More on sus bridge

Queen's Park Bridge:

(not yet published)

In 1852 a new pedestrian suspension bridge with an innovative design was completed in Chester to provide a link between a speculative up-market housing development and the city. It was not the first such bridge in Chester.

A few years earlier, in October 1849, the “Civil Engineer and Architect's Journal” had reported on the construction of “Novel Suspension Bridge” at Chester. This crossed “The Dingle” between the embankment of the Grosvenor Bridge and Curzon Park where new housing was being developed by Earl Howe. The new bridge was of a unique design as it dispensed with piers and suspension rods above the level of the roadway. The deck of the bridge was instead supported on “chains” made-up of 15-foot long wrought-iron rods which had an eye at each end and were joined together. One end of these chains was secured to an abutment at the Grosvenor Road end, but at the Curzon Park end and extension of the the chains passed around a “strong grooved barrel” and dropped into a pit, where they supported a cast-iron plate loaded with a large quantity of masonry. The effect of this movable weight was to keep the bridge under tension while allowing for expansion and contraction as the temperature varied. This “self-adjusting” bridge was reported far and wide, including in the American press.

The 1852 Bridge
The bridge of 1852 was a slightly more standard design and its construction to link another new suburb to the city, that of Queen's Park may well have been prompted by the Curzon Park bridge. Queen's Park was being developed by Enoch Gerrard, a Chester businessman. He no-doubt hoped that the convenience of a footbridge across the Dee would encourage people to move. It also gave them a way to avoid passing the noxious skinner's yard which lay between Queen's Park and the Hand-bridge End of the Old Dee Bridge. The original Queen's Park Bridge cost £850.

A simple suspension bridge is but one of several sorts of bridges. Among others are stone arches as can been seen at the Old Dee Bridge and the Grosvenor Bridge. Chester also has several truss-bridges, of which one was Stephenson's somewhat experimental cast-iron railway bridge over the Dee which famously failed. The Old Dee Bridge is medieval, the Grosvenor Bridge was built between 1827 and 1833 to a design which could allow tall-ships to pass, and Stephenson's railway bridge of 1846 is much lower, showing perhaps how the fortunes of the port of Chester had changed over a short span of years. In arches the stone is compressed by the weight of the structure above to lock it firmly into place and the bridge needs to be supported by temporary “false-work” until the arch is complete whereas with most suspension bridges the deck of the bridge hangs from chains or cables and is simpler to put in place. Early stone arches used a semi-circular form which is not the most efficient and thus tend to be bulky. A good example of such a massive arch can be seen in the Norman north transept of the Cathedral. However the Gothic (pointed) arch replaced them. The ideal shape of an arch is actually a catenary curve, which is close to a parabola and is the shape that a chain forms when hanging between to posts.

In such a system the weight of the flexible chain is carried by tension along it, and inverting this produces the most efficient arch with a minimum tendency for the arch to buckle or “burst”. A parabolic curve within pointed Gothic arches forms the “thrust-line” along which the forces are borne. Much early architecture would have been built without the advantages of modern mathematics and early engineers would have based designs on what had worked before. There was the possibility of making models, but these were poorly understood. The weight of a structure increases as the cube of its size whereas the failure stress grows as the square. The “scale” model of the Grosvenor Bridge on Castle Drive is actually a bit of a con-trick.

No doubt the earliest suspension bridges were of rope or vines and formed the sort of “jungle bridge” which spanned The Dingle prior to replacement. However the Tibetan siddha and bridge-builder Thangtong Gyalpo originated the use of iron chains in his version of simple suspension bridges. In 1433, Gyalpo built eight bridges in eastern Bhutan, at least one of which survived into modern times. According to some sources the “first” chain bridge in the west was the Winch Bridge, built around 1741 across the Tees in North-eastern England, however bridge-enthusiasts seem remarkably disputatious about who did what first.

Suspension bridges are, sometimes notoriously, flexible. This makes some sense as tensions in the bridge will tend to redistribute with expansion and movement of loads. A good example of a chain bridge can be seen crossing the river Dee just above Llangollen, but the original Queen's Park bridge was not a pure, simple chain suspension bridge, but a sort of hybrid with elements of the “cable-stayed” bridge. The “hangers” on the bridge were angled and the formal name is a “double cantilever”.

Dredge's Design
Perhaps little mathematics was used in it's design as the bridge was well-known for “dancing about”. “The Builder” described it thus:


 * “To Queen's Park there is a foot-bridge, on Dredge's suspension principle, east of St John's Church...It is exceedingly slight and sways and undulates by the tread of the crowds passing over it on Sundays, in what appears to be a dangerous manner”.

James Dredge was a brewer from Bath who, in had patented the “taper principle” and had built the Victoria Bridge (1832) in that city to carry his beer. His original bridge is still standing. The “taper” refers to the fact that that suspension chains are thicker toward the top of the piers where they carry more tension, something which can be seen in the photographs of the first Queen's Park bridge. The advantage of the taper system is that the resulting design is cheaper to build than a conventional suspension bridge of the period because it uses less iron and is quicker to build. In theory a Dredge bridge can be cut through the middle and will not collapse due to the cantilever design. Dredge never tried that experiment, but he did load model bridges with what he could conveniently find in his brewery – beer, horses, sacks of malt and men.

Dredge's bridge designs were however surrounded by controversy and several collapsed, including a few in India. In October 1846 news from India arrived that:


 * “A bridge on Mr. Dredge's principle, which was put up a short time since across the Kubudduck River, near Jessore, has fallen. On testing, the bridge was found to be weak even though 'guaranteed by Mr. Dredge to stand any traffic' and before its use could be restricted, 'some grand festival took place on the water, to witness which, a crowd of natives rushed on the bridge, nearly filling the platform, and after a few minutes it gave way, and drowned nearly one hundred and fifty of them.”

