Study On Mechanism Of Composite Beam Structures Under The Condition Of Progressive Collapse

Structural progressive collapse refers to a sudden destruction of key components in the structure,which results in local structure failure,and eventually leads to entire structural failure or disproportionately damage compared to initial destruction.The significant characteristics of progressive collapse that different from other failure mode is the disproportionate damage size that the local initial damage compare to final destruction.In China,research in this field started a little late,and it is still in the state of development.Design of progressive collapse is still in concept phase.There are still many problems need to be researched.Because of the large plane stiffness and good characteristics of bidirectional tensile force,the cast-in-situ concrete slab which has been wildly applied can significantly improve the capability of resistance of structural progressive collapse.There has been a comprehensive theoretical and experimental analysis about performance of steel frame structures under the condition of progressive collapse.Existing researches have focused on the theoretical and experimental analysis of concrete slab-column structures,or the study of slab as single component under the condition of progressive collapse.And for cast-in-situ reinforced concrete slab-steel frame structures,there are few researches about their performance and interaction between each component under the condition of progressive so far.Based on the theory of energy balance principle,this paper mainly focused on the performance of reinforced concrete floor-steel frame structures under the condition of progressive collapse by using theoretical analysis and numerical simulation methods.The main research is listed as followed:(1)Based on energy balance principle,the energy flow within structures and the characteristics of progressive collapse was compared. The performance,working mechanism and resistance development process of composite beam structure under the condition of progressive collapse was analysized from the perspective of energy.Analysis assumes applied to progressive collapse with energy method was put forward.And formulas of resistance curve at every stages by using energy method was tried to get.Its rationality was also proved(2)A composite beam structure was simulated using finite element analysis software ANSYS.The stress mechanism and failure mode of structure and components under the condition of progressive collapse was determined.The abovementained energy method was applied to the composite beam structure,and formulas of resistance curve at every stages of composite beam structure was established based on the energy principle.The influence of five parameters: strength of concrete slab,diameter of rebar,depth of concrete slab,the relative slip between steel girder and concrete slab, and the strength of steel beams was analysized.(3)Based on the basic dynamics theory,the dynamic characteristics of composite beam structure under the condition of progressive collapse at various stages,including its inherent vibration mode and natural frequency was analysized according to the method of infinite degree of freedom system.The composite beam structure was simplified into a single degree of freedom system,and the calendar function of the failure point deflection was obtained based on structural dynamics.(4)Composite beam structure dynamic characteristics in progressive collapse was analysized by using the finite element analysis software SAP2000.The working condition and mechanical characteristics of the structure under the condition of dynamic progress was studied.The failure point deflection,and key components such as internal force of beams and columns was analysized.The relations between DMF obtained by this paper and results from existed researches was compared,and its rationality was discussed.