The loading performance standards have a much higher performance requirement to restrain loads from moving forward than in other directions. This is to allow for the forces generated on the load by braking which results in the largest forces on the load (80% of the weight)
Because of this many loads use a combination of blocking and tie downs to restrain the load to resist 80% of the weight in the forward direction.
This is typically done using a headboard, loading rack or barrier to provide blocking forces to constrain some or all of the movement in the forward direction. They are typically used in conjunction with other restraints such lashing or side gates to resist forces in other direction or to supplement the forces provided by the headboard, loading rack or barrier.
The “BLOCKED” load restraint tie down tables on pages 267,269,271, 273,275 and 279of the load restraint guide assume that the headboard or barrier will be rated to at least 30% of the load and that the tie down lashings will provide sufficient force to restrain 50% of the weight in the forward sideways and rearward directions. This will be discussed further in lesson 4.2.1
Headboards are structures immediately behind the cabin or at the front of a trailer which are fixed to the body of the vehicle.
Rated Headboards are headboards which have been designed and certified to withstand a level of force. This should be stated on the headboard. If no rating is stated they should be assumed to be unrated. If they are unrated other restraint methods must be used to resist the forces. If the load exceeds the rating of the headboard additional restraint maybe needed to resist the remaining force.
Loading Racks and Barriers
A loading rack is a pipe gate that has been restrained by direct restraint chains. Loading racks may be rated but will generally rely on the chains to provide the forces to resist forward movement. Unrated gates should only be used for very light loads. Barriers are moveable blocking devices similar to loading racks which are typically used to provide restraint when there are gaps between loads along the length of the vehicle and additional support is required to provide additional blocking force in the forward direction. Barriers are often used when the positioning of loads along the length of the vehicle is required to comply with axle masses.
Loading racks may be supplemented with plywood, metal sheeting or mesh to spread the load and support product packaging. Loading racks are not suitable for loads where spearing is an issue.it is also important that chains used to support loading packs are properly positioned and correctly attached to the trailer or truck bed. Please see pages 152 and 153 of the load restraint guide if you are using loading racks.
Positioning the load
To ensure effective blocking it is important that the load is placed as close as possible to the headboard or loading rack. The maximum gap allowed is 200 mm front to back, and 100 mm side to side. This also applied to the sum of any gaps present between multiple items. Barriers are typically placed against the load and then chained to the tie rails.
It is also important to ensure the load does not sit above the height of the headboard if the strength of the packaging is not sufficient to restrain the movement of the load in the forward direction.
Pages 149 to 155 of the load restraint guide provide more detailed guidance to the use of headboards, loading racks and barriers.