Our design concept is to cross the Thames from riverbank to riverbank in one span as a gentle curve and in a straight line which is not quite perpendicular to both banks of the river. A bridge where you can feel the scale of the structure at the beginning of the crossing and touch it again when you leave.
We have located the bridge adjacent to the St Paul’s steps, accessed by a gentle ramp. It crosses the Thames in line with the east end of the Tate Gallery of Modern Art. It can be seen coming into view as one begins descending St Paul’s steps. It lands at the edge of a new landscape in front of the Tate Gallery. It is not in line with the only available view from the river of St Paul’s as a bridge in this location would offer only a view of the underside of the bridge.
We have aimed to produce an elegant and simple bridge which is a delight to cross and a bridge which uses as little material as possible. It is crossed as close to the water as possible and offers opportunities to provide shelter and viewing decks if required. It can be enhanced to accommodate an increase in the numbers of people crossing it, as required in the competition documents., should the bridge and the Tate Gallery prove more popular than envisaged.
The bridge structure consists of a pair of stainless steel, arched, pre-stressed cable trusses 7m apart, which resolves all horizontal forces within it, and results only in applying vertical loads at the river banks. This will avoid huge disruption to the adjacent City of London School and Salvation Army HQ. Each arched truss is composed of a tubular steel spine, with ‘obelisk’ cable spacers every 12m, which resists the cable tension and carries shear. The arched trusses are stabilised by horizontal bracing between the tubular spines. Applied horizontal loads are carried by this bracing and the steel framed glass and timber deck which spans between the lower cables. The assembly joints between spine, obelisks and horizontal bracing would be made of stainless steel castings, as would be the cable attachments connecting to the bridge deck.
The bridge is crossed at the level of the lower cables. It is a 6m wide bridge deck gently rising 5m to the middle. The deck surface is timber, running parallel with the main span. Two linear inserts of glass run the full length of the bridge and the deck would be uplit through them. The balustrade is clear, composed of a glass/acrylic/glass laminate, the handrail being a tactile timber profile designed to be leaned upon.