Hawkesbury River Railway Bridge

The Hawkesbury River railway bridge carries the Main Northern railway line across the Hawkesbury River, connecting just north of the town of Brooklyn, on the northern outskirts of Sydney with Cogra Bay, New South Wales. The railway bridge was to be the last link in a railway network that linked Adelaide, Melbourne, Sydney and Brisbane.

The Original Bridge

The original bridge was regarded as a major engineering feat at the time. It was officially opened on 1 May 1889.

The contract for the original bridge was awarded to Union Bridge Co of New York in January 1886.

The Union Bridge Co sub-let nearly all manufactured parts of the project, retaining only the manufacture of the eye-bars and pins for the pin-jointed trusses (using steel from the Steel Company of Scotland). Louis Samuel of Sydney was the contractor for masonry work. Anderson and Barr, New York, were the contractors for the foundations. The deepest pier was 205 ft below rail level. In accordance with their experience and common practice of the day, Anderson and Barr decided to sink the caissons by 'open dredging' although provision was made in the caisson design for compressed air working.

The superstructure was erected by sub-contractors Ryland and Morse, of Chicago. The steel superstructure was obtained from Arrol and Co., the steel bars being specified to be rolled by the Steel Company of Scotland and Colville, Glasgow, the manufacture of the steelwork and ironwork for the caissons being undertaken by Head, Wrightson and Co., Stockton-on-Tees. Burge and Barrow, of Rainham, Kent supplied the cement. 'The upper boom, or compression member, and the vertical member connecting it with the lower chord or tension member are built up of steel plates and angles. The lower chord and the diagonals are formed of solid steel eye-bars in groups. The whole forms what is known as a Whipple truss,...'.

See Engineering 1887/02/25, Engineering 1887/03/11 and Engineering 1887/04/08 for details of the girders. The foundation caissons were described and illustrated in Engineering 1887/04/22.

1890 C. O. Burge described aspects of the construction work, including the considerable difficulties in attempting to sink the caissons in a truly vertical position

Operational problems came to light in connection with the river piers at an early stage. Possible causes and solutions were offered by W. Ewald, a bridge engineer from Fahrhaus, Hamburg, in a letter to The Engineer

Inspection of the piers in March 1890 revealed poor quality concrete, unprotected by the iron shell of the caisson. The Union Bridge Company spent nine months replacing faulty material. In 1937 a crack formed in one pier due to tension applied by the contraction of adjacent spans resting on seized roller bearings. Inspections by divers revealed extensive rusting of the caisson, but more importantly, the concrete inside could be easily penetrated by pushing a rod into it. Other piers had similar faults. Drilling indicated a potentially dangerous condition. Alignment of the piers had been regularly measured since 1890 and the results showed that all piers were settling gradually and moving laterally, downstream. Therefore, after only fifty years of service, the bridge was earmarked for replacement. In the meantime temporary repairs were made, a speed restriction was imposed and single line working was introduced. The new bridge was built on the upstream side of the old bridge by the Railway Department.

In 1928 the floor system was strengthened to take higher loading. The main truss members were not strengthened, except for four 5-inch-diameter pins in the top chord of each truss, where the stress was relieved by the provision of U-bolts supported in heavy cast-steel saddles. Within twelve months of the opening of the bridge the Contractors were called upon to remove faulty material at the top of the caissons. A cofferdam erected successively at each pier exposed concrete of the poorest quality in each case. At No. 2 pier, for example, 15 cubic yards of what amounted to a mixture of sand, mud, and a little cement had to be removed.

Numerous problems arose, and in 1938 a severe crack in one of the piers was discovered and it became necessary to replace the entire structure. The amount of traffic being carried during World War II made the replacement extremely urgent.

Regarding the severe crack in No.4 Pier in 1938, Major-Gen Albert Cecil Fewtrell of the NSW Railways found in an American text book that the interior of the piers of the bridge comprised rubble, and noted this was contrary to the specification, which required concrete to ensure stability when the iron casings rusted. Fewtrell maintained that he was responsible for identifying this defect and avoiding a major rail catastrophe.

Early Controversy

The selection of an American main contractor was controversial. Criticism from British commentators was to be expected, and liable to be dismaissed as 'sour grapes', but the following extracts of a letter in The Engineer in 1886 may be of interest:
'Sir,- I am a foreman bridge·builder in a big shop, and perhaps not quite so much polished as some of your correspondents. Our firm paid their guinea and sent in a design, and of course I had to take the drawings in hand, to see what the work could be done for; and having done a lot of New South Wales work, I knew very well what Sir John Fowler's inspectors would want, and shaped my estimate accordingly. This week the Union Bridge Company's agent asked for another guinea, for which he is going to let our people give them a tender for the caissons, and the photograph copies of drawings have been given me to look over for a price to be made up. No wonder Americans can get work, if they can get their customers to take such light jobs. When our engineer was on with his designs he made a deal to do about collapsing pressures, in case caissons had to be Pumped dry for excavation, and a deal of stuff of that kind; but it appears he did not know much. The Yankee caissons are quite a different thing, and if we get the job, my men will say we had better start on milk-cans. Except the bottom lengths, the plates are 3/8in. and 1/4in. thick for the outer skin and inner tubes, with a few light braces between, that, for what they are worth, might almost be dispensed with. Iron, 20 tons per square inch, as against 22 tons when English work is wanted; no planing specified for edges of plates; only one piece of each kind to be put together ; holes punched instead of being drilled or rimered out. Mr. Dixon might well say it was a light bridge - cheap and nasty. We pay so many guineas for tendering that I feel myself transformed into a
GUINEA PIG.'

Editorial in The Engineer 1886/04/09: 'Either the Union Bridge Company, of New York, has very much under-estimated the work to be done in the construction of the Hawkesbury Bridge, in New South Wales, or our English engineers have not only over-estimated it but put on a big sum for possible difficulties in constructing foundations 185ft. below high water. The site of the bridge is across the tidal estuary about thirty miles above Sydney, and the depth of mud and sand very great. The Union Company's tender of £327,000 was accepted as the lowest ; but in accepting it, alterations requiring an increase of £40,000 were, we believe, stipulated. This will bring the cost up to £367,000, without any of the extras which are no doubt to be built up as the work proceeds. How the New South Wales people will like the bridge twenty years after its completion of course remains to be seen ; but how they will like some kinds of tension members connected with it, commonly called wire pullers, will perhaps be seen much earlier. It is to be regretted that this bridge is not to be constructed by English constructors, but they are better without it if they could not get a fair price in a fair way. English firms of repute do not seek extras; but it must also be said that some of them want what, in the face of world-wide competition, are prohibitory prices for what they do.'

The Present Bridge

Design and construction of a replacement bridge commenced in 1939. The design, foundation work and fabrication of the new bridge were undertaken by the New South Wales Government Railways. See here for an I.C.E. Paper on the construction of the new bridge

See Also

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