Modern cladding systems for big sheds: The emerging state of the art

Stressed skin theory was first introduced in the 1960’s and intensive development continued until the mid-1980’s. This development was characterised by extensive research into the behaviour of low-rise portal frame structures clad with a single skin of profiled metal sheeting. The resulting state of the art was formalised in ECCS (1995). Since then, frames have become much taller and more slender while alternative cladding systems have proliferated. About 10 years ago, the construction industry in the UK was shaken by a small number of failures in the roofs of ‘Big Sheds’ clad with sandwich panels. Investigation by numbers of experts was inconclusive and non-disclosure orders (NDO’s) were issued by the companies concerned. In the UK, the Standing Committee on Structural Safety (SCOSS) was informed of this and, after discussion with the Institution of Structural Engineers issued an Alert entitled ‘Effects of scale’ (SCOSS, 2018). This drew attention to the fact that validation of our current design rules has been largely based on years of satisfactory building performance. However, such evidence may not be indicative of satisfactory performance as structures increase in scale. In deference to the NDO’s, a research program has been commenced based entirely on structural mechanics without making any direct reference to either forensic evidence from the sites of the failures or test results etc. that are not in the public domain. This is one of the papers arising from this research. It recognises significant deficiencies in the design procedures in the European Recommendations (ECCS, 1995) and the need for a full, non-linear, 3D numerical analysis of the complete clad structure. This, in turn, has resulted in the development of the ‘component method’ of analysis for structure cladding interaction problems that concentrates on the development of numerical models together with the performance of their ‘components’. The main alternative cladding systems are considered in turn and their characteristics and potential failure modes identified.