For structures assigned to Seismic Design Category D, E or F, precast prestressed piles shall have transverse reinforcement in accordance with the following:
1. Requirements in ACI 318, Chapter 21, need not apply, unless specifically referenced.
2. Where the total pile length in the soil is 35 feet (10 668 mm) or less, the lateral transverse reinforcement in the ductile region shall occur through the length of the pile. Where the pile length exceeds 35 feet (10 668 mm), the ductile pile region shall be taken as the greater of 35 feet (10 668 mm) or the distance from the underside of the pile cap to the point of zero curvature plus three times the least pile dimension.
3. In the ductile region, the center-to-center spacing of the spirals or hoop reinforcement shall not exceed one-fifth of the least pile dimension, six times the diameter of the longitudinal strand or 8 inches (203 mm), whichever is smallest.
4. Circular spiral reinforcement shall be spliced by lapping one full turn and bending the end of each spiral to a 90-degree hook or by use of a mechanical or welded splice complying with Section 12.14.3 of ACI 318.
5. Where the transverse reinforcement consists of circular spirals, the volumetric ratio of spiral transverse reinforcement in the ductile region shall comply with the following:
| ρs = 0.25(f'c/fyh)(Ag /Ach - 1.0) [0.5 + 1.4P/(f'c Ag)] | (Equation 18-6) | |
| ρs=0.12(f'c/fyh) [0.5 + 1.4P/(f'c Ag)]3 0.12f'c/fyh | (Equation 18-7) |
| ρs = 0.021 | (Equation 18-8) |
| Ag | = | Pile cross-sectional area, square inches (mm2). |
| Ach | = | Core area defined by spiral outside diameter, square inches (mm2). |
| f'c | = | Specified compressive strength of concrete, psi (MPa). |
| fyh | = | Yield strength of spiral reinforcement ≤ 85,000 psi (586 MPa). |
| P | = | Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-7. |
| ρs | = | Volumetric ratio (vol. spiral/vol. core). |
6. Where transverse reinforcement consists of rectangular hoops and cross ties, the total cross-sectional area of lateral transverse reinforcement in the ductile region with spacing, s, and perpendicular dimension, hc, shall conform to:
| Ash= 0.3s hc (f'c /fyh)(Ag /Ach - 1.0) [0.5 + 1.4P/(f'c Ag)] | (Equation 18-9) |
| Ash = 0.12s hc(f'c /fyh) [0.5 + 1.4P/(f'c Ag)] | (Equation 18-10) |
| fyh | = | yield strength of transverse reinforcement ≤ 70,000 psi (483 MPa). |
| hc | = | Cross-sectional dimension of pile core measured center to center of hoop reinforcement, inch (mm). |
| s | = | Spacing of transverse reinforcement measured along length of pile, inch (mm). |
| Ash | = | Cross-sectional area of tranverse reinforcement, square inches (mm2). |
| f'c | = | Specified compressive strength of concrete, psi (MPa). |