1、PRESCRIPTIVE METHOD FOR RESIDENTIAL COLD-FORMED STEEL FRAMING Second Edition Prepared for The U.S. Department of Housing and Urban Development Office of Policy Development and Research Washington, DC Co-Sponsored by The American Iron and Steel Institute Washington, DC and The National Association of
2、 Home Builders Washington, DC by NAHB Research Center, Inc. 400 Prince Georges Boulevard Upper Marlboro, MD 20774-8731 August 1997 CONTENTS 5.0 STEEL FLOOR FRAMING . 21 5.1 Floor Construction . 21 5.2 Floor to Foundation or Bearing Wall Connection . 21 5.3 Allowable Joist Spans . 21 5.4 Joist Bracin
3、g . 21 5.5 Floor Cantilevers . 22 5.6 Splicing. 22 5.7 Framing of Floor Openings . 22 5.8 Floor Trusses . 22 5.0 STEEL FLOOR FRAMING 5.1 Floor Construction Cold-formed steel framing members shall comply with the provisions of Section 2.0. Steel floors shall be constructed in accordance with this sec
4、tion and Figure 5.1. 5.1.1 Applicability Limits The applicability limits of Section 1.3 and Table 1.1 shall apply. 5.1.2 In-Line Framing. Load bearing steel floor framing, wall framing, and ceiling/roof framing shall be constructed in-line with the vertical load bearing members (i.e. studs) located
5、below. A maximum tolerance of 3/4 inch (19 mm) between the centerlines of the in-line members shall be permitted in accordance with Figure 1.2. 5.2 Floor to Foundation or Bearing Wall Connection Cold-formed steel floor framing shall be anchored to foundations, wood sills, or load bearing walls in ac
6、cordance with Table 5.1 and Figures 5.1 through 5.10. Fastening of steel joists to other framing members shall be in accordance with Table 5.2. 5.3 Allowable Joist Spans The clear span of cold-formed steel floor joists shall not exceed the limits set forth in Table 5.3 for single spans and Table 5.4
7、 for multiple spans. When continuous joist members are used for multiple spans, the interior bearing supports shall be located within two feet (0.6 m) of mid-span of the steel joists, and the individual spans shall not exceed the applicable spans in the table. Floor joists shall have a bearing suppo
8、rt length of not less than 1.5 inches (38 mm) for exterior wall supports and 3.5 inches (89 mm) for interior wall supports. Bearing stiffeners shall be installed at each joist bearing location in accordance with Section 2.9. The thickness of joist tracks shall be a minimum of 33 mils (0.84 mm) thick
9、 except when used as part of floor header or trimmer in accordance with Section 5.7. 5.4 Joist Bracing The top flanges of floor joists shall be laterally braced by the application of floor fastened to the joists in accordance with Table 5.2. Floor joists with spans that exceed 12 feet (3.7 m) shall
10、have the bottom flanges laterally braced in accordance with one of the following: 1. Gypsum board installed with minimum#6 screws in accordance with the applicable building code, or 2. Continuous steel strapping installed in accordance with Figure 5.1 and 5.2. Steel straps shall be at least 1-1/2 in
11、ches (38 mm) in width and 33 mils (0.84 mm) in thickness. Straps shall be fastened to the bottom flange of each joist with at least one #8 screw and shall be fastened to blocking with at least two #8 screws. Blocking or bridging (X-bracing) shall be installed between joists at a maximum spacing of 1
12、2 feet (3.7m) measured along the continuous strapping (perpendicular to the joist run). Blocking or bridging shall also be located at the termination of all straps. 5.5 Floor Cantilevers Floor cantilevers for the second floor of a two-story building or the first floor of a one-story building shall n
13、ot exceed 24 inches (610 mm) as illustrated in Figure 5.1. Cantilevers shall support interior floor loading only. Cantilevers, not exceeding 24 inches (610 mm) and supporting one floor and roof (first floor of a two story building), shall be permitted provided that all cantilevered joists are double
14、d (nested or back-to-back). The doubled cantilevered joists shall extend a minimum of 6 feet (1.8 m) toward the inside and shall be fastened with a minimum of two #8 screws spaced at 24 inches (610 mm) on center through the webs (for back-to-back) or flanges (for nested joists). Approved design is required for cantilevered areas supporting uniform live loads greater than 40 psf (1.92 kN/m2).
