Mechanical Behavior Analysis of the Circular Steel Tube Confined Concrete Stub Columns

Based on continuum mechanics,the calculation model for circular steel tube confined concrete(STCC) stub columns of concentric cylinders of circular steel tube with concrete core under concrete section loaded entirely is determined.The theoretical calculation formulas are presented for composite elastic modulus and composite stress-strain relationship of the stub columns.A FORTRAN program for the elastoplastic analysis of STCC stub columns under concentric loading is developed and the behavior of STCC stub columns is analyzed.Analysis results are in good agreement with the experiment ones from references.The behavior of the columns is simulated when loaded to failure,the perimeter stress-axial strain relationship of steel,the axial stress-axial stain relationship,and the radial stress-axial strain relationship of concrete are analyzed.The comparisons between STCC stub columns and concrete-filled steel tubular(CFST) stub columns on the behavior are discussed.From the result,it is indicated that: for STCC stub columns,compared with CFST stub columns,the radial stress,axial strength of concrete core,and the perimeter stress of steel tube increase;the confinement effect between concrete core and steel tube strengthens and the ultimate capacity,residual capacity and the ductility of the columns increase,but composite elastic modulus decreases.