Bridges

Fibre reinforced polymer (FRP) footbridges were investigated by British Rail in the early 1980's due to the benefits of lightweight construction. FRP bridge applications have continued to be developed for railway infrastructure in the UK, including aqueducts and footbridges, highway bridges, and railway bridge decks.

Following this work, a new modular footbridge concept has been developed (www.flowbridge.co.uk) for improved level crossing replacement solutions, led by Network Rail with a collaborative team including Jacobs as an FRP bridge specialist. Footbridge user experience was a focus, as well as reduced cost due to simple and efficient construction methods. The footbridge comprises a primary trapezoidal spine, spanning approximately 20m over the railway, manufactured from units of autoclaved GFRP sandwich composite (E-glass and epoxy resin), and forming a S-shape in plan with the stairway units leading to and from the main span. The main span deck and stairway units are formed from ambient cure moulded sandwich GFRP sandwich units (E-glass fibre and polyester resin) with internal rib stiffening and bulkheads, which are gravity-clamped onto the primary structural spine. Toughened laminated glazed parapets were also used to improve user visibility on and around the footbridge. The low weight of the footbridge allowed use of a proprietary micro-pile system, avoiding any use of concrete.

A trial erection in 2021 confirmed that the primary spine/secondary decking concept and lightweight modular units (each generally less than 1 tonne) enabled efficient construction. Controlled load testing confirmed the expected structural behaviour and identified the need for some minor changes, such as stiffer connections, that could be used to optimise the structure further.

Future options for this footbridge concept are described, including use of bio-composite materials for certain components, and the ability for FRP bridges to be resilient to loss of intermediate support loss in derailment design situations.