Wave loading on rock lighthouses

Historical and contemporary observations of wave-impact loading on rock lighthouses during storms are presented. With climate change potentially causing sea level rise and more energetic wave climates, the longevity of these heritage structures cannot be taken for granted. To obtain a better understanding of the wave–structure interaction, Plymouth University has been working with the General Lighthouse Authorities to develop monitoring and modelling techniques suitable for these isolated masonry structures. Details of the field campaign, in which 2978 impact events were recorded during the winter storms of 2013/2014, are presented together with an initial analysis that begins to shed light on the dynamic response of these iconic structures. The results indicate that the response can be sensitive to the type of wave impact and that the overall motion of the Eddystone tower was less than might have been expected. A finite-element model of the tower was able to reproduce accurately the frequencies of the first and third modes of vibration but, unlike the field data, failed to show response at a frequency near the second mode. Preliminary attempts to apply wave loads estimated on the basis of ISO 21650 show reasonable agreement between the model displacements and those measured.