The load-span ratio recommends the use of the metal truss as structural model. In order to resist the strong torsion stresses associated with the support-less zigzagging shape of the bridge, we need to structurally activate all the planes of its distorted volume. Together, the vertical and the horizontal surfaces of the bridge behave like a three-dimensional beam, working as a whole, like a tube that is deformed along the direction of its axis.