SPECIFICATION FOR THE DESIGN OF - Transcon Steel

86 Commentary on the Prescriptive Method for One and Two Family Dwellings - 2004
F2.7 Shear Capacity
Nominal shear strength x Φ v = 1,532 lb (punched section)
w = uniform load (plf) = 86 plf
wL 2V
2x1532
V = L = L = = 35’-7”
2 w
86
F2.8 Deflection Limit
δ = 5 4
wL
384EI = L/180 (simply supported single span deflection equation)
L =
3
384(29,500,000)(4.581)
5(180)(57.7)
12
where, w = (7/cos26.56 psf + 0.7x30 psf)(24”/12”) = 57.7 plf
L= 19’-1"
Bending controls the design, hence the allowable rafter span is L = 16'-8". This is
adequate for the given example.
F3 Ridge Member Shear Connection
Consider the horizontal projection of a simply supported rafter.
V max = wL/2 (L=16 ft, w = 86 plf)
V max = 86 x 16/2 = 688 lb
Screw Shear Capacity (calculated per Section E4.3 of the Specification (AISI, 1999)).
Screw diameter, d = 0.19 inches (# 10 screw, based on AISI Commentary to Specification
Table C-E4-1).
Ultimate capacity of steel = 45 ksi (tensile)
Steel design thickness = 0.0451” (43 mils minimum thickness)
Φ = 0.5
t 2 /t 1 ≤ 1.0, The nominal shear strength per screw, P ns , is the smallest of:
3
P ns = 4.2⎜⎛ t2d
⎟⎞
F ⎠
u2
⎝
(Eq. E4.3.1-1)
P ns = 2.7t 1 dF u1
(Eq. E4.3.1-2)
P ns = 2.7t2dF u2
(Eq. E4.3.1-3)
where: t 1 = t 2 = 0.0451” and F u1 = F u2 = 45 ksi
P ns = 789 lbs.