Merseyside Bridges: 9. Acton Swing Bridge

From the Dutton Horse Bridge, my journey ran south along the River Weaver. The next bridge of significance gives its name to the small town of Acton Bridge.

It was designed by the same John Arthur Saner who designed the Dutton Horse Bridge, and apparently many other structures along the River Weaver. The current bridge opened in 1933, replacing a previous structure which had been able to carry only one line of traffic with an axle weight limit of 8 tons.

It is 83.5m long, with two slightly skew spans of 25m each. It's estimated cost at the time of construction was £52,000, excluding the diverted approach roads. The superstructure comprises twin riveted steel trusses, supported on a mass concrete pontoon chamber. One website describes it as "the first floating swing bridge in Britain", although I think there is some confusion there with the nearby Northwich Town Swing Bridge, which has a plate on it claiming it to be "the first road swing bridge on floating pontoons".

In its structural form it is typical of many truss swing bridges of the period, and not as elegant as some. The overhead bracing seems particularly over-designed. The curved profile of the truss is visually satisfactory but does not optimise the level of stress in the main members. Structurally, this particular profile's main benefit is to keep the overhead bracing clear of vehicles.

The use of contrasting black-and-white paint is common to many of the structures along the River Weaver.

With the truss main members and verticals painted white, and the diagonals black, there seems to be an intention to define a visual hierarchy of members and perhaps de-emphasise some. There is no great structural logic behind this, as the diagonals are as important to the bridge's overall strength as the verticals.

The edge of the bridge deck is painted with black and white bars, presumably to warn of limited headroom. Interestingly, the footway parapets are painted with the same alternating pattern. This makes the parapet appear to dissolve into a series of isolated panels with open gaps between them, which is a peculiar effect, if intentional.

Further information:

• Google maps / Bing maps
• movablebridges.org.uk
• British Bridges: An Illustrated Technical and Historical Record (Public Works, Roads and Transport Congress, 1933)

Merseyside Bridges: 8. Dutton Horse Bridge

This is a short detour from Merseyside, however broadly that area might be defined. From Runcorn, the journey heads south-east towards Northwich. I stopped off at two bridges before returning north to the River Mersey. In broad outline, this route follows the course of the River Weaver, which is a tributary to the Mersey.

The first of the two structures is Dutton Horse Bridge. This twin-span timber bridge was completed in 1919 to a design by John Saner, who was the engineer responsible for many works along the River Weaver when its navigability was improved. The Dutton Horse Bridge spans alongside the river's main course, over a secondary channel used to help regulate the water level.

It is historically significant as one of the earliest surviving bridges to feature laminated timber. The laminated arches span about 31m, with two ribs slightly out of line with each other. Triangulated timber struts stiffen the arches and support the deck.

As with many timber structures, it's certainly an attractive bridge, and it's great to see it has survived so well. Two span bridges are reputed to suffer from the problem of the "unresolved duality", where the viewer lacks a primary visual focus and so feels discomfited. This is a phenomenon that has received support from at least one experimental study, where viewers consistently tended to prefer one or three-span bridges to those with two spans. At Dutton, the bridge is rarely seen in full elevation, as the footpath on the opposite side of the river seems not to be the main route. From any other angle, the number of spans is hardly relevant. Even in full elevation, I think it looks fine.

The black-and-white paint scheme is characteristic of several bridges along the Weaver, including the one I'll come to next.

Further information:

• Google maps / Bing maps
• Engineering Timelines
• British Listed Buildings
• An Encyclopaedia of Britain's Bridges (McFetrich, 2010)