The new Horsey Cycleway crosses a wetlands area where two footbridges with service vehicle access were required to cross waterways on the route. Due to the poor ground conditions the bridges needed to be lightweight to aid installation and reduce the abutment loadings. The Client, East Sussex CC, had already used an FRP composite footbridge on a previous scheme and commissioned Lifespan Structures to design and manufacture the two FRP composite footbridges.
The bridges were both 3m wide and had clear spans of 14.8m and 10.6m with respective deck weights of 5600Kg and 3350Kg. The bridges were designed to the BD90/05 standard with a 60 year design life and provided over a 50% reduction in carbon and energy embodiment when compared to the steel footbridge option. The parapets are 1.4m high galvanized steel and powder coated. The bridges are designed with a longitudinal camber to improve the visual aesthetics and the client was able to select a colour scheme which complemented the surrounding environment.
The outputs from the design process were;
- Deck Lengths 11.0m and 15.2m and Clear Width 3.0m
- Designed to the requirements of Eurocodes, and BD90/05
- The maximum deflection under a characteristic live load of 5kN/m2 was 28mm and 42mm, less than span/300
- The minimum natural frequency was 12.93Hz and 9.9Hz, Greater or equal to 5.0Hz
- All strains were kept below allowable limits under ULS load cases