Southwark Bridge

Tiled illustration of original bridge, in the Southwark Bridge Underpass

Original bridge: connections between arch ribs and transverse plates. From The Engineer, 17 April 1914

1914. Rennie's bridge, shortly before demolition

1914.

1914.

1915.

Tiled illustration of original and new bridges, in the Southwark Bridge Underpass

2016

2016

2016

2016

Crosses the Thames from Queen Street, Cannon Street, to Bridge Street, Southwark

The Original Bridge

The first bridge was designed by John Rennie (the elder). It comprised three large cast-iron arches, with two stone piers and abutments. The arches were flat segments of circles, the centre one being not less than 240 feet span, rising 24 feet, so that it was 6 feet above high-water at spring tide. The two side arches were of 210 feet span, each rising 18 feet 10 inches. The two piers were 24 feet wide each at the springing, and 30 feet at the base.

The 240 ft centre span is said to have been the longest cast iron span ever built.

Robert Stephenson observed: "As an example of arch construction, it stands confessedly unrivalled as regards its colossal proportions, its architectural effect, and the general simplicity and massive character of its details." Though, on the other hand, an adverse critic has alluded to it as being "little more than a heavy and wasteful imitation of a stone ring." '

Bridge historian John G. James was highly critical: '.... this was to some extent an ego-trip for the great man and, apart from showing to what lengths top-notch founders could go when driven to their limit, it was really an expensive monstrosity. Many of the parts were unneccessarily large and they were over-complicated by inappropriate details such as dove-tailing; they caused the founders much trouble and the contract, which was taken on during the post-war slump, led to their bankruptcy; ....'.

It was certainly a bold undertaking, and it was evidently a highly durable structure, but the constructional details seem to have been overly demanding from the viewpoint of the ironwork contractor. There are parallels here with Eads Bridge (St. Louis).

1813 Construction started; Samuel Walker and Co were contracted to supply iron castings

1815 the Southwark Bridge Co failed.

The first stone was laid by Admiral Lord Keith on 23 May 1815.

1815 'Southwark Bridge proceeds with great activity and may be expected to be completed in about twelve months from this time. One of the piers is finished to high water mark. The centre arch, of 240 feet span, is cast, and erected (pro tempere) at Rotherham, in Yorkshire, where it attracts particular notice, for its beauty and solidity. Two of the three arches of which this bridge is to consist, will be delivered early in the spring.'

1819 '.... Many of the iron single or solid castings weigh 10 tons each ; and the total weight of iron exceeds 5,308 tons.
The centerings of this bridge on which the arches were formed or turned, were of such a novel and peculiar construction, that the navigation of the Thames was comparatively unimpeded during the building of the bridge — similar was the fact at Waterloo Bridge. At the Southwark Bridge the entire centering of one arch, containing 480 load [?] of timber, was removed in two tides, having been previously and gradually sunk by loosing of the wedges. Unlike the Pont Neuilly (near Paris), where the centerings were all struck simultaneously, or rather thrown into the River Seine, the arches settled the surprising depth of 18 inches almost instantly. It was calculated and allowed that the centre arch of the Southwark Bridge would settle at the vertex two inches, yet, in reality, it has only settled or sunk one inch 7-8ths precisely; thus the wide expanse is within one-eight of an inch of the figure and form it was originally designed to assume.'

1819 The bridge was opened for traffic in March.

Zoomable photo here, showing the bridge, strangely lacking any pedestrians or vehicles.

John Rennie Jr.

John Rennie (the elder) gave his son responsibility for aspects of the work, as recounted in the autobiography of John Rennie Jr.. Mr Meston was appointed as the Resident Engineer, but young Rennie was given 'the arduous task of making out the working drawings under his direction, and of carrying them into effect. He notes that the ironwork was carried out by Samuel Walker and Co of Rotherham, under the able management of Mr Yeats, while the masonry work and piling was undertaken by Jolliffe and Banks.

The Iron Structure

The following description draws largely on Rennie Jr's account (in italics), partly on the description in The Engineer of 17 April 1914, with the addition of a small amount of speculation.

Each cast iron arch had eight main ribs. Each rib consisted of thirteen pieces. Rennie Jr. states that these thirteen pieces were solid, 2½ inches thick in the mass and 3 inches thick at the bottom, and 2½ thick at the top, and formed so many radiating blocks, like arch-stones.

The 1914 Engineer article stated that the plates ('blocks') were about 2 5/8in. thick near the centre of the arch, increasing to 3in. at the springing, and that the cast iron was cold blast of excellent quality.

The ends of the individual arch rib plates butted against a transverse frame which extended the whole width of the bridge; (See sketch above, which is a plan view showing the junctions between the ribs and the transverse frame). Against each side of these frames the main ribs abutted and were nicely fitted to them, and in order to prevent them from moving laterally there were projecting dovetailed cheeks cast on the frame, and between these cheeks and the ends of the main ribs solid cast-iron wedges the whole depth of the main rib were fitted, then drawn home against the ends of the rib; by this means the ribs were kept firmly within their places, and as an additional precaution strong diagonal braces, having a strong feathering rib on each side, were inserted diagonally between the ribs from one end of the arch to the other, and secured to the ribs by projecting dovetailed cheeks on them, and wedges and bolts, so that these cast-iron arches were constructed in the same manner as a stone arch, being almost as it were a solid mass depending upon the equilibrium of the different pieces for its stability. The depth of the main rib of the centre arch at the crown is 6 feet and 8 feet at the piers, whilst the depth of the ribs of the side arches at the crown is 6 feet and 8 feet at the abutments. As these ribs with their attendant transverse frames and diagonal braces formed the main part of the arches upon which the whole of the superstructure depended, it was necessary that they should be extremely well put together and properly united to the piers and abutments.

The sketch hints at the difficulties imposed on the foundry by the design of the connections between the rib plate castings and transverse frames. It appears that the wedges had to be shaped to fit the dovetail groove on one side and a rounded groove on the other side. Machining was out of the question, so a great deal of chipping and filing would be required on all the relevant surfaces of the massive castings to make them smooth and straight in readiness for the tapered wedges, which would also have to be hand made. For some reason the joints between the inner ribs and the transverse plates were also provided with bolts. The 1914 Engineer article noted that during demolition the wedged joints were found to be locked solid, and it was necessary to drill a series of holes in the wedges, split them using drifts, and remove them piece by piece. This was insufficient on its own: to free the rib plates, the 'key' plate had to be drilled and split to allow its removal. Fortunately electric drills had become available.

For comparison, similar bridges built later had simple bolted flanged joints. For example, see Bigsweir Bridge, Chetwynd Bridge, and Mavesyn Ridware Bridge. In fairness, these were smaller and later than Southwark Bridge.

Between the frame plates fitted on the skewbacks or masonry of the piers and abutments, and those fitted on the ends of the rib plates of each arch, solid cast-iron wedges, 9 feet long and 6 inches thick at the back, and 2 inches thick at the bottom, 9 inches wide, three being behind each rib, were accurately fitted by chipping and filing, so that it would slide down to within 12 inches of the bottom; when these wedges were all accurately adjusted at the same temperature to the same depth, they were simultaneously driven home by wooden rams to their full depth, so as to reach about an inch below the bottom of each rib; by this means the whole of the three arches were gradually brought to their bearing without being raised wholly from their centres.

Matters were then allowed to remain in this state for a few days in order to give time for every part to come to its bearing and to ascertain whether there was any defect in any part. After the minutest search in every part no defect could be discovered; the wedges between the centres and the under sides of the ribs were then gradually slackened until the whole of the arches came to their full bearing, and were removed entirely, leaving the arches perfectly free of support. During the whole of these operations, from first to last, which occupied about a week, not the slightest accident or fracture occurred; the total subsidence of the main arch barely exceeded 2½ inches, whilst the subsidence of the two side arches barely exceeded 2 inches, which had been allowed for in the construction.

In order to ascertain the effects of expansion and contraction of the arches by the variation of the temperature of the atmosphere, I constructed steel, brass, and wooden gauges, accurately divided into decimal parts of an inch, and erected them upon different parts of the centres, where the effects were most likely to be apparent, and I kept the register for several weeks, during the height of summer, autumn, winter, and spring. I found that the variation in the rise and fall of the crown of the arches, the abutments being fixed, was 1/10th of an inch for every 10° of temperature, so that, taking the extremes of temperature at London to be 10° below freezing point of Fahrenheit in winter, and 80° in summer; the utmost rise and fall of the arches may be taken at 7/10ths, or at most one inch; but as any variation in the temperature, unless continued for some time, has no sensible effect upon such a large mass of iron, so, in our variable climate, the rise and fall of the crowns of the arches may be taken upon the average somewhat below the amount above given.

After the arches had been brought to their bearing and had been relieved from the centres, the superstructural framework was carried up and firmly connected and bracketed together by diagonal ties and wedges; in doing this the ends of the superstructural frames were too tightly wedged to the masonry of the piers, without my knowledge, so that they would not allow the main ribs of the arches to play freely, and some of the masonry courses above the main ribs were slightly splintered and deranged; the wedges were then slackened, and some of them removed entirely, and thus the evil was immediately remedied; the whole structure has ever since remained in a perfect state.

Clearly Rennie did not blame himself. An 1818 newspaper report did not specifically apportion blame: 'Southwark bridge. In the erection of this work, it appears as if an attempt had been made prevent the natural effect of heat upon iron, that is, to prevent its expanding; for where the spandrils enter the masonry of the abutments and piers, they ate wedged in tight by iron wedges, from the bottom to the top: the consequence is, that on expansion taking place, a very unequal strain and injurious effect is the consequence; for the radius the intrados of the arch being 312 feet, and of the extrados about 6,600; and both being confined between abutments, yet connected together, locking them as two separate and distinct arches, it becomes evident that the latter would require to rise in the centre, for every degree of heat, considerably more than the former, but cannot without lifting it, or parting from it by fracture. To avoid this, which it is somewhat extraordinary was not guarded against in the first instance, the masons are now employed night and day in the tedious operation of working away the stone work at the back of the wedges, in order to remove them.'

The Replacement Bridge

The old bridge suffered from being too narrow, and from the approaches being too steep, particularly on the City side. The new bridge was to have five spans instead of the old bridge's three. This seems a retrogate step, but the objection came from river users, due to the fact that the near neighbouring bridges each had five spans.

1914 The old bridge was demolished in preparation for construction of the new bridge. See 1914/5 photos. Sir William Arrol and Co. were contractors for the demolition and for building the replacement, which was designed by Messrs. Basil Mott and Hay, with Sir Ernest George as consulting architect.

1921 Description of new bridge

1921 The new bridge, with 5 rather than 3 arches, was opened by the King and Queen

The attractive Southwark Bridge Underpass on the north side of the river is decorated with tiles incorporating historic illustrations relating to the history of the bridge. More information here.

See Also

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