Dr. N. Subramanian,
Consulting Engineer, Gaithersburg, MD 20878, USA
IntroductionFootbridges have a longer history than road or railway bridges. Ancient footbridges comprised of natural materials such as roots of trees, ropes, stones, masonry, and wood. Modern footbridges are built using reinforced concrete, steel, prestressed concrete, and fibre reinforced plastics. Though earlier footbridges were built using beams and arches, current footbridges are built in various configurations like inclined arch, trusses, stress-ribbon, cable stayed, cable suspended and a combination of these forms. In recent decades, footbridge designers have been able to push the boundaries of what is possible, much further than ever before. This is largely due to growing capabilities in computer visualization and analysis techniques, as well as developments in materials technology and other factors, with the result that creative designers are able to imagine and create more adventurous designs. However, such imaginative and creative designs should obey economic, environmental, social, and other constraints, in order that the built footbridges are safe, economical, durable, aesthetic and sustainable.
A bridge or a footbridge leaves an impression, and that impression remains as long as the bridge remains; hence bridge designers should strive to create something that is beautiful. Modern technology and tools provide ample opportunity to create dramatic bridges which not only provide safe passage but also result in creating adventurous structural and artistic expression. However, it is not always appropriate to build extravagant foot bridges, just because it is possible to do so, and in many cases the right solution may be much more modest and gentle.
A variety of special characteristics set footbridge design apart from other bridge work. Some of these special characteristics are (Wells and Clash, 2008):
- Live load actions are not significant in comparison with dead load actions; however dynamic behaviour must be carefully studied.
- The light loadings of footbridges, allow structures of extreme delicacy and simplicity to be built and make expressive or experimental designs economically viable.
- Unlike bridges (which are usually conceived, planned and designed by structural engineers), footbridges are built in urban environment and hence may require collaboration between the architect and the structural engineer. The relative input from them varies widely between projects. However, it is possible to build footbridges which are lightweight and have elegance and slenderness.
- Many types of structural materials such as steel, concrete, prestressed concrete, masonry, timber and fibre-reinforced plastics, and a number of different forms like simple beam, arch, truss, stress-ribbon, cable stayed, and cable supported systems could be used efficiently.
- As the user of a footbridge will have a slow speed, it will allow him/her to have a slow and measured interaction with the design of the bridge and its surrounding environment, which may demand the utmost attention to the design of its component parts. As the parts of a footbridge can be touched, the tactile and visual details must be carefully planned and executed.
- Construction technique can have a significant impact on form.
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