page_title: Cantilever bridge
section_title: Origins
hierarchical_section_title: Cantilever bridge / Origins
caption_attribution_description: English: Postcard of Benjamin Baker's human cantilever bridge model.
context_page_description: A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams; however, large cantilever bridges designed to handle road or rail traffic use trusses built from structural steel, or box girders built from prestressed concrete. The steel truss cantilever bridge was a major engineering breakthrough when first put into practice, as it can span distances of over 1,500 feet, and can be more easily constructed at difficult crossings by virtue of using little or no falsework.
context_section_description: Engineers in the 19th century understood that a bridge that was continuous across multiple supports would distribute the loads among them. This would result in lower stresses in the girder or truss and meant that longer spans could be built. Several 19th-century engineers patented continuous bridges with hinge points mid-span. The use of a hinge in the multi-span system presented the advantages of a statically determinate system and of a bridge that could handle differential settlement of the foundations. Engineers could more easily calculate the forces and stresses with a hinge in the girder.
  Heinrich Gerber was one of the engineers to obtain a patent for a hinged girder (1866) and is recognized as the first to build one.  The Hassfurt Bridge over the Main river in Germany with a central span of 124 feet (38 metres) was completed in 1867 and is recognized as the first modern cantilever bridge.
  The High Bridge of Kentucky by C. Shaler Smith (1877), the Niagara Cantilever Bridge by Charles Conrad Schneider (1883) and the Poughkeepsie Bridge by John Francis O'Rourke and Pomeroy P. Dickinson (1889) were all important early uses of the cantilever design. The Kentucky River Bridge spanned a gorge that was 275 feet (84 metres) deep and took full advantage of the fact that falsework, or temporary support, is not needed for the main span of a cantilever bridge.
  The most famous early cantilever bridge is the Forth Bridge. This bridge held the record for longest span in the world for twenty nine years, until it was surpassed by the Quebec Bridge. Benjamin Baker illustrated the structural principles of the suspended span cantilever in the photo on the right. The suspended span, where Kaichi Watanabe sits, is seen in the center. The need to resist compression of the lower chord is seen in the use of wooden poles while the tension of the upper chord is shown by the outstretched arms. The action of the outer foundations as anchors for the cantilever is visible in the placement of the counterweights.
caption: Human demonstration of the principle
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