Cyclic behaviour of a hybrid steel-elastomer bearing system for the seismic protection of timber bridges: An experimental and numerical investigation

This paper presents an experimental and numerical investigation of a hybrid seismic protection system for timber and timber-concrete composite (TCC) bridges, combining reinforced elastomeric bearings with U-shaped Flexural Plate (UFP) dampers. Although timber bridges offer well-recognised sustainability and prefabrication advantages, their adoption in seismic-prone regions is currently constrained by the absence of dedicated provisions in the EN 1998–2, which explicitly excludes timber bridges from its scope. The proposed system addresses this regulatory gap by enhancing strength and energy dissipation at the deck-to-abutment interface, while preserving the re-centring capability of conventional elastomeric bearings. The investigation is based on quasi-static cyclic analyses and is structured in three stages. First, cyclic tests are performed on two nominally identical specimens of cold-formed UFP dampers in order to characterise their hysteretic response, and a finite element model of the test setup is developed in ABAQUS and calibrated against the measured curves, providing an effective yield strength equal to 470 MPa, considerably higher than the nominal value of S235 steel. Second, a single explorative full-scale test is performed on the combined UFP-elastomer assembly, and a finite element model of the complete bearing assembly is developed and compared with the measured response, providing a preliminary corroboration of the model. Third, the modelling strategy is applied to three representative single-span TCC bridge sections, with deck widths equal to 4.5 m, 6.0 m and 7.5 m, in order to quantify the contribution of the proposed system compared with a conventional elastomer-only solution. The results show that the hybrid system increases the lateral resisting force by factors ranging from 2.05 to 3.00 and the energy dissipation capacity by factors ranging from 4.6 to 7.6, both quantities increasing monotonically with the deck width. Building on these results, a simplified design framework is proposed to support the preliminary sizing of the UFP dampers as a function of the main bridge parameters. The findings provide a preliminary tool to extend the use of timber and TCC bridges to moderate and high seismicity regions.