Behavior of Partially Concrete Encased Steel Beams Under Cyclic Loading

This paper presents an experimental study of the behavior of partially concrete encased steel beams (PE beams) under seismic loading. The effects of a floor slab in providing lateral and torsional support to the strength and ductility of the beam are also investigated herein. One steel beam and six PE beams were tested herein. The strength development in bare steel beam was insufficient and significant lateral torsional buckling (LTB) was observed. The concrete encasement of the PE beam delayed the occurrence of LTB and hence increased the strength and ductility of the beam. The plastic rotation capacity of PE beam is enhanced by the additional lateral and torsional support provided on the top of a PE beam. For the beam tested in this study, the concrete encasement permits the beam to reach its plastic strength and have plastic rotation of at least 3.42 rad, which is larger than 2 rad required for Intermediate Moment Frames, when no lateral or torsional support is provided at the top of the beam. To satisfy the 4 rad plastic rotation limitation for special moment frames, lateral support with sufficient torsional stiffness is needed.