Theoretical model for concrete-filled stainless steel circular stub columns under axial compression

Experimental studies on concrete-filled stainless steel (SS) circular stub columns (in the form of fully filled and double-skin) have been reported in the last 10 years, but there is still a lack of theoretical model to predict the complete load-axial strain curve of such stub columns under axial compression. This study presents a load-axial strain model for concrete-filled SS tubes, which takes account of the interaction between the encasing tube and concrete core. A dilation model is first proposed in which the dilation rate is expressed as a function of axial strain and outer tube diameter-to-thickness ratio. The theory of metal plasticity in the form of deformation type is adopted to calculate the bi-axial stresses in the SS outer tube. The SS inner tube is assumed to be under uni-axial compression and continuous strength method (CSM), which is suitable for strain hardening material such as SS, is adopted. The effect of SS tube buckling on reducing the axial stress and confining stress is considered in the model. Numerical procedures are proposed to generate the complete load-axial strain curve which involve an incremental process. Finally, the predicted load-axial strain curves are compared with the experimental results obtained by the authors and other researchers, and a good agreement is achieved.