Dredge went bankrupt in 1849, but appears to have still been building bridges and mentions the Dee bridge in his literature of 1855 by which time his 1836 patent had expired. While his bridges were still collapsing Thomas Penson, the noted Chester architect was still trying to avoid building them, including one at Caerhowel in 1854 where his objections were overruled (it collapsed in 1858 and Penson got his own design instead).

More Concerns
The first Queen's Park bridge was the subject of some further concerns in August 1877 following the collapse in June of the Widcombe “Suspension” Bridge in Bath – which was not actually a suspension bridge. The cause was an influx of tourists who crowded onto the bridge, rushing to see an agricultural show. As reported in “The Engineer”:


 * "The Grosvenor and Queen's Parks, Chester, are united by a suspension bridge for foot passengers, of considerable span. This bridge requires careful examination, if the Bath catastrophe is not to be repeated. When there are regattas on the river it is almost impossible to keep the crowd off. The Board of Trade ought certainly to have this bridge examined and reported upon. If it is all right, well and good; no harm will have been done by our word of warning. If it is found to be as dangerous as we assume it to be, then our advice may prevent the recurrence of a very grave calamity."

“The Engineer” also stated the following about the Chester bridge:


 * “The main chains consist of ¾ inch round rods with eyes turned-up and nominally welded, on the ends, which are united by transverse pins. The roadway has no vertical or lateral stiffness, and sways in a high wind. A policeman is kept patrolling it to prevent persons from standing on it.”

According to Chester historian Thomas Hughes, author of “The Stranger's Handbook to Chester”:


 * "It was a pretty object in the landscape. Though of such spider-like construction, its capabilities and strength have been fully tested"

We know nothing of the tests mentioned by Hughes, although they may have been little more than “many have crossed it”.

One myth which sprang up about the suspension bridge was that its construction was brought about by the “Fenian Assault” on Chester. According to this myth, of which several versions exist, the bridge was built so that troops could be rushed into the city of Chester from their garrisons on the opposite bank given that the Republicans had taken the Old Dee Bridge. There is no truth to this story – the “Assault” was in 1867, long after the bridge had been built.

The 1923 Bridge
There were several attempts to replace the original bridge. In one, a new, high-level bridge “for carriages” was proposed from St John's churchyard to Queen's Park. Although the days of the original bridge were said to be numbered, this 1895 idea went nowhere. The next attempt to change things was a 1902 proposal to extend the bridge so that it crossed Lower Green Street to meet the steps to St John's half-way down to The Groves. Once again this went nowhere. The Queen's Park Suspension Bridge had been privately funded and maintained. When Chester Corporation accepted the responsibility for this bridge in the early 1920s, they at once decided to demolish it, something which had been expected for many years. Demolition took place in August 1922, and a new bridge took its place. It is often said that the new bridge was constructed to the design of Mr Charles Greenwood, City Engineer and Surveyor – he was also a qualified lawyer. This is either untrue or Greenwood's input was very minor. The Chester bridge bears a strong resemblance to the Porthill Bridge in Shrewsbury and was in fact built earlier in the same year by the same firm: David Rowell & Co, a company based in Westminster, London. They fabricated wrought iron and wire rope, built suspension footbridges, and structural steel frame buildings. They were established in 1855 and closed in 1970. They were well-know for their ready-made steel bridges which were exported in kit form all over the world.

The designer of the new Queen's Park bridge was actually named as William E. Barker, an engineer who frequently worked with Rowell & Co, and the new bridge cost £5,650 (Porthill cost £2,600). Greenwood was possibly only involved with the decorative details. The contractors for the foundations and masonly work was W. H. Brocklesby of Birkenhead. It spans 277 feet (84 m), and is supported on vertical hangers from two 2.75-inch (70 mm) diameter locked-coil steel cables, each capable of carrying up to 340 tons. It is founded on the north side on a 230-ton concrete block, and on the south side by anchoring into sandstone bedrock. It is finally, a more or less standard suspension bridge with the deck simply hung from the cables.

Greenwood had major plans for the redevelopment of the area around the bridge. He wanted to demolish all the houses fronting onto the River Dee just upstream of it and carry Grosvenor Park down to the bank (with an outdoor swimming pool). These were not his only plans for Chester. In the post-war years he devised a huge “Northgate Scheme” which proposed to route the inner ring-round up King Street and out through a rebuilt Northgate. The possible demolition of properties blighted the area for years, until the plan was scrapped in favour of a new gate through the Walls.

From its opening the new bridge was decorated with the supposed shields of the Norman Earls of Chester. In fact during the time of the first few Earls heraldry was not particularly developed and the shields most probably were retrospectively assigned. There is general agreement about the symbols associated with the various Earls but the ones on the bridge appear to be wrong: the arms of Ranulf de Meschines and Ranulf de Gernons have been switched around, and one is the wrong colour.

The photographs which show the opening of the new bridge in 1923 are monochrome but it is just possible to make out the names of the Earls in their correct places. The shields had become rather weather-beaten over the years, and were impressively restored by David Kynaston in 2012/13. Cast out of lead, broken and missing parts were repaired. The shield were fully repainted and finished in 23 1/2 carat gold leaf. Unfortunately older records shows Ranulf de Meschines as having a red lion on a gold field and Ranulf de Gernons having a white (silver) lion on a red field. The restorer was somewhat dumb-founded when the error was pointed out, but it was hardly his fault given that he had been given detailed instructions. Elsewhere in Chester, in Grosvenor Park and in the Town Hall the arms of the Earls are correctly displayed.