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TM 55-2350-252-14
APPENDIX A
CHAIN TIEDOWN CALCULATIONS
A-1. Introduction
A-2. General Rules
The following information is required:
The number of chains needed to safely transport a
a. Vehicle Weight (VW--when preparing to load
vehicle depends on the weight of the vehicle, the
use the vehicle's actual weight if possible; other-
strength of the tiedown, the method of transport,
wise, use the GVW.
b. Load Restraint Factor (LRF)-the "G" (accel-
and blocking and bracing. This appendix provides
eration of gravity) loading factors that a vehicle
a conservative method of calculating the number
can expect to see during military transport (table
of tiedown chains required to restrain a load. The
A-l).
following calculations do not account for blocking
c. Tiedown Strength (TS)--the strength of the
and bracing. The procedures given in the text are
weakest part (provision, chain, loadbinder, and so
based on actual tiedown angles; while the follow-
forth) of a tiedown assembly.
ing calculations are based on estimated angles.
d. Angle Effect (AE)the percent of tiedown
Therefore, the number of chains given in the text
strength available in each direction (lateral, longi-
may be less than what you will calculate here.
tudinal, and vertical) (table A-2).
Table A1. Load Restraint Factors
Vertical
Aft
Lateral
Forward
Mode of Transport
0.3
0.1
0.3
Highway (semitrailer)
0.7
2.0
2.0
3.0
3.0
Rail*
0.2
0,9
0.3
0.3
Marine (Fast Sealitl Ship)
0.2
1.2
0.7
0.7
Marine (other)
2.0
1.5
1.5
3.0
Air
*To approximate AAR rules, use LRF = 0.7 in these calculations.
Table A2. Angle Effects
Vertical
Lateral
Aft
Angle
Forward
Mode of Transport
0.71
0.50
0.50
45
0.50
Highway (semitrailer)
0.71
0.50
0.50
45
0.50
Rail
0.50
0.43
0.75
0.75
Marine (Fast Sealift Ship)
30
0.50
0.43
0.75
30
0.75
Marine (other)
0.50
0.43
0.75
30
0.75
Air
The following steps will give the total number of chains required to be placed symmetrically about the
vehicle.
Note: The LRF and AE are for the same mode of transport in the same direction.
1. Calculate the number of chains required for each direction.
(VW x LRF)
= number of chains
(TS x AE)
2. Multiply the maximum number of chains calculated in step 1 by 2.
3. Round the number of chains calculated in step 2 to the next highest number divisible by 4.
A-3. Example Calculation
Problem: It is required to transport a tracked 43,000-pound GVW vehicle by semitrailer without blocking.
The provisions are rated at 40,000 pounds, the chains have a 13,700-pound WLL, and the loadbinders
have a 9,000 pound WLL.
Informatwn required:
VW = 43,000 pounds
LRF - from table A-1
Forward = 0.7, Aft = 0.3, Lateral = 0.1, Vertical = 0.3
TS = 9,000 pounds (weakest part of the tiedown assembly)
AE - from table A-2
Forward = 0.50, Aft = 0.50, Lateral = 0.50, Vertical = 0.71
A-1

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