AbstractThis paper is part of a larger project that considers the design of large steel‐framed warehouses and distribution centres (‘Big Sheds’) in the context of the SCOSS Alert “Effects of Scale” [1]. These buildings are currently designed to Standards and design procedures that were intended for much smaller structures, and are now long out of date. In the UK, the steel frames of such buildings are generally designed on the basis of plastic theory [2], the fundamental research initiated at the University of Cambridge being continued under Horne at the University of Manchester and culminating in the publication in 1981 of Horne and Morris [3]. Since that date, design procedures have largely stood still while Big Sheds have increased enormously in both scale and complexity. In the UK, plastic design is still largely used; while the early design procedures have been automated so that the entire calculation can be dedicated to a computer. Nevertheless, the fundamental plastic design procedures have changed little. In this context, which is continuing to evolve, this paper returns to the fundamentals and questions some of the basic premises. Current design procedures, based on laboratory tests on small stocky sections, can only be extrapolated to the contemporary situation with the aid of advanced numerical modelling and this process has only just begun. Even at this early stage of the research, it is suggested that the use of plastic theory for the design of large structures typified by Big Sheds needs serious reconsideration.