IBC Design 721.1(1) 2-4.2

3-Hour Fire Rated Webs or flanges of steel beams and girders — Three layers of 5/8" Type X gypsum wallboard, 0.018" thick…

IBC Table 721.1(1), Item 2-4.2 (Webs or flanges of steel beams and girders): protection by Three layers of 5/8" Type X gypsum wallboard, 0.018" thick (No. 25 carbon sheet steel gage) 1" x 2" lower corner angles. The framing is located so that a 2-1/8" and 2" space is provided between the inner layer of wallboard and the sides and bottom of the beam, respectively. The first two layers of wallboard are attached as described immediately above. A layer of 0.035" thick (No. 20 B.W. gage) 1" hexagonal galvanized wire mesh is applied under the soffit of the middle layer and up the sides approximately 2". The mesh is held in position with the No. 6 1-5/8"-long screws installed in the vertical leg of the bottom corner angles. The outer layer of wallboard is attached with No. 6 2-1/4"-long screws spaced 8" on center. One screw is installed at the mid-depth of the bracket in each layer. Bottom corners are finished as described above. Minimum insulating material thickness — 3-hr: 1-7/8". Prescriptive protection from the adopted building code — see table footnotes for conditions.