ANALYSIS OF CONCRETE CONFINEMENT BY CIRCULAR HOOPS

Abstract

Confining effect of concrete pillar by circular hoops is analyzed assuming as follow. 1) Mohr's theory of failure is applicable to concrete under triaxial compression. 2) Stress field is given by functions so that principal stresses distribute like an onion with a core. The equilibrium conditions are considered approximately, but not rigorously. Thus, imaginary body forces are assumed to satisfy the conditions. The functions of principal stresses are determined so that the imaginary body forces are minimized. According to the lower bound theorem, the maximum strength may be chosen as the strength of a pillar. The pillar strength decreases as the hoop spacing increase, even if shear reinforcement ratio is the same. This tendency agrees with existing experimental results quantitatively.