The elastic-plastic behavior of steel and concrete (SC) composite column encased crusiform steel and covered by thin steel tube has been investigated. Encased crusiform steel raio, material strength of steel and concrete, width-to-thickness ratio of thin steel tube and axial force ratio are thought to effect the elastic plastic behavior of SC columns. In order to evaluate quantitatively of the seismic performance of the columns, skelton curves of restoring force characteristics were investigated. The model of skelton curves was suggested to be composed of four points : flexural crack point, yield point, maximum strength point, ultimate deformation point. Effect of the above mentioned factors on skelton model of SC column was investigated quantitatively and skelton curves formulae were proposed. They were able to pursue the elastic plastic analysis and experiment results of columns.
