.(3)The existence of horizontal boundary conditions can improve load bearing capacity through improving catenary action and tensile membrane action.(4)Through comparison,it indicates that the stiffness of connctions can influence the performance of the whole frame system.At last,it is recommended to use end-plate connections in practical projects.(5)Experimental tests with three-dimensional specimen can reflect real mechanical performance of the structure.And the tests with two-dimensional specimen will overestimate catenary action,underestimate bending action and ignore tensile membrane action under exterior column loss scenario.Innovations:(1)It is the first time to study the performance of the three-dimensional steel frame-composite floor system under exterior column removal scenario to resist progressive collapse in experimental method.In the frame,the endplate connections are used to connect the main beams and columns.(2)By comparing the tests between two-dimensional and three-dimensional specimen under exterior column loss scenario,it is found that the test of two-dimensional frame can not reflect load bearing capacity of the composite frame exactly.It will underestimate bending action and overestimate catenary action.Besides,boundary conditions and stiffness of connections can influence mechanical performance of the frame system.(3)In terms of this composite frame system,catenary action can be ignored under exterior column loss scenario.And the main actions to resist vertical load at the stage of large deformation are bending action and tensile membrane action.