Elasto-plastic behavior of weak-panel beam-column joints with RC slabs under bidirectional loading

This paper presents an experimental and numerical study to examine the elasto-plastic behavior of the weak-panel type beam-column joints with RC slabs subjected to bidirectional and unidirectional loading. The effect of the RC slab on the behavior of the beam-column joints was investigated. The steel beam-column joint specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before the columns and beams. The specimens failed at 0.04 rad story drift under bidirectional loading, while the specimens sustained a story drift of 0.08 rad under unidirectional loading. The existence of the RC slab led to various failure modes in this test, including the local buckling of the upper column, the weld fracture at the lower panel section, and the weld fracture at the beam bottom flange. It was worth noting that the panel-to-diaphragm weld cracks always initiated in the lower panel section and developed into severe fractures. Both the top and bottom surfaces of the slab suffered concrete crushing in the area around the column. Concrete cracks on the top surface were basically along the direction of the steel beam, while the cracks along the direction of the slab diagonal were also observed for the specimens under bidirectional loading. The RC slab increased the plastic strength of the specimens by 15%–20%. An equation was proposed to quantify the slab effect on the plastic strength of the specimens. Finite element analysis was conducted to validate the proposed equation.