The design of small suspension bridges

Suspension bridges rely totally on the integrity of their main suspension cables. Small suspension bridges usually have cables which are supplied as prefabricated components complete with the end anchorages made from a single casting or forging. The integrity of such anchorages relies on testing of the design with full-scale tests to failure and testing of the production with ultrasonics and other methods. In Europe the Eurocodes now require that bridges are not susceptible to disproportionate damage resulting from any single failure or event. This seems to imply that in future small suspension bridges will be designed with multiple anchorages so the bridge can survive the loss of any one of them. This paper considers the implications of this change and looks at systems with multiple cables in parallel. The effects of an anchorage failure are quantified. The force distribution between components is considered together with the effect of tolerances on the assembly of the cable system. It is shown that the new requirements will probably affect the whole cable system in a fundamental way, both in the components and in the configuration of the cables and hangers.