Effects of joint flexibility on lateral response of reinforced concrete frames

It is known that shear deformation of beam-column joints have a significant contribution to lateral response of reinforced concrete structures. Most of the available analysis programs assume rigid joints regardless of reinforcement details in the joint region. Slip of the beam longitudinal reinforcement in the joint and shear deformation of joint panel significantly decrease rigidity of the joint, especially in non-seismically detailed beam-column joints. In the current study, these effects were modelled in the OpenSees software framework and a modified joint element for analysis of multi-storey frames was used. The model was verified by experimental results and the verified model was used to analyze five and ten storey frames with various joint details using nonlinear static and incremental dynamic analyses. The results of frames with flexible joints were compared with those of frames with rigid joints assumption. The analytical results confirmed that the modified joint element successfully predicted experimental cyclic behaviour of beam-column joint specimens and also was found that existing RC structures with deficient beam-column joints are very vulnerable when subjected to severe earthquakes and the rigid joint assumption was not appropriate when assessing the behaviour of existing non-seismically detailed structures. The results also showed that the effect of joint deformation on lateral response of RC frames depends on the peak acceleration values of the ground excitation.