PSI - Issue 78

Martina Sciomenta et al. / Procedia Structural Integrity 78 (2026) 253–260

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not because of inferior mechanical or durability properties, but due to market inertia, lack of standardization, and limited industrial processing. This scenario is gradually evolving, as European policies encourage the use of locally sourced timber to red uce CO₂ emissions from transport, foster regional economies, and broaden the raw material base. Recent researches have highlighted the strong mechanical performance of non-traditional species such as beech, birch, and bamboo, with beech glulam beams demonstrating superior strength and stiffness compared to their spruce counterparts, leading to reduced deflections (Sciomenta et al., 2022) (Pramreiter and Grabner, 2023). Chestnut which is one of the most prevalent hardwoods in Mediterranean regions has shown promising potential for structural use (Martins et al., 2025). It has already undergone the European Technical Assessment (ETA) process for "Uso Fiume" beams (Brunetti et al., 2013) and has been integrated into machine strength grading systems. Current investigations are exploring its suitability for EWPs production. Within this evolving context, the application of hardwood glulam—particularly from underutilized species such as chestnut—in timber–timber composite (TTC) floor systems represents a valuable and sustainable alternative for future structural design. Beyond the material perspective, the behaviour of diaphragms is central in seismic design, as it governs lateral stiffness, the distribution of horizontal actions, and influence the overall dissipation mechanisms of the structure. The current Italian technical code - NTC 2018 (Ministero delle Infrastrutture e dei Trasporti, 2018) assigns panel systems with screw-connected diaphragms a higher energy dissipation capacity (behaviour factor q =3,0 in low ductility class and 5,0 in high ductility class) compared to diaphragms realized through gluing (behaviour factor q =2,0 in low ductility class and 3,0 in high ductility class). This highlights the importance of investigating how the nature and characteristics of connections in TTC systems can influence global structural performance, with the aim of establishing more reliable and efficient design criteria and eventually their dissipative behaviour. 2. State of the art In recent years, the potential application of hardwood in both new floor systems and the refurbishment of existing ones has attracted growing research interest. According to (Nero et al., 2025), high- EWPs and composite mass timber products (CMTPs) are being employed more frequently in residential projects with increasing interest in more sustainable systems that achieve long-spans. Therefore, they examined the mechanical performance of four EWPs and CMTPs elements for flooring, made with both hardwood (Eucalyptus nitens and Eucalyptus globulus) and softwood. The research highlighted substantial improvements due to the use of hardwood, specifically in structural efficiency, global warming potential and fire performance. These outcomes confirm the potential use of hardwood for high performance, long-span EWPs. (Spera et al., 2024) analysed the application of 3-layered CLT panels made of beech to increase the out of -plane strength of existing TTC one-way timber floors. A comparison with two additional well established retrofit methods as the double-crossed timber planks and the reinforced concrete slab were also considered. The performances of three reinforcement methods were estimated for the ULS and SLS conditions and compared each other. The proposed solution represents an interesting compromise between the concrete slab and the additional timer layer since it led to an increment of bending stiffness at the SLS ranging between +145% to +177% (depending on the diameter of the screws which varied from 8 to 12 mm) with a smaller increase of weight (+40%) compared to the concrete slab (+69%). These findings underscore the potential of hardwood-based solutions in floor systems and support their application in TTC floors—currently the most widespread solution in existing buildings. TTC systems also offer a reversible and sustainable alternative to timber–concrete composites in new construction. The dowel-type connections for TTC have been deeply investigated during the last decade, especially the screw connections. These latter attracted the interests from both researchers and engineers, due to their advantages of ease of execution, easy availability, and relatively Nomenclature CMTPs Composite mass timber products EWPs Engineered wood products ETA European Technical Assessment TTC Timber-timber composite