Stiffness Warming Potential: An Innovative Parameter for Structural and Environmental Assessment of Timber–Concrete Composite Members

Timber hybridization with concrete is a rising widespread strategy to obtain members with a structural performance comparable to traditional ones—e.g., RC members—but characterized by a greater sustainability potential thanks to the presence of timber-based materials; this solution is of great interest due to its low embodied carbon content, which supports the decarbonization goals set, especially for the building sector. Such systems enhance the concrete and timber favorable properties and ameliorate their detrimental characteristics, both from the structural and environmental perspectives. In general, since these two aspects are generally considered separately, a new parameter is proposed to simultaneously combine a structural performance indicator with a warming potential one. Focusing on composite slabs in bending, the stiffness warming potential (λ) is introduced, which combines the evaluation of effective bending stiffness (according to Eurocode 5 γ-method) with the Global Warming Potential—GWP (on the basis of data from Athena Impact Estimator for Building software and data from an Environmental Product Declaration of a timber panel). The method provides a multi-criteria analysis concerning the slab design accounting for vibration, deflection, and acoustic criteria when optimizing the member span. On the other hand, GWP is assessed according to cradle-to-cradle Life Cycle Assessment analysis, where two scenarios with different sustainability levels are encompassed. Results firstly confirm the viability of the novel methodology, with a different outlook on timber–concrete hybrid members, stressing the importance of maintaining thinness of the concrete layer and clearly bringing out the importance of correct re-use and/or a timber recycling management to guarantee effective reductions in terms of CO 2 emissions.