Bearing Capacity Of Green High Performance Concrete Filled Steel Tubular Stub Columns Under Axial Load

With the rapid development of super high-rise buildings and large span structures, thedemand for concrete strength grade is increasingly high. In addition, the demolition processwill produce large amounts of waste concrete with the development of accelerated pace urbanconstruction and demolition projects. The green high performance concrete is the futuredevelopment direction of the concrete. The application in combination structure will form thegreen high performance concrete filled steel tubular structures. In this regard, it is of greattheoretical significance and engineering application value to study the RPC filled steel tubularcomponents and recycled-concrete-segment/lump filled steel tubular members.In this paper, axial behavior and calculation method of bearing capacity of the green highperformance concrete filled steel tube is analyzed based on the unified strength theory, finiteelement simulation. Combining with the bond-slip theory，new ultimate bearing capacityformula is derived with the highest regard for bond stress. The principal results are as follows:(1) With consideration of the intermediate principal stress，the calculation formula ofaxial load bearing capacity of RPC filled steel tubular columns and recycled concretesegment/lump filled steel tubular stub columns with inner CFRP tendons is deduced based onthe twin shear unified strength theory. Compared with the theoretical results and theexperimental data，good agreement can be found. The results show that unified strengththeory has the good applicability in theoretical analysis of the short columns of green highperformance concrete filled steel tube.(2) Based on the bond-slip mechanism of RPC filled steel tube, the equation of bond-slipconstitutive relations between steel tube and concrete are deduced through theoretical analysis.Critical factors affecting the cohesive action were analyzed, involving many aspects, such asconcrete strength, slenderness ratio and confinement index. And how the behavior of thestructure was influenced by the bond-slip between the steel tube and core concrete was alsostudied. Combining the twin shear unified strength theory with the bond-slip theory，newultimate bearing capacity formula is derived with the highest regard for bond stress.(3) The stress-strain curve and stress contour of steel tubular stub columns filled withreactive powder concrete are analyzed based on the commercial finite element analysissoftware ANSYS. In addition, the influences of the confinement index and the strength gradeof core concrete on the mechanical performance of the short columns are discussed accordingto numerical results. In order to take the interaction between the steel tube and RPC into account, combination39elements were used to simulate the three directional interactions withnormal direction, longitudinal and ring tangential direction. The results indicated that thesimulation results were good agreement with the experimental data and theoretical calculationresults.