Effect Of Two Key Factors On The Capacity Of Steel-Concrete Composite Axially Loading Members

Many factors affect the capacity of steel-concrete(SC)composite axially loading members.Most specifications and codes consider the capacity issue in terms of material strength and overall structure stability.Long term loading and local stability of steel are two important factors to the capacity of SC composite structures.The long term loading leads to concrete creep and stress redistribution between steel and concrete,which results in variation of member capacity.Local buckling of steel makes insufficient utilization of material strength and weakens member capacity.This paper focuses on the effect of the two above issues,including long term loading and local buckling of steel,on the capacity of SC composite axially loading members.To study the effect of local buckling of steel on the capacity of SC composite axially loading member,this paper focuses on steel-concrete-steel(SCS)composite column.Ten SCS composite column specimens with different sizes were designed for axially compressive loading experiment.Member displacement and steel faceplate strain were measured and analyzed to get local buckling stress and member capacity.Based on the plate theory,the mechanical modeling of local buckling of steel faceplates in SC composite compressive members is deducted.The critical elastic buckling strain is solved through energy method.The solution is modified with experiment results and compared with related specification.With the modified critical buckling strain solution,capacity of SC compressive members after steel faceplate buckling is analysed.On the other side,to study the effect of long term loading on the capacity of SC composite axially loading member,this paper focuses on square concrete-filled steel tubes(CFST).To get the load-strain fuctional relationship of square CFST during axially loading,internal force of steel and concrete section was superposed,taking consideration of long term loading and no long term loading respectively.The maximum value of preceding fuction was regarded as the member capacity.Based on this method of capacity calculation,capacity of members in some current papers was computed.The calculation results and experiment results were compared to prove the rationality and accuracy of the method.Time effects on ultimate capacity of square CFST members were analyzed,taking consideration of local buckling of steel tubes,reinforcement ratio,steel yield strength and concrete creep.Parameter analysis indicated that long term loading had limited influence on static ultimate capacity of square CFST under uniaxial loading.