FOOT AND BICYCLE BRIDGE ALBI
Albi, a city with a rich and tumultuous history, earned UNESCO World Heritage status for its historic centre in July 2010. Within this context, the creation of a cyclo-pedestrian footbridge cantilevered from a 19th-century railway viaduct was conceived. The viaduct, still in service today, is a fully masonry structure of remarkable coherence. The footbridge, made entirely of steel, is attached to it and subtly interacts with the existing structure in its design. More than just an addition, the whole project results in a new composition that possesses its own architectural and landscape qualities. In terms of use, the footbridge provides a direct link between the city centre and the peripheral neighborhoods, as well as a series of balconies beneath the arches of the existing viaduct, inviting people to pause and explore the built and landscape heritage of Albi. Ney & Partners, along with its collaborators, won a design competition in 2013. After a challenging journey, the project is now delivered to the people of Albi.
Client’s request
The client’s — Communauté d’Agglomération de l’Albigeois — brief was clear and threefold: the new bridge had to encourage and improve sustainable mobility in the city centre. Secondly, the new construction had to provide access to the peripheral neighborhoods of La Madeleine and the new recreational green space at Pratgraussals. The whole operation also needed to support the implementation of the management plan for the episcopal city, which earned UNESCO World Heritage status in July 2010.
Context
Originally developed on the southern bank of the Tarn River, the city centre of Albi is distinguished by its architectural coherence, primarily composed of rose-colored masonry bricks — known as “briques foraines” — with typical dimensions of 36 x 24–26 x 3.5–4 cm. The most notable landmarks are undoubtedly the Palais de la Berbie and the Sainte-Cécile Cathedral. The setting is breathtaking, with the Tarn River flowing through a valley, its slopes adorned with lush greenery and foliage.
The city centre is characterized by its medieval urban layout, centred around a large public square in front of the Saint-Cécile Cathedral, complemented by a network of smaller streets and intimate squares. This sequence of public spaces, providing occasional moments of openness within the dense urban fabric, is specific to Albi and served as a key inspiration for the design process.
The railway viaduct in Albi, owned by the French railway company SNCF and still in use today, was built around 1865. This seven-span arch bridge was constructed entirely of baked masonry. The spans are regular and are 29 m long. The railway is located approximately 30 m above the Tarn River. The width of the bridge structural arch is approximately 4.70 m. Prior to the architectural competition, a series of tests were conducted to characterize the material properties of the viaduct. The results showed that the bridge is structurally sound, with high-quality masonry and minimal deviation along its length. A preliminary study, carried out in close collaboration with SNCF’s bridge experts, confirmed that the viaduct can support a new, lightweight footbridge.
At the time the viaduct was built, planners had little consideration for the public spaces. The viaduct effectively cut the open space, creating an intra-muros Castle Square and, extra-muros, Calvary Square, the latter being experienced as a leftover place. The new footbridge was seen as an opportunity to restore meaning and quality to the historic ensemble formed by Calvary Square and Castle Square. The renewal of both public squares was part of the commission and designed by the Belgian architects-urbanists MS-A.
The footbridge
The competition brief left open the possibility to position the new footbridge upstream or downstream of the existing viaduct. For several reasons — users’ safety, the opportunity to heal the urban wound created by the viaduct construction, and from a landscape point of view — we opted to build the bridge downstream. In that way, the 19th-century masonry viaduct remains the main compositional element in the scenery, its materiality responding adequately to the built heritage of Albi.
The footbridge has been conceived as a continuity of the network of smaller public places found in the city centre. Its downstream position generates unique views towards the heritage perimeter, with the arches of the railway viaduct framing the perspectives. Therefore, it was only natural to incorporate viewpoints on the footbridge.
The footbridge geometry is closely related to that of the railway viaduct. Their walking lines run parallel. Furthermore, a waving pattern has been introduced to the walking line of the footbridge, matching the rhythm of the viaduct’s arches. This sinusoidal movement of the bridge deck adds value to the user’s crossing, as pedestrians and cyclists physically experience the historical bridge’s geometry. It also animates the otherwise rather simple 180 m long straight line.
This waving geometry in elevation is also found in plan. While the 3.5 m wide crossing, located downstream, is conceived as a direct, straight link between both riverbanks, the bridge deck unfolds upstream to form balconies above the Tarn, reaching a total width of 7.5 m at its largest. Each balcony is equipped with a bench and is located exactly at mid-span of each arch of the railway viaduct, which provides shade and protection to passers-by. The geometry shows great spatial coherence, not only for the new footbridge as an independent object but also with the existing railway viaduct.
Structurally, the footbridge is a seven-span continuous beam. However, to minimize the internal forces in the new structure and to keep the masonry counterfort of the railway viaduct intact, a double support has been introduced on each of the six piers. This reduces the footbridge’s main span from 29 m to 24.5 m. For obvious reasons — weight, structural performance, and construction methodology — the new footbridge is fully designed in steel. Being supported in cantilever from the railway viaduct, the cross-section is a closed box girder, providing sufficient torsional resistance and stiffness.
The fixed point is positioned on pier P3, as centrally as possible, to minimize thermal expansion at both abutments. The other cantilever supports allow for the longitudinal movement of the bridge while transmitting the vertical reaction force and torsional moment. They are therefore doubly hinged on both the footbridge side and the viaduct side.
This project shows that the impact of the new infrastructure over the Tarn goes well beyond solving a mobility issue. It restores meaning to an urban situation that had been spoiled by previous interventions and the vicissitudes of urban history. It also provides a new visual experience to people crossing the Tarn, offering new perspectives on the city that reinforce its historic character.
A subtle dialogue takes place between the compact, uniform brick of the viaduct and the lightness and materiality of the footbridge. This dialogue enhances both structures, forming a coherent new whole that the people of Albi are already embracing.
