The expansive-concrete filled steel-pipe members have high tensile and compressive strengths due to the existence of the triaxial compressive prestress in the concrete induced by the expansion of concrete.
In the present paper, the mechanism of the increase in strength of the members by the prestress was investigated on the basis of the elasto-plastic analysis by use of the flow theory of plasticity. The theoretical results agreed comparatively well with the experimental ones for the specimens having various initial expansions of the concrete and volume ratios of the steel-pipe to the concrete.
The tensile strength of the members was nearly equal to the cumulative strength obtained by adding the failure strength of the concrete to the yield strength of the steel-pipe, and the compressive strength was higher than the cumulative one. The plastic strain induced by the first loading became to shakedown in the subsequent cyclic loadings.
