18.10.7 Coupling Beams
(a) Vn shall be calculated by
where α is the angle between the diagonal bars and the longitudinal axis of the coupling beam.
(b) Each group of diagonal bars shall consist of a minimum of four bars provided in two or more layers. The diagonal bars shall be embedded into the wall at least 1.25 times the development length for fy in tension.
(c) Each group of diagonal bars shall be enclosed by rectilinear transverse reinforcement having out-to-out dimensions of at least bw/2 in the direction parallel to bw and bw/5 along the other sides, where bw is the web width of the coupling beam. The transverse reinforcement shall be in accordance with 184.108.40.206(a) through (e), with Ash not less than the greater of (i) and (ii):
For the purpose of calculating Ag, the concrete cover in 20.6.1 shall be assumed on all four sides of each group of diagonal bars. The transverse reinforcement shall have spacing measured parallel to the diagonal bars satisfying 220.127.116.11(c) and not exceeding 6db of the smallest diagonal bars, and shall have spacing of crossties or legs of hoops measured perpendicular to the diagonal bars not exceeding 14 in. The transverse reinforcement shall continue through the intersection of the diagonal bars. At the intersection, it is permitted to modify the arrangement of the transverse reinforcement provided the spacing and volume ratio requirements are satisfied. Additional longitudinal and transverse reinforcement shall be distributed around the beam perimeter with total area in each direction of at least 0.002bws and spacing not exceeding 12 in.
Longitudinal spacing of transverse reinforcement shall not exceed the lesser of 6 in. and 6db of the smallest diagonal bars. Spacing of crossties or legs of hoops both vertically and horizontally in the plane of the beam cross section shall not exceed 8 in. Each crosstie and each hoop leg shall engage a longitudinal bar of equal or greater diameter. It shall be permitted to configure hoops as specified in 18.104.22.168.