Serviceability reserves of historic reinforced concrete slabs implications for structural reuse

The transition to a circular economy in the construction sector requires reliable methods to assess whether existing reinforced concrete elements can be reused in new load‐bearing structures. A central question is whether slabs designed according to historical standards also meet today's serviceability requirements. This study presents a comprehensive parametric investigation in which the serviceability (particularly crack widths and deflections) of simply supported reinforced concrete slabs, designed according to five generations of German and European standards, is compared: DIN 1045:1978, DIN 1045:1988, DIN 1045‐1:2001, Eurocode 2:2011, and Eurocode 2:2025. The study includes 1785 configurations per code–steel–concrete combination, covering practical ranges of span (4.0–8.0 m), slab thickness (160–300 mm), and imposed load (2.0–5.0 kN/m 2 ). Each configuration is evaluated for BSt 420/S reinforcing steel and BSt 500/S reinforcing steel, as well as two concrete grades (C20/25 and C35/45), resulting in a total of 35,700 individual calculations. Each configuration is designed in the ultimate limit state according to the respective historical code, while the serviceability limit state is consistently assessed using current Eurocode 2 methodology. The results reveal a systematic trend: slabs designed according to more recent codes exhibit larger deflections and wider cracks under identical geometric and loading conditions. This is primarily due to the modern semi‐probabilistic safety format, which requires less reinforcement compared to earlier global safety concepts. A reuse‐oriented deflection limit of l/150 is introduced as a classification criterion, and slenderness‐based screening limits are derived. In addition, a load amplification factor α qp is proposed, relating the maximum permissible quasi‐permanent load to the original design load, thereby enabling a direct allocation of reused elements to new usage categories.