It has been stated that the load restraint system must be capable of preventing movement of the load under four particular conditions:
The forces resulting from these deceleration and acceleration factors, which must be safely contained by the load restraint system, are greatly increased if the load is allowed to move relative to the vehicle, ie the ‘battering ram’ effect. The restraint system must be designed, constructed and used in such a way as to prevent this.
The ram effect increases rapidly with the increase in distance through which the load may be free to move relative to the vehicle. It is hazardous to locate loads away from the headboard or other fixed abutment unless the means used for load restraint are adequate to prevent such movement under the conditions described above. Failure of the load restraint system in these circumstances could result in the load developing sufficient momentum, if allowed to slide, to demolish the headboard or other abutment with potentially serious consequences.
As indicated in Basic criteria and precautions section, the forces involved in restraining a load from movement will normally be provided by:
Basic criteria and precautions
In most circumstances, it will be appropriate to obtain half the total restraint required from baulking arrangements and the remaining half from lashings and load friction.
Traditional rope hooks or rings and the method by which they are attached to the vehicle structure are only suitable for the restraint of light loads. For this reason, platform vehicles in particular should be equipped with load anchorage points, designed and integrated into the structure so that the maximum forces likely to be imposed on them are transmitted to the main chassis frame of the vehicle.
It is common practice to utilise the coaming tie rails, and in the case below, it is necessary to tie in the vicinity of the cross member and tie rail junctions to prevent distortion of the tie rail (see figure 6).
Figure 6Each anchor point must have a strength at least equal to the rated strength of the lashings secured. All vehicles must comply with NZS 5444 Load anchorage points for vehicles, in accordance with the Heavy Vehicles Rule.
Where load anchorage points are provided, they should suit the type and payload capacity of the vehicle and the nature of the load to be carried. Twist locks for containers are not regarded as anchorage points for other loads.
When it is feasible to modify existing vehicles to include anchor points, their mounting must in no way weaken the chassis/body structure. In particular, no holes may be drilled in the top or lower flanges of the chassis side members. Welding to the chassis without the approval of the original manufacturer or another reputable manufacturer is not recommended.
Trucks fitted with tipper bodies should have a clamping device to secure the front of the body to the chassis when the vehicle is being used for general freight, etc.
For safe loading every vehicle should, if possible, be fitted with a loading rack or headboard. Otherwise twice the strength of lashings are required. The design of this loading rack or headboard should be consistent with the type and nature of the load being carried.
Loading racks or headboards fitted to the front of the platform of a vehicle used for the carriage of miscellaneous loading must be capable of withstanding a horizontal force uniformly distributed over the vertical area equal to half the rated payload capacity of the vehicle.
The headboard should meet the following requirements:
Some loads, eg coils, sheet steel, pipe, structural steel, timber are more prone to movement under extreme circumstances. Rapid deceleration or an accident can cause the loads to shift and this can result in the penetration or crushing of the vehicle cab. When dealing with such loads, the vehicle, in addition to having the load secured properly to anchorage points, should be equipped with an adequate headboard or cab guard. These must be of sufficient strength to resist any penetration or crushing of the driver’s compartment when involved in an accident or subject to emergency braking deceleration.
Where possible, loads should be placed tight against the headboard or cab guard. If this is not possible, additional packing or chocks should be placed between the headboard or cab guard and the load to prevent any initial movement.
Headboards and cab guards should be high enough to block the forward motion of any item loaded on the vehicle. Alternatively they should extend from the platform of the vehicle to a height of 1 metre. Such headboards or cab guards should be as wide as the vehicle itself.
Headboards and cab guards should be secured to the platform structure to ensure adequate transfer of forces to the vehicle structure.
Headboards should be of solid construction without apertures and may be made of steel, aluminium or wood.
In the case of closed vans of 3.5 tonnes gross weight or more where the driver’s cab is integral with the body, the transverse headboard behind the driver must be the full height of the load compartment and of sufficient width to afford adequate protection.
When fitted to the rear and side of the vehicle platform, they must be capable of withstanding a horizontal force uniformly distributed over the vertical area equal to half of the payload mass.
When in use they must be capable of withstanding a horizontal force uniformly distributed over the vertical area equal to half of the payload weight. Side posts should be arranged or braced so that the width of the vehicle, when laden, does not exceed legal limits. Also posts should be designed such that they cannot unintentionally become detached from their holders.
