Damage Assessment of Reinforced Concrete Columns Under High Axial Loading

Abstract

This paper describes how damage assessment has become more important than ever since structural designers have started to employ performance based design methods that require structural and member behaviors at different limit states be predicted precisely. This paper aims at clarifying the confining effect of concrete of a plastic hinge zone of a reinforced concrete column confined by shear reinforcement, so that a designer can accurately predict damage when columns experience seismic loadings that include large axial force and bilateral deformations. In an experimental program, eight half-scale columns and eight full-scale columns were tested under the reversal bilateral displacement with constant or varying axial load in order to study the effects of loading history and intensity on the confining effect. Since shear failure was inhibited by providing enough transverse reinforcement, as defined by the previous Japanese design guidelines, damage gradually progressed in a flexural mode with concrete crushing and yielding of reinforcing bars. The damage level depended on the bilateral loading paths and the axial load history. In an analytical program, a section analysis using a fiber model was employed and the effect of confinement on the behavior of core concrete was studied. The analysis predicted the observed deterioration of moment capacity and longitudinal shortening under different loading conditions and for different specimen sizes. The paper is considered to increase the accuracy with which damage in reinforced concrete columns subjected to severe loading is assessed.