1810.3.8 Precast Concrete Piles
Longitudinal steel shall be arranged in a symmetrical pattern and be laterally tied with steel ties or wire spiral spaced center to center as follows:
- At not more than 1 inch (25 mm) for the first five ties or spirals at each end; then
- At not more than 4 inches (102 mm), for the remainder of the first 2 feet (610 mm) from each end; and then
- At not more than 6 inches (152 mm) elsewhere.
The size of ties and spirals shall be as follows:
- For piles having a least horizontal dimension of 16 inches (406 mm) or less, wire shall not be smaller than 0.22 inch (5.6 mm) (No. 5 gage).
- For piles having a least horizontal dimension of more than 16 inches (406 mm) and less than 20 inches (508 mm), wire shall not be smaller than 0.238 inch (6 mm) (No. 4 gage).
- For piles having a least horizontal dimension of 20 inches (508 mm) and larger, wire shall not be smaller than 1/4 inch (6.4 mm) round or 0.259 inch (6.6 mm) (No. 3 gage).
The effective prestress in the pile shall be not less than 400 psi (2.76 MPa) for piles up to 30 feet (9144 mm) in length, 550 psi (3.79 MPa) for piles up to 50 feet (15 240 mm) in length and 700 psi (4.83 MPa) for piles greater than 50 feet (15 240 mm) in length.
Effective prestress shall be based on an assumed loss of 30,000 psi (207 MPa) in the prestressing steel. The tensile stress in the prestressing steel shall not exceed the values specified in ACI 318.
|Ag||=||Pile cross-sectional area 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||=||Spiral reinforcement index or volumetric ratio (vol. spiral/vol. core).|
For structures assigned to Seismic Design Category D, E or F, precast prestressed piles shall have transverse reinforcement in accordance with the following:
- Requirements in ACI 318, Chapter 18, need not apply, unless specifically referenced.
- 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.
- 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.
- 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 25.5.7 of ACI 318.
For structures assigned to Seismic Design Category C, D, E, or F, the maximum factored axial load on precast prestressed piles subjected to a combination of seismic lateral force and axial load shall not exceed the following values:
- 0.2f 'c Ag for square piles
- 0.4f 'c Ag for circular or octagonal piles