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2308.12 Additional Requirements for Conventional Light-Frame Construction in Seismic Design Category D
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For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
Exception: Masonry veneer is permitted to be used in the first story above grade in Seismic Design Category D provided the following criteria are met:
1. Type of brace in accordance with Section 2308.9.3 shall be Method 3 and the allowable shear capacity in accordance with Table 2306.4.1 shall be a minimum of 350 plf (5108 N/m) (ASD).
2. The bracing of the first story shall be located at each end and at least every 25 feet (7620 mm) o.c. but not less than 45 percent of the braced wall line.
3. Hold-down connectors shall be provided at the ends of braced walls for the first floor to foundation with an allowable design of 2,100 pounds (1768 kg).
4. Cripple walls shall not be permitted.
Spacing between interior and exterior braced wall lines shall not exceed 25 feet (7620 mm).
Braced wall lines shall be braced by one of the types of sheathing prescribed by Table 2308.12.4 as shown in Figure 2308.9.3. The sum of lengths of braced wall panels at each braced wall line shall conform to Table 2308.12.4. Braced wall panels shall be distributed along the length of the braced wall line and start at not more than 8 feet (2438 mm) from each end of the braced wall line. A designed collector shall be provided where the bracing begins more than 8 feet (2438 mm) from each end of a braced wall line. Panel sheathing joints shall occur over studs or blocking. Sheathing shall be fastened to studs and top and bottom plates and at panel edges occurring over blocking. Wall framing to which sheathing used for bracing is applied shall be nominal 2 inch wide (actual 11/2 inch, 38 mm) or larger members.
Cripple walls having a stud height exceeding 14 inches (356 mm) shall be considered a story for the purpose of this section and shall be braced as required for braced wall lines in accordance with Table 2308.12.4. Where interior braced wall lines occur without a continuous foundation below, the length of parallel exterior cripple wall bracing shall be one and one-half times the lengths required by Table 2308.12.4. Where the cripple wall sheathing type used is Type S-W, and this additional length of bracing cannot be provided, the capacity of Type S-W sheathing shall be increased by reducing the spacing of fasteners along the perimeter of each piece of sheathing to 4 inches (102 mm) o.c.
|STORY LOCATION||SHEATHING TYPEb||0.50 ≤ SDs <0.75||0.75 ≤ SDs ≤ 1.00||1.00 < SDS|
|Top or only story||G-Pd||14 feet 8 inches||18 feet 8 inchesc||25 feet 0 inchesc|
|S-W||8 feet 0 inches||9 feet 4 inchesc||12 feet 0 inchesc|
|Story below top story||G-Pd||NP||NP||NP|
|S-W||13 feet 4 inchesc||17 feet 4 inchesc||21 feet 4 inchesc|
|Bottom story of three stories||G-Pd
|Conventional construction not permitted; conformance with Section 2301.2.1 or 2301.2.2 is required.|
- Minimum length of panel bracing of one face of wall for S-W sheathing or both faces of wall for G-P sheathing; h/w ratio shall not exceed 2:1. For S-W panel bracing of the same material on two faces of the wall, the minimum length is permitted to be one-half the tabulated value but the h/w ratio shall not exceed 2:1 and design for uplift is required.
- G-P = gypsum board, fiberboard, particleboard, lath and plaster, or gypsum sheathing boards; S-W = wood structural panels and diagonal wood sheathing. NP = not permitted.
- Applies to one-and two-family detached dwellings only.
- Nailing as specified below shall occur at all panel edges at studs, at top and bottom plates, and, where occurring, at blocking:
For 1/2-inch gypsum board, 5d (0.113 inch diameter) cooler nails at 7 inches on center;
For 5/8-inch gypsum board, No. 11 gage (0.120 inch diameter) at 7 inches on center;
For gypsum sheathing board, 13/4 inches long by 7/16-inch head, diamond point galvanized nails at 4 inches on center;
For gypsum lath, No. 13 gage (0.092 inch) by 11/8 inches long, 19/64-inch head, plasterboard at 5 inches on center;
For portland cement plaster, No. 11 gage (0.120 inch) by 11/2 inches long, 7/16-inch head at 6 inches on center;
For fiberboard and particleboard, No. 11 gage (0.120 inch) by 11/2 inches long, 7/16-inch head, galvanized nails at 3 inches on center.
Conventional light-frame construction shall not be used in irregular portions of structures in Seismic Design Category D. Such irregular portions of structures shall be designed to resist the forces specified in Chapter 16 to the extent such irregular features affect the performance of the conventional framing system. A portion of a structure shall be considered to be irregular where at least one of the conditions described in Items 1 through 6 below is present.
- Where exterior braced wall panels are not in one plane vertically from the foundation to the uppermost story in which they are required, the structure shall be considered to be irregular [see Figure 2308.12.6(1)].
Exception: Floors with cantilevers or setbacks not exceeding four times the nominal depth of the floor joists [see Figure 2308.12.6(2)] are permitted to support braced wall panels provided:
- Floor joists are 2 inches by 10 inches (51 mm by 254 mm) or larger and spaced not more than 16 inches (406 mm) o.c.
- The ratio of the back span to the cantilever is at least 2:1.
- Floor joists at ends of braced wall panels are doubled.
- A continuous rim joist is connected to the ends of cantilevered joists. The rim joist is permitted to be spliced using a metal tie not less than 0.058 inch (1.47 mm) (16 galvanized gage) and 11/2 inches (38 mm) wide fastened with six 16d common nails on each side. The metal tie shall have a minimum yield of 33,000 psi (227 Mpa).
- Joists at setbacks or the end of cantilevered joists shall not carry gravity loads from more than a single story having uniform wall and roof loads, nor carry the reactions from headers having a span of 8 feet (2438 mm) or more.
- Where a section of floor or roof is not laterally supported by braced wall lines on all edges, the structure shall be considered to be irregular [see Figure 2308.12.6(3)]. Exception: Portions of roofs or floors that do not support braced wall panels above are permitted to extend up to 6 feet (1829 mm) beyond a braced wall line [see Figure 2308.12.6(4)].
- Where the end of a required braced wall panel extends more than 1 foot (305 mm) over an opening in the wall below, the structure shall be considered to be irregular. This requirement is applicable to braced wall panels offset in plane and to braced wall panels offset out of plane as permitted by the exception to Item 1 above in this section [see Figure 2308.12.6(5)].
Exception: Braced wall panels are permitted to extend over an opening not more than 8 feet (2438 mm) in width where the header is a 4-inch by 12-inch (102 mm by 305 mm) or larger member.
- Where portions of a floor level are vertically offset such that the framing members on either side of the offset cannot be lapped or tied together in an approved manner, the structure shall be considered to be irregular [see Figure 2308.12.6(6)].
Exception: Framing supported directly by foundations need not be lapped or tied directly together.
- Where braced wall lines are not perpendicular to each other, the structure shall be considered to be irregular [see Figure 2308.12.6(7)].
- Where openings in floor and roof diaphragms having a maximum dimension greater than 50 percent of the distance between lines of bracing or an area greater than 25 percent of the area between orthogonal pairs of braced wall lines are present, the structure shall be considered to be irregular [see Figure 2308.12.6(8)].
Steel plate washers shall be placed between the foundation sill plate and the nut. Such washers shall be a minimum of 3 / 1 6 inch by 2 inches by 2 inches (4.76 mm by 51 mm by 51 mm) in size.