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M1 motorway standardised bridges, example
typical example, south east of Junction 14, M1 motorway, Buckinghamshire
M1 motorway standardised bridges, example
associated engineer
Sir Owen Williams
Sir Owen Williams & Partners
date  1st April 1958 - November 1959
era  Modern  |  category  Bridge  |  reference  SP915395
photo  Owen Williams archive, part of Amey plc
In 1955, the go-ahead was given for the construction of the first 53.5 miles of the M1 motorway. It included some 130 overbridges and underbridges in this first phase, which took the motorway from Pepperstock near Luton to Crick. The engineering design team was Sir Owen Williams, his son Owen Tudor Williams and his partner Thomas Vandy.
To handle land acquisition, roadwork design and site supervision, Owen Williams & Partners set up an office at Welton Station (just north of Daventry, Northamptonshire), which is at the northern end of the route. Structural engineering remained in their London office. Welton was a symbolic choice since it's very near the West Coast railway line, the Grand Union canal and the A5 road — all major transport links from London to the Midlands at that time.
The bridges were conceived as a series of standard designs capable of variation depending on span, height, width and skew. Models were made of each standard design — such as the one shown above, which illustrates a straight span. The typical example we have chosen near Junction 14 is a skew span.
The idea was to construct them in a straightforward way using in situ or mass concrete. The intention was to re-use the shuttering (formwork) from one bridge to the next but as it turned out, they had to be built concurrently and re-use opportunities were limited. A decision was made not to use precasting because of transport difficulties — the only bridge site access was along the unfinished motorway. Pre-stressing was in its early stages of development so was not considered.
Typical of the bridge types, and the most common, is the two-span overbridge (see photo). Its design was approved by the Royal Fine Arts Commission. It has strong low pier walls with an expressed coping, surmounted by inclined tapering haunches that curve up directly into the reinforced concrete deck slab. Mid-support is provided by two substantial cylindrical columns with rectangular bases to the height of the pier walls. The columns share a flared rectangular head just below deck level. The concrete parapet walls were solid, though many have since been replaced with steel balustrading.
The various bridge locations dictated a range of spans, deck thicknesses and parapet heights. Spans were typically (measured from abutment to mid span) 19.5m for crossing three lanes and 15.85m for two. Deck thicknesses range from 535mm to 1065mm.
A distinctive feature of the overbridges is the banding along the edge of the decks. It consists of recessed channel-shaped grooves cast into the concrete. The number of bands varies from two on short-span single carriageway underbridges, to five on skewed two-span overbridges.
The banding is repeated on the visible faces of the abutment copings. At the low point of the haunches, where they meet pier walls, the coping terminates in a capstan-like embellishment. The standard abutment looks like a double-curved construction — the semicircular curve of the haunch into the bridge deck plus its sweeping taper culminating in a cylindrical pier.
The design of the concrete detailing was influenced by Owen Williamsí earlier bridge work done in association with architect Maxwell Ayrton. There they used architectural embellishments to bring formal design composition to mass concrete construction.
The standard overbridges are: the two-span one described above, a four-span continuous slab design (with cyclindrical mid-span columns, hard shoulder columns and sitinctive flared column heads) and a railway overbridge. There are three basic types of underbridge: single span portals (similar to the two-span overbridge, minus the columns), mass concrete arches, and railway underbridges (with two rows of rectangular columns). Design work on the railway underbridges and overbridges was done in co-operation with railway engineers.
The motorway construction contract was let in four stages, each some 12 miles in length and containing up to 35 bridges. Construction started on 1st April 1958.
Thus was produced the first comprehensive harmonious phase of motorway building — an idea envisaged by the European Modern Movement. They dreamed of concrete highways linking concrete buildings in new town settings, an example of Megastructure. The northern end of the new M1 is therefore quite appropriately located next to the New Town of Milton Keynes.
Most of the original motorway bridges are still in use, though many have been modified in some way to meet more recent standards. Some are now being replaced, especially at the southern end.
Main contractor: John Laing Construction Ltd
Research: ND
bibliography
"The London-Birmingham Motorway M1/M45, Luton to Crick to Dunchurch - a personal recollection" by R.H. Soper
The Motorway Archive : www.iht.org
reference sources   OWWOW
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M1 motorway standardised bridges, example