Nominal shear strength limits for short diagonally-reinforced concrete coupling beams

Sections 21.9.4.5 and 21.9.7.4 of ACI 318-08 limit the nominal shear strength, V_n of concrete coupling beams, including short beams with diagonal reinforcement, to V_n≤0.83A_cw√f' _c (with f'_c in MPa units, or 10A_cw√ f'_c with f'_c in psi units). Many experimental studies have been conducted on the design and detailing of diagonallyreinforced coupling beams for ductile behavior under seismic loading. The primary objective of the current ACI strength limit is to prevent the splitting and/or crushing of the diagonal strut in these beams. Through an analytical parametric investigation of isolated floor-level subassemblies, this paper shows that the boundary conditions utilized in the previous coupling beam experiments may not be adequate to investigate this important failure mode. The analytical model that forms the basis of the study uses a strut-and-tie representation of the forces developing inside a coupling beam under lateral loading. Multi-story coupled wall analyses are also conducted.