Cyclic Tests of Reinforced Concrete Coupling Beam with Intermediate Span-to-Depth Ratio

The seismic performance of intermediate clear span-depth ratio (2.0 [less than or equal to] [l.sub.n]. [less than or equal to] 4.0) coupling beams with hybrid layout were evaluated in this study. By combining the conventional ductile beam detailing and the benefit of the presence of diagonal bars, this study shows that the hybrid layout may serve as one of the possible alternatives to ease construction difficulty. Test results found out that, at the maximum considered earthquake (MCE) level, the shear strength of a coupling beam was governed by the crushing of concrete strut in the plastic hinge regions and yielding of diagonal bars. To allow a full development of concrete strut capacity and to maintain integrity of core concrete, sufficient internal support must be provided by the transverse reinforcement. Using the proposed shear-strength equation, a more rational approach can be adopted to determine the appropriate reinforcement layout and the efficient amount of diagonal bars for a coupling beam with 2.0 [less than or equal to] [l.sub.n] [less than or equal to] 4.0. Keywords: coupling beam; hybrid layout; intermediate clear span-depth ratio; internal support; seismic behavior.