In some ways attaching is the simplest of the direct restraint methods because it focusses on locking the load onto the vehicle so they move as one and it uses a single method for doing this. Please see page 254-256 of the LRG.
The principle is that all of the forces necessary to meet the performance standards are provided by the restraint equipment. There is no reliance on friction. Therefore, there is no need to press the load onto the load surface of the vehicle more than is required to meet the upward force performance requirement. This means that in the case of direct attachment having the lashings vertical is less important and angles closer to the horizontal are more effective. As was the case with the tie down method, if you don’t know your trigonometry the load restraint guide provides some tables to assist you with the angles.
It is important to ensure that the attachment points to the load, the attachment points to the vehicle and the lashings all need to be strong enough to take the forces and in the case of the lashings they need to be oriented in the right direction to provide the required forces.
In the case of ISO container fittings, the attachment points on the container and the vehicle are rated according to the ISO standards and there is no intermediate lashing because the attachment points interlock. However, it is important to ensure that the supporting structures for the ISO fittings on the vehicle have sufficient strength to handle the required loads.
If you are not confident that you understand how to calculate the required restraints, you should consult an expert and consider getting certification for your load restraint system.
When a lashing is attached to the load the forces it imposes on the load need to be resolved into the directions they act in so you can determine if they are sufficient to meet the performance standards. The Load Restraint Guide provides the following diagram and table to allow you to calculate the angle effect(AE)
These angle effects calculated above are then fed into table 10 or 11 on pages 281 or 282 to determine the minimum lashing capacity to restrain various loads.
This section on calculations provides an overview of the material in the direct attachment section of the load restraint guide and other issues such as pre tensioning are discussed in the Guide. Any operator using direct attachment should read this section of the guide or have an expert certify their strategy for restraining these loads.