British Iron Bridges

Wales

DOLDOWLOD FOOT BRIDGE 1867 (also known as the Ystrad Bridge) nr. Rhayader, Wales HEW 1245 SO 003 617 N52o 14' 38.3" W3o 27' 44.6"

PRIVATE LAND This bridge was designed by James Dredge (1794-1863), a brewer in Bath who became a successful self-educated engineer. He developed a very distinctive type of suspension bridge which combined the principles of suspension and cantilever. Each half of the bridge works as a right angle triangle, the hypotenuse of which is formed by the wrought iron rods extending along the deck at oblique angles up to the top of the pylons - . The bottom tips of these two triangles meet at the center of the bridge. If you cut a Dredge bridge in two at the center, both halves would still stand whereas if you did that with a conventional suspension bridge, it would collapse.

The chain of rods that loop from the top of each tower down to touch the outer edges of the deck at the center are simply positioning the rods which are actually supporting the bridge rather than having the chain itself provide its support as in a conventional suspension bridge. "Each chain (in a Dredge bridge) increased from a single wrought iron rod at the centre of the bridge to the requisite number over the … (towers) by progressively adding an extra rod at each link position. This resulted in a significant reduction in the quantity of iron and in the self-weight of the suspension system. … Connected to each joint in the main chains was a pair of inclined bars which gave support to the deck. These 'oblique' rods … were all set at different angles to the horizontal. … This introduced compression into the deck: a fact which Dredge argued in his favour, since the conventional suspension bridge decks of his era were greatly affected by wind-induced oscillatory motion." (Don Mc Quillan "Dredge Suspension Bridges in Northern Ireland", THE STRUCTURAL ENGINEER Vol. 70, No. 7 April 1992)

Of the fifty or so bridges Dredge built in the British Isles, only eight survive today: this one, the Victoria Bridge in Bath, the Stowell Park Bridge in Wiltshire and two in Scotland, at Aberchalder and at Inverness plus three in Northern Ireland. His client in this case was the nephew and heir of the inventor James Watt. This bridge on the River Wye was built to Dredge's patented design by his son William four years after Dredge's death.

The bridge is used daily on a private estate off the A470 in Wales. From two 14 foot cast iron pylons, the 7' 4" long wrought iron rods, five on each side at the pylon, descend to the center in decreasing number. At each rod link, hanger rods run down at varying angles to support the wooden deck which has a span between pylons of 125 feet. In this Dredge bridge, there is a slight but unique variation in his 'taper' principle The iron work was made by the Llanidloes Railway Foundry.

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Category: Wales

CONWY TUBULAR RR BRIDGE 1848-1850 Robert Stephenson Caernarvonshire. HEW108 SH785 774 N53 16’ 53.5” W3 49’ 15.8”

This bold bridge over the Conwy River was built at the same time as and in the same innovative style as Stephenson’s nearby Brittainnia tubular railroad bridge. A single 400 foot span of two parallel square iron tubes is supported by massive stone tower piers added in 1899. It lies alongside Thomas Telford’s graceful suspension bridge of 1822 crossing the Conwy River in front of the medieval Castle of that name. It carries two tracks of the Holyhead Chester railway line.

The massive tubes were built on the shore and floated by barge to the site and lifted by hydraulic jacks into place exactly as Stephenson had done with his very similar tubular bridge at the Menai Straits begun in 1846.

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Category: Wales

CONWY SUSPENSION BRIDGE 1826 Gwynedd, Caernaronshire Thomas Telford HEW 107 SH785 776 N53 16’ 53.5” W3 49’ 15.8”

Thomas Telford designed and built this bridge over the River Conwy as part of his London to Holyhead road. In architectural sympathy with the ancient Conwy Castle adjacent to it, the suspension bridge towers are massive arches with crenellated columns which support the chains. The span between the 40 foot towers is 327 feet. Telford described it as having “the appearance of a huge drawbridge” opposite the water-entrance to the castle. The wrought iron chains are in tiers of five 9’ long links with alternating plate joints. Vertical rods suspend the deck from the junction rods. The bridge was strengthened in 1812 with extra cables and cross girders. In 1958 a modern bridge was built alongside to accommodate the heavy traffic on A55. Conwy bridge is now the property of the National Trust.

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Category: Wales

CLYDACH TRAMWAY BRIDGE “Smart’s Bridge” Gwent 1824 SO131 228 {N51o 48’ 45.6” W3o 7’ 12.4”}

This charming bridge, decorated with gothic arches in its spandrels, carried the tracks into the at Clydach Ironworks. The ruins of the furnaces and forges in the glen complement its gothic theme. Just after crossing the Monmouth Canal on the A465 in the village of Gilwern, look on the left for the entrance to a modest county park which was once the site of the famous Clydach Works. Go to the very far end of the park at the head of the little meadow to find the bridge.

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Category: Wales

CHIRK AQUEDUCT 1801 Wales Thomas Telford HEW 111 SJ286 37 N52o 55’ 39.3” W3o 3’ 23.6”

Although this striking aqueduct appears to be a masonry structure, Telford pioneered the use of cast iron plates cast by William Hazeldine to make up the five feet deep troughs which carries the Llangollen Branch of the Ellesmere Canal above the valley of the Ceidriog River. The flanged plates were bolted together and incorporated into the masonry. By using iron Telford was able to reduce the depth of the masonry side and hence the weight above the piers which meant that the arches while bold in profile at the piers seem breathtakingly thin and elegant at the tops of the arches. This aqueduct was built after his Longdon-on-Tern and before the Pontcysyllte Aqueducts.

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Category: Wales

CHEPSTOW BRIDGE 1816 Monmouthsh. HEW 145 ST536 943 {N51o 38’ 44” W2o 40’ 15.9”}

This early bridge of cast iron still carries the A48 traffic across the River Wye under the ramparts of Chepstow Castle albeit in alternating directions of one lane. It was designed by J.U. Rastrick and cast by William Hazledine. Of the five arches, the center span is 112 feet flanked by spans of 70’ and then 34’ on either side of it. It has a very striking grid pattern on the spandrels reminiscent of Telford’s design for his Cantlop, Cound II, and Meole Brace bridges of a few years earlier. They have the optical illusion of being contoured (but actually are flat in profile) which gives the bridge a bold, vigorous aspect. It has been strengthened and upgraded over the years, most recently in 1979-80.

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Category: Wales

CAER HOWELL BRIDGE 1858 Mid-Wales, nr. Newtown HEW851 SO 197 982 N52o 34’ 29.3” W3o 11’ 11.4”

Between Abermule Bridge and Welshpool on the A483 is a similar cast iron bridge over the Severn manufactured by the Brymbo Company. It has two spans of 72’8” each of them having five ribs. It has been reinforced to support modern traffic loads, but is still graceful and old fashioned in appearance.

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Category: Wales

BUCKLANDS SUSPENSION BR. Nr. Pen y pont, Wales PRIVATE PROPERTY N51o 52’ 51.4” W3o 16’ 7.3”

There is a derelict suspension bridge spanning the Usk River on the Bucklands Estate that was built by “Rowell London” in the very early 20th century. It give access to the farm lands on the south side of the property from the main buildings on the north bank. The road bed consists of planks laid down on iron cross bars. There are high towers to carry the cables topped by decorative finials. It is similar in design and execution to the Llanstephan Bridge over the Wye not far away. Evidently, it was leased to an anglers’ club for many years and is no longer in use.

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Category: Wales

BROCKWEIR BRIDGE 1906 near Tintern Abbey {N51o 41’ 58.6” W2o 40’ 58.7”

This late cast iron girder bridge supported on rather thin masonry piers spans the Wye River just upstream from Tintern Abbey. Its decorative X patterned white painted railings make a bold contrast to the sylvan setting. It replaced a ferry service there and ws perhaps built by the Rye Valley Rail Road so its customers could get their goods across the river to its station at Tintern. It was built in 1906 and restored in 1986.

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Category: Wales

BRITANNIA RR BRIDGE Anglesly, Wales 1850 Robert Stephenson HEW 110 SH542 710 {N53 12’ 58.5” W4 10’ 24.2” These coordinates are ¼ mile east of the bridge end and down river}

Robert Stephenson was the first to conceive of the tubular bridge: in essence a giant box girder. He used this concept (later adopted by his great friend and rival I.K. Brunel) to build his two famous tubular rail road bridges at Conway (1848) and here at Anglesly (1850). The tubes were built of wrought iron plates in a method that the iron foundries had developed for ship building.

The Britannia Bridge, which had paired central spans of 460’ with paired spans of a further 230 feet on either end, marked a huge advance in the use of this material since the longest wrought iron span to date had been of only 31 feet. They were to be joined end-to-end within the huge masonry tower piers.

“The four tubes for the two mainstream spans, each weighing 1800 tons, were built on the Caernarfon shore, then floated out and jacked up 100 feet onto the towers, a procedure like that at Conway and subsequently adopted for his Chepstow and Saltash bridges by I.K. Brunel. In June 1849, Brunel stood beside his great friend and rival Robert Stephenson to watch the launching of the first Menai tube.” (T. Seyrig “The different modes of erecting iron bridges” Min. Proc. Instn. Civ. Engrs. 1880-81 Pt 1 p. 63, 161-162 as quoted by W.J. Sivewright editor of “Civil Engineering Heritage: Wales and Western England” Thos Telford, London 1986) The hydraulic jacks that could lift such a weight were designed and built by the Cornwall firm of Tangye.

The massive bridge with its bold towers rising 100 feet above the bridge are to scale with the magnificent site. In 1970 an accidental fire in the timber roofing of the tubes caused them to warp. In the reconstruction that followed, a road bed was added on top of the rail road tracks and to support that extra weight, steel truss arches were added underneath the bridge. The resulting modern bridge still uses the masonry towers, but the airy effect is completely different than that of Stevenson’s original bold design.

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Category: Wales

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