This lesson will discuss how to use tables 10 and 11 in the appendices (page 281 and 282) for calculating maximum lashing capacity for direct restraint.
It is important to also ensure that the capacity and type of the vehicle and any attachment points are adequate for the load, you are using. Your organisation may also have standard procedures for restraining these types of loads which you should follow.
If you are not confident in your ability to make these calculations, you should ensure that your consult a suitably qualified expert.
These table are simpler that the tables for calculating the number of tie down lashings covered in Lesson 4.4 because they are based on a different principle. These tables use the mass or the load and the angle effect to calculate the capacity that the lashings (typically chains) need to have to restrain the load.
They assume that there will be two chains constraining movement in each direction (in practice this means that there will be four chains attached to the load but different pairs of chains will be used to restrain the movement in different directions).
It is important to calculate the important to calculate the angles effects for both forward movement (where the chains need to restrain 80% of the weight – Table 10) and for side to side or rearwards movement where they only need to restrain 50% of the movement- Table 11)
The calculation of the angles was covered in more detail in lesson 4.2 Please review the method for calculating able effect if you are unsure.
To provide an example of how to use the look up tables we will use a worked example show on page 224 to 226 of the load restraint guide.
This example uses an 8 Tonne steel roller on a steel deck (effectively no friction which is why direct restraints are being used).
In this case the chain is 2 metres long (L 1 =2m) and the distance between the tie points is 1.5m (F 1 =1.5m) So the angle effect AE= L 1 =1.5÷2=0.75.
Table 9 only has entries for AEs of 0.85, 0.7 and 0.5 so we will use 0.7 as the value to look up in the table
The following animation shows how to look up the minimum lashing capacity
Once you have the minimum lashing capacity (4.6 tonnes) check with Chain manufacturers specifications to find a suitable combination of chain and hook type. In this particular example the Load Restrain guide suggests 10mm transport chain using claw hooks or winged grab hooks or 10mm transport chain using plain grab hooks.
The video used in this lesson illustrates the use of Table 10 to calculate the chain size necessary to prevent forward movement of an 8 Tonne Steel wheeled roller on a steel decking ###Try and get an image to match this description### and is based on an example discussed on page 254 to 256 of the load restraint guide.
In this example the length of the chain was 2 m (L1) and the distance between the tie points in 1.5m (F1)
So the Angle effect for forward movement = 1.5/2.0= 0.75. and the load is 8 Tonnes
The columns in the table on deal with angle effects of 0.85, 0.70 and 0.5. Because 0.75 is greater than 0.7 but less than 0.85 we use the 0.7 column and 8 tonne row to determine that the capacity of the chains needs to be at least 4.6 tonnes.
The person restraining the load then needs to confirm the two chains they are using have a capacity of at least 4.6 tonnes. This is best done by checking the manufactures specification. In the example in the load restraint guide they indicate that the 4.6 tonne requirement could be met by 10mm transport chain with claw hooks or winged grab hooks or by 13mm transport chain using plain grab hooks.