Plastic Hinge Length of Reinforced Concrete Columns

Abstract

Severe damage can be observed in regions subjected to large moments when a column experiences earthquake-induced lateral displacements while supporting gravity loads. These regions, which experience large inelastic curvatures, are referred to as plastic hinges. The inelastic curvatures in plastic hinges are typically assumed to be constant over the plastic hinge length (lp) to simplify the estimation of the tip displacement of a column. Therefore, if the plastic hinge length is known, the tip displacement of a column can easily be obtained by integrating curvatures, and vice versa. In this paper, the effects of axial load and shear span-depth ratio on lp are evaluated experimentally. Results from experimental data on four full-scale concrete column tests indicate that ACI 318-05 provisions for the length of potential plastic hinge rations are slightly unconservative for columns supporting high axial loads. The level of axial load included the length of the plastic hinges that formed in the full-scale column specimens. Specimens tested under high axial loads developed longer plastic hinges than those tested under low axial loads. An equation is developed to estimate the length of the plastic hinges forming in columns supporting a wide range of axial loads.