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METTLER TOLEDO Weigh Module Systems Handbook
(12/99)4-2
When wind exerts a simple horizontal force on one side of a tank, it creates a suction
force on the opposite side of the tank. These combined forces work to tip the tank in the
direction the wind is blowing. There are also right angle suction forces pulling on each
side of the tank, but they tend to cancel each other out. The overall effect is that the
wind exerts an uplift force on some load cells, a download force on other cells, and a
shear force on all the cells.
You should determine wind loading for two scenarios: when a tank is empty and when it
is full. The equation for calculating wind force is based on wind velocity, tank location,
tank geometry, and accepted local standards and codes. Reaction forces (downward
upward, and shear) should also be determined. The following information will be
needed to calculate these forces:
• Gross Weight of the Tank (
W
G
)
• Empty Weight of the Tank (
W
T
)
• Diameter of the Tank (
D
)
• Height of the Tank’s Legs (
h
L
)
• Height of the Tank (
h
T
)
• Number of Supports (
N
)
• Wind Velocity (
V
)
• Safety Factor (
SF
)
Reaction forces at the weigh modules are calculated via Statics (Equilibrium) based on
the wind force at the center of gravity (c.g.) of the tank (see Figure 4-2). Methods for
calculating reaction forces are covered in Appendix 4. Compare the reaction forces with
the allowable loads for the weigh modules (see Appendix 5). You can then select weigh
modules that are sized to accommodate both the weight of the full tank and the wind
loading. It is possible that the load cells required to accommodate both the weight of the
tank and wind loading could be large enough to compromise system resolution. If that
is the case, consider adding external restraints to the weigh module system (see
“Additional Vessel Restraint Methods” in Chapter 5) instead of using the larger load
cells. For extra safety, construct wind breaks to shield the tank.
F
Wind Force
W
c.
g
.
h
t
h
l
d
Figure 4-2: Tank Dimensions and Wind Force
F
W
h
T
h
L