A new pedestrian and cycle bridge is required over the River Colne to connect the Aquadrome Boat House to Riverside Drive (the A404).
This will replace an existing, timber pedestrian bridge - which had reached the end of its useful life.
The proposed span of the bridge is approximately 25m between the new abutments – with a clear foot/cycle path width of 3m and a minimum clear height above the River Colne of 1.5m.
As the existing bridge was demolished prior to the construction, construction access the far side of the bridge was extremely limited.
Additionally, the large number of trees in the bridge vicinity severely limited the mobile crane options.
Both for aesthetic considerations and to minimise the overall weight, a galvanised, steelwork, Bow String Truss design was adopted – with the (timber) deck supported, via steel cross members, onto the bottom chords of the trusses.
The bridge has been designed for pedestrian and cycle use only (5kN/m2) – and so permanent bollards are provided to prevent vehicular access, even for emergency access.
The loads from the two primary Bow String Trusses are carried by new galvanised, steelwork abutments on galvanised, steelwork grillages at either end of the bridge.
To avoid the need to demolish the existing, substantial concrete abutments, new abutments were located immediately behind the existing abutments.
The steelwork grillages carrying the new abutments were supported on concrete pile caps on screw piles. Screw piles were utilised because of the extremely limited site access and to avoid unnecessarily deep excavation adjacent to the River Colne.
