Section 10.7.6/Column Transverse Reinforcement (Ties and Spirals)
ACI 318-19 Section 10.7.6 covers tie and spiral requirements for concrete columns including bar size, spacing, and arrangement of lateral support for longitudinal bars.
Columns with tie reinforcement must use at least No. 3 ties for longitudinal bars No. 10 and smaller, and at least No. 4 ties for No. 11, No. 14, and No. 18 longitudinal bars and for bundled bars. Tie spacing must not exceed the smallest of: 48 tie bar diameters, 16 longitudinal bar diameters, or the least dimension of the column. Every corner bar and every alternate longitudinal bar must have lateral support provided by the corner of a tie with an included angle of not more than 135 degrees, and no bar can be farther than 6 inches clear on each side from a laterally supported bar. Columns with spiral reinforcement must have spirals with a minimum diameter of 3/8 inch, clear spacing between turns of at least 1 inch and not more than 3 inches, and a volumetric ratio not less than that required by Section 25.7.3.3.
Why this section exists
Transverse reinforcement in columns prevents longitudinal bars from buckling outward under compressive load and confines the concrete core, improving ductility. Without adequate ties or spirals, the longitudinal bars can buckle between tie locations, causing sudden loss of load-carrying capacity. The 135-degree hook requirement ensures ties are anchored into the confined core. Spiral columns provide superior confinement and ductility, which is why the ACI strength reduction factor phi for spiral columns (0.75) is higher than for tied columns (0.65). In seismic design categories D through F, significantly more stringent transverse reinforcement is required per Section 18.10 for special structural elements.
What plan reviewers look for
Plan reviewers check column schedules and sections for tie size, spacing, and arrangement. They verify that tie spacing satisfies all three limits (48 tie diameters, 16 bar diameters, least column dimension). They check column cross-section details to confirm every corner bar and every alternate bar has lateral support from a tie with a 135-degree hook. For columns with more than 4 longitudinal bars, they verify that interior bars are supported by cross-ties or additional tie legs. They check that ties are specified at the top and bottom of the column and within the splice region per Section 25.4.2.