On the conceptual design of R/C footbridges with the deck supported by shells of minimal surface

Designing footbridges (pedestrian bridges) with the deck supported by R/C shells is an interesting approach, that is illustrated in this paper. The advantage of this structural solution is that R/C shells can be shaped in accordance with the “minimal surface” criterion. In so doing, the shells are mainly subjected to biaxial compression with membrane stresses. The shape of the minimal surface shells is first studied by suitably choosing the position of the boundary restraints and of the applied forces. Then, through a form-finding process containing an optimisation algorithm, different R/C footbridges with architecturally-valuable shapes are worked out. It is also shown how Maillart’s bridges can be re-shaped in order to avoid the well known undesired bending effects, even though some tensile stresses may occur. In the case of footbridges having a straight deck, it is shown how: (a) the choice of the position of the deck supports, (b) the shape of the shell close to the abutments, (c) the arrangement of the shell edges along the abutments, and (d) the stiffening beams (if any) along the free edges can minimize the bending effects and improve the behaviour of this type of structures.