Are big sheds safe?

This paper provides comprehensive background, theory, and evidence to address the critical question: Are Big Sheds safe? The paper is structured such that each section independently answers a constituent question; while the sections may be read independently, together they present a comprehensive examination of the logical arguments and counterarguments surrounding the safety of Big Sheds. This study reveals fundamental design inadequacies in large, steel portal-framed structures clad with sandwich panels. The paper criticises the outdated design practices, particularly the 2D plastic design approach and inadequate consideration of the interaction between framing and cladding systems in structural analysis. It also highlights the limitations of the current European guidelines in accurately predicting the behaviour of these complex structures. A new design framework is presented, together with the first serious attempt at the detailed analysis of a multi-bay Big Shed clad with sandwich panels. The paper argues that, given the existing design methodologies and regulatory guidelines, the safety of Big Sheds cannot be definitively assured. This research emphasises the urgent need for a paradigm shift in the structural analysis and design of Big Sheds, advocating updated methodologies and the need for collaborative efforts between the construction industry and academia in order to ensure their safety and sustainability. • Steel-framed portal structures have increased in size with no corresponding change in design. • Failures have occurred, caused by parasitic diaphragm action due to effects of scale. • The industry's response to these recent cladding system failures in “big sheds” is presented. • A detailed history of the development of stressed skin theory and plastic theory. • A realistic large structure analysed using the component method, failure modes are presented.