Experimental study on the mechanical behavior of 3D sandwich joints under bi-directional loading

The core area of "equal beam equal strength" sandwich beam-column joints has the advantage of easy construction and quality control, compared with the core area of traditional"equal column equal strength joints;however, there have been no explicit calculation methods but only simple provisions in current Chinese design codes regarding the weak-strength joint. In this paper, three groups of sandwich joint specimens with different concrete strength were tested under bi-directional reversed cyclic loads, and their seismic performance was investigated, including the failure mode, ductility, energy dissipation, deformation and carrying capacity. The test results show that with low-to-moderate axial compression ratio, the seismic performance of sandwich joints is slightly weaker than that of traditional joints with insignificant difference. For the case where the ratio of the column concrete compressive strength to the beam concrete compressive strength is less than 1.5, the joint concrete can be of the same strength as the beam;otherwise, the failure mode may change from flexural failure of the beams to shear failure of the joint, and thus some strengthening measures are needed. Finally, a new formula is presented for calculating the shear capacity of the sandwich joints, which is consistent with the experimental results.