Client: Balfour Beatty Engineers: Format Engineers Location: Shere Heath, United Kingdom
Date: 2020-12-01 00:00:00 +0000 UTC Tags: bridge, steel, optimisation
The brief from our client Balfour Beatty, on behalf of Network Rail, was to design a 24m span, 2m high equestrian/pedestrian footbridge on a rural site over a rail cutting in Shere Heath, Guildford, South East England. Both the programme and the budget were very tight. From a blank canvas to installation was to take no more than 6 months and the cost was to be similar to that of a standard Network Rail footbridge. The brief also demanded that the design be a creative and non typical solution but one in visually harmony with the natural surroundings. It should have a degree of visual porosity but not so much that horses become unsettled when crossing the bridge.
Having proposed a number of options the favoured solution was a vierendeel U-frame truss with parapet stiffening members re-arranged by a simple genetic algorithm to stiffen and lighten the structure, saving material weight whilst still giving adequate restraint to the top chord. The design used standard open steel sections wherever possible in the spirit of the economic but crisp and refined design. A great deal of work was invested in the perforated stainless steel plate parapets. The pattern of these part reflects the outer primary structure to give visual clues about the external main members and the different variations of size and pitch of holes was chosen after use of Augmented Reality to test the porosity and much detailed structural analysis.
Format Engineers were responsible for the full design and submitted a complete Form 002/003 Technical proposal and detailed 3d model for fabrication.