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MILHDBK1038
standards (CMAA #70, CMAA #74, and MH27.1). Percentages of increase for other
types of cranes may be determined by a rational method of analysis, or by the
manufacturer's standard practice, but for portal and floating cranes, they should
not be less than the minimum values given in Table 1.
Table 1
Percentages of Increase for Impact
Portal Cranes
Floating Cranes
Rated Hook
Upperworks
Portal
Travel
Upperworks
Capacity
Base/
System*
Tub
(Pounds)
Tower
Under 100,000
30
15
25
15
10
100,000 to 160,000
25
12
25
15
10
161,000 to 240,000
20
10
25
15
10
Over 240,000
15
10
25
15
10
* Impact on travel system is applied to the total vertical load.
5.1.1.4
Wind Load. Cranes operating in outdoor environments must be designed
with the consideration of loads due to wind, both for operating and nonoperating
wind conditions. ("Operating wind" does not restrict crane operation; "non
operating wind" prohibits crane operation.) Wind loads for OET, gantry, and semi
gantry cranes are addressed in CMAA #70; and for underrunning cranes, in CMAA #74.
Past design practice was to represent the operating wind load by a uniform
pressure of 5 pounds per square foot (psf); and the nonoperating wind load by a
uniform pressure of 20 psf. Current practice is to use wind loads due to a wind
velocity of 40 miles per hour (mph) for the operating wind case (55 mph for
container cranes), and the maximum wind gust velocity at the geographic location
for the nonoperating wind case.
The magnitude of the wind load is to be determined by a procedure
contained in a generally recognized engineering standard or code, and which
accounts for maximum gust velocity (for nonoperating wind load), shape factors,
and height effects on portions of the crane above a 30 foot elevation. The
preferred procedure is contained in MILHDBK1002/2, Loads, Section 7. Using this
procedure, the wind velocity is related to its corresponding velocity pressure (q)
in psf, at a 30 foot elevation, as follows:
q = 0.00256V2
(1)
EQUATION:
Where
V = the wind velocity in mph.
The wind load (p) in psf, for any portion of the crane, is obtained by multiplying
the velocity pressure by the appropriate shape factor (Cs) and height correction
factor (Ch) as follows:
EQUATION:
p = q x Cs x Ch
(2)
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