Effects Of Long-term Loads On In-plane Mechanical Behavior Of Steel-concrete Composite Members

Steel-concrete-steel composite(SCS)member refers to a new type of composite member that consisted of lateral double skin steel plates and internal filled concrete.The double steel plates are connected to the concrete core by welded shear stud connectors to ensure the system can work together well.Steel-concrete composite member is as a kind of composite material structure.Under long-term loading,concrete creep but steel don't.This deformation difference which caused by the difference of material properties will make the members' section stress redistribution,which affect the member's stiffness and deformation,and even reduce the member capacity and stability.Researchers from home and abroad did a series of experimental research work on the long-term effects in concrete-filled tube member capacity and deformation under sustained loading.While SCS structure developed in recent years,few studies has been conducted on the effects of long-term loads on mechanical behavior of SCS composite members,lagged behind the pace of engineering practice.This paper investigates the effects of long-term loads on in-plane mechanical behavior of SCS composite members respectively from the experimental and theoretical way.The obtained results can provide a reference for the further structure application in practical engineering.Experimentally,this paper focuses on the steel-concrete-steel composite axially loading member.Fourteen SCS composite column specimens with different stress level and kinds of concrete were designed and applied the long-term loads with the axial deformation recorded.After remove the long-term loads devices,the axially loading test were finished at once.The test phenomenon and member load-displacement curve were analyzed to get member capacity.Combined with test results,based on the superposition of ultimate bearing capacity calculation theory,the SCS composite member capacity and stiffness under long-term loads is analyzed.On the theoretical side,based on the creep theory of concrete under multi-axial stresses and basic theory of elastic-plastic mechanics,the effects of long-term loads on in-plane ultimate bearing capacity,the capacity when steel yield after loading(yield capacity)and stress-strain relationship of steel-concrete composite(SCS)member were analyzed by means of proportional loading mode.On the basis of the theoretical analysis,the influence of loading ratio,time under sustained loading,reinforcement ratio and creep of concrete on the long-term effects was discussed.The comparison calculated results indicated that long-term loads had limited influence on the ultimate bearing capacity of SCS wall elements,but had obvious influence on yield capacity.Furthermore,the SCS composed member capacity and stiffness under long-term loads from this experiment are calculated and contrasted by the proposed method in this study.The comparison results indicate that the accuracy and applicability of the theoretical capacity and stiffness model of the SCS composed member is verified well.