Civil Engineering Reference
In-Depth Information
Figure G7-13
Two load cases for
step roof in Example 7-3.
(a) Uniform load case.
(b) Balanced- plus-drift-
load case.
(a)
(b)
Example 7-4
Roof Step Drift, Adjacent
Structure
Problem
Solve the same problem as Example 7-1, except the unheated storage facility
is separated from the heated, unventilated roof facility by 8 ft.
Solution
The balanced load on the unheated space remains unchanged at 34 lb/ft
2
.
Although the heated space is no longer adjacent to the unheated space, it
still serves as an obstruction (refer to the footnotes for Table 7-2). Given
h
o
is 10 ft and the separation distance of 8 ft
100 ft, the heated space
qualifi es as an obstruction for the roof of the unheated storage facility.
Because the separation distance
s
<
10
h
o
=
=
8 ft is less than 20 ft and less than
6
h
60 ft, drifts need to be considered. The unmodifi ed leeward and wind-
ward drift heights for a roof step without a separation are still 3.8 ft and
3.6 ft, respectively. Hence, the leeward drift governs in this case. The drift
height is the smaller of
h
d
=
=
3.8 ft and (6
h
−
s
)/6,
6
h
s
(6
10)
8
=
=
8.66 ft
6
6
Thus, the surcharge height is 3.8 ft. Using the snow density of 19 lb/ft
3
from
Example 7-1, the peak surcharge load is 3.8 ft (19 lb/ft
3
)
72 lb/ft
2
. The
=
