Behavior of tubular stub columns of axially loaded steel-reinforced concrete-filled circular steel

In order to understand the mutual effects among section steel,concrete and steel tube of steel reinforced concrete-filled circular steel tubular(SR-CFST) stub columns under axial compression and to propose the formula of ultimate bearing capacity for SR-CFST stub columns,both 3D finite element model and elasto-plastic method were applied to analyze the load-deformation curve of SR-CFST stub columns.Based on the finite element method,the changes of axial stress and perimeter stress of steel tube,the axial stresses of concrete and section steel in both SR-CFST stub columns and concrete-filled circular steel tubular(CFST) stub columns were discussed.Based on the limit equilibrium method,simplified formula of ultimate bearing capacity for the axially loaded SR-CFST stub columns was proposed.The results show that at yield state,the axial stress of section steel is slightly lower than its yield stress due to the restriction effect from section steel to concrete.Compared with CFST stub columns,the axial stress of concrete in SR-CFST stub columns increases slightly for the concrete confined by both section steel and steel tube,and axial stress decreases and perimeter stress of steel tube increases after yield weakens slowly.The confinement effect from steel tube to concrete also weakens slowly.The analysis results by limit equilibrium method are close to those by finite element method,and both are in safe range compared with the experimental results from references.