Long Gully Bridge, Northbridge, NSW
Miller Street, Northbridge, NSW
The original bridge as a suspension bridge
From the RTA website
With the land boom of the 1880s, land to the north of Long Bay, Middle Harbour, was sold and resold. The North Sydney Investment and Tramway Company or the North Shore and Middle Harbour Land Company made major investments in the area and planned to build a tramway and a bridge across Long Bay gully in order to open up the area for sales of residential land. A suspension bridge across the gully was opened to traffic in January 1892. It had taken two years and nine months to complete and cost 42,000 pounds. With a suspension span of 500ft centre to centre of towers, it was considered one of the engineering wonders of Sydney and became a great tourist attraction. A toll of threepence return for adults and one penny for children was charged. The disastrous crash of 1892 saw both the above companies go into liquidation. The Depression of the 1890s slowed land sales and Northbridge did not develop as had been hoped; the tramway was not built. In 1912 the bridge was handed over to the Government as a gift, on the condition that a tramway be extended to the north side and no toll charged. The tramway was extended over the bridge in 1913/4, with its terminus in Sailors Bay Road. (www.willoughby.nsw.gov.au/help/library/Northbridge.htm) Between its construction and its handing over to the Department of Public Works, the bridge was little used and poorly maintained for many years. Repairs and some strengthening works were carried out in conjunction with the construction of the tramway. (Main Roads Journal, August 1937, p 152) The DMR assumed control of the bridge in 1935 and inspections soon revealed serious corrosion in the steelwork and cables, partly attributable to defects in the design of the bridge. For example, water had been allowed to accumulate around the suspension rods as they passed through the cross girder ends in small, undrained reserves that had originally been filled with a bituminous mixture, which had not stood the test of time. The main suspension cables were also found to be weakened by corrosion. The bridge was carefully monitored and it rapidly became clear that replacement or substantial rebuilding would be necessary. From several options, it was decided that a large concrete arch span to support the deck of the old suspension bridge was the most satisfactory solution. The towers themselves were in very good condition and were recognised by the DMR as having local significance as a landmark and tourist attraction and as having considerable historical value. For these reasons they were retained and repeated in the design of the new work, with much attention to sympathetic design. The arch was designed and tested through the analysis of models within the DMR. (Main Roads Journal, August 1937, p 152-155) The construction contract was awarded to Hornibrook Bros. & Clark Pty. Ltd. The bridge was closed to tram and vehicular (but not pedestrian) traffic and work began at the beginning of June, 1937. While a 'Melan' system using a steel rib to serve as falsework and then reinforcement in the completed structure had been considered, the tenderers favoured the conventional system of timber falsework, and it was this system which was employed. An interesting innovation, however, was employed in the form of steel cylinders with base plate partly filled with a fine dune sand and fitted with a hardwood piston. The pistons bore the weight of the girders until it was time to strike the falsework when two small screw plugs on the cylinders could be opened to a carefully prepared schedule, with a large team of operators working to signals, and sand released so that the crown and then, gradually, the whole arch took up its own load. Worker safety was also an important factor in the design of construction methods for the bridge. The bridge was re-opened to traffic in late 1939. (Main Roads Journal, August 1939, p 113-116)
Long Gully Bridge, Northbridge, NSW
Miller Street, Northbridge, NSW
The original bridge as a suspension bridge
From the RTA website
With the land boom of the 1880s, land to the north of Long Bay, Middle Harbour, was sold and resold. The North Sydney Investment and Tramway Company or the North Shore and Middle Harbour Land Company made major investments in the area and planned to build a tramway and a bridge across Long Bay gully in order to open up the area for sales of residential land. A suspension bridge across the gully was opened to traffic in January 1892. It had taken two years and nine months to complete and cost 42,000 pounds. With a suspension span of 500ft centre to centre of towers, it was considered one of the engineering wonders of Sydney and became a great tourist attraction. A toll of threepence return for adults and one penny for children was charged. The disastrous crash of 1892 saw both the above companies go into liquidation. The Depression of the 1890s slowed land sales and Northbridge did not develop as had been hoped; the tramway was not built. In 1912 the bridge was handed over to the Government as a gift, on the condition that a tramway be extended to the north side and no toll charged. The tramway was extended over the bridge in 1913/4, with its terminus in Sailors Bay Road. (www.willoughby.nsw.gov.au/help/library/Northbridge.htm) Between its construction and its handing over to the Department of Public Works, the bridge was little used and poorly maintained for many years. Repairs and some strengthening works were carried out in conjunction with the construction of the tramway. (Main Roads Journal, August 1937, p 152) The DMR assumed control of the bridge in 1935 and inspections soon revealed serious corrosion in the steelwork and cables, partly attributable to defects in the design of the bridge. For example, water had been allowed to accumulate around the suspension rods as they passed through the cross girder ends in small, undrained reserves that had originally been filled with a bituminous mixture, which had not stood the test of time. The main suspension cables were also found to be weakened by corrosion. The bridge was carefully monitored and it rapidly became clear that replacement or substantial rebuilding would be necessary. From several options, it was decided that a large concrete arch span to support the deck of the old suspension bridge was the most satisfactory solution. The towers themselves were in very good condition and were recognised by the DMR as having local significance as a landmark and tourist attraction and as having considerable historical value. For these reasons they were retained and repeated in the design of the new work, with much attention to sympathetic design. The arch was designed and tested through the analysis of models within the DMR. (Main Roads Journal, August 1937, p 152-155) The construction contract was awarded to Hornibrook Bros. & Clark Pty. Ltd. The bridge was closed to tram and vehicular (but not pedestrian) traffic and work began at the beginning of June, 1937. While a 'Melan' system using a steel rib to serve as falsework and then reinforcement in the completed structure had been considered, the tenderers favoured the conventional system of timber falsework, and it was this system which was employed. An interesting innovation, however, was employed in the form of steel cylinders with base plate partly filled with a fine dune sand and fitted with a hardwood piston. The pistons bore the weight of the girders until it was time to strike the falsework when two small screw plugs on the cylinders could be opened to a carefully prepared schedule, with a large team of operators working to signals, and sand released so that the crown and then, gradually, the whole arch took up its own load. Worker safety was also an important factor in the design of construction methods for the bridge. The bridge was re-opened to traffic in late 1939. (Main Roads Journal, August 1939, p 113-116)