Project Description
This structure, with a length of approximately 30 m (98.4 ft) and a width of 4.5 m (14.8 ft), rests on a frame structure composed of two longitudinal inclined truss beams and a horizontal beam. Fully welded, it supports a secondary beam grid on which a concrete slab and cladding are placed.
The steel structure, finely modeled in 3D using RFEM 6, was the subject of a precise calculation that took into account the specific constraints of this type of structure, such as dynamic behavior, aesthetics, and neoprene supports. The project reflects ACML's ability to design, manufacture, and install both technical and architectural structures.
Out-of-Plane Buckling Resistance of Upper Chords
The design of the pedestrian bridge required particular attention to be paid to the behavior of its U-shaped truss beams. The upper chords of the structure, subjected to significant axial compression, did not provide direct resistance to out-of-plane buckling. To ensure their stability, the engineers used advanced modeling with the “Structure Stability” add-on.
This precise calculation allowed to identify the critical load for the members and to deduce the buckling length.
Neoprene and Dynamics
Like most pedestrian bridges, this one was checked in accordance with the French guidelines SETRA.
In this project, the bridge rests on neoprene supports of Type C, which are capable of absorbing longitudinal forces depending on their level of stiffness.
The engineers had to find a delicate compromise: too low a stiffness would have caused excessive displacement and a too low vibration frequency, while too high stiffness would have limited movement but generated excessive stresses due to temperature variations. After numerous discussions with the supplier, SNAC, and extensive modeling, the optimal solution was defined. It allows the pedestrian bridge to meet comfort criteria while complying with safety and durability requirements.
Fully Welded Structure
The unique feature of the pedestrian bridge is that it does not have any bolts on its main structure. Fully welded, the structure is impressive in size—30 m (98.4 ft) long, 4.5 m (14.8 ft) wide, and 2.1 m (6.9 ft) high—with a total weight of 27 tons (30 US tons).
With such dimensions, it was impossible to transport the bridge in one piece. Therefore, the teams decided to manufacture the pedestrian bridge in three separate sections. After a pre-assembly in the workshop to check the precision of the assembly and the correct fit of the frames, the first two sections were welded before being transported to the construction site.
On site, the final assembly was carried out with meticulous care, before the structure was lifted in one piece by crane onto its neoprene supports. This precision operation demonstrates the expertise of the ACML teams.
| Location | La Babinière 44240 La Chapelle-sur-ErdreFrance |
| Investor | Nantes Métropole / Semitan |
| Architect | Lavigne Cheron
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| General Contractor | ACML |
