Prince Alfred Bridge

About

The Prince Alfred Bridge is a wrought iron truss and timber beam road bridge over the Murrumbidgee River and its floodplain at Middleton Drive, Gundagai, Cootamundra-Gundagai Regional Council, New South Wales, Australia. The name originally applied to the iron truss bridge over the river and some 800 metres of timber beam bridge across the floodplain but most of the timber beam sections have been demolished. The heritage-listed road bridge was designed by William Christopher Bennett and built from 1864 to 1867 by Francis Bell. It is also known as Prince Alfred Bridge – Iron Road Bridge and Iron Bridge over Murrumbidgee River at Gundagai. The iron bridge is owned by Transport for NSW and the timber viaduct was owned by Crown Lands. The bridge was added to the New South Wales State Heritage Register on 5 July 2019 and on the (now defunct) Register of the National Estate on 21 March 1978. In 1977, the 1,143-metre-long (3,750 ft) Sheahan Bridge replaced the Prince Alfred Bridge as the Hume Highway crossing of the Murrumbidgee River. The Sheahan Bridge was duplicated in 2010. Since the opening of the Sheahan Bridge, the Prince Alfred Bridge has served local traffic only. The timber spans...

The bridge was named for the then reigning Queen Victoria 's son, Prince Alfred, Duke of Saxe-Coburg and Gotha, and was built to carry the Great Southern Road (now the Hume Highway) across the Murrumbidgee. It has existed in three forms, with only the main spans across the river itself being common to all three.

The site was historically known as the "crossing place" and is where Charles Sturt first crossed the Murrumbidgee. It became known in the mid-19th century as the safest location to cross the river. Periodic flooding of the Murrumbidgee had already had detrimental effects on the pioneering settlement of Gundagai, situated on the floodplain. In 1852 almost 100 people were drowned in a severe flood. By 1853 a new town site had been chosen on the high ground north of the floodplain and its main street, Sheridan Street, became part of the Great South Road, subsequently the original Hume Highway until it was bypassed in 1977.

On 30 January 1861 The Sydney Morning Herald reported that the NSW Legislative Assembly had rejected a motion for a road bridge at Gundagai due to lack of funds and lack of evidence of a need. A public meeting was held in September at the Gundagai Court House and resolutions from the meeting together with a subsequent petition from the district were forwarded to Sydney for consideration by the NSW Government.

The river crossing had become a major obstacle for travellers and teams following the Hume and Hovell route to the Riverina and Victoria, and there had been regular petitions and deputations to the Colonial Government for a bridge. Successive governments deferred on the grounds of low traffic flows and the high cost of any bridge project to cross the half-mile flood plain, but political and commercial factors forced the Government's hand. The merchants at Wagga Wagga favoured trade with Victoria since that colony's railway had reached Echuca in 1864, and they accused the distant Sydney-based Government of neglect. They formed a joint-stock company and built a substantial three span timber bridge over the Murrumbidgee River in order to direct traffic from the surrounding districts through the town. It was reported that as a financial speculation the bridge has proved successful. A similar bridge had been erected over the Murray River at Albury. The NSW Government was forced to act in order to turn the flow of wealth towards Sydney. Not only was a bridge planned, but an expensive iron structure was approved as a clear indication to the south-western districts of the Government's legitimate interests in those regions.

In late 1861, the Government placed A£ 24,000 in the estimates for a modest scheme with a short viaduct, which would have left the floodplain impassable during a flood. However, in 1864 the estimate was increased to A£37,000 for the whole river flat to be bridged. The Prince Alfred Bridge over the Murrumbidgee River was opened on 24 October 1867 and named after Queen Victoria 's second son who was touring Australia that year. It was the first metal truss bridge to be built in NSW. A short sloping viaduct descended to join the road over the river flats until the long timber viaduct was complete in 1869.

In England in 1848, James Warren and Willoughby Monzani had obtained a British patent for a configuration of repetitive equilateral triangles that could support a road on either its top or bottom chord. Warren's name became synonymous with this form. The first major spans using this configuration were built in England, and English construction firms built prefabricated versions for use in the British colonies, especially India. Thomas Kennard then applied a more detailed analysis of the stress distribution, allowing further economy in the use of iron by varying the cross-sectional area of the top and bottom chords without adversely affecting strength. Kennard patented his invention in 1853, and it was the Warren and Kennard patent that was used by Bennett in his design of the Prince Alfred Bridge.

According to Bennett, the Warren girder had been adopted, because it required the least workmanship on the ground, and because of the rapidity with which it could be erected, incurring least risk from the violent floods of the Murrumbidgee during construction. However, Bennett, along with many other engineers of his day, considered the lattice truss superior. The main objection to the Warren truss was that all the strains are taken by a single pin, whereas in the lattice system the strain is divided amongst a number of rivets instead. Francis Bell, the contractor, also preferred the wrought iron lattice, which, he said, could be imported from England and launched into position very economically. For these (among other) reasons, very few Warren truss bridges were constructed during this period. The iron for the superstructure was furnished by Messrs Lloyds, Fosters, and Company's Wednesbury, Old Park Ironworks in Staffordshire, and was inspected by eminent engineer Mr. Fowler. Testing of the wrought iron was conducted, and the strength was found to be much in excess of the specification. The testing in England of the first span for the bridge was also reported as very satisfactory; the deflection with a load did not exceed an inch.

In 1848, three Sydney businessmen had joined a local man in an attempt to exploit the iron resources of the Nattai district, which became the Fitzroy Iron Works. The Fitzroy Iron Works were the first ironworks in Australia, but their story is one of persistent failure over half a century despite numerous and repeated ambitious, entrepreneurial and optimistic attempts. For finished products (cast or rolled), land or water transport to an English port plus sea freight to Sydney were less than the cost of cartage between Mittagong and Sydney. Pig iron, also, could not compete against British iron, mostly brought out as ballast in wool ships.

The Prince Alfred Bridge, with the Denison Bridge at Bathurst, has the distinction of being one of only two early Australian bridges that contained Australian iron. While the iron for the piers of Denison Bridge at Bathurst was cast at P. N. Russell & Co 's Foundry in Sydney from pig iron obtained from the Fitzroy Iron Works, the cast iron piers at Gundagai were cast by the Fitzroy Iron Works from largely local iron. The piers are therefore a rare example of a substantial finished product produced completely by the Fitzroy Ironworks at Mittagong.

The four pairs of cast iron cylindrical columns for the piers were made at the Fitzroy Iron Works in 56 sections. Each was two metres (six feet) long, two metres (six feet) in diameter, with a 29-millimetre (1.125 in) wall thickness and each weighed approximately one point eight tonnes; one point eight long tons (two short tons). They were delivered by bullock drays, although delays occurred in carting the cylinders to Gundagai because scarcity of feed and water between Yass and Gundagai deterred carriers from undertaking the work.

When a 2-metre (6 ft) section of cylinder was placed in its required position, the material inside and under the cutting edge was excavated by hand, causing the cylinder to sink under its own weight. As the cylinder descended, additional lengths were added with internal bolted connections until the necessary depth or foundation had been reached. The hollow cylinder was then filled with rubble consisting of red sandy soil with the odd stone. An immense amount of difficulty was at first experienced in reaching the necessary depth; borings to a great depth had to be made, through huge masses of timber brought down by floods in bygone ages, but the indomitable energy of the superintending engineer, Frederick Augustus Franklin, overcame every obstacle. Franklin, who worked for Francis Bell, was well regarded and gained the cordial good wishes and esteem of the people of Gundagai by his work.

The design for the three iron truss spans of the Prince Alfred Bridge are based on the British pin-jointed Warren and Kennard trusses, and have the unique feature of the trusses being suspended from a continuous horizontal top chord, supported on roller bearings on vertical posts at each pier. The end roller detail has five rollers placed between the extended upper chord and a pillar which rises from the pier top. A similar detail is provided at the central pier, where each upper chord is continued from one span to the next across a nest of rollers. The Warren truss, as originally patented, consisted of a configuration of repetitive equilateral triangles but the Prince Alfred Bridge has additional verticals at each cross girder location, designed to provide lateral support to the top chord. It and the railway truss downstream (constructed more than 30 years later) are two of only three pin-jointed metal trusses remaining in NSW - the other is the Whipple truss road bridge at Nowra.

The deck on the truss spans originally consisted of two 5-centimetre (2 in) thick layers of diagonal decking, the upper layer being approximately at right angles to the lower layer. The deck was finished with a light curved iron kerb, similar to the kerb which still exists on Denison Bridge (see photo). This arrangement of deck for the truss spans was retained when Percy Allan designed the new northern viaduct which was constructed in 1898, but by 1932, there was just a single layer of transverse decking on the truss spans similar to the viaduct approaches, and a timber kerb rather than the original iron kerb.

By 1932, it was thought that, "the iron spans, then being sixty-five years old, could hardly be relied upon for a further period of service much in excess of thirty years (the average expected life of a timber girder span as used on viaducts), which would bring them to an age of practically 100 years. Apart from not being heavy enough to carry the present-day standard bridge loading, old age had probably affected the iron and caused some loss of strength." However, after considering a number of options for a new bridge it was admitted that, 'It was plain that the existing iron trusses, though light and of unusual design, viewed from the aspect of modern structural practice, were in good order and were capable of rendering efficient service for the life of at least one more timber approach.'

Since that time, the timber deck has changed arrangement a number of times, and the ironwork has been painted with a number of different systems (originally white, now grey). In the early 1960s a footway was added to one side of the bridge, which remains today. Good design and quality construction have given a durable bridge able to carry much heavier loads that originally intended or foreseen, and for much longer than had been imagined.

Located on the main Sydney to Melbourne route, the Prince Alfred Bridge carried huge volumes of traffic in its lifetime until 1977 when the Hume Highway was realigned to bypass Gundagai with the construction of Sheahan Bridge. The Prince Alfred Bridge continued to carry local traffic over the Murrumbidgee River between North and South Gundagai; until it was declared unsafe for vehicular and pedestrian traffic.

Two spans of the wooden viaduct over O I Bell Drive and a span over Landon Street were demolished in May 2021 due to safety concerns, as the sections had significantly deteriorated.

Due to further significant deterioration, the remainder of the timber viaduct was demolished in November 2021 due to the significant safety risk that the deteriorated timber viaduct posed to the public.

The Prince Alfred Bridge over the Murrumbidgee River is a three span, wrought iron, pin jointed Warren truss on cast iron cylindrical piers. A Warren truss, as originally patented, consists of a configuration of repetitive equilateral triangles that support a road on either the top or bottom chord. The trusses of the Prince Alfred Bridge have additional verticals at each cross girder location, designed to provide lateral support to the top chord. The trusses are suspended from a continuous horizontal top chord, supported on a nest of five rollers located on vertical pillars attached to the top of each pier. The four cylindrical cast iron piers are filled with soil and stones. The trusses support a timber deck, which carries two lanes of traffic. Longitudinal timber sheeting was added to the deck in 1959, and a footway was added on the outside of the truss in the early 1960s.