Transverse Reinforcement

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Symbols

d_b = nominal diameter of bar, wire, or prestressing strand, in
A_ch = cross-sectional area of a member measured to the outside edges of transverse reinforcement, in.²
f'_c = specified comprehensive strength of concrete, psi
f_yt = specified yield strength of transverse reinforcement, psi
A_g = gross area of concrete section, in.² For a hollow section, Ag is the area of the concrete only and does not include the area of the void(s)
ρ_s = ratio of volume of spiral reinforcement to total of core confined by the sprial, measured out-to-out of spirals

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25.7.2 Ties

Ties, applies closed loop of deformed bar, satisfies the rules:

• Center-to-center spacing does not exceed the least of 16d_b of longitudinal bar, 48d_b of tie bar and smallest dimension of member

Minimum diameter of tie bar is controlled automatically according to ACI 25.7.2.2. Diameter of tie bar is at least:

• No. 3 enclosing No. 10 or smaller longitudinal bars

• No. 4 enclosing No.11 or larger longitudinal bars or bundled longitudinal bars

According to ACI 25.7.2.3 Rectilinear ties are arranged to satisfy (a) and (b):

• (a) Every corner and alternate longitudinal bar have lateral support provided by the corner of a tie with an included angle of not more than 135 degrees
  (b) No unsupported bar is farther than 6 in. clear on each side along the tie from a laterally supported bar

Anchorage of individual circular ties are controlled according to ACI 25.7.2.4.1.

(a) Ends overlap by at least 6 in.
(b) Ends terminate with standard hooks in accordance with ACI 25.3.2 that engage a longitudinal bar
(c) Overlaps at ends of adjacent circular ties are staggered around the perimeter enclosing the longitudinal bars

25.7.3 Spirals

Minimum clear spacing of spirals are satisfied:

• At least the greater of 1 in.

• Not greater than 3 in.

Minimum diameter of spiral bar or wire is at least 3/8 in. for cast-in-place construction.
The volumetric spiral reinforcement ratio ρ_s is controlled according to ACI Eq.25.7.3.3, this condition isn’t apply for transverse reinforcement in deep foundations.

Note: the value of f_yt is not taken greater than 100,000 psi. Spirals are anchored by 1-1/2 extra turns each end.

Spirals' lap splices in accordance with 25.7.3.6 for f_yt not exceeding 60,000 psi. Spiral lap splices are at least the greater of 12 in. and the lap length in Table 25.7.3.6.

25.7.4 Hoop

Hoops consist of a closed tie or continuously wound tie, which can consist of several reinforcement elements each having seismic hooks at both ends.
The ends of the reinforcement elements in hoops are anchored using seismic hooks that conform to ACI 25.3.4 and engage a longitudinal bar.

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