When it was built, Isambard Kingdom Brunel’s Maidenhead Bridge over the River Thames boasted the flattest yet widest brick constructed arches in the world.
The London to Bristol main line crossed the River Thames via the Maidenhead Bridge. As the Thames was a navigable river used by barges, the Thames Navigation Commissioners insisted that neither the channel nor the towpath was obstructed, which allowed only one pier to be set in the river. Brunel designed the bridge so that his philosophy of minimal gradients on the line was not compromised (the inclined approaches towards either end of the bridge are only 1 in 1,320, or 0.076 per cent), so that existing tow paths were uninterrupted on each river bank for the benefit of bargemen, and the point at which it crosses the Thames took advantage of a small island on which the middle pier could stand.
An engineering sensation
Built entirely of brick, and comprising of two shallow spans over the river, which combined a rise of only 24ft (7.3m) with an unprecedented width of 128ft (39m), the design of the bridge caused an engineering sensation when it was completed. During construction wooden scaffolding was built to support the building of the masonry arches. The Great Western Railway directors did not share Brunel’s faith in his own abilities and insisted that this scaffolding, initially at least, remain in place to reinforce the bridge. Secretly, Brunel arranged for the timber frame to be slightly lowered - without the support he knew that the bridge would remain solid. In the end the timber frame was washed away by the forces of Nature, either by strong winds or the river in flood according to different accounts. The bridge remained, and was immediately recognised as a triumph of engineering on the Great Western line.
As built and opened on 1 July 1839, the bridge carried two 7ft (2.14m) broad gauge railway tracks. In due course traffic to and from London increased enormously, and mixed gauge tracks were provided between London and Bristol during 1861. In anticipation of the final conversion to the standard rail gauge, during 1890-1892 the bridge was widened on each side in order to carry four standard gauge tracks. This work was carried out under the supervision of Sir John Fowler, the width overall being increased from 30ft to 57ft 3in. (9.1m to 17.5m). However, this was undertaken so sympathetically that the outward appearance of the bridge remained almost unaltered.
Did you know?
The painting, 'Rain, Steam and Speed' (1844) by J W M Turner, shows a Great Western Railway broad gauge locomotive and train passing over the Maidenhead Bridge.