Bockstael

Light, the footbridge unfolds its heavy concrete mass, skimming the ground, for almost sixty metres. It is lashed to the edge of the bridge deck and supported by two steel columns, one short and one long, acting as ball joints and by a single support at the low point. The structure as a whole is post-tensioned: the steel cables were put under tension after the concrete had set. Like a large pin, it features two straight sections connected by a third, in a very tight bend. In cross-section, a constant triangular section streamlines the silhouette, reduces the material and twists, following the twisted path of the structure. The concrete is left unfinished, the post-tensioning having the advantage of limiting cracks, ideal for an outdoor environment. Only a guardrail made of tubular metal profiles ornaments this flat surface, drilled into the concrete and topped with an H-shaped profile that can be found in other places in the park as a handrail. A line of LED lights has been discreetly integrated into it and illuminates the steps of passers-by. 

The challenge and elegance of the proposal lies in the conceptual and physical plasticity of the work, as if this concrete beam had literally been bent. The fold has just taken place, it cannot be unfolded, the work does not explain to us at first how or why this bend makes it hold up. Plasticity is understood as the capacity of a material to be shaped after the point of no return and before breaking. The uniqueness of the material and of its implementation, a concrete that carries and displays itself as a finish, underlines the assertive expression of this sculpture. However, the simple and visible expression of the work actually conceals the complexity of the invisible lines of force and moments, which are present everywhere and regulated down to the millimetre by the precise but changing position, depending on the section of the work, of the post-tensioning cables and strands embedded in the concrete. The only indication of their presence are the two ‘doormats’, two rectangles at the top and bottom of the structure that betray the place where the cables are tightened by means of screw jacks. Or the position of the two steel columns, at the place of the moments of force, which give the ramp a sense of balance. These crutches, which take up the vocabulary of the steel structure of the host bridge, in a metallic structure, are displayed as props well placed at imaginary breaking points.

The concrete work would not exist without the short-lived existence of a first construction, more reticulated, complex, resistant. The formwork itself was the construction of the construction. A large part of the time spent on the site was devoted to the complex construction of this giant mould. A wooden bridge with a complex and meticulous implementation, a phantom and a mise en abime of the final bridge, before the drying time of the concrete seals the material in a few days and finally reveals the design. The landscaping itself answers the question as to whether a landscaped embankment would not have simplified things. Indeed, the simplicity of the treatment of the ground, spared any retaining structure and large volumes of embankment, contrasts with the curve and slope of the ramp. The choice of a structure, a footbridge, in dialogue with the existing bridge, offers a significant landmark in the geography of the park, whose singular character perhaps makes it easier to accept the overflow of the normative slope. The bridge adds another link to open up the park, and skaters, pedestrians and cyclists can glide along it, in the landscape and filled with joy.