Flexural, axial load and elongation response of plastic hinges in reinforced concrete member

Previous research in New Zealand has indicated that elongation of plastic hinges in reinforced concrete (RC) beams can have a significant effect on the seismic performance of RC structures. A number of empirical formulas have been proposed to predict elongation. However, no satisfactory analytical models are currently available which can be used to predict the influence of elongation on the seismic performance. This paper describes a plastic hinge model developed to predict the combined flexural, axial load and elongation response of plastic hinges in RC beam. The model is a filament type element which consists of layers of longitudinal and diagonal axial springs to represent the flexural, shear and elongation response of a plastic hinge. Analytical predictions for beams with different levels of axial load are compared with the experimental results. It is found that the plastic hinge model predicts the response satisfactorily. With this newly formed element, seismic analyses may be performed to assess the significance of beam elongation on seismic performance of RC structures