Prestressed Timber-To-Timber Composites With A Novel 30° Screw Connection For The Retrofit Of Existing Floors: Experimental And Analytical Investigations

This study investigates a new retrofit solution for existing timber floors based on a cambered and prestressed timber-to-timber composite (CP-TTC) approach. A novel 30° inclined screw connection, used with angled washers, was evaluated through an extensive experimental campaign including fastener compression tests, push-out shear tests, and full-scale floor bending tests. Hybrid GluedScrewed (HGS) variants were also assessed to examine potential enhancements in the retrofit performance. Results confirm the screw system’s ability to induce significant prestressing, and the retrofit method substantially improved both serviceability and ultimate limit states. Comparisons with benchmark solutions and numerical predictions evidence the effectiveness and feasibility of the CP-TTC strategy for floor rehabilitation. Analytical models were validated and the impact of novel code provisions (FprEN1995-1-1:2025) was discussed.