SPECIFICATION FOR THE DESIGN OF - Transcon Steel

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42 Commentary on the Prescriptive Method for One and Two Family Dwellings - 2004 D2 Header Joist Design Check the adequacy of a 550S162-33 (33 ksi steel) header joist for a 6-foot floor opening width. The joists are spaced at 12” on center. The floor live load is 30 psf. 6’ 30 psf Live Load 6’ 11’-7” Header Joist The maximum joist span per Table D3.1 of the Prescriptive Method is 11’-7”. The load on the header joist is calculated as follows: [ 1.2(10) + 1.6(30)](11.6' ) W T = = 348 plf 2 2 M = 348(6) = 1,566 ft-lb 8 The factored nominal flexural strength of the header joist is calculated using the AISIWIN computer program. The header joist is fabricated from a joist nested in a track (550T125-33) as per Detail D7-1 of the Prescriptive Method. ΦM 1 = 783.65 ft-lb (for 550T125-33) ΦM 2 = 1,099.57 ft-lb (for 550S162-33) ΦM T = 783.65 ft-lb + 1,099.57 ft-lb = 1,883.22 ft-lb M/ΦM T = 1,566/1,883.22 = 0.83 < 1.0 ok Note that the above calculation assumes that both header joists size and material are the same and hence posses similar stiffness. In most residential application this assumption is valid. However, in cases where header joist materials and/or sizes are different, stiffness calculations must be done and the appropriate load should be applied to each header joist (i.e., C-shape section and track section). D3 Trimmer Joist Design Check the adequacy of an 800S162-68 trimmer joist for an 8-foot wide by 6-foot long opening. The joists are spaced at 24” on center and the floor live load is 40 psf.
Commentary on the Prescriptive Method for One and Two Family Dwellings - 2004 43 4’ 4’-2” Trimmer Joist 8’ 6’ 40 psf Live Load 14’-2” The maximum joist span per Table D3-1 of the Prescriptive Method is 14’-2”. The factored nominal flexural strength of the header joist is calculated using the AISIWIN computer program: ΦM 1 = 3,501 ft-lb ΦM 2 = 5,332 ft-lb (for 800T125-68) (for 800S162-68) Since the opening width is 8 feet, Section D-7 and Figure D7-2 of the Prescriptive Method require the trimmer joist to be fabricated from two joists and a track. ΦM T = 2(5,332) + 3,501 = 14,165 ft-lb The loading on the trimmer joist is as shown below. All loads are factored loads. 608 lb 630 lb 152 lb/ft 76 lb/ft 152 lb/ft 4’ 6’ 4.1’ R1 R2
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SPECIFICATION FOR THE DESIGN OF - Transcon Steel

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