Appendix A. CHAIN TIEDOWN CALCULATIONS

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

3.0

Rail*

0.2

0,9

0.3

Marine (Fast Sealitl Ship)

0.2

1.2

0.7

Marine (other)

2.0

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

Highway (semitrailer)

0.71

0.50

Rail

0.50

0.43

0.75

Marine (Fast Sealift Ship)

0.50

0.43

0.75

Marine (other)

0.50

0.43

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