Flexure-axial-shear interaction of ductile beams with single-crack plastic hinge behaviour

One of the key damage observations in modern reinforced concrete (RC) frame buildings, damaged following the 2010/2011 Canterbury and 2016 Kaikoura earthquakes, was localised cracking at the beam-column interface of capacity-designed beams. The localised cracking in the beams was due to curtailed longitudinal bars at the beam-column interface. Following these observations, without experimental data to justify desirable seismic performance, modern beams controlled by localised cracking were assumed to be potentially earthquake-vulnerable. To address this, an experimental program was carried out on six RC beam specimens susceptible to single-crack plastic hinge behaviour due to curtailed longitudinal bars. The experimental data show that RC beams with single-crack plastic hinge behaviour can undergo significant inelastic drift demands without loss of lateral resistance. However, contrary to conventional beams with distributed cracking, the response of RC beams with single-crack plastic hinge behaviour due to curtailed longitudinal bars is mainly dominated by hinge rotation (via bond-slip) and shear sliding at the column face. The current paper studies the interdependence of axial elongation, bond-slip and shear sliding deformation of RC beams with single-crack plastic hinge behaviour under cyclic demands. A procedure for seismic assessment of RC beams with single-crack plastic hinge behaviour due to curtailed longitudinal bars is proposed. The proposed formulations can be adopted to develop adequate numerical models for simulating the response of RC frames with beams susceptible to single-crack plastic hinge behaviour due to curtailed longitudinal bars.