Elongating plastic hinge element for nonlinear analysis of RC structures using OPENSEES

Abstract

During inelastic cyclic loading, the length of plastic hinges in reinforced concrete (RC) members increases irreversibly which significantly affects the seismic performance of RC structures. It is hence necessary for numerical and analytical models to capture elongation of hinges for reliable prediction of nonlinear cyclic response of RC structures. This paper reports the implementation of a new plastic hinge element capable of simulating elongation in the structural analysis program OPENSEES. The element is similar to the multi-spring plastic hinge element developed by Peng et al (2013) and implemented in RUAUMOKO2D. The element includes two parallel rigid links interconnected by a number of axial springs modelled by cyclic stress-deformation behaviour of concrete and reinforcing bars and two diagonal springs, which collectively enable simulation of nonlinear cyclic response of RC members under combined axial, flexure and shear actions. As concrete models available in OPENSEES library are unable to capture the contact stress of cracked concrete, a new concrete hysteresis model is added to be used in the plastic hinge element. The new element can be used in both vertical and horizontal configurations (i.e. in beams as well as columns and walls). A preliminary verification is conducted by simulating a quasi-static cyclic loading test on a cantilever RC beam. Comparing the predicted and experimental results, it was found that the model was able to capture with reasonable accuracy the hysteretic response as well as the elongation of the beam throughout the cyclic loading history.