Tell us about the early design brief
Designed by architect AHMM in conjunction with our own engineering expertise, Chobham Academy is a new all-ages school set within the 2.5km² Olympic Park. Our brief was to build a footbridge to the school that would provide safe pedestrian access to the school across the busy Temple Mills Lane.
What challenges did you face along the way?
The solution was a new 90 metre-long footbridge that rises up outside the school’s specialism building and descends onto a man-made mound within playing fields on the other side of the road. As well as providing essential access to the school, the footbridge also creates a new landmark for the area.
A key aspect of our design approach with AHMM was creating an ‘honest’ structure with a 120-year design life, which visually expresses the structural forces within the bridge.
In terms of construction, the bridge is made from welded plates of Cor-Ten weathering steel and external fins were welded to the outside of the ‘U’-shaped trough that forms the bridge deck and upstands. These provide additional stiffness, and are spaced with a frequency that directly relates to the shear force diagram along the bridge.
Two pre-cast concrete piers also provide intermediate support to the deck, and from the piers spring double pairs of ‘V’-shaped support trees fabricated from weathering steel hollow sections that provide lateral and rotation support to the deck. The ends of the bridge also feature reinforced concrete abutments clad with pre-cast panels.
Early on in the project we undertook geotechnical analysis on the site which revealed a composition of made ground on top of alluvium to a depth of 15m. We decided to produce piled foundations to support the bridge as a result of this geotechnical analysis. We also constructed 600mm diameter piles to support the applied loads under both the piers and abutments.
How did it feel to be involved in such an important British project?
It was very exciting to be involved in such a high profile project. The footbridge will help to offer a lasting legacy in an area of regeneration.