Plastic Hinge Analysis

Abstract

Predicting behavior of plastic hinges subjected to large inelastic deformations caused by extreme loads such as earthquakes plays an important role in assessing maximum stable deformation capacities of framed concrete structures. This paper presents an analytical procedure that can be used to predict the behavior of plastic hinges in reinforced concrete columns. Since the behavior of plastic hinges in concrete columns is a 3D problem, the plastic hinge analysis technique considers equilibrium, compatibility, and constitutive relations in 3D space. Complex behavioral phenomena such as softening of longitudinal bars due to inelastic buckling and reinforcing cage-concrete core interaction are incorporated in the analysis. To establish a constitutive relationship for reinforcing bars under axial compression an experimental study on 56 reinforcing bar specimens having unsupported length to bar diameter ratios ranging between 4 and 10 was conducted, and results are reported herein. Finally, the suggested analytical procedure is compared with conventional analysis techniques by predicting the sectional response of concrete column specimens. It is concluded that through the use of the analytical procedure presented here it was possible to obtain realistic estimations for the maximum deformation capacities of the plastic hinge regions of the specimens that were tested under constant axial loads and reversed cyclic displacement excursions. The concrete core-reinforcing cage interaction, which caused outward deflections in longitudinal bars, did not only reduce the ductility of longitudinal bars under compression but also reduced the maximum stress that the bars were able to achieve.