The Callender-Hamilton bridge is a modular portable pre-fabricated truss bridge. It is primarily designed for use as permanent civil bridging as well as for emergency bridge replacement and for construction by military engineering units. Assembling a Callender-Hamilton bridge takes much longer than the more familiar Bailey bridge as it is made up of individual lengths of galvanised steel bolted together with galvanised high-strength steel bolts, all of which require torque settings. It is stronger and simpler in design concept than the Bailey bridge.
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The Callender-Hamilton bridge system was designed by the New Zealand civil engineer, A. M. Hamilton, and patented by him in 1935. The system is currently fabricated by Painter Brothers, Hereford, operating within the Balfour Beatty Power Networks Division. [1] The former name of Balfour Beatty was British Insulated Callender's Cables.
Hamilton's bridge concept was inspired by his work between 1928 and 1932 as principal engineer on the 'Hamilton Road' through Iraqi Kurdistan. He described the building of this road in his book, Road Through Kurdistan: Travels in Northern Iraq, 1937. Hamilton became aware of the need for strong, adaptable bridges made from simple components that could easily be transported and erected in remote locations or on difficult terrain. Hamilton’s patent was later partly breached by the design of the Bailey bridge. He successfully claimed breach of patent to the Royal Commission on Awards to Inventors. [2]
The Callender-Hamilton bridge system is a prefabricated Panel/Floor Beam/Deck system designed to span bridging lengths ranging from 30 to 150 metres with road widths of one to three or more lanes. The design uses Warren Trusses and is centred on a series of gusset plates that allow the direct attachment of the longitudinal, diagonal, vertical, and cross framing members. Centralised connection points increase the speed of construction and allow identical panels to be fabricated from identical members and then installed on site. An important feature is that all connections are bolted, so removing the need for onsite welding.
The bridge is usually built on falsework. A reinforced concrete deck is then superimposed on, and acts compositely with, the fabricated steel truss deck, thereby eliminating the use of scaffolding. A steel orthotropic deck, steel open grate deck or a timber deck are alternatives to a concrete deck. As with the Bailey bridge, a useful feature of the Callender-Hamilton bridge is that it can be assembled entirely on one side of a gap and with a removable launching nose added then be projected to the other side. [3]
All bridge elements are small enough to be transported by road and site operations can be carried out without skilled labour, special plant or heavy equipment. Because of the modular design, repairs are as structurally efficient as the original construction and at the end of service dismantled bridges can be reduced to initial components for reuse. Salvability is high due to the galvanisation of each individual component.