Diagonally Reinforced Concrete Coupling Beams with Grade 120 (830) High-Strength Steel Bars

Four large-scale coupling beams were tested under fully reversed cyclic loads to investigate the effects on behavior of diagonal bar grade (60 or 120 [420 or 830]), beam shear stress (9.5 or 14√fc′, psi [0.79 or 1.17√fc′, MPa]), and longitudinal bar detailing (either terminated near the beam-wall interface or developed into the walls). Coupling beam chord rotation capacity was 7.1% for the beam with Grade 60 (420) bars and between 5.1 and 5.6% for the beams with Grade 120 (830) bars, a difference likely due to having hoops spaced at 3.4db and 4db for Grade 60 and 120 (420 and 830) bars, where db is the diagonal bar diameter. Effective stiffness, energy dissipation, and residual chord rotations were approximately inversely proportional to bar grade. Developing the secondary longitudinal reinforcement reduced rotation demands at beam ends but did not improve deformation capacity. Beam shear stress did not affect beam chord rotation capacity.

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