Dumb Bell Bridge (MLN12263), Taplow, Buckinghamshire

Summary

An underbridge designed by IK Brunel spanning the A4, with a single skewed semi-elliptical arch, set in a tall embankment. Erected c.1838 and widened on the north (Up) side c.1875-84.

Description

MATERIALS: London stock brick, with Bramley Fall stone coping and string course. Large patch of engineering brick repair on the east abutment of the north (Up) side. Small metal ties inside the north (Up) arch ring.

DESCRIPTION: single 32ft (9.8m) semi-elliptical span, skewed across the road. Detailing and materials are generally consistent between the c.1838 south (Down) face and the c. 1875-84 north (Up) face. A straight joint between the two phases is visible in the soffit of the bridge. Both elevations with bold stone cornice/string course and abutments treated as broad pilaster strips. Originally with a stepped brick plinth, but this has been cut back.

Some variation between the two façades:

South (Down) side: the c.1838 elevation, with radiused abutments, on top of which the parapet steps up. The west abutment projects slightly to form a rectangular enclosure for pedestrian steps from road to rail level. These were approached through the tall semi-circular opening. The opening is now closed by a timber fence and gate; it is not clear if the steps survive. The east abutment adjoins a long raked wing wall following the skewed line of the road. The brick arch ring has been damaged by road vehicles.

North (Up) side: the c.1875-84 elevation is slightly simplified. The abutments are not curved. The east abutment is rectangular in plan but has blank elevations and no stairs; the west abutment is splayed into a long raked wing following the skewed line of the road.

History

The Great Western Railway was authorised by an Act of Parliament in 1835 to construct a line from London to Bristol. At 118 miles this was slightly longer than the other major trunk railway of its time, the London and Birmingham (112 miles) and considerably longer than other pioneering lines. Construction of the line began in 1836, using a variety of contractors and some direct labour. The first section to be completed, from London to Maidenhead (Taplow), opened in 1838, and thereafter openings followed in eight phases culminating in the completion of the whole route in 1841.

The engineering of the railway was entrusted in 1833 to Isambard Kingdom Brunel (1806-59), who was already known for his engineering projects in Bristol. More than any other railway engineer of his time he took sole responsibility for every aspect of the engineering design, from surveying the line to the detailing of buildings and structures. He sought to achieve as level a route as possible and, working from first principles, he persuaded the Directors of the GWR to adopt a broad gauge of 7ft 0¼ in rather than the then standard (4ft 8½in) gauge in use on other lines. A two track broad gauge line was 30ft wide, and this determined the span of the overbridges and other structures. Except for larger bridges such as Maidenhead Bridge, the majority of Brunel’s masonry bridges did not need to be as innovative as his works in timber and iron, and his structures followed the typical architectural idioms of his time, but they were all beautifully detailed and built and together they formed integral parts of a consistently-designed pioneering railway.

By the 1870s the growth of traffic, especially at the London end of the route, necessitated the widening of the line from two to four tracks. This was carried out in two stages, from London to Taplow in 1875-84 and from Taplow to Didcot in 1890-93. By the time of these widenings the broad gauge was being phased out (the final conversion to standard gauge took place in 1892), and the design of the extended or new structures took this into account. However the designs were exceptionally sympathetic to Brunel’s original designs, in form and detail; also in the choice of materials, although engineering brick, seldom or never used by Brunel, began to make an appearance in the 1890s. The engineers chiefly responsible for the widened lines, whose names appear on the surviving archive drawings, were William George Owen (1810-85), Lancaster Owen (1843-1911) and Edmund Olander (1834-1900).

Dumb Bell Bridge was built c.1838 (Contract 5L) to carry the line over the London-Bath Turnpike (A4), and takes its name from a now-demolished coaching inn known as the Dumb Bell Hotel. The acute angle at which the line intersects with the road meant that a skew underbridge was required, a technical challenge to which Brunel responded with considerable ingenuity. The angle here is so sharp (about 30 degrees) that a skew arch aligned with the tracks themselves would have been impossible; Brunel initially considered eliminating the skew altogether by means of a conventional tunnel, but finally settled on a more elegant solution with a 45 degree skew and angled fascias flanked by tower-like abutments. Early drawings show these crowned with Italianate loggias like those initially proposed for Maidenhead Bridge, and although the loggias were ultimately omitted in both cases, the two bridges are closely related in their design. The abutments also contained stairs giving access to the original Maidenhead Station, which stood on the embankment immediately to the west of the bridge, and served as the GWR's temporary western terminus between June 1838 and the extension of the line to Reading a year later. The station, later known as Maidenhead Riverside, eventually closed in 1871 when the present town-centre station was built, and when the quadrupling of the Paddington-Taplow line (c.1875-84) necessitated the widening of the bridge, its north elevation - previously the mirror image of its southern counterpart - was rebuilt with the steps omitted.

Reasons for Listing

Dumb Bell Bridge is designated at Grade II for the following principal reasons:
* Date and historic interest: an early (pre-1840) railway underbridge dating from the first phase of the Great Western and the ‘pioneering’ era of railway development in England, relating both to the now-vanished Maidenhead Riverside station (the GWR's first temporary western terminus) and to the London-Bath turnpike, with which the new line was in direct competition;
* Design, engineering and material interest: a skew-arched bridge of unusual and ingenious design, devised by Brunel himself and closely related to his slightly later Maidenhead Bridge 800m to the west;
* Intactness: most of the original structure survives, including the south elevation with its distinctive angled stair tower, while the later widening on the north side was carried out sympathetically.

External Links

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