Experimental And Theoretical Study Of Reactive Powder Concrete Filled Steel Tube Column Under Compression

In Reactive Powder Concrete (RPC) filled steel tube, RPC is confined by the steel tube and it is in triaxial stress state when the RPC-filled steel tube column is under axial compression. So it can delay its longitudinal cracking under compression. At the same time, the core RPC can help to delay or avoid local buckling of thin-walled steel tube.Those two kind of materials can make up for each other’s weaknesses, which provides satisfactory strength, toughness and durability. Due to these characteristics, it presents broad application prospects in civil engineering field. RPC-filled steel tube stub column tests and RPC-filled steel tube slender column tests have been carried out in order to study the performance of RPC-filled steel tube columns. Constitutive model for core RPC is established and the mechanism of the stub columns is analyzed in this paper, which provides the basis for the standard enaction for RPC.The main work is as follows:(1)RPC-filled steel tube stub column tests ware carried out by changing loading method and hoop coefficient, etc.The influence of loading method on the failure mode, load-deformation curve and ultimate bearing capacity of specimens were analyzed.The results showed that loading method itself has little effect on the failure modes and ultimate bearing capacity of specimens, the main factor was still hoop coefficient. When the hoop coefficient was small, the specimens showed shear failure; when the hoop coefficient was large, it appeared to drum-like expanding yield in the middle of the specimens.(2)RPC-filled steel tube slender column tests were carried out by changing slenderness ratio and hoop coefficient.The influence of slenderness ratio and hoop coefficient on the failure mode, load-deformation curve and ultimate bearing capacity of specimens were analyzed.The results showed that the compressive failure modes of the columns are entire inelastic bucking and accompanied by local buckling for specimens with smaller slenderness. The specimens with smaller slenderness acted more ductile failure characteristics and the failure mode turned into bucking with increasing of slenderness ratio. For specimens with the same hoop coefficient, ultimate strength and ultimate displacement of them gradually reduced with increasing of slenderness ratio. For specimens with bigger slenderness ratio, ultimate strength increased with increasing of hoop coefficient, however, the rate of increase gradually decreased, which showed that effect of confinement from steel tube to RPC is less than that to ordinary concrete(3) Parameters for Mohr-Coulomb failure criterion and Willam-Warnke failure criteria were obtained based on existing triaxial compressing tests of RPC. Formulas for caculating RPC-filled steel tube stub columns and RPC-filled steel tube slender column were given.(4) An analytical model of the RPC filled steel tube column system is provided and the analytical model accurately represents the ultimate load and peak strain of RPC filled steel tube column.The concept of limit casting hoop coefficient for judging whether the circumferential stress of steel tube was yield or not was presented, and the caculation formula of limit casting hoop coefficient was given. The coefficient could be defined to analyze the reasons for different development trends with different casting hoop coefficient appeared in axial compression stress-strain curves.(5)Confined constitutive model for core RPC was proposed based on data analyzing of steel tube and RPC, it showed that the peak stress of confined RPC increases with increasing of yield strength for steel, hoop coefficient and compressive strength for RPC. Formulas for caculating peak stress and strain of confined RPC were also given in the study.(6)Mechanic model for steel tube was proposed by analyzing testing data of circumferential, vertical stress and deformation of steel. Force transmission characteristics between steel tube and core RPC were analyzed and the friction coefficient is taken as0.6in ABAQUS. Confined constitutive model for core RPC proposed before was used in ABAQUS analyzing.