Nonlinear Behavior of the Concrete Core of the Diagonally Reinforced Coupling Beams

Coupled shear walls with coupling beams are constructed because of openings such as doors, windows, or other installations that are left behind due to functional reasons in shear walls. The seismic behavior of coupled shear walls with coupling beams depends on the structural performance of the coupling beams. In coupling beams having a ratio of span-to-depth less than two, shear fracture occurs rather than flexural fracture. In order to meet the shear force and the bending moment formed by the coupling beams, diagonal bundles are used in the coupling beams. Diagonal reinforced coupling beams are generally preferred because diagonal reinforced coupling beams exhibit better behavior than conventional reinforced coupling beams. The diagonal reinforcement bundles have to be confined by transverse reinforcements prescribed in the codes. Confined concrete in the diagonal reinforcement bundles has stress-strain characteristics that are distinctly different from those of plain concrete. The effects of longitudinal and transverse reinforcement ratios on the stress-strain behavior of confined concrete inside the diagonal reinforcement bundles were investigated. Fifty-four reinforced concrete coupling beams with different confining parameters of the diagonal reinforcement bundles and different variables were analyzed using the program. It was demonstrated that the strength and the maximum strain of the concrete inside the diagonal reinforcement bundles increase with the reinforcement ratio of the confinement reinforcement. The increase in the diameter of the transverse reinforcement and the decrease in the transverse reinforcement spacing in the diagonal bundles, increase the confining effect in the concrete sections, increasing the ductility and strength, and has a significant effect on the seismic behavior of the coupling beams.