Specifications

Chapter 14: Appendices
Appendix 4: Calculating Reaction Forces
(12/99) 14-11
Full Tank, Solve for
R
G
ΣF
Y
= 0
2R
1
+ 2R
2
= W
G
assuming equal load distribution
R
1
= R
2
= R
G
R
G
=
W
4
G
Empty Tank, Solve for R
T
ΣF
Y
= 0
2R
1
+ 2R
2
= W
T
assuming equal load distribution
R
1
= R
2
= R
T
R
T
=
W
4
T
Download Force on a Full Tank
F
D
= R
1
+ R
G
F
D
=
F
1 414 d
.
[ h
L
+ 0.5 h
T
] +
W
4
G
The maximum downward force ( F
D
) on a single weigh module equals the distributed
weight of the full tank (
R
G
) plus the downward reaction force caused by the wind or
seismic event. Compare this maximum downward force to the download rating for the
weigh module being considered (see Appendix 5). If the maximum downward force is
greater than the load rating, you should consider using a larger capacity weigh module
to avoid overloading.
Uplift Force on an Empty Tank
F
U
= R
1
- R
T
F
U
=
F
1 414 d
.
[ h
L
+ 0.5 h
T
] -
W
4
T
Overloading the weigh modules is not the only potential problem for tanks exposed to
wind or seismic forces. You should also consider uplift forces acting on the tank. The
distributed weight of an empty tank will help prevent the tank from uplifting. So the net
uplift force (
F
U
) equals the upward reaction force minus the distributed weight of the
empty tank (
R
T
). Compare the net uplift force ( F
U
) with the uplift load rating of the weigh
module being considered (see Appendix 5). If the net uplift force is greater than the uplift
load rating of the weigh module, you should consider using a larger capacity weigh
module or installing external check rods. A negative number indicates that the weight of
the empty tank is greater than the uplift force caused by the wind or seismic event.