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The response of coupled core wall systems is governed by the performance of their coupling beams. Moreover, coupling beam design is controlled by the post-elastic behavior of the entire coupled system. This paper presents the results of an experimental investigation dealing with the effects that transverse reinforcement ratios have on the post-elastic performance of diagonally-reinforced coupling beams. Two coupled wall subassemblages, with two different transverse reinforcement detailings, were designed and tested under cyclic reversed loads. The design philosophy for both specimens is presented and discussed, and the detailing is compared with what is required by ACI 318-05. The experimental results are presented, with particular attention to the post-elastic performance of the specimens tested. Overall performance comparisons are made. It is concluded that providing a higher transverse reinforcement ratio greatly benefits ductility and hysteretic stability of diagonally-reinforced coupling beams.
Keywords: coupling beams; reinforcement detailing; seismic design; walls.
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INTRODUCTION
Coupled core wall systems (CCWs) are advantageous lateral force-resisting (LFR) systems that combine the large shear and axial stiffness of shear walls with the ductility of the coupling beams. Many studies in literature amply demonstrate the desirable attributes of CCWs as a whole as well as the issues and advantages related to the components within the system: some examples include Fortney (2005), Harries et al. (2005), Shahrooz et al. (1992, 1993), and Aristizabal-Ochoa (1982). The overall lateral stiffness largely depends on the type and detailing of the coupling beams used. Previous work by the authors (Fortney et al. [2004a,b]; Fortney [2005]; Harries et al. [2005]; Shahrooz et al. [1992, 1993]) highlighted the difference in response between steel, steel-concrete, and diagonally-reinforced concrete coupling beams. Traditionally, the coupling beam typology chosen for CCWs is represented by diagonallyreinforced concrete beams. These beams, if properly detailed, can provide considerable stiffness, strength, and ductility; but sometimes they can be very complicated, if not impossible, to fabricate and construct. Harries et al. (2005) clearly showed that diagonally-reinforced coupling beams with practical span-depth ratios cannot practically be built when designed for shear demands larger than 0.50 [the square root of]f'^sub c^ (f'^sub c^ in MPa) (6 [the square root of]f'^sub c^ [f'^sub c^ in psi]), whereas ACI 318-05 (ACI Committee 318 2005) allows for a maximum shear demand of...