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Railway Structures
Pre-stressed Concrete

The major advance that greatly expanded the utility of concrete, was the development of pre-stressed concrete. This has steel reinforcement in the form of wires that are stressed, so they are in tension as the concrete hardens. The resulting force keeps the concrete in compression, overcoming its tensile weakness. The technique was developed between the wars, principally by the French engineer, Freyssinet, and enabled significantly longer and stronger concrete beams to be used. Following experiments at Southall in 1938, the Pre Stressed Concrete Company started manufacture of beams at Tallington, Lincolnshire. This was the first production of pre-stressed concrete beams in Britain and the Tallington plant, now owned by Tarmac Concrete Products Ltd, remains in production to this day. Since 1942 its output has included pre-stressed concrete railway sleepers.

Following the outbreak of war a significant number of pre-stressed concrete bridge beams were made at Tallington for use in repairing bomb-damaged structures. Exactly how many beams were manufactured and where they were used is not recorded. The majority appear to have been used for post-war reconstruction. The first pre-stressed concrete bridge to carry a railway, was the Adam Viaduct, near Wigan Wallgate, built by the LMS and the Pre Stressed Concrete Co in 1946.

Kingston Bypass bridge, Hinchley Wood Kingston Bypass bridge, Hinchley Wood, photographed on 22nd September 2007.

photograph by Gregory Beecroft

 
Kingston Bypass bridge, Hinchley Wood.

photograph by Gregory Beecroft

Kingston Bypass bridge, Hinchley Wood

When the Kingston Bypass was built between 1924 and 1927 the reinforced concrete bridge over the railway at Hinchley Wood required two spans. Columns between the tracks support the concrete beams. When the bridge was widened using pre-stressed concrete beams, only a single span was needed. This was possible because of the greater strength of pre-stressed concrete and particularly its ability to resist the tension in the lower edge of the beams.

Elmers End Road bridge, Elmers End Elmers End Road bridge, Elmers End, photographed on 27th October 2007.

photograph by Gregory Beecroft

 
Station Road bridge, Otford, photographed on 21st October 2007.

photograph by Gregory Beecroft

Station Road bridge, Otford

Elmers End Road bridge (left) is a typical example of a bridge reconstructed with a deck of pre-stressed concrete beams. The parapet is of concrete, in order to comply with modern containment standards, but has been faced in brick. The underside of Station Road bridge at Otford (right) clearly shows the pre-stressed concrete beams.

Skew bridge, Salisbury Skew bridge, Salisbury, photographed on 2nd May 2009.

photograph by Gregory Beecroft

Skew Bridge, between Salisbury and Wilton, was widened in 2004, by adding pre-stressed concrete beams either side of the original brick arch.

Pre-stressed concrete underbridges are less usual than overbridges.

Trinity Road bridge, Wandsworth Town, photographed on 22nd September 2007.

photograph by Gregory Beecroft

Trinity Road bridge, Wandsworth Town
 
Trinity Road bridge, Wandsworth Town Trinity Road bridge, Wandsworth Town.

photograph by Gregory Beecroft

Trinity Road bridge takes the Reading line over a dual carriageway at Wandsworth Town. It was constructed by jacking a series of rectangular cross-section concrete tubes through the railway embankment. These formed the abutments and the centre pier, each comprising three separately jacked sections. The bridge deck could be built off those, after which the remaining embankment material was removed. The span over each carriageway is 15 metres wide and comprises 33 pre-stressed concrete beams, plus the parapet beams.

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This page was created 9 January 2010

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