There is the expectation that the curvature ductility demand would be met if there were adequate capacity. A
brittle shear failure may ensue, even if there has been some ductile response, if there is inadequate lateral
reinforcement at the critical section. The role of axial load can be significant. Under cyclic loading, the axial
compression contributes to the closing of both flexural and shear cracks, thus mitigating premature failures due
to sliding shear. High axial loads limit the sections post ultimate response thus reducing the available ductility.
Models to predict shear strength in columns that include axial load and the hinge rotation/curvature have been
used in the Japanese design code [1992] and a model proposed by Priestley [1995]. Both models try to account
for the degradation in the concrete’s shear strength contribution as the rotational/curvature ductility of the section
increases.
Priestley’s model for shear strength uses the contribution of the concrete, lateral reinforcement and axial load.