When supported by cold-formed steel framed walls in accordance with Section R603, cold-formed steel floor framing shall be constructed with floor joists located in-line with load-bearing studs located below the joists in accordance with Figure R505.1.2 and the tolerances specified as follows:
- The maximum tolerance shall be 3/4 inch (19.1 mm) between the centerline of the horizontal framing member and the centerline of the vertical framing member.
- Where the centerline of the horizontal framing member and bearing stiffener are located to one side of the centerline of the vertical framing member, the maximum tolerance shall be 1/8 inch (3 mm) between the web of the horizontal framing member and the edge of the vertical framing member.
Load-bearing cold-formed steel floor framing members shall comply with Figure R505.2(1) and with the dimensional and minimum thickness requirements specified in Tables R505.2(1) and R505.2(2). Tracks shall comply with Figure R505.2(2) and shall have a minimum flange width of 11/4 inches (32 mm).
COLD-FORMED STEEL JOIST SIZES
|MEMBER DESIGNATIONa||WEB DEPTH |
|MINIMUM FLANGE WIDTH |
|MAXIMUM FLANGE WIDTH |
|MINIMUM LIP SIZE |
For SI: 1 inch = 25.4 mm, 1 mil = 0.0254 mm.
- The member designation is defined by the first number representing the member depth in 0.01 inch, the letter "S" representing a stud or joist member, the second number representing the flange width in 0.01 inch, and the letter "t" shall be a number representing the minimum base metal thickness in mils [See Table R505.2(2)].
MINIMUM THICKNESS OF COLD-FORMED STEEL MEMBERS
|DESIGNATION THICKNESS |
|MINIMUM BASE STEEL THICKNESS |
For SI:inch = 25.4 mm, 1 mil = 0.0254 mm.
Load-bearing cold-formed steel framing members shall have a legible label, stencil, stamp or embossment with the following information as a minimum:
- Manufacturer's identification.
- Minimum base steel thickness in inches (mm).
- Minimum coating designation.
- Minimum yield strength, in kips per square inch (ksi) (MPa).
Load-bearing cold-formed steel framing shall have a metallic coating complying with ASTM A 1003 and one of the following:
- A minimum of G 60 in accordance with ASTM A 653.
- A minimum of AZ 50 in accordance with ASTM A 792.
Screws for steel-to-steel connections shall be installed with a minimum edge distance and center-to-center spacing of 1/2 inch (12.7 mm), shall be self-drilling tapping, and shall conform to ASTM C 1513. Floor sheathing shall be attached to cold-formed steel joists with minimum No. 8 self-drilling tapping screws that conform to ASTM C 1513. Screws attaching floor-sheathing to cold-formed steel joists shall have a minimum head diameter of 0.292 inch (7.4 mm) with countersunk heads and shall be installed with a minimum edge distance of 3/8 inch (9.5 mm). Gypsum board ceilings shall be attached to cold-formed steel joists with minimum No. 6 screws conforming to ASTM C 954 or ASTM C 1513 with a bugle head style and shall be installed in accordance with Section R702. For all connections, screws shall extend through the steel a minimum of three exposed threads. All fasteners shall have rust inhibitive coating suitable for the installation in which they are being used, or be manufactured from material not susceptible to corrosion.
Where No. 8 screws are specified in a steel-to-steel connection, the required number of screws in the connection is permitted to be reduced in accordance with the reduction factors in Table R505.2.4 when larger screws are used or when one of the sheets of steel being connected is thicker than 33 mils (0.84 mm). When applying the reduction factor, the resulting number of screws shall be rounded up.
SCREW SUBSTITUTION FACTOR
|SCREW SIZE||THINNEST CONNECTED STEEL SHEET (mils)|
For SI: 1 mil = 0.0254 mm.
Web holes in floor joists shall comply with all of the following conditions:
- Holes shall conform to Figure R505.2.5.1;
- Holes shall be permitted only along the centerline of the web of the framing member;
- Holes shall have a center-to-center spacing of not less than 24 inches (610 mm);
- Holes shall have a web hole width not greater than 0.5 times the member depth, or 21/2 inches (64.5 mm);
- Holes shall have a web hole length not exceeding 41/2 inches (114 mm); and
- Holes shall have a minimum distance between the edge of the bearing surface and the edge of the web hole of not less than 10 inches (254 mm).
Framing members with web holes not conforming to the above requirements shall be reinforced in accordance with Section R505.2.5.2, patched in accordance with Section R505.2.5.3 or designed in accordance with accepted engineering practices.
Patching of web holes in floor joists not conforming to the requirements in Section R505.2.5.1 shall be permitted in accordance with either of the following methods:
- Framing members shall be replaced or designed in accordance with accepted engineering practices where web holes exceed the following size limits:
- 1.1. The depth of the hole, measured across the web, exceeds 70 percent of the flat width of the web; or
- 1.2. The length of the hole measured along the web, exceeds 10 inches (254 mm) or the depth of the web, whichever is greater.
- Web holes not exceeding the dimensional requirements in Section R505.2.5.3, Item 1, shall be patched with a solid steel plate, stud section, or track section in accordance with Figure R505.2.5.3. The steel patch shall, as a minimum, be of the same thickness as the receiving member and shall extend at least 1 inch (25 mm) beyond all edges of the hole. The steel patch shall be fastened to the web of the receiving member with No. 8 screws spaced no more than 1 inch (25 mm) center-to-center along the edges of the patch with minimum edge distance of 1/2 inch (13 mm).