RESPONSE OF CIRCULAR REINFORCED-CONCRETE COLUMNS TO MULTIDIRECTIONAL SEISMIC ATTACK

Sixteen circular reinforced concrete column models with aspect ratio o f 2 and different spiral reinforcement contents were tested to investi gate the sensitivity of the strength and stiffness of shear-resisting mechanisms to various displacement patterns and axial compression load intensities. Shear deformations were expected to be significant for t hese squat columns, particularly under low axial compression. The hyst eretic performance and displacement ductility capacity of the columns were improved by increased spiral steel content or by increased axial compression. In comparison with uniaxial displacement paths, biaxial d isplacement patterns led to more severe degradation of strength and st iffness. However the displacement ductility capacity was not sensitive to the type of biaxial displacement pattern. Simple orthogonal displa cement patterns were found to be sufficient to represent horizontal tw o-dimensional seismic effects. Current code provisions were found to u nderestimate the shear strength of circular columns. A shear design pr ocedure which enables the shear strength-displacement ductility relati onship to be estimated, while also including the effects of displaceme nt history, is proposed.