No matter the size or nature of your scaffolding project, the safety and durability of the scaffold is essential. Sometimes supplementary couplers are used to ensure the safety and strength of a scaffolding structure. So, what exactly are supplementary check couplers and what do Eurocodes say about them?
What Are Supplementary Check Couplers?Supplementary couplers are included in a scaffolding structure when the estimated working force in a scaffolding connection point is exceeding its capacity. Although scaffolding couplers are designed to hold tubes firmly in place and not move, if too much load is placed on them, they will slip along the tube. By introducing a second coupler, called a supplementary coupler placed in direct contact next to the original coupler, they work together to distribute the load. Care must be taken to ensure the supplementary coupler is positioned on the correct side of the original fitting depending on the direction of force.
Why Are Supplementary Check Couplers Useful?If the force that is exerted at the connection point between two tubes is greater than the slip capacity of the fitting, the scaffolding structure will be unsafe for use. This will ultimately cause project delays if the problem is identified or create huge personnel risks if the problem is unidentified. Supplementary couplers are useful in scaffolding where there are likely to be higher load forces, such as lifting gantries and loading towers. Supplementary couplers are also recommended for suspended or underslung scaffolds, even if the forces are within the capacity of a single fitting. This should be observed in situations where only a single fitting is preventing a working platform from falling a distance greater than 2.0m. As a precaution against a coupler not being tightened properly a supplementary coupler should be added under the main fitting where the ledger is fixed to the puncheon or vertical member. In this situation it is known as a check coupler.
What Do Eurocodes Say About Supplementary Check Couplers?It is important to be aware of the European code regulation for supplementary check couplers as there is some debate in the scaffolding industry about the load distribution between the couplers and how much additional load a supplementary check coupler will take. Eurocodes specify that the second coupler is only able to take 50% of the load capacity of the original coupler. For example, if the first coupler has a slip value of 10kN, the second is only able to take an additional 5kN. There is some contradiction between Eurocodes and TG20:13 scaffolding guidelines, as Eurocodes state that ordinary Class A couplers have a higher initial value than stated in TG20:13. Eurocodes give the allowable slip value of a Class A coupler as 10kN and therefore a supplementary coupler will allow another 5kN giving a total of 15kN for the pair. TG20:13 gives a downrated slip value of 6.1kN for the main fitting, so it could be argued that it is acceptable to consider the full 100% of the slip value for a supplementary coupler as this would still only give a total slip value of 12.20kN for the pair, some 2.8kN less than stated in the Eurocodes.
Should I Include Supplementary Check Couplers In My Scaffolding?Generally supplementary couplers are not required for standard scaffolds erected within the parameters of a TG20:13 compliance sheet. Where a scaffold has been designed the designer will indicate the use of supplementary couplers if/where required. Supplementary couplers should be used under the boarded platform for suspended or underslung scaffolds.
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Image source: Eurocodes