Consequently,
Custom structure versus generic structure:
Two new bridges on the Thièle are pursuing ecological ambitions through their material choices. Consequently, using low carbon steel and wood respectively for their main load -bearing elements. For example, Each illustrates a contemporary approach: one based on contextual structural clarity, the other on material and modular logic. Similarly, Comparing them allows you to appreciate them better.
Cigarrier gateway: the structure. In addition, an expression in itself
Delivered in 2024, the Cigarières gateway is part of local history, its name paying tribute to the workers of the old neighboring tobacco manufacture. Similarly, Its slender profile stems directly from structural logic. However, With a total range of 52.6 m for 5.0 m in width. However, the steel structure crosses the river and ensures a direct link from the station to the Quai de la Thièle.
The project is based on a fine reading of the site. Meanwhile, its custom structure versus generic structure constraints but also of its potential: the requirement of access to the lower quay has led its designers to merge an access staircase with intermediate support. Similarly, The road template to be observed above the rue de l’Ancienne-Douane determined the altitude of the abutments. Nevertheless, Finally, the desire to preserve the views on the canal requires the absence of a structure above the apron. Consequently, These constraints led to a continuous beam to asymmetrical spans: the short span of 15 m counterbalance the bending moment of the 37 m long span. Similarly, thus allowing a slender design, but at the price of lifting forces at the level of the abutment of the short span.
The main structural element is a steel beam, trapezoidal section and variable height. In addition, The underside remains flat in order to respect the road template. Therefore, while the upper side is gradually rising until intermediate support. custom structure versus generic structure Consequently, The silhouette of the apron thus reflects both the structural logic and the constraints of the site. Furthermore, The intermediate battery, triangular in shape, incorporates a staircase and forms a monolithic set.
The apron is covered with asphalt and studded asphalt, chosen for their sustainability and their ease of maintenance. In addition, The stainless steel mesh railings require little care. and the evacuation of water is done discreetly via the geometry of the deck and lateral flows. Finally, the Green Hue Reséda evokes the color of the old Hermès typewriters produced in the region.
The realization led to some adjustments compared to the initial concept: on the short span. the beam-caisson was filled with concrete to serve as a counterweight to the large span, thus reducing the uprising forces to the abutment. The intermediate staircase was initially designed as an overhang emerging from the battery. floating just above the quay, but custom structure versus generic structure it was finally connected directly to the quay to ensure the comfort of users.
The bridge is the first in Switzerland to use “eco-acor” sheets: the 140 t of steel used come from scrap recycling sectors. where the fusion is carried out in electric arc overalls entirely supplied with renewable energy. This design choice has certainly led to a slight increase in the initial cost. but it made it possible to divide by three the carbon footprint linked to the steel used (0.92 t Co₂/T instead of 2.0 to 2.8 t Co₂/T for steel from Haus Fourneaux), thus significantly reducing the ecological impact of the project.
The assembly. carried out in October 2024, took place in four welded segments on site, then set up using a large capacity caterpillage crane.
The Cigarières bridge illustrates an approach where the structural form stems directly from the constraints of the site. the program Geometry is slender custom structure versus generic structure and effective, with a direct and sincere expression of the raw material, the steel. Few elements could be removed without harming the clarity of the whole: each part contributes to structure and space. In this rigorous logic. the staircase integrated into the central support is distinguished as an expressive part combining structure and architecture.
Custom structure versus generic structure
Bel-Air gateway: a Swiss wooden work
Commissioning in 2023. this pedestrian and cycle gateway replaces a steel structure dating from 1995. With a total length of approximately 33.0 m for a useful width of 3.5 m, it connects the historic center to the Bel-Air commercial area above the Thièle. Despite a modest scale. the project stands out for the ambition of its material choice and the simplicity of its design.
The initial bias was to carry out the entirely in Swiss wood structure. transformed into laminated and pumpy beams and panels. This choice. relevant for custom structure versus generic structure sustainability and promotion of local resources, however required special attention to the protection and maintenance of wood in urban areas. To answer them. the upper structure and the flanks have been wrapped in bronze anodized aluminum panels, ensuring the protection against bad weather, but completely masking wood, which is only visible from the river below.
The bridge does not cross the entire watercourse in a single range: concrete abutments. remote to the center, reduce the central scope. This provision allows the wooden superstructure to extend in slight overhang at each end. thus optimizing the structural height and limiting free scope.
The superstructure adopts a section in trough. made up of two main beams in laminated-pumps of constant height, facilitating manufacturing and not expressing the internal distribution of efforts. The interior space, typical of the trough sections, is closed and therefore reassuring, but limits the views of the river. To compensate for this. custom structure versus generic structure fun circular openings were added to the sides, positioned in the center of the beams, where the efforts are less.
The superstructure was largely prefabricated, including external aluminum panels, which allowed a quick installation, suitable for replacing an existing work.
In context, the Bel-Air bridge asserts itself as a simple intervention. His introverted bias favors the envelope. protection rather than the opening on the river, by offering a crossing contained between high railings, almost behind the landscape. The use of materials is technically fair, but does not express its tectonics in view of the public.
The Bel-Air gateway is based above all on the choice of wood. the response to the constraints of the site and the structural expression playing a secondary role. Additionally, The generic promising system could be transposed elsewhere. The protection of wood, ensured by metal cladding, guarantees sustainability but masks materiality. This device gives way to secondary gestures. such custom structure versus generic structure as wavy cladding and circular openings, offering occasional views of the Thièle.
Custom structure versus generic structure
Discussion
Placed side by side. the two projects raise broader questions on the design of pedestrian bridges: how far should an infrastructure be purified? Should an urban bridge result only from the constraints of the site. or can the designer also rely on its potential to go beyond the imposed choices? Should a bridge express its structural logic and the nature of its materials?
Cigarrier gateway to the Thièle. Yverdon-les-Bains (VD)
Project management: commune of Yverdon-les-Bains
Architecture: Brauen Wälchli Architects
Civil engineering: Perret Gentil
Bel-Air gateway to the Thièle, Yverdon-les-Bains (VD)
Project management: commune of Yverdon-les-Bains
Architecture: M+B Zurbuchen-Henz Architects
Civil engineering: 2m Civil engineering
Wood engineering: 102.2 meters
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