Stressed skin theory and structure cladding interaction: Safety concerns with Big Sheds

Abstract

Stressed skin theory was born in the 1960’s and intensive research and development took place in the UK and Europe up to the mid 1980’s. During this time, much of this research was directed towards utilising stressed skin action to reduce the amount of structural steelwork in the portal frames of relatively stocky, low rise “shed” type structures. By the end of this period, the theory appeared to be quite stable and almost all further development ceased. Subsequent Standards and Codes of Practice therefore reflect the state-of-the-art at or around the mid-1980s. Since then, there has been a massive evolution in shed type structures (e.g. large warehouses and distribution centres also known as ‘Big Sheds’) as they have increased greatly in size, the frames have become taller and more slender and alternative cladding systems have proliferated. Some recent roof failures have been attributed to ‘parasitic’ (unwanted) diaphragm action in such ‘Big Sheds’ and this has drawn attention to the inadequacy of current stressed skin theory. This paper summarises an on-going response to this situation within which interest broadens to include the response of the unclad frames and the interface between the frames and the cladding, as well as the cladding system. Within this context, the theory is better discussed under the more general heading of ‘structure cladding interaction’.