By Emilia MargarethaIn the space of a few weeks, the English architectural office Knight Architects has won two competitions for bridges in London and Ulm. While the Merchant Square footbridge planned in Paddington will be filigree in appearance and moveable, the design for the new tram bridge leading to the Kienlesberg in Ulm will be low-key and pragmatic.
The planning and construction of the Merchant Square footbridge in London’s Paddington will take from 2012 to 2014. The pedestrian bridge, designed in collaboration with AKT II Consulting Structural Engineers, will span the Grand Union Canal over a width of 20 metres while guaranteeing a required clear passage of 5.5 x 2.5 metres.
The concept is simple and at the same time spectacular: an inconspicuous three metre wide deck is divided with the aid of hydraulic jacks into a series of cantilevered beams which rotate around the transverse axis – an elegant movement which resembles the opening of a Japanese fan. The rotary movement of the five prefabricated steel beams is staggered so that they start to move simultaneously and come to rest at the same time at different angles of inclination of between 20 and 80 degrees.
The load on the hydraulics is relieved by counterweights, which also reduce the energy required for operation. The balustrades are formed by stainless steel rods which intersect in a skewed pattern, creating a filigree structure. Continuous LED lighting is integrated into the handrail, illuminating the deck adequately and dramatically highlighting the balustrade.
The design of the bridge was chosen so that it will harmonise well with the prestigious, upmarket environment of Merchant Square. During the opening process, the bridge is transformed into a kinetic sculpture, the silhouette of which will emphasise the surrounding open space of 'Sunset Terrace'.
The architects developed the successful design for the combined tram, cycle and pedestrian bridge in Ulm together with the engineering practice Krebs and Kiefer. The design competition forms part of the planning of the tram line 2, which urgently requires the building of a new bridge. The new bridge will provide a rail connection from the city’s science park to the city centre as well as a convenient and rapid crossing of the intercity, regional and goods railway lines in the vicinity of Ulm’s central station.
The design provides for a 270 metre long steel bridge with a constant gradient. It can be used comfortably and safely by both pedestrians and cyclists. The rest areas provided at regular intervals allow an unobstructed view of the historic old town and the Minster.
The technical prerequisites present the planners with a major challenge, since the land around the railway tracks which have to be crossed only offers very little space for a permanent building site and is difficult to access with construction equipment. The bridge has to be built while rail operations are continuing and for this reason will be erected by longitudinal extension. The steel segments will be welded together on site and extended across the tracks step by step. Whereas the underside of the main beams remains constant in order to allow an even extension, the height of the beam on the upper side of the bridge is variable, following the distribution of moments in the final condition. The flowing wave-like form of the beams is optically understated but varied and makes deliberate reference to the steel lattice structure of the nearby Neutorbrücke, built in 1907. The use of weather-resistant steel for the superstructure will make the maintenance of the structure significantly more economical and safer.
It has not yet been announced when construction work will begin; the estimated building costs amount to approximately 11 million Euros. The people of Ulm will be able to make suggestions for the name of the planned bridge as part of the public consultation process. www.knightarchitects.co.uk