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Technical


Methods of Load Restraint


Tie Down Restraint
 
The most common form of restraint is tie down lashing which prevents the load from moving by increasing the friction between the load and the vehicle.
 
These lashings work like a giant G clamp and also prevent the load from moving upwards. The total friction is achieved by both the weight of the load and the downward force of the tie downs.
 
Varying surface conditions can give a different friction performance, ie A “grippy” surface gives a high friction coefficient while a slippery surface gives a low friction coefficient.
 
If the load is standing on the load floor, a "micro-interlocking" between the surface of the load floor and the surface of the load occurs, which will be stronger, the rougher the surface is.
 
This micro-interlocking characterises the coefficient of kinetic friction.




 
If the load does not shift, it is not the strength of the lashing that determines the holding ability of a tie-down lashing. It is determined by the amount of tension in the lashing from initially operating the ratchet, winch or dog, in conjunction with the amount of friction present. Tie-downs should not be used on slippery loads because too many lashings are needed
 
Friction cannot be increased by additional surface area. Adding extra timber dunnage as at right achieves exactly the same result.
 
Friction between smooth surfaces such as steel can be increased using anti-slip rubber mat. Oil, water, dust and sand can also act as a lubricant and greatly reduce friction.






 
Direct Restraint
 
Direct lashing relies on the strength of the assembly to restrain the load, as opposed to friction to clamp the load. The lashing is at its most efficient in a straight line but needs to be de-rated when angles are introduced (most loads).


 

 
 
For further load control technical information see our Load Control Catalogue.