Hydrodynamic loading and structural dynamic assessment of offshore concrete lighthouse

Historic rock-mounted lighthouses play a vital role in the safe navigation around perilous reefs. Their longevity is threatened by the battering of waves which may be set to increase with climate change. The protection of this historic heritage needs the identification of both structural dynamic parameters (natural frequencies and shape modes), and of the worst-cases wave load combination, able to affect that natural frequencies. This dissertation was developed during a period of five months at University of Plymouth, along with the researching team of the project STORMLAMP. The project is divided in three parts; the first involving a meteocean analysis, developed by means of peak over threshold technique, aimed to address realistically a test campaign held afterwards. The second, focused on the dynamic analysis of the Dubh Artach lighthouse and was developed by means of a Matlab toolbox provided to the group by Prof. Brownjohn from Exeter University, partner of the project as well. It is aimed on one hand to detect the dynamic properties of the structure and, on the other hand, to recognize eventual directionality in the structural response. The third phase was held at Plymouth University laboratory “COAST”. During this phase, a laboratory campaign, involving more than 100 tests, allowed to perform a parametric analysis aimed to identify the parameters, of an extreme wave, that influence more the impact force and that the wave exerts on the structure. To extract impact time history, force signals were decomposed by means of Empirical mode decomposition and Duhamel integral algorithms. Image analysis, moreover, allowed to locate run-up caused by those waves upon a steel cylinder and to integrate a study of the run-up as well. The analysis led to several considerations useful on one hand for the prediction of the worst-case loading of the Dubh Artach lighthouse and, on the other hand, for the introduction of the NewWave theory for the design of coastal structures.