SPECIFICATION FOR THE DESIGN OF - Transcon Steel

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.