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Concrete footbridges will use either in situ construction or precast units and may be either reinforced or prestressed. The use of in situ construction allows the greatest versatility. Specially created shapes can be used to improve the appearance. Soffits and ramps may be curved to give flowing shapes. Arched bridges are elegant and the concrete is in compression.
Precast units may be appropriate when a bridge is erected over an existing road or for situations where falsework for in situ construction would be difficulty to install. Bridge width depends on frequency of use and user type. The absolute minimum is 1.2 m but a minimum of 2 m is preferable. If cyclists use the bridge as well as pedestrians, they should be segregated with a minimum width of 3.5 m. Footbridges that form part of bridleways have special requirements, specified by the British Horse Society.
Because of their small scale and light load-bearing requirements, footbridges offer considerable freedom for engineering innovation compared with most other bridge types. Practicality and aesthetics are important considerations. Because of their slenderness, issues such as wind loading, vibrations and the effect of collision must be considered in design.
Acknowledgement: The Concrete Society
Other references:Concrete Society, Current Practice Sheet 126, ´Concrete footbridges´, CONCRETE, November/December 2001.
(Note that copies of Concrete Society Current Practice Sheets can be downloaded from the Members Area of the Concrete Society web site.)