Specifications

Chapter 4: Environmental Considerations
Shock Loading
(12/99) 4-7
Find your application in the table, based on tank location, tank contents, and seismic
zone. Multiply the corresponding factor by the gross weight of the tank or vessel. The
resulting value will equal the horizontal shear force (F
EQ
) applied at the tank’s center of
gravity (see Figure 4-5).
W gross
V =
eq
Figure 4-5: Horizontal Shear Force Applied to Tank
Reaction forces at the weigh modules are determined using Statics (see Appendix 4)
based on the shear force (
F
EQ
) applied at the tank’s center of gravity. Compare the
reaction forces with the allowable loads for the weigh modules (see Appendix 5). The
weigh modules can then be sized to accommodate the resulting seismic loads, or
external checking can be added as needed to counter seismic loads.
Shock Loading
Shock loading can affect a scale’s design, especially for conveyor applications or floor
scale conversions. It is caused by an abrupt change in the weight placed on a scale, for
example, when an object is dropped on the scale. If shock forces are strong enough,
you will need to install higher capacity load cells. To estimate a shock force, you must
know the weight of the object being dropped, the vertical distance it is dropped, and the
empty weight of the scale structure. You must also know the spring rate of the nominal
load cell capacity. The spring rate constant for a load cell is its rated capacity divided by
load cell deflection at rated capacity. For crane loading applications, you need to know
the crane’s rate of descent.
Determine the nominal load cell capacity by multiplying the scale’s gross capacity by
1.25 and then dividing by the number of supports. Then use one of the following
equations to estimate the shock forces caused by dropped or lowered weights.
Equation for Dropped Weight:
F
MAX
= W
2
+ W
1
[
1 + 1 +
]
V = F
EQ
2KH
W
1
+ W
2