Post-tensioned modular structure raises architectural potential
The technology behind the world’s first modular glass-fibre reinforced plastic (GRP) bridge could open up exciting new possibilities for architectural design, its engineers claim.
The post-tensioned bridge, launched by design consultancy Arup and bridge specialist Mabey, is 70% lighter than steel and designed for assembly at locations with restricted access for large cranes or heavy machinery.
The system comprises identical 1m-long modules that are fixed together with bolted shear connectors, then post-tensioned to enable spans of up to 30m.
Ian Wise, structural engineer at Arup, told RIBAJ: ‘Our system could be suitable for building lightweight roofs, or even ambitious bespoke pieces of architecture. The variety of geometry and types of form that can be created is almost unlimited. It’s also possible to tailor the materials and fibres to alter texture and stiffness.’
The variety of geometry and types of form that can be created is almost unlimited. It’s also possible to tailor the materials and fibres to alter texture and stiffness
The first bridge to be built using the technology (being marketed by Mabey as Pedesta) was installed at a Site of Special Scientific Interest for Network Rail in Oxford, England. The modules were light enough to be transported on an articulated lorry, then assembled on site and lifted into position from a distance. Modules only require a pallet truck or forklift to move, making installation faster, safer and more efficient.
The key innovation behind the bridge concept is the combination of GRP, smaller module sizes and the post-tensioned structure. ‘Traditionally, if you wanted to build a 20m long bridge in GRP you would have to make a 20m-long mould then infuse it with resin,’ says Wise.
‘If the process went wrong you’d have to bin all the materials and start again and entirely different moulds would be required for different projects. Creating small modules makes tooling cheaper and puts less material at risk.’
In addition, post-tensioning the structure simplifies connections between modules as they are only required to withstand compression forces. The structure is stiff enough to prevent contortion, an issue that can affect plastic structures, and could last over 100 years. Wise comments: ‘The only aspects of GRP that can degrade over time are from UV radiation and water ingress on exposed edges, which de-bond fibres from the resin, but these are fairly easy to manage by applying a coating.’
The modular bridge concept was developed by Arup and part-funded by the UK Rail Safety and Standards Board. Mabey is the first licensed distribution partner.