IBC Design 721.1(1) 2-4.1

2-Hour Fire Rated Webs or flanges of steel beams and girders — Two layers of 5/8" Type X gypsum wallboard, U-shaped…

IBC Table 721.1(1), Item 2-4.1 (Webs or flanges of steel beams and girders): protection by Two layers of 5/8" Type X gypsum wallboard, U-shaped brackets spaced 24" on center. 0.018" thick (No. 25 carbon sheet steel gage) 1-5/8" deep by 1" galvanized steel runner channels are first installed parallel to and on each side of the top beam flange to provide a 1/2" clearance to the flange. The channel runners are attached to steel deck or concrete floor construction with approved fasteners spaced 12" on center. U-shaped brackets are formed from members identical to the channel runners. At the bent portion of the U-shaped bracket, the flanges of the channel are cut out so that 1-5/8"-deep corner channels can be inserted without attachment parallel to each side of the lower flange. As an alternative, 0.021" thick (No. 24 carbon sheet steel gage) 1" x 2" runner and corner angles shall be used in lieu of channels, and the web cutouts in the U-shaped brackets shall not be required. Each angle is attached to the bracket with 1/2"-long No. 8 self-drilling screws. The vertical legs of the U-shaped bracket are attached to the runners with one 1/2"-long No. 8 self-drilling screw. The completed steel framing provides a 2-1/8" and 1-1/2" space between the inner layer of wallboard and the sides and bottom of the steel beam, respectively. The inner layer of wallboard is attached to the top runners and bottom corner channels or corner angles with 1-1/4"-long No. 6 self-drilling screws spaced 16" on center. The outer layer of wallboard is applied with 1-3/4"-long No. 6 self-drilling screws spaced 8" on center. The bottom corners are reinforced with metal corner beads. Minimum insulating material thickness — 2-hr: 1-1/4". Prescriptive protection from the adopted building code — see table footnotes for conditions.