PSI - Issue 79

Aikaterini Marinelli et al. / Procedia Structural Integrity 79 (2026) 182–189

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2. Case study 2.1. The structure

This study will contribute to the structural assessment of the Bell Rock lighthouse (NLB, 2025a), located on Inchcape Rock, off the coast from Arbroath. It is one of the world’s oldest surviving and the world’s oldest working sea-washed lighthouse, standing 35 metres high in the North Sea, itself on the rock known as Bell Rock. Built by Robert Stevenson in 1811, its construction was a triumph of engineering in the face of harsh conditions. The Stevenson family are renowned for their lighthouse designs in Scotland, with three generations of their family having designed and built 82 lighthouses around the Scottish coastline between 1791 and 1937 (Bathurst, 2000, NLB, 2025c). The Bell Rock’s iconic design has inspired lighthouses worldwide. Before this lighthouse, there was no way of seeing the rock that lies just below the surface of the water at low tide and many a ship was caught out. Robert Stevenson’s Account Of the Bell Rock Light-house (Stevenson, 1824) provides a fascinating account of the hazardous rock and the building of the beacon, railway and the light itself (Fig.1). The structure is a tapered cylindrical tower (12.8m at its base and 4.11m at its top) with balcony, including a copper Dome roof, mounted on a plate glass lantern, fixed to a masonry murette. Facilities housed in the tower include batteries, engines, solar panels, overnight personnel accommodation, workshop space, bulk fuel oil and water storage (NLB, 2023). The tower is of solid dovetailed masonry for the first 9 metres, half of which is below high water, and above are 5 chambers and the lightroom. Stone was quarried from Mylnfield, near Dundee (sandstone) and from Rubislaw, Aberdeen (granite) – with both quarries now closed. Two types of mortar, ‘Bell Rock Mortar’ and ‘Roman cement’ were used in the construction of the structure, with the first being a mixture of lime, pozzolana/tarras, sand and seawater, while the second - mostly used for the lower levels - was selected for its quick-setting and waterproofing qualities (Hurst, 2002). Masonry work is of such high standard that has not been replaced or adapted in 200 years. Owing to the scale and logistical challenges of any future major upgrades, these would constitute a long-term operation.

(a)

(b)

Fig. 1. (a) The Account of the Bell Rock Light-house (Stevenson, 1824); (b) the Bell Rock Lighthouse (NLB, 2025a)

2.2. Methodology Processes necessary to create a suitable three-dimensional numerical model were followed (Fig. 2), having as a starting point a previous preliminary study by the same research group (Cleghorn, 2019). The modelling effort was further refined to address loading scenarios representative of critical environmental actions, considering the tools and resources available and compatible with the scope of the project.