Suspension Bridge

Item

Name of Item	Suspension Bridge
Item Number	4309506
Type of Item	Built
Item Sub-Type	Pre-1948 Concrete Slab and Arch Bridges
Roadloc
Address	**** Miller Street Northbridge 2063
Local Government Area	Willoughby
Owner	Roads and Maritime Services (replacing Roads and Traffic Authority)
Current Use	Road bridge
Former Use	Road bridge

Statement of significance

The Suspension Bridge in Northbridge is of State significance. It was built as a steel suspension bridge with sandstone turreted towers by a private syndicate to promote residential development and was opened to traffic in in 1892. It was transferred to the Department of Main Roads in 1935 and rebuilt as a reinforced concrete two rib arch bridge, with original towers in tact, in 1939.

The bridge is intimately associated with the residential development of the area to the north of the bridge, essential infrastructure which allowed the area's development to proceed in the late nineteenth century. The process of the design and construction of the arch is illustrative of an era in the history of bridge building in the Department of Main Roads (DMR) and of contemporary concern with aesthetic and historical landmarks and their preservation. The bridge is a distinctive structure, both graceful and impressive, and situated in a highly attractive setting. The design of the arch demonstrates creativity in its response to a highly individual technical problem and in its aesthetic sympathy with the original towers of the suspension bridge. The concrete arch makes an important historical, technical and aesthetic contribution to the suspension bridge, which is already highly valued by the community, and is of considerable interest in its own right.

Date Significance Updated

03 November 2003

Description

Designer	J E F Coyle with input from Prof W H Warren (Sydney University)
Builder	Concrete arch by Hornibrook Bros & Clark Pty Ltd

Construction years	1892 - 1939
Physical description	The original suspension bridge had a 500 ft main span supported by steel cables and steel hanger rods. The deck was stiffened by an undertruss which was pin connected at the centre of the span. The steel cables were supported on ornate sandstone towers and anchored into bedrock at each end of the gorge. The wooden deck carried two lanes of traffic plus two tram tracks and footways. Deterioration of the bridge due to corrosion led to the replacement of the suspension design by an arch in the 1930s. With a main span of 344 feet, the arch consists of two concrete ribs, peaking some 167 feet above stream level. Supported on the arches are columns carrying the deck on 14 reinforced concrete beam slab spans. The deck has expansion joints at the large piers directly over the arch springings. These also transfer wind load from the arch and deck back to the foundations. Connecting these to the original towers are 50 foot concrete beam spans. The concrete detailing was done in Gothic and Norman styles to reflect the Gothic sandstone towers, the main piers being given Norman castle features. As part of the reconstruction the roadway openings through the towers were increased to thirty feet, and walkway openings cut through the towers. The bridge has light standards supported by the concrete railings.
Physical Condition and/or Archaeological Potential	Original condition assessment: 'Both the original sandstone towers and the concrete arch structures are in good condition. The towers show minor blemishes from leaching and there is some vegetation growth in need of removal. Concrete is generally in very good condition although some of the pedestrian railing areas have some vertical cracking. Close inspection of the arch was not possible, but the concrete appears in very sound condition. The original suspension system has been removed, and no evidence of the original anchorages was noted, but these may exist. The arch was supported during construction by timber trestles supported in turn by timber piles. As the area under the bridge has now been developed as playing fields with the creek carried in a culvert system, it is likely that any original piles would be well buried' (Last updated: 22/10/2003.) 2007-08 condition update: 'Fair.' (Last updated: 17/4/09.)
Modifications and dates	Suspension system (which was corroded) was replaced by a concrete arch in 1937-39. Floodlighting was installed by Sydney electricity on 1992.
Date condition updated	17 April 2009

History

Historical notes

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 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. (http://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)

Listings

Heritage Listing	Reference Number	Gazette Number	Gazette Page
Local Environmental Plan		107	9268

Local Environmental Plan	-	141	7887

Register of the National Estate	002888	1/13/027/0

Heritage Act - s.170 NSW State agency heritage register

Assessment of Significance

Historical Significance	The bridge is intimately associated with the residential development of the area to the north of the bridge, essential infrastructure which allowed its development to proceed in the late nineteenth century. The concrete arch which was built 1936-9 is a fascinating episode in the bridge's history. The process of the design and construction of the arch is illustrative of an era in the history of bridge building in the Department of Main Roads. It is linked with the local historical theme of engineering and building the road system. The use of the concrete arch solution to support the older bridge and to allow its landmark features to be retained was a creative and heritage-sensitive response to an infrastructure problem in an era long before heritage values and processes were enshrined in legislation.
Historical Association	****
Aesthetic/Technical Significance	The bridge is a distinctive structure, both graceful and impressive, and situated in a highly attractive setting. The design of the arch demonstrates creativity in its response to a highly individual technical problem and in its aesthetic sympathy with the original towers of the suspension bridge.
Social Significance	****
Research Significance	The technical aspects of the arch's construction are well documented and the fabric of the bridge, with the associated documentation are of enduring technical and research interest.
Rarity	The bridge is unique in NSW in appearance, and as a solution to a unique problem.
Representativenes	****
Integrity/Intactness	Intact
Assessed Significance	State

References

Type	Author	Year	Title
Written	Willoughby Council website �		http://www.willoughby.nsw.gov.au/help/library/Northbridge.htm

Written	Department of Main Roads	1937	Main Roads

Written	Department of Main Roads	1939	Main Roads

Study details

Title	Year	Author	Inspected by	Guidelines used
Pre-1948 Roads and Maritime Services (replacing Roads and Traffic Authority) Controlled Concrete Slab and Concrete Arch Bridges in NSW	2004	Burns and Roe Worley and Heritage Assessment And History (HAAH)		Yes

Custom fields

Roads and Maritime Services (replacing Roads and Traffic Authority) Region	Sydney
Bridge Number	172
CARMS File Number	****
Property Number	Bridge
Conservation Management Plan	****