Manitowoc National Crane NBT50 Series, Operator'S Manual

Page: 24 / 158

2-10
Published 03-23-2018 Control # 243-14
SAFETY PRECAUTIONS NBT50 OPERATOR MANUAL
Determination of 3-second wind gust speed at boom
tip height:
The following example illustrates how to calculate 3-second
wind gust speed at boom tip height based on mean wind
speed recorded by the device located at the crane operation
site:
V(z) is the 3-second wind gust speed at boom tip
height Z then:
Metric, with Z [m] and V [m/s]
V(z) = [ ( Z /10)
0.14
+ 0.4] x V (2.1)
Non-metric, with Z [ft] and V [mph]
V (z) = [( Z /33)
0.14
+ 0.4] x V (2.2)
where:
V [m/s] [mph] - Mean wind speed at 10 m (22 ft)
elevation (upper limit of Beaufort scale)
Example : Suppose you want to lift the load with the
maximum boom tip height of 30 m (100 ft) and the recorded
mean wind speed by the device located at the crane
operation site is 5.5 m/s (13 mph). This mean wind speed of
5.5 m/s (13 mph) corresponds to Beaufort number 4 (see
Table 2-1). The maximum wind velocity according to the
Beaufort scale of 4 is 7.9 m/s (17.7 mph).
The mean wind speed (upper limit of Beaufort number) at
10 m (33 ft) height, to be used for calculation is:
V = 7.9 m/s (17.7 mph)
Boom tip height for this lift is Z = 30 m (100 ft)
then:
Metric, with Z [m] and V [m/s]
V(z) = [(30/10)
0.14
+ 0.4] x 7.9 = 12.4 m/s
Non-metric, with Z [ft] and V [mph]
V(z) = [(100/33)
0.14
+ 0.4] x 17.7 = 27.8 mph
Since V(z) is ≤ 13.4 m/s (30 mph), the allowable loads are
the published rated capacities from the Load Chart and can
be lifted at this condition.
Size and Shape of the load:
These rated capacities are also based on the assumption
that the Wind Resistance Area of load,
Awr
(load)
is not more
than 0.0012 square meters per kilogram (0.0059 sq.ft per
pound of load. (See below Formulas 2.4 and 2.5.)
The load capacities shall be reduced to account for the larger
wind resistance area of load and 3-second wind gust speed
at boom tip height. Use tag lines when the wind gust speed is
above 13.4 m/s (30 mph) to help control the movement of the
load.
Manitowoc recommends that a lift not be made if
the wind can cause a loss of control in handling the
load.
The lift may also be limited by the projected wind area of the
load
Ap and by the wind drag coefficient Cd . This limit can be
determined by comparing the actual wind resistance area of
the load with the allowable wind resistance area.
Awr
(load)
= Ap x Cd (2.3)
where:
Awr
(load)
[m
2
] [ft
2
] . - Wind resistant area of the load
Ap [m
2
] [ft
2
] - projected wind area,
Cd - wind drag coefficient.
Ap is determined by using the calculation of maxi-
mum height x maximum length (see Figure 2-3).
For Cd , refer to Table 2-2. If the Cd cannot be cal-
culated or estimated, use a value of 2.4.
The allowable wind resistant area of the load Awr
(allow)
is
equal to 0.0012 square meters per kilogram (0.0059 sq.ft per
pound) of allowable load:
Metric, with m
(load)
[kg] - Mass of the allowable load
Awr
(allow)
= 0.0012 × m
(load)
(2.4)
Non-metric, with m
(load)
[lb] - Mass of the allowable load
Awr
(allow)
= 0.0059 × m
(load)
(2.5)
If Awr
(load)
is greater than Awr
(allow)
, then lifting this load at
this wind speed V(z) is NOT permitted.