Setting Up the Bearings.

From Engineering Heritage New South Wales


   The components of the first bearing arrived in Sydney in late 1926 and were unloaded from the ship on 14 October. This was done by the ship’s cranes onto a barge which was taken via the dock of the workshop at Milsons Point for storage until it was needed.

Base-castings for the first bearing being unloaded at Milsons Point. 14 October 1926. SARA NRS 12685
Bearing components being moved into the workshop dock for unloading and storage. 14 October 1926. SARA NRS 12685<

   The description of the procedure for erecting the bearings which follows is given by Bradfield in his paper to the Institution of Civil Engineers in 1934 and is here quoted in full. The included photographs and captions do not appear in the original publication. The limited number of photographs available means that the sequence of events is illustrated using images from different bearings.

   Main Bearings:– The skewbacks for the main bearings were poured up to the limits of the special concrete under the bearings. Preparations were then made for securing the twenty-four 4½-inch diameter bolts holding down the six base castings of the bearing, and in order to locate these bolts and to maintain them in correct position a temporary adjustable steel template was utilized.

Eastern bearing Dawes Point with the holding down bolts held by the steel template. 24 February 1927. SARA NRS 12685
Base-castings in position at Milsons Point. Museum of Sydney, Erection Wages Album.<


   The base-castings were lifted in turn from the punt to a position close to the skewback by the 25-ton crane, and were then hoisted into position by a special electric winch on a steel gantry spanning the location. With the aid of special shackles, which allowed the castings to hang approximately at their correct slope, the first casting on the outside was lowered into place and accurately checked for position. The remaining castings were then lifted and bolted to the preceding ones.

Viewed from above looking towards the harbour the lower web is in place and the diaphragms are being fitted. Museum of Sydney, Erection Wages Album.
The upper web-plate about to be lifted. Museum of Sydney, Erection Wages Album.<


   The lower web-plate, weighing 33-tons, was next erected, bolted to the castings beneath and held up by a steel bridle ; the cast steel diaphragms were bolted to the web-plate, and the upper web plate was lowered into position, resting on the upper edges of the diaphragms. The lower saddle, weighing 20 tons, was next erected and the bearing was ready for checking in its correct position.

The upper web-plate nearing its position. Museum of Sydney, Erection Wages Album.
The lower saddle of the bearing pin is in place and the bearing is resting on jacks, ready for concreting. The tower of large concrete slabs in the distance is probably the temporary concrete pier used to mount the theodolite to position the bearing. 25 October 1927. SARA NRS 12685<

   The completed bearing formed a rigid unit which was capable of being supported at the four corners of the base, clear of the space beneath the bearing. Heavy steel stools were placed outside the limits of the bearing, carrying 100-ton hydraulic jacks perpendicular to the plane of the base at each corner, and a 100-ton jack parallel with the plane of the base at each lower corner. Special steel castings were bolted on the sides of the outer base-casting to receive the jacks, and by means of the six jacks and two screws near the lower jacks any desired small adjustments of the position of the bearing could be made.

The bearing ready for concreting. Note the heavy cast steel castings bolted to the base-castings and the jacks. The frame for the overhead hoist is also visible. SARA NRS 12685 26 May 1927.
Beneath the bearing the stools at first used to support the base-castings are seen, and will soon be removed to allow concreting. The more distant stool which supports the jack will remain. Heavy reinforcing bars below the bearing are ready to be spaced out and fixed.24 April 1927. SARA NRS 12685<

   The check survey to locate the position of the main bearing was made on discs of the same diameter as the main pin, 14½ inches, which were placed in the pin recess in the lower saddle, necessary adjustments being made with the jacks. A theodolite was set up with its line of collimation coinciding with the true axis of the main pin, on a temporary concrete pier erected on the centre-line of the bridge between the two main bearings.

Concreting beneath the Eastern main bearing. 26 May 1927. SARA NRS 12685
Concreting beneath the Eastern main bearing.26 May 1927. SARA NRS 12685<

   With the load of the bearing taken by the jacks, the steel stools under the base-castings were removed, the reinforcement placed beneath the base, and the No. 1 special concrete poured in one continuous operation lasting 15 hours. When the concrete had set, the jacks were removed, and the main pin, upper saddle, nuts and washers were assembled in place ready to receive the lower chord.

The upper saddle being lifted and moved into position. Museum of Sydney, Erection Wages Album.
The upper saddle about to be mated to the main bearing pin. Museum of Sydney, Erection Wages Album.<
The bearing would seem to be complete as the upper saddle is in place, though the hoisting and jacking gear is yet to be dismantled. 5 February 1927 SARA NRS 12685.
A bearing completed and the site tidied of construction gear. . Museum of Sydney, Erection Wages Album.<

  

Cookies help us deliver our services. By using our services, you agree to our use of cookies.