The other common method for restraining loads is direct restraint. Many (but not all) loads can be restrained by either method. Direct restraint of loads can be used as a method of restraint for most loads and is often useful for loads that are difficult to tie down.
Direct restraint differs from the tie down method in that it does not rely on friction and the forces restraining the load are provided by structures or equipment on the vehicle or directly by lashings or chains.
There are three sub strategies within direct restraint: attaching, blocking, and containing.
The attaching strategy involves using lashings such as webbing straps or chains or ISO twist locks (for containerised goods) to directly attach the load to the vehicle structure. It is important that the lashings have sufficient capacity to take all the forces defined in the loading performance standards. Lashings or chains have manufacturers ratings which specify the capacity of the lashing or chain in terms of operational or safe working loads. As was the case for tie down lashings it is important that the angle of the lashing is taken into account when calculating the number of lashings required to meet the loading performance standards.
Attaching is a common method for restraining loads such as vehicles, machinery and containers (both ISO shipping containers) where the load has sufficient structural integrity to be able to withstand the forces necessary to meet the loading performance standards. It is also important to ensure that the attachment points for the webbing or chains and the webbing or chains themselves have adequate strength (this depends in part on the angles of the lashings)
The blocking strategy uses features of the vehicle such as the body of the vehicle, curtains, headboards, side or tail gates to block the load from moving horizontally in one or more directions. This requires that the body, curtains headboard or gates are strong enough to resist the forces required by the loading performance standard.
It is important to understand the rating of these structures to determine whether it is necessary reinforce the structures or to use lashings (using tie down or direct restraint) or other restraint mechanisms within the vehicle to manage forces in directions not covered by the body, curtains headboard or gates.
Involves using the structure of the vehicle structure or other parts of the load to restrain the load from moving in one or more horizontal direction. (other directions may still be constrained by tie down.
Meeting the vertical performance standard may require the use of nets or lashings to restrain the load in the vertical direction to prevent them bouncing out of their containment.