Cargo Securement With Ratchet Tie Down Straps
The ratcheting tie downs are the assembly of webbing and ratchet buckle , it’s a widely known fact, but if we use cam buckle in place of ratchet buckle in the assembly we have cam buckle tie down, it’s as simple as that. Due the low strength of the cam buckle, we usually see these cam buckle tie downs being used on pick up trucks, 1” cams are all over the place while 2” cams are being used in box trucks. Compare to cam buckle the ratchets are stronger and more widely used, the available sizes of ratchets are 1”,2”,3” and 4”, and the ratchet buckle generally has higher working load limit than the cam buckle, they have working load limit of 3,333lbs, 5,400lbs and 5,400lbs respectively, these assemblies have design factor of 3:1, thus the minimum breaking strength is 10,000lbs, 16,200lbs and 16,200lbs respectively.
So far we discussed about tie down devices for flatbeds or similar transportation vehicles, in reality semi trailers are much more than flatbeds in numbers, since they are box trucks the tie down needs are different, you will see most semi trailers have E Track installed and use logistic tie downs . It is estimated that 80% trucks are box trucks, and the e track tie down system is just for semi trailers , so logistic straps are most popular tie down straps. And these straps are not as strong as the one we use on flatbed truck, the working load limit of typical e track straps is 1,000lbs, with minimum breaking strength of 3,000lbs. It’s easy to understand that why e track straps are not as strong as regular ratchet tie down straps, inside the box truck the loads already have strong support, at least there is no risk of falling off, all the e track straps will do is to fixate the loads more than tie them down.
In first paragraph we talked about design factor of ratchet tie downs, which is 3:1, so the working load limit is 1/3 of maximum breaking strength for ratchet straps, for comparison purpose we know that the binder chain has a design factor of 4:1, which basically says that for the chains the working load limit will be 1/4 of their breaking strength, which indicates that tie down chains are designed for tougher environment than tie down straps are in. The standard material of which tie down webbing is made is nylon webbing or polyester webbing, depends on different tie down applications. The typical application for nylon webbing is motorcycle tie down, while polyester webbing is ideal for tying down concrete pipes. When making the webbing, we have to take following characteristics in to consideration, the breaking strength, elongation, abrasion and the environment. When making tie down straps , manufacturer has to follow the recommendation of breaking strength and elongation requirements, when it comes to abrasion and environment, there are much more variations to be considered.
