Société Nautique de Genève’s new lighthouse project seeks to reconcile the functional demands of a lighthouse with a strong and distinctive aesthetic, giving it a symbolic dimension and creating a new landmark for the expanded harbor and wider city.

Architecturally, the challenge was to design a structure that would be both light and elegant. Rising to height of 17 meters, the tower springs from a base of stone blocks built into the new jetty and houses a ‘living area’ with a plant room below it. The reinforced concrete base is clad in the same dressed stone blocks as the jetty and serves a double function: to anchor the tower and to protect it from the waves and spray of Lake Geneva.

The lighthouse itself is a hyperboloid tower measuring some 13 meters in height, and consists of an outer envelope comprising a latticework of 10mm-diameter prestressed cables and a compressed central element. To produce a lightweight structure that in turn reduces wind exposure, the light itself can be maintained from the base of the tower. The central column is split into three slender metal tubes just 100mm in diameter to incorporate the light’s lifting and lowering mechanism. In a design similar to that of a bicycle wheel, these tubes are connected to the cable lattice by prestressed radial tie rods and a compressed ring that forms part of the outer surface. The interaction between the outer envelope and the columns reduces the buckling length of the columns, allowing them to be kept as slim as possible. At the top, the tie rods are anchored in a metal ring reinforced by radial bars that transfer the loads from the cable lattice to the three central columns.

The first floor houses the ‘Start’ cabin and forms the interface between the metal structure of the tower and the stone base. The three central columns are anchored in a reinforced concrete column that ensures the overall stability of the structure at this level. Sitting behind the octagonal glazed facade are eight slim metal columns. To ensure even load distribution they are connected to the cable lattice by a rigid metal ring embedded in a concrete slab below the cabin. The outer envelope is placed under tension by means of turnbuckles – designed so that a concentrated tensile force can be applied with ease – at the foot of each column. The columns run vertically down to the basement level, where metal components set into the concrete during casting ensure the transfer of horizontal loads to the slab.

The entire lighthouse structure sits on a reinforced concrete raft which distributes loads to a series of micro-piles anchored in the load-bearing substrates at the bottom of the lake.