Hysteretic behavior and design specification of composite beam with slit around column

This paper discusses the seismic performance of composite beams. Compared with structural steel beams, classical composite beams increase flexural stiffness and strength under positive bending moments. Due to the asymmetry of the section, however, these values are much lower for the case of a negative bending moment. Fractures at the bottom flange of the beam were also observed after the 1995 Kobe earthquake. Therefore, a new composite beam system is proposed to solve such problems, which is characterized by a slit in the concrete slab around the column and a non-composite region at the end of the beam. The seismic behavior of the proposed composite beam system with a slit was investigated experimentally under reversed cyclic loading on three beam-to-column assemblies. Analytical investigations with test results were also conducted. The research results clearly show that the proposed system combines the desirable attributes of earlier systems: the high flexural stiffness typical of classical composite beams and the large beam rotational capacity typical of steel beams. Finally, a method for evaluating the flexural stiffness, strength and rotational capacity is presented in the form of design recommendations.