Civil Engineering Reference
In-Depth Information
accumulation area. Hence, the upwind fetch varies from 50 to 100 ft. To
simplify matters, the average value of
W
=
75 ft is used. As a result,
h
=
0 43
.
3
Wp
+
10
−
1 5
.
=
0 43 75
.
3
10
+
10
−
1 5
.
=
2 33
.
ft
4
4
d
g
and
h
γ
(.
233
ft)(15.3 lb/ft
6
3
)
d
=
=
14 5
.
lb/ft
2
S
This results in a total load (balanced plus surcharge) of 20.7 lb/ft
2
. The hori-
zontal extent is
8
3
hS
=
8
3
233
(.
ft)
6
=
152
.
ft
d
The resulting unbalanced load case for wind out of the north is sketched in
Figure G12-8
.
The upwind fetch distance also varies for wind out of the east or west.
Along the extended ridge there are 50 ft of windward sloped roof and 80 ft
of upwind fl at roof (
W
130 ft). Along the eave, the fetch is 180 ft. To sim-
plify matters, the average of
W
=
=
155 ft is used. As a result,
3
3
h
=
0 43
.
Wp
+
10
−
1 5
.
=
0 43 155
.
10
+
10
−
1 5
.
=
3 38
.
ft
4
4
d
g
and
3
h
γ
(.
338
ft
)( .
153
lb/ft
)
d
2
=
=
21 1
.
lb/ft
S
6
Hence, the total load (balanced plus surcharge) is 27.3 lb/ft
2
, and the hori-
zontal extent is
8
3
hS
=
8
3
338 6
.
=
22
ft
d
Figure G12-8
Unbalanced load case
for wind out of the
north for Design
Example 2.
1.9 LB/FT
2
17.7 LB/FT
2
20.7 LB/FT
2
20.7 LB/FT
2
6.2 LB/FT
2
