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Plastic fantastic

Heavy steel scaffolding poles could soon be a thing of the past if composite tubes currently in development get the thumbs up from the industry, as Margo Cole reports.

Lightweight composite scaffolding could soon be on the market as a genuine alternative to steel tube and fittings, thanks to UK company Syncromesh Systems, which last month filed a patent for it. Attempts have been made in the past to develop plastic scaffolding, but this can only be used for a limited range of applications, not for general scaffolding purposes, according to Syncromesh.

The company’s head of development, Jim Croll, a former professor of civil engineering at University College London and an expert in structural composites, says the secret behind the new invention, called “s2ubes”, is the manufacturing method.

New method

Until now, the standard method of making plastic tubes has been pultrusion, which only allows for fibre reinforcement to be incorporated along the length of the tubes. Stiffness is vital for scaffolding poles, and plastic is inherently less stiff than steel, so the tubes have to be longitudinally reinforced to prevent them bending under load.

However, they also require strength and stiffness in the “hoop” direction to take the forces imposed by the scaffolding clips that link the tubes together.

“We felt it was imperative that the tubes were compatible with the existing range of couplers and clips,” explains Croll. “But these fittings are very rigid, and employ a very localised form of grip that generates point loads that are diametrically opposed.”

Recent developments in technology now allow tubes to be fabricated with axial and hoop reinforcement, made up of layers of glass fibres. “That’s the bit people haven’t done before,” says Croll, who adds that, until this new process was developed, “it wasn’t possible to manufacture tubes with enough strength”.

Stoobs

The s2ubes (pronounced “stoobs”) are made with a number of separate layers of fibre within the walls, typically three along the length of the poles and two layers of spirally wound fibres sandwiched between
these longitudinal fibres.

“Because of the lightness of the tubes, even though they are less stiff, you can build scaffolds up to 30 or 40 platforms high”

Jim Croll, Syncromesh

 

Croll, who used the system on his own house earlier this year, is now putting the tubes through independent tests to prove they are as strong as he claims, and has written a set of design codes and an operators’ manual giving guidance on how to build scaffolding using the composite tubes. These documents are currently being examined by members of the National Access and Scaffolding Confederation’s (NASC) technical committee.

Steel scaffolding in the UK should be designed and erected in accordance with the NASC’s TG20 manual, which includes tables showing how high it can be built for a variety of different load cases and platform configurations. This document in turn is based on the steel design Eurocode EC3.

As there is no such equivalent Eurocode for structural composites, Croll has started from scratch by drafting a design guide for all the sections that could relate to structural tubes, and then used this as the basis for a scaffolding manual equivalent to TG20. This shows that the composite tubes used in configuration with standard couplers and timber boards can go just as high as traditional steel tubes, with the advantage that they are 75% lighter.

Lighter tubes

“Because of the lightness and weight of the tubes, even though they are less stiff you can build scaffolds up to 30 or 40 platforms high, using a part-boarded configuration,” says Croll. “The dead load is so low that even fully-boarded you can get quite high - up to 20 or 30 lifts.”

The next tranche of independent tests is set to include studies to see if there is any effect of differential thermal expansion between the steel clips and the light composite tube, as well as further verification of the system’s strength and stiffness. Once these are complete, the company is hoping major scaffolding contractors will start testing the tubes for themselves.

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