Tharwa Bridge - Historic Engineering Marker #28 Cuppacumbalong, Australian Capital Territory, Australia
By Team MavEtJu on 18-Oct-15. Waypoint GA7634

Tharwa Bridge - Historic Engineering Marker #28

The bridge is a direct and continuing connection with technical, commercial and social environments in Australia 100 years ago, in the decade before federation of colonies into one nation. It is the oldest bridge in the A.C.T., and the four central spans are the oldest surviving examples in service of an innovative timber truss designed by Australian born engineer Percy Allan - more than 100 bridges of this type were built in the next 35 years.

In a period marked by financial difficulties in the emerging nation, Allan's truss design demonstrated the ability of Australian engineers to research and develop up-to-date and cost effective technology specific to Australian materials, workers skills and construction methods.

Allan's truss designs used newly published (1893) structural data on Australian hardwood timbers by Professor Warren of Sydney University. Warren's data, applied by sound analytical methods, allowed Australian hardwoods to be used efficiently in major bridge construction. Allan's designs modified the American Howe truss to provide a standard (90 feet = 27.5 metres) pony truss as at Tharwa, and a longer (110 feet = 33.6 metres) overhead braced truss.

Tharwa is one of the earliest "Allan truss" structures - possibly the fourth completed. Its construction in 1894/95 followed immediately after publication in 1893 of Warren's test results.

Use of timber as the principal material - in this case NSW North Coast hardwoods - reflected a policy to reduce imports, and to use local labour. Timber workers were more available inland than stone masons or bricklayers, with cost advantages for construction and later maintenance.

Construction of the bridge followed forty years of political pressure - over that time agricultural and grazing development expanded in the region, and Government railway extended to nearby Michelago in 1887 with increasing need to move sheep and wool across the Murrumbidgee and to give access to the Monaro region to the south, including the goldfields at Kiandra.

Contemporary local significance of the bridge and the extent of settlement in the area can be gauged from newspaper reports of the opening ceremony. Report of 30 March 1895 in "The Queanbeyan Age" newspaper stated that approximately 1000 people were in attendance, with band and local military unit. This report also provides an interesting comment on rural society of the time.

During 1994 the A.C.T. Government Department of Urban Services undertook timber replacement and restoration of some metal sections. The life of the bridge can be extended indefinitely, and this effectively meets the Tharwa community view that the bridge gives a distinctive quality to the locality, as well as direct access at the village.

Contents of the plaque:

THARWA BRIDGE

This first permanent bridge over the Upper Murrumbidgee river was opened on 27 March 1895. It provided a reliable road crossing between the Sydney-Cooma railway and Tharwa district grazing lands. The four central spans remain from the original bridge. They are the oldest examples in service of the durable cost effective timber trusses designed in 1893 specifically for Australian conditions by Percy Allan of the NSW Public Works department.

DEDICATED ON THE CENTENARY OF THE BRIDGE OPENING BY THE INSTITUTION OF ENGINEERS, AUSTRALIA AND THE DEPARTMENT OF URBAN SERVICES, ACT. 1995

When logging this virtual, please add