Civil Engineering Reference
In-Depth Information
and the horizontal extent is
8
hS
8397
3
(.
ft
)
24
d
=
=
51 8
.
ft
3
The resultant unbalanced load is sketched in
Figure G6-7
. Any partial load-
ing (e.g., continuous purlins) would be a separate load case.
Example 6-3
Unbalanced Snow Load,
Asymmetric Gable Roof
Problem
Determine the unbalanced loading condition for the asymmetric gable roof
shown in
Figure G6-8
. The structure is unheated, fully exposed, located in
open country, and has ordinary occupancy. The ground snow load is 20 lb/ft
2
.
Solution
Because the structure is unheated,
C
t
is 1.2. Open country is taken to be Ter-
rain Category C, and because the roof is fully exposed,
C
e
is 0.9 from Table
7-2. The importance factor
I
s
is 1.0 because the occupancy is classifi ed as ordi-
nary. Given that
C
t
is 1.2 and
C
s
is 1.0 for both the 1-on-12 and 2-on-12 por-
tions from Figure 7-2(c), the balanced load for both sides of the ridgeline is
0.7(0.9)(1.2)(1.0)(1.0)(20 lb/ft
2
)
15.1 lb/ft
2
p
s
=
0.7
C
e
C
t
C
s
I
s
p
g
=
=
Hence, the load on the windward side of the roof becomes 0.3
p
s
or 4.5 lb/ft
2
.
For wind from the south, the upwind fetch for the drift on the northern
portion is 100 ft, and the space available for drift formation is controlled by
the 1-on-6 (
S
=
6) slope. Therefore,
h
=
0 43
.
3
Wp
+
10
−
1 5
.
=
( .
0 43
)
3
100
20
+
10
−
1 5
.
=
3
.
16 ft
4
4
d
g
Figure G6-7
Unbalanced load
and elevation for
Example 6-2.
