1811.6.3.2.2 Design in Seismic Design Category D.
BC § 1811.6.3.2.2
Where a structure is assigned to Seismic Design Category D in accordance with Section 1613.3.5, the requirements for Seismic Design Category C in Section 1811.6.3.2.1 shall be met, in addition to the following: 1. Requirements in ACI 318, Chapter 18, do not apply, unless specifically referenced.
2.Where the total length of the deep foundation 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 precast prestressed concrete pile. Where the precast prestressed concrete pile length exceeds 35 feet (10 668 mm), the ductile region of the deep foundation 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 dimension of the precast prestressed concrete pile.
3.In the ductile region, the center-to-center spacing of the spirals or hoop reinforcement shall not exceed one-fifth of the least dimension of the deep foundation element, six times the diameter of the longitudinal strand or 8 inches (203.2 mm), whichever is smaller.
4.Circular spiral reinforcement shall be spliced by lapping one full turn and bending the end of the spiral to a 90-degree (1.6-rad) hook or by use of a mechanical or welded splice complying with Section 25.5.7 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: (Equation 18-2) but not exceed: ρs = 0.21 (Equation 18-3) where: Ag = Pile cross-sectional area, square inches (mm 2 ). 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). This required amount of spiral reinforcement is permitted to be obtained by providing an inner and outer spiral. Exception: The minimum spiral reinforcement required by Equation 18-2 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 and the applicable overstrength factor, Ω0 . In such cases, minimum spiral reinforcement index shall be as specified in Section 1811.6.1.2.
6.When 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 to dimension, hc , shall conform to: (Equation 18-4) but not less than: (Equation 18-5) where: fyh = Yield strength of transverse reinforcement ≤ 70,000 psi (483 MPa). h c = 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 transverse reinforcement, square inches (mm 2 ). f 'c = Specified compressive strength of concrete, psi (MPa). The hoops and cross ties shall be equivalent to deformed bars not less than No. 3 in size. Rectangular hoop ends shall terminate at a corner with seismic hooks. Outside of the length of the pile requiring transverse confinement reinforcing, the spiral or hoop reinforcing with a volumetric ratio not less than one-half of that required for transverse confinement reinforcing shall be provided.
