Design recommendations for achieving “strong column-weak beam” in RC frames

This paper deals with the realization of ductile failure of RC frames with cast in-situ slabs. The cyclic loading experiments of two spatial reinforced concrete (RC) frames, a control specimen and a RC frame with cast in-situ slabs, are carried out. The failure pattern and the role of slabs are experimentally studied. Tests results indicate that slabs can change the failure pattern of RC frames from a typical “strong-column-weak-beam” failure to the “strong-beam-weak-column” failure. The slab reinforcement enhances the resistance moment of the beams, which is the main reason to form “strong-beam-weak-column”. The parameters such as axial compression ratio, thickness of slab, concrete strength, reinforcement ratio of slab and stiffness of transverse beam are investigated by Finite Element Analysis (FEA). Strut and tie model of slab is proposed to calculate the effective slab width. Simple equations are derived by a 95% guarantee rate based on 200 models. The required ratio of column-to-beam strength is studied based on the tests and FEA data. A reasonable required ratio is proposed to avoid the brittle failure of the RC frames for seismic design.