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Seismic response of diagonally reinforced slender coupling beams Gonzalez, Emilio

Abstract

The seismic response of diagonally reinforced slender coupling beams is investigated. Primarily, a typical coupling beam found in high-rise buildings in the Vancouver area is studied. Compared to past experiments, this study takes into account a new variable, the axial restraint given by the concrete slab surrounding the coupling beam. Desirable and ductile properties of the beam are studied throughout this work, such as ductility capacity, stiffness degradation, overstrength and energy dissipation capability. A finite element analysis was performed to study the axial restraint parameter mentioned above and assess the degree of restraint given by the slab to the coupling beam. Parameters such as the slab dimensions, slab pre-cracking, slab thickness, mesh size of the model and tension stiffening model are considered. This analysis indicated that the tension stiffening model used for the concrete is the most important parameter. A full-scale coupling beam specimen was tested to develop an analytical model and compare the results with well-known formulas recommended by various Codes. The specimen represented a typical coupling beam found in high-rise buildings in the Vancouver area. The specimen was subjected to cyclic loading and Dywidag bars were provided to model the slab axial restraint. The results showed higher overstrength and stiffness degradation factors than the ones expected from well-known formulas. As expected for diagonally reinforced coupling beams, the specimen showed good ductility and energy dissipation properties. An analytical model based on a truss structure was developed to better understand the behaviour of diagonally reinforced coupling beams. The model gave insight to main factors of the problem, such as diagonal reinforcement, geometry, concrete considered and slab restraint. The monotonic prediction of the model was reasonably similar to the envelope given by the experimental results. Expressions were developed from this model to predict the cracked stiffness and overstrength factor.

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