The Müller footbridge, allying safety and aesthetics
After a long period closed to traffic, the Müller footbridge was reopened last spring. This type of structure incorporates a number of special features. Apart from disassembly of the old footbridge, carried out at night and integrated, in collaboration with SNCF, a programme of obviously restrictive track closures, the specific characteristics of this type of architectural achievement should be noted.
Footbridges involve an intimate blend of architectural and structural aspects, aesthetic and long-term approaches, urban pragmatism and social environment. As from the design phase, all the many facets of the project – calculations and technical projections, drawings and mock-ups, financial constraints and environmental ambitions, had to interleave in a natural way. For DVVD, the choice of a suspension bridge with a single span, finely tuned, transparent and original, was quickly made. The Müller footbridge is the first French suspension bridge crossing SNCF rail track. But this choice was also an ambitious one, involving delicate work on the guard rails, flooring, lighting, access points, etc.
The guard rails in question
Foremost among the environmental features of the footbridge are the guard rails. These are of particular importance in an environment where the safety of pedestrians, cyclists and SNCF passengers is a major issue. Without even mentioning the height of the footbridge and the risk of falling, it should be emphasised that the footbridge passes over high voltage electrified cables. In other words, there can be no question of amusing oneself by "nipping over to the other side" - at the risk of electrocution. Another constraint: the guard rails have a negative impact on the wind stability of the footbridge, the more so as the bridge is suspended!
Tests were therefore run in the CSTB wind tunnel in Nantes. Modelling results left a doubt concerning the stability of the footbridge profile. Exchanges between the CSTB and DVVD led to replacement of the solid guard rails initially planned with porous guard rails, accompanied by opaque horizontal deflectors. This modification met safety constraints and stabilise the structure. The guard rails of the Müller footbridge now impart a certain rhythm to the crossing following a 4-metre grid pattern. Comprising a stainless steel anti-projectile mesh, they have the triple advantage of transparency, strength ? and... an absence of graffiti! The footbridge is clad to a height of 2.5 metres, sufficient to dissuade any dangerous impetuosity.