Structural Response of ‘’La Jument’’ Lighthouse under Extreme Wave Loading – Analysis and Concept of Maintenance

Ancient off-shore lighthouses have a phenomenal cultural significance. They were built as physical aid for navigation to guide mariners and to warn them from dangerous shallow rocky reefs. Understanding their structural response under waves loading is a challenging task. La Jument lighthouse, off the coast of Brittany, has sustained extreme environmental loading for more than 110 years. The main motivation of the present study is to characterize its structural response under extreme waves loading by 3D Finite Element Modeling using the commercial software DIANA. The model is calibrated based on the data collected from accelerometers and photographical documentations during a measurement campaign in winter 2018 in which the highest wave recorded with 19 meters height is considered for this study. The effect on the lighthouse’s structural response of slamming pressure magnitude, tide level, and slamming area is investigated in a parametric study. The predictions of the FE model were comparable to the actual measurements confirming the main hypothesis in this study. The tide level was proven to be an important factor contributing to the structural response parameters. The FE model suggested 230 kPa as the most likely pressure of the wave under consideration. Moreover, intervention methods using UHPFRC combined with a measurement campaign are proposed to preserve the outstanding cultural significance of La Jument lighthouse. Extending the life of off-shore lighthouses is essential to understand non-linear characteristics of extreme waves in future field measurements which helps validating numerical computations and removing uncertainties about their dynamic behavior.