Reserve capacity and vertical extension potential in steel framed buildings

Reusing existing buildings is key in transitioning to a circular economy and meeting associated decarbonisation targets. Many adaptive reuse strategies, including vertical extensions, result in increased loads that are required to be resisted by reserve structural capacity and/or strengthening. Previous work identifies structural underutilisation within existing buildings and suggests numerous sources of this. However, understanding of associated contributions to reserve capacity and how this influences a building’s ability to be extended is limited. To address this, 11 scenarios, each modelling a different source of underutilisation, have been developed and applied in the design and reappraisal of 11,252 hypothetical steel framed office buildings. An average reserve capacity of 10% is found in optimal Eurocode designs, rising to around 20% for British Standards and over 30% in the conservative or defensive application of Eurocodes. Office to residential conversions are shown to unlock an average reserve capacity of more than 20%. Across the 11 scenarios, between 9% and 89% of considered cases are shown to be extendable without the need for strengthening. This demonstrates potentially significant extension potential within steel framed buildings, but that this varies with frame configuration, design/appraisal approach, and the extension’s use and structural material.