Prolyte blog: Why you should stick to the allowable loading
In the video of last month, Matthias Moeller, Senior Technical Advisor at Prolyte, showed a 10m span of X30V truss that was overloaded on purpose during a Prolyte Campus. The truss broke and made the effect of the compression force in the top chords very clear. The reason for this test was to repeat an earlier test, carried out at a previous Campus event, last year.
During last years test, the setup was almost the same: a X30V truss span of 10m, a ProLyft Aetos Electric Chain hoist and a concrete block as ballast. The allowable CPL for the truss span was 410kg. The test load was rated at 984kg, including the selfweight of the AETOS Hoist. In this set up, the truss did not fail and showed no visible damage after the test.
As explained in the previous article, the truss in this years test failed at 3.4 times its allowed Centre Point Load (CPL), using a 2 tonne test load. For last years test a load of 1 tonne was used, apparently not enough to break the truss (permanent plastic deformation).
Now, what have we proven? What can we learn from these tests? Fun as it is to see a truss break, it’s someting we want to avoid at all times.
As stated in the Prolyte BlackBook: “If a truss is used to carry loads (e.g. lighting or sound equipment) and is lifted by hoisting devices, e.g. chain hoists, the truss can be regarded as a lifting accessory, as such, the truss is subject to the machinery directive (DIRECTIVE 2006/42/EC). The machinery directive demands a safety factor for lifting accessories of 1.5 against plastic deformation. This is slightly lower than the demands of Eurocode 9”.
As soon as the lifting accessory is used to move or suspend loads above persons – which is quite common in our industry, it’s common practise to double the safety facors. Since Prolyte trusses are certified by a notified body this is not needed.
The tests clearly show that Prolyte trusses comply to these regulations and factors. That doesn’t mean that next time you apply a load you can use the safety factor to play with the loading capacity.
The safety factors are there for a reason – all the unforseen cases where someting happens that wasn’t calculated or taken into account. So stick to the allowable loading and always be safe!