14 Jul What is Scaffold Sheeting Strength at ‘Yield’ (And Why You Should Care)
I have to admit, different brands of scaffold sheeting, including brands of shrink wrap scaffold sheeting look pretty similar at the point you buy them. It is only when you start to use sheeting that you discover just how well it welds or shrinks and only after some weeks or months how well it will withstand bad weather. However, by that time you are shrink wrapping a scaffolding, it is normally too late to do much about it.
For that reason, I always urge scaffolders and contractors who are looking to buy scaffold sheeting to look beyond the claims materials suppliers and to check out the specifications and performance data for competing scaffold wrap suppliers for themselves to determine scaffold sheeting strength.
However, that is often easier said than done. Once you have obtained the data sheet for a scaffold shrink wrap film, which numbers should you be looking at?
A common point of comparison for determining scaffold sheeting strength is the overall tensile strength of a shrink wrap film. Tensile strength is a good measure of the strength of a shrink wrap film and is important for point loading performance, such as where the shrink wrap film is covering a sharp scaffold fitting. However, in my opinion, one of the most important yet overlooked points of comparison between scaffold wrap film is tensile strength at yield.
Tensile Strength at Yield
Tensile strength at yield relates to the strength of the shrink wrap film but with a focus on elasticity – i.e. the ability of the film to return to it’s original form when hit by a force such as the wind. You may notice that scaffold sheeting with poor elasticity may sag after time, even if they at first seem ‘drum tight’ when initially installed. This is due to poor tensile strength at yield.
In a similar way, traditional style scaffold sheeting is tied to the scaffolding using elasticated bungees. In many cases it is the bungee ties that experience wind loadings which stretch them past the ‘point of no return’. They then become saggy and allow the sheeting to flap and even detach if the wind is strong enough.
The tensile strength at beak for Rhino Verisafe® ia 20,000 kN / m2. The tensile strength at yield is 13,700 kn / m2.
Testing Shrink Wrap Yourself!
Rather than relying on data sheets and specifications, it is quite easy to get an idea of the a shrink wrap film’s tensile strength at yield by testing the film yourself! If you can ask a couple of suppliers to send you just a small sample, it will give you a really good idea of how one shrink wrap film is going to withstand wind loadings when compared with another.
Build a 1-2 metre square frame from scaffolding which is supported 40-50cm from the ground. Cover the square with shrink wrap scaffold sheeting as normal by welding and heat shrinking drum tight. Then load the shrink wrap sheeting. In the image above, SCA Protect used bags of sand up to 800Kg were used which caused the Verisafe® shrink wrap to deflect by around 20cm. Finally, remove the load and the shrink wrap should return to it’s original ‘drum tight’ form.
Why Tensile Strength at Yield is important for scaffold sheeting?
All scaffolders and contractors are looking for a ‘fit and forget’ scaffold sheeting. If shrink wrap sheeting has poor tensile strength at yield it will soon begin to sag and lose the signature ‘drum tight’ finish that shrink to fit sheeting is known for. At this point it will begin to flap and ultimately self destruct and detach from the scaffolding.
Most scaffold sheeting has a tensile strength at break that is able to withstand high wind loads. However, in ‘real world’ scenarios it is the ability to have an elasticity to the scaffold sheeting that can withstand wind loads over a period of time and remain ‘drum tight’ that is perhaps even more important than it’s ultimate strength.
I hope you found this article useful, if so please share! If you need help and advice with any aspect of using shrink wrap film for scaffolding encapsulation andcontainment call myself or my team on 01477 532222. Alternatively drop us a line to firstname.lastname@example.org.