Plastic Hinge Length in Reinforced Concrete Flexural Members

For reinforced concrete (RC) flexural members, the plastic deformation is localized in a small zone namely the plastic hinge zone after the yielding of the member. The performance of the plastic hinge zone is critical for flexural members as it governs the load carrying and deformation capacities of the member. Therefore, plastic hinge has been of great interest to structural designers and researchers for decades. The length of the plastic hinge zone is an important design parameter where intense confinement should be provided to increase the ductility of the member for survival from extreme events such as earthquakes. The behavior of plastic hinges is very complicated due to the high nonlinearity of materials, interaction and relative movement between the constituent materials, and strain localization. As a result, most researchers investigated the problem through experimental testing. Restricted by the time and cost involved in large tests, very limited knowledge has been obtained up to date. This work tries to investigate the problem analytically with Finite Element Method (FEM) using the computational software DIANA. A computational model is built and verified with existing experimental data including load deflection response, rotational capacity, and strain and stress distributions of reinforcement. With the calibrated FEM model, the extent of the rebar yielding zone, concrete crush zone, curvature localization zone and the real plastic hinge length are studied. Parametric studies are subsequently employed to investigate the plastic hinge length in terms of material properties of rebar and concrete, dimensions of the member, and reinforcement ratio.