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Chepstow BridgesWhen William Fitzosbern was looking to build his castle in the west after the Norman invasion, Chepstow - surrounded on two sides by large rivers - was the ideal location. But for people with more peaceful intentions, the rivers have proved an obstacle and bridges have been a necessity. The original motorway bridge over the Severn is 31 years old, but the first bridge across the Wye was built by the Romans and remained in use hundreds of years after they left Wales. Bridging the River Wye Chepstow Bridge The Normans built a bridge in the 13th century and wooden bridges spanned the river up until the beginning of the last century when the present iron bridge was built. In 1810 magistrates who inspected the bridge decided that it was "in decay" and asked for estimates to patch it up. John Rennie, the engineer who built Waterloo Bridge in London, submitted a report relating to the repair of the bridge, but recommended replacement rather than repair and put the cost of a new bridge at £41,890. but that was considered too expensive. No action took place until after an accident involving further damage to the bridge and the loss of six lives. The contract for the bridge was let on 14th June, 1814, at an estimated cost of £17,150 - a figure which rose to nearly £20,000. The bridge was made of cast iron, the total length being 372 feet (113m) with the span of the centre arch being 112 feet (34m). The bridge was built by John Rastrick of the Bridgenorth (Shropshire) firm of Hazeldine, Rastrick & Brodie. The design has been credited to Rennie. Rastrick is understood to have produced a much more elegant version of the plans that Rennie submitted for the repair of the old bridge. The bridge was opened on Wednesday, 24th July, 1816, with an elaborate form of ceremony: "Company to assemble in the Square at One o'clock. The Procession. A pair of Colours. Engineer and Surveyor. Workmen in Divisions according to their order, walking two and two. A Pair of Colours. Band of Music. Solicitor. Magistrates walking abreast Seniors in the Centre. Gentlemen, Farmers, Tradesmen, and others who may chuse to join the Precession walking two and two". The age of the railway made a second bridge across the Wye necessary and the tubular suspension bridge that took the Cardiff to Gloucester railway line across the river was designed by one of Britain's most famous engineers - Isambard Kingdom Brunel. The line from the present station (then called Chepstow West) to Swansea was opened on 18th June, 1850, and the line linking the Chepstow East station at Tidenham and Gloucester came into use on 19th September, 1851. Passengers were taken between the stations by coach until the bridge was opened in July, 1852. Brunel's tubular suspension bridge was dismantled and replaced by the present span in 1962. The latest bridge to cross the Wye was the road bridge opened in 1988 to take the inner relief road, the A48, across the river. Prior to that all road traffic into Gloucestershire had to pass through the town and over the old cast-iron bridge. Bridging the River Severn Aerial View of Severn Bridge The idea of a bridge across the Severn had been a dream for 1,900 years but it took modern techniques to solve the problems. Until the queen opened the bridge on 8th September, 1966, the only ways to get from the west of England to South Wales by road was by taking a 50-mile detour around Gloucester or face a long wait to board a ferry. By the 1960's the Beachley-Aust ferry was being swamped. The largest of the three ferries carried just 17 vehicles! Railway passengers have avoided the long detour via Gloucester since the Great Western Railway opened their Severn Tunnel in 1886. The first designs for a bridge over the River Severn were submitted as early as 1845 but no attempt was made to use them. The task of building the bridge to a modern design was given to the Associated Bridge Builders consortium which had previously built the Forth Bridge in Scotland. Work on the 90,000 ton anchorage and foundations began in 1961. The towers are 455 feet (137m) high and comprise of 55ft 6in (17m) sections erected using a climbing structure which could lift itself up each section in around six hours. The bridge was designed to withstand winds of 100mph but wind was the biggest obstacle in the construction. Acceptable wind speeds dropped as the towers grew and in the latter stages winds of 10mph could stop work. The 60 feet (18m) long deck sections, 75 feet (23m) wide and 10 feet (3m) deep, were floated out from the yards of Fairfield Mabey and winched into position. The road surface is 38,000 square yards of hand-laid mastic asphalt. The bridge was built five years four months, and the complex, including the crossing of the Wye and motorway links, cost a total of £16m, compared with a projected £238m for the second crossing built a couple of miles downstream and opened spring 1996. When the bridge opened, its span was the seventh largest in the world. In the first full year of operation 6 million vehicles used it, and today an average of 50,000 vehicles a day use it. (3 times the first-year volume!) The highest daily usage was on 26th May, 1989, when 76,182 vehicles crossed it. Although high winds often close the bridge to high-sided vehicles, until the end of 1991 it had been completely closed on just 11 occasions.
Brunel's Railway BridgeAt Chepstow, during the building of the Great Western Railway, Isambard Kingdom Brunel was faced with the task of taking two tracks of 7 ft gauge across a 600 ft gap. The bridge cost £77000 - Brunel had to sink foundations far below the water level of the river Wye which has the second highest tidal range in the world. His first thoughts were on a timber trussed arches type, but the Admiralty insisted on one with a headroom of 50 ft above water over a 300 ft width, as sailing ships used to go up to Rastrick's iron road bridge less than half a mile away, this being the location of the customs house. River navigation also had to be considered as traffic on the Wye still went to Brockweir, Redbrook and Monmouth.
The two sides of the river are very different. On the Gloucester side, there is a 120 ft limestone cliff whereas on the Monmouth side, there is level wash land. Therefore the bridge is not symmetrical - unusual for Brunel. He planned a single high level span of 300 ft long and 100 ft above high water and across the wash land by three approach spans each 100 ft long. The cliff forms a natural end one side, the railway emerging from a cutting. The other end of the bridge is supported by cast iron piers which were sunk through soft ground until they found a solid foundation and then filled with concrete. The railway then continues on a high embankment into Chepstow station. Brunel decided to use tubular construction as tubes are ideal to carry the stresses and weigh much less. The tube would hold apart the ends of "suspension chains" which would look after the tensile forces in a truss carrying the plate girder railway bridge below. Brunel argued that the tube would be stiff, and with the railway deck "strutted" and "trussed" to the tube, the excessive distortions, to which a suspension bridge is liable under the passage of concentrated load, would be avoided. Each 300 ft span depended upon a 9 ft tube of riveted wrought iron plates to resist the inward strain of the chains. Brunel built his tubes on the flat land behind the shore of the right bank of the river; they had to be raised more than 100 ft. and lifted clear of shipping within 12 hours. Brunel kept the weight as low as possible. The tubes were 9 ft in diameter, 312 ft long and weighed a mere 138 tons apiece, but were not self-supporting. Without the inward pull from the chains at each end, and the upward support of the posts or struts of the "trusses", the tubes could not be expected to carry their own deadweight. Temporary trusses were therefore used and tested. The tube was built on low ground and floated by manoeuvring into launching position at right angles to the bank. A pontoon of 6 barges was brought under the overhanging tube. The tube was launched end on across the river. On 8th April 1852 launch began at 9 o' clock A.M.. The tube was lifted during the course of the day well clear of ship masts. Shortly afterwards the tube reached tower top level, built of cast-iron above the pier cylinders which Brunel had sunk by "pneumatic method", the upper end being sealed and compressed air introduced to keep water out. The down line spans were opened for single line traffic on 14 July 1852. The up line spans were dealt with in the same way and completed the following April. The secondary stresses caused by deforming of the truss were alarmingly high and in 1944 one of the plate girders in the land spans partially collapsed. For many years, all trains crossing Chepstow bridge were restricted to speed limits of 15 mph.. The right-hand main girder of the down line broke on 4th April 1944. Temporary repairs were made. Gradually, more extensive repairs were made, and by 1962, the bridge had changed completely, being rebuilt into an inverted box girder form. After Chepstow bridge, Brunel built his last great railway work, the Royal Albert bridge at Saltash. |
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If you have any comments about The Striguil Zone, please contact webadmin@striguil.co.uk ©Russell Higgins 2003 Some of the information about Chepstow is extracted from the
Town Guide. |
