SPECIFICATION FOR THE DESIGN OF - Transcon Steel

44 Commentary on the Prescriptive Method for One and Two Family Dwellings - 2004
The concentrated loads are calculated as follow:
⎡4⎤
⎡8⎤
P u1 = [ 1.2(10)
+ 1.6(40) ]
⎢
⎣
⎥
x
2⎦
⎢
⎣2⎥ = 608 lb
⎦
P u2 = 630 lb
The maximum moment is calculated to be 5.08 ft-k
M/ΦM T = 5.08/14.165 = 0.36 < 1.0
ok
Note that the above calculation assumes that both trimmer joist sizes and materials are the
same and hence posses similar stiffness. In most residential application this assumption is valid.
However, in cases where trimmer joists materials and/or sizes are different, stiffness
calculations must be done and the appropriate load should be applied to each trimmer joist
component.
D4 Floor Diaphragm Design
Check the adequacy of a 7/16” OSB unblocked floor diaphragm for a 40x60 ft, two-story
building subjected to 110 mph wind speed. The building has a roof slope of 12:12, mean roof
height of 30 ft, and 8’ wall studs at each floor. The building is located in Exposure Category C.
The OSB floor sheathing is fastened to the floor joists with No. 8 screws spaced at 6” o.c. at
panel edges and at 12” o.c. at intermediate supports.
Building
Roof
40’
60’
Force
Direction
40’
Building Width
60’
Building Length
Plan View
From Table C2.1, the following wind pressures are obtained for the given wind speed,
exposure and roof slope:
Roof pressure
Roof corner pressure
Main building pressure
Main building corner pressure
= 11.7 psf
= 14.6 psf
= 24.1 psf
= 30.3 psf
Calculate corner area width (2a), where “a” equals 10% of least width or 0.4h (whichever is
smaller) but not less than either 4% of least width or 3 feet.
a = 10%(40) = 4’
a = 0.4(30) = 12’
a = 3’