A Conceptual Approach to Design Of Funicular Spatial Arches In Footbridges

A funicular spatial arch is a compression-only form free of bending stresses thanks to its warped geometry, i.e. which cannot be contained within a plane. Therefore, its design and construction may become more complicated than for classical planar arches. However, these arches can be, simultaneously, very efficient in structural terms and aesthetically pleasing. The great potential of these type of structures, that reduces dramatically the bending stresses due to out-of-plane loads, has not been fully developed yet. So far, very few theoretical studies have been carried out, and only some design proposals have been eventually built, such as the pioneering Ripshorst footbridge in 1997.

Thus, this paper tries to help to understand, from a conceptual point of view, the design process and advantages of a funicular arch (the so-called antifunicular). Some form-finding methods that can be used are briefly described, and the successive design steps are studied, beginning by the selection of the load case to be considered. The process is always iterative and may lead to redefine the structure topology, normally due either to functional requirements, such as clearance needs, or to aesthetical restrictions, such as self-imposing a previously defined cable arrangement. The paper finishes by emphasizing that the process cannot choose by itself the most efficient form, which must be selected by applying a secondary criterion, normally related to serviceability states.

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