Sunday, 29 December 2013

1874 technical details of the Windsor Bridge

The Windsor Bridge over the Hawkesbury River was officially opened on the 20 August 1874. The town celebrated in great style with about 7000 attendees and the day was observed as a general holiday. The Australian Town & Country Journal published the interesting sketch below, as well as an informative article about the construction of the newly opened Windsor Bridge on the 22 August 1874.

The New Bridge over the Hawkesbury at Windsor. Australian Town & Country Journal, 22 August 1874, p. 20. 

 The article, retrieved from Trove, is reprinted in full below:

This want of a bridge over the Hawkesbury River at Windsor has been felt for many years. In 1864, [politician James Augustine Cunneen 1826-1899] presented a petition from the inhabitants of the district for the erection of a bridge at Windsor, but it was not until June, 1871, that the Legislative Assembly voted the necessary funds for the construction of a low level bridge.

There was much diversity of opinion as to the advisability of constructing a low level bridge at the site proposed, as the floods rise there to a height of more than 50 feet above low water. The Commissioner and Engineer for Roads was however, instructed by the Government to prepare designs for a low level bridge, and to invite tenders for its construction. Mr. Andrew Turnbull's tender was accepted in December 1871 and the work began on the 15 January 1872.

According to the original design, the total length of the bridge was to be 406 feet, composed of eight main spans of 44 feet each, and of two approaches 32 feet and 22 feet respectively. The abutments were to be of timber; and the nine intermediate piers of cast iron cylinders and screw piles braced with strong wrought iron beams. The screw piles and cylinders to be sunk to the rock, and lewised thereto by heavy wrought iron bolts, previous to being filled up with cement concrete.

In October 1872, three of the iron piers had been sunk 4 feet into the rock to the depth of 25 feet below river bed; each column was lewised with four inch bolt and filled up with strong cement and concrete, supporting a ring of 9-inch radiating bricks; enclosing a cone of concrete to the top of the pier. From the nature of the strata found in sinking those piers, it became doubtful whether screw piles could be used, as the bed of the river to the rock consisted of drift timber, silt, and boulders deposited by floods.

A test screw-pile, 2 foot 6 inches in diameter, was, however, put down in the middle of the stream; but the rock could not be reached, owing to the difficulty of removing the drift timber. Mr. Bennett, the Commissioner and Engineer for Roads, then decided to give up the screw-piles and to use cylinders for all the piers.

Many freshes and several heavy floods retarded operations; and the sinking of all the piers could not be completed until December, 1873. Although a few feet only of the iron columns appear above water, the cylinders reach to an average depth of 40 feet below summer level. By the use of the sand-pump and air-lochs, boulders, drift-wood, and logs, several feet in thickness, were removed at considerable depths, and each pillar firmly bedded and lewised four feet into the solid rock. The bracing beams were also fixed below water by divers, before the erection of the superstructure.

The extraordinary floods at Windsor which reach to a height of 51 foot above low water, or 36 feet above the decks of the bridge, made it necessary to have the superstructure unusually strong; and much ingenuity is shown in tho design for securely fastening it to the piers. The deck is 21 feet 6 inches wide; and is composed of planks five inches thick, securely fixed to five ironbark girders 17 and 18 inches by 16 inches and 44 feet long, strongly bolted to corbels and capsilla firmly secured to-the iron piers. The whole of the timber is ironbark, which has little buoyancy under water, and the girders are fine specimens of our colonial wood.

All the joints are covered with iron fish-plates, bolted with inch bolts, and it is evident from the massive fastenings throughout, and the great strength of the structure in every detail, that the engineer has taken every precaution to prevent the floods from making a breach in any part of the bridge. The handrail is also ingeniously contrived to protect it from the large quantity of drift timber brought down by the floods. The foot of every rail post swings on a stout bolt secured to the girders, and the top is jointed to a two-inch wrought iron pipe, provided with sockets and collars at every 44 feet; the total length being held in place by two iron couplings in such a manner that one man can lower the whole alongside the girders in ten minutes.

The amount of Messrs. Turnbull and Dixon's contract was £8287; but an additional expenditure of about £2000 was rendered necessary by the substitution of cylinders for screw piles in the piers, and by the addition of two spans to the bridge to prevent future encroachment on the approaches. It was observed that moderate floods bring large deposits of sand and drift; but that heavy floods scour the river bed to a considerable extent.

The total length of the bridge as completed is 480 feet. The abutment on the Windsor side is built of iron backed with masonry in cement; and that on the opposite bank is protected by sheet piling reaching below summer level. A new cutting has also been made on the Wilberforce side for the approach, which is covered with ironstone gravel. The number of cast-iron cylinders used in the piers is 130. They are six feet long, and 3 feet 6 inches in diameter, and their weight exceeds 150 tons. They were cast at the Mort's Dock and Engineering Works at Balmain; and are another instance of the facility afforded for such works by colonial establishments.

The inhabitants of the district may well be pleased at the completion of this fine bridge; and it will be satisfactory for them to know that it has been ascertained by the officers of the Department of Roads and Bridges, in reference to the traffic and the disastrous floods of the Hawkesbury River, that, while the deck of the Windsor bridge is free from flood, the Richmond bridge is covered with three feet eight inches of water, and that the Windsor bridge is crossable twenty-two hours after the stoppage of the traffic at the Richmond bridge.

Great credit is due to the contractors, Messrs, Turnbull and Dixon, for their energy and perseverance in carrying out, without any accident, such an important and difficult work, to the satisfaction of the Commissioner and Engineer for Roads.

More about the official opening of the bridge will follow.

1 comment:

  1. Very interesting article, especially under the circumstances of the RMS approved demolition of the bridge.