A cyclic shear stress–strain model for joints without transverse reinforcement

In many older reinforced concrete frames, the joints contain no transverse reinforcement. Under seismic loading, those joints may suffer damage and deform, and thereby contribute significantly to the displacements of the frame, which significantly impacts its performance. However, engineers typically ignore joint deformations in seismic analyses, largely due to the lack of appropriate analytical models and reliable data against which to verify them. To improve the simulation of two-dimensional response of frames with joints without transverse reinforcement, a constitutive model was developed for the shear deformations of the joint. The model replicates cyclic degradation in strength and modulus, and energy dissipation of the branch curves. It was calibrated using measured data from tests on joints without transverse reinforcement that were subjected to a range of displacement histories and joint shear stress demands. The model has a general form, and is supplemented by recommendations for the values of the model parameters, which are expressed as functions of the joint geometry and material properties. An independent data set was used to validate the proposed model.