After around 15 years the original oak footbridge in Hilly Fields Park needed replacement due to damage caused by flood water. The damp nature of the tree covered location, over the stream in the north east London park, lead the client to consider the use of an FRP bridge deck to maximise durability and minimise whole life costs of the new structure. The new 7.5m long and 2m width footbridge was design and supplied by Lifespan Structures.
A galvanised and powder coated steel parapet was attached to the outside edge of the bridge, and colours of both parapet and bridge deck were selected to match the environment. The thinner deck allowed the bridge to be raised 300mm above the 100 year flood level. Fast installation of the lightweight structure minimised disruption to users of the park. The existing abutments were reutilised, with only simple modifications to allow for the thinner deck.
The outputs from the design process were;
- Deck Length 7.5m & Clear Width 2.0m
- Designed to the requirements of Eurocodes, and CUR Recommendation 96
- The maximum deflection under a characteristic live load of 5kN/m2 was 55mm, less than span/100
- The minimum natural frequency was 6.8 Hz, Greater or equal to 2.3Hz
- All strains were kept below allowable limits under ULS load cases
- Bolted connections shall accommodate an allowance of at least +/-3.2mm for thermal expansion