Cantilever bridges normally use pairs of cantilevers back to back with
a short beam bridge in between the cantilevers. Modern motorways have
cantilever bridges stretching across them, they have a cantilever coming
out from each side and a beam bridge in between them.
The photograph above is of one of the greatest cantilever bridges the
Forth Bridge. The bridge was completed in 1964 and has a main span of
3,300 feet crossing the River Forth in Scotland. The intentions for
the bridge was that it would carry a railway engine and carriages up
to 260 metres from the nearest support which at the time was quite an
From the image it clear that the huge pillars take up the compression
which are held up by the narrow top members. Attached to these are the
complicated struts and cross bracing which withstand the forces causing
buckling and twisting.
The outer cantilevers have counterweights at the ends to maintain balance.
The bridge was designed and built by Benjamin Baker in the late 1880's
and was one of the first cantilever bridges to be constructed.
|This diagram shows a cantilever bridge supporting a load.
1. Name two basic types of bridges and explain with drawings
and notes how each one carries a load. In your answer you need
to explain where the load forces act and where the resisting forces
2. Research another Cantilever bridge in a different part of the
world. Compare this bridge with the Forth Bridge noting the differences
in size, types of metals used and the amount of traffic that both
are expected to carry? You may wish to use the internet to research
this question and present your answer in a word document?