Shear Performance of Heavily Reinforced High-strength Concrete Coupling Beams

High-strength, heavily reinforced concrete coupling beams that have compact designs are critical to the building economics of high-rise structures. There is concern with these heavily reinforced designs that the phenomenon of concrete side cover spalling may occur as the coupling beams approach failure, causing an unintended loss of strength and stiffness. To investigate these consequences, four full-scale coupling beams with varying concrete strengths, reinforcement ratios, and side cover thicknesses were tested. It was observed that the concrete side cover spalled for all four specimens. In situations where the beam design capacity is close to the upper limits of shear capacity, a significant reduction in strength could occur as the concrete crushes before the stirrups yield. While the CSA Code had an average test-to-prediction ratio of 1.05 for the specimen peak load, the limits imposed by the ACI Code under predicted the peak load with test-to-prediction ratios as high as 1.45.M.A.S