Seismic performance and prediction equations of sandwich beam-column joints subjected to skew cyclic loads

To study the seismic performance of sandwich beam-column joints constructed with high strength concrete column and normal strength concrete floor system and joint regions, four specimens with different column to beam concrete strength ratios (α) were tested under skew cyclic loads. The performance indices of the specimens including the failure mode, ductility, energy dissipation were compared and analyzed. The results show that the failure modes of the sandwich joints are in form of joint shear failure after yielding of the beam, while the ductility coefficient is found to be greater than 3.0. Compared to the joints with low concrete strength ratios α, the specimen with a high concrete strength ratio α features larger deformation at the joint. Based on the softened strut-and-tie model, a set of shear strength prediction equations for the sandwich beam-column joint, taking into account the effects of the concrete strength ratio α, floor slabs and plastic region of beams, is proposed. Comparison of the present tests against the published literature confirms that the shear strength of the sandwich joints can be well predicted by the proposed model.