Nonlinear Modeling Parameters For Diagonally Reinforced Concrete Coupling Beams

A database of diagonally reinforced concrete coupling beam tests was formulated and used to assess strength, stiffness, and deformation capacity. The shear strength equation provided in ACI 318-19 considers only the transverse strength of the diagonal bars and was found to be overly conservative. A new equation that includes shear strength of concrete and transverse reinforcement was found to provide a better fit to test data. Existing recommendations were found to underestimate deformation capacity. A plastic hinge model that includes bond slip was formulated to estimate deformation capacity based on strain at crushing of confined concrete and strain at onset of diagonal reinforcement buckling. Favorable agreement was found between the model and test data. An empirical equation based on ratio of diagonal bar diameter to section depth, db/h, and ratio of spacing of transverse reinforcement to diagonal bar diameter, s/db, was fit to data. The empirical equation led to reduced scatter relative to the plastic hinge model. A parametric study was conducted using the plastic hinge model and the empirical equation, and reasonable agreement was found between the two models over this practical range of parameters. New recommendations for determining the deformation capacity of diagonally reinforced concrete coupling beams are provided.