SPECIFICATION FOR THE DESIGN OF - Transcon Steel

Commentary on the Prescriptive Method for One and Two Family Dwellings - 2004 59
E6 Double L-Header Design (Uplift Loading Case 2)
Calculate the maximum span for a 2-L800S150-54 L-header located in the first story of a the
two-story building described in Section F1, subjected to 110 mph Exposure Category C wind
speed and 20 psf ground snow load.
E6.1 Design Loads
Dead Loads:
Ceiling Dead Load = 5(24/2)
Roof Dead Load = 7(24 + 4)/2
Floor Dead Load = 10(24/2)
Wall Dead Load
Total Dead Load =
= 60 plf
= 98 plf
= 120 plf
= 100* plf
= 378 plf
* Note: conservatively use 100 plf instead of 8x10 psf = 80 plf
Live Loads:
Floor Live Load = 30(24/2)
= 360 plf
Roof Snow Load = 0.7(20)(24 +4)/2 = 196 plf
Roof Live Load = 16(24 + 4)/2 = 224 plf controls
Wind Uplift Load:
Wind pressures are taken from Table C2.1 (roof corner MWFRS wind pressures for 9:12
roof pitch, 110 mph Exposure Category C). The tabulated pressures (Table C2.1) are
perpendicular to the vertical projection of the roof. The uplift component of the pressure
can be calculated as follows:
⎛ cos(36.86°
) ⎞
Wind Uplift Load = 12 .4⎜
⎟ = 16.54 psf (acting perpendicular to header)
⎝ sin(36.86°
) ⎠
Applying this wind pressure over a 14-foot member length, the wind uplift load is:
Wind Uplift Load = 16.54 psf x 14 ft = 232 lbs./ft
E6.2 Load Combinations
1. 0.9D – 1.6W = 0.9(378) – 1.6(232) = -31 plf controls
2. 1.2D – 1.6W + 0.5(L r or S) = 1.2(378) – 1.6(232) + 0.5(224) + 0.5(360) = 374 plf
3. 1.2D – 0.8W + 1.6(L r or S) = 1.2(378) – 0.8(232) + 1.6(224) = 624.4 plf
E6.3 Member Properties
L 1 = 8.0”
L 2 = 1.5”
t = 0.0566”
S xtop = 0.8564 in 3
E6.4 Bending Capacity
M nu = R M ng
Long leg of angle
Short leg of angle
Design thickness
Section modulus for one angle
where:
M ng = gravity moment capacity determined by Eq. B3.1.1-1
R = uplift reduction factor
= 0.25 for L h /t ≤ 150
(Eq. B3.1.2-1)