Gaunless Bridge

Gaunless Bridge was a railway bridge on the Stockton and Darlington Railway. It was completed in 1823 and is one of the first railway bridges to be constructed of iron and the first to use an iron truss. It is also of an unusual lenticular truss design. LocationThe bridge crosses the River Gaunless at West Auckland, Co. Durham. Although never part of the main line, it was on a branch West of Shildon serving Witton Park Colliery. This branch included two rope-worked inclines at Brusselton and Etherley. Between these, wagons were pulled by horses, rather than the heavier locomotives. The bridge was only required to carry the weight of these horse-worked trains. Despite this, a postcard exists showing a locomotive of the 'Director' class on the bridge, possibly during a test or demonstration. DesignIt was designed in 1823 by George Stephenson, who was the chief engineer of the railway. As well as being one of the first iron railway bridges, the bridge is the first to use the lenticular truss design. This design uses two curved girders in a lens shape, one above and one below. The upper member is in compression, as for an arch bridge, and the lower in tension, as for a suspension bridge. The idea is that this forms a balanced truss, where the sideways forces in each member cancel out, being equal but opposite in direction. This leads to a truss with no side forces on its supports and so only requiring simple piers with no need for endways stiffness. Vertical members connect the two girders and support the load-carrying deck of the bridge. These vertical members must also transfer some load between the two girders, as to maintain their lens shape. An efficient truss distributes the load of the deck between the two girders, rather than placing the majority of the load on one truss member, and so requiring it to be excessively strong compared to the other.

Gaunless Bridge was a railway bridge on the Stockton and Darlington Railway. It was completed in 1823 and is one of the first railway bridges to be constructed of iron and the first to use an iron truss. It is also of an unusual lenticular truss design. LocationThe bridge crosses the River Gaunless at West Auckland, Co. Durham. Although never part of the main line, it was on a branch West of Shildon serving Witton Park Colliery. This branch included two rope-worked inclines at Brusselton and Etherley. Between these, wagons were pulled by horses, rather than the heavier locomotives. The bridge was only required to carry the weight of these horse-worked trains. Despite this, a postcard exists showing a locomotive of the 'Director' class on the bridge, possibly during a test or demonstration. DesignIt was designed in 1823 by George Stephenson, who was the chief engineer of the railway. As well as being one of the first iron railway bridges, the bridge is the first to use the lenticular truss design. This design uses two curved girders in a lens shape, one above and one below. The upper member is in compression, as for an arch bridge, and the lower in tension, as for a suspension bridge. The idea is that this forms a balanced truss, where the sideways forces in each member cancel out, being equal but opposite in direction. This leads to a truss with no side forces on its supports and so only requiring simple piers with no need for endways stiffness. Vertical members connect the two girders and support the load-carrying deck of the bridge. These vertical members must also transfer some load between the two girders, as to maintain their lens shape. An efficient truss distributes the load of the deck between the two girders, rather than placing the majority of the load on one truss member, and so requiring it to be excessively strong compared to the other.