02 May 2017
02 May 2017
A 30 m tall composite lighthouse at Rava Port near Kakinada in South India was constructed from composite modules incorporating Diab core material. The structure was designed to be sturdy enough to withstand both seawater and cyclones.
Durable lighthouses are needed for the Indian coast. The traditional way of constructing these is with masonry or concrete, since the Indian climate causes corrosion of steel frame structures. This is costly and time consuming, and materials, workers and machinery must be transported to the build site, sometimes in difficult terrain.
A solution is provided by prefabricated lightweight fibre reinforced plastic (FRP) modules which can be transported and assembled on site. The lightweight composite materials make transportation and assembly quick and easy. In addition to high resistance to the corrosive seawater and one-tenth of the weight compared to traditional materials, FRP is also more suitable for earthquake-prone areas.
Recognising the benefits of FRP, the Department of Lighthouses (DLH) in India initiated a development project to erect a 30 m tall composite lighthouse at Rava Port. Vignesh Marine Technical Services (VMTSPL), Chennai, India, was contracted to carry out the project. VMTSPL engaged NGN Composites to develop the modular construction scheme, carry out geometric and structural designs and guide the manufacturing process of the world’s tallest hand lay-up composite tower, reports Diab. The project was completed under the supervision and guidance of the Department of Structural Engineering, IIT Madras. NGN Composites selected Diab's Divinycell H60 core material with OD30 finishing for the design.
A hand lay-up modular construction was adopted to manufacture the modules. With a 3.6 m diameter cylindrical shell structure the idea was to create a streamlined air flow around the shell which would reduce wind pressure by 70%. To make moulding and transportation easier, the maximum length of each module was set at 5 m. Instead of providing a tapered profile along the length, a uniform diameter profile was chosen in order to reuse the same mould. Five modules of 5 m and two modules with a length of 2.5 m make up the 30 m tower.
The cylindrical shell walls were made of rigid IPN foam from Diab. Flanges were moulded both inside, at both ends of the modules, and outside, in order to attach them to the foundation as well as to the flat roof at the top. FRP inward flanges were provided for module-to-module bolting from the inside of the lighthouse. This method of bolting eliminated the need to erect scaffolds. A spiral staircase was built of sandwich FRP and landing platforms made of FRP gratings with FRP skins on top and bottom surfaces were inserted in between the modules. At every landing, the adjacent modules and the landing platform were bolted together. A polyurethane coating was applied to the outer surface to provide UV protection.
The lighthouse has been operating for several years, without any signs of corrosion or fatigue. Diab reports that as a result of the structural strength of the core material, the lighthouse has already been exposed to 120 km/hr cyclonic wind pressure with no visible deformations.
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