History and Development of Steel Railway Bridges - Design of Modern Steel Railway Bridges - page 22

FIGURE 1.11b The Tay River Bridge, England after the 1879 collapse.
A revitalized interest in the cantilever construction method occurred, particularly
in connection with the erection of arch bridges. Early investigations by Stephenson,
Brunel,andEadshadillustratedthattheerectionoflongarchspansusingthecantilever
method ∗ was feasible and precluded the requirement for falsework as temporary
support for the arch.The cantilevered arms were joined to provide fixed or two-hinged
arch action † or connected allowing translation of members to provide a statically
determinatestructure.Thecantileverconstructionmethodwasalsoproposedforlong-
span truss erection where the structure is made statically determinate after erection by
retrofitting to allow appropriate members to translate. This creates a span suspended
between two adjacent cantilever arms that are anchored by spans adjacent to the
support pier, which provides a statically determinate structure. ‡ Alternatively, the
cantilever arms may progress only partially across the main span and be joined by a
suspended span erected between the arms. § Other benefits of cantilever construction
are smaller piers (due to a single line of support bearings) and an economy of material
for properly proportioned cantilever arms, anchor spans, and suspended spans.
Iron trusses continued to be built in conjunction with the rapid railroad expan-
sion of the 1860s. However, in the second half of the nineteenth century, steel
started to replace iron in the construction of railway bridges. ∗∗ For example, the iron
Kinzua Viaduct of 1882 was replaced with a similar structure of steel only 18 years
∗ Often using guyed towers and cable stays as erection proceeds.
† Depending on whether fixed or pinned arch support conditions were used.
‡ Statically indeterminate structures are susceptible to stresses caused by thermal changes and support
settlements. Therefore, statically indeterminate cantilever bridges must incorporate expansion devices
and be founded on unyielding foundations to ensure safe and reliable behavior.
§ This was the method used in the 1917 reconstruction of the Quebec Bridge.
∗∗ In 1895, steel completely replaced wrought iron for the production of manufactured structural shapes.