Reuse limit state: A multi-factor framework for circular steel construction: Foundational concepts and research needs

Direct reuse of structural steel components offers substantial environmental benefits but remains hindered by the absence of generalised design methods for predicting the remaining strength of reclaimed members under diverse reuse scenarios. This paper proposes a “Reuse Limit State” framework that extends current Eurocode-based design by introducing explicit reuse resistance factors to quantify the reusable strength of steel members. Remaining resistance is expressed as the product of the original design resistance and a suite of resistance factors that address: (i) degradation from repeated reuse cycles, (ii) uncertainty in material properties, (iii) time-dependent structural degradation due to fatigue and corrosion, (iv) changes in governing load regimes such as compression-to-bending, and (v) residual capacity after extreme events, supplemented by a serviceability reuse factor for stiffness and deflection. The suggested Reuse Limit State represents the structural design strength of a reclaimed member to perform safely in a future application (direct reuse), either for the same or a different purpose. Although the proposed factors are based on existing literature, code background documents, and mechanics-based reasoning with conservatism, they are presented as framework recommendations requiring systematic experimental and probabilistic validation before codified adoption.