Finite Element Modelling and Limit Analysis of Fastnet Lighthouse Under Impulsive Ocean Waves

Being exposed to strong ocean waves for more than a century, the Fastnet lighthouse is assessed for its structural response to the intense lateral loading. The Finite Element Method (FEM) was implemented for the structural analysis using the commercial software Abaqus. The lighthouse is built with large and meticulously dovetailed granite blocks which make it a very unique structural system. Three different finite element model configurations were tested, modelling the lighthouse as continuous homogeneous (elastic and nonlinear), and as discontinuous with contact interfaces between each course of blocks allowing uplift and sliding. The applicability and efficacy of these approaches is discussed. The impact load of the wave was applied as a time-history sequence, assuming that the wave breaks just in front of the structure surface corresponding to the least favourable scenario. Different intensities and heights were considered for the impact load. Finally, the FEM results are also compared with the results of the limit analysis method which calculates the minimum intensity of lateral static load that is necessary for causing uplift and overturning of rigid bodies. This comparison demonstrates the usefulness of the limit analysis method as a tool for quick preliminary assessment of the lateral load bearing capacity of this particular structural typology. This work is part of the STORMLAMP project (STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves) funded by the UK Engineering and Physical Sciences Research Council, which is gratefully acknowledged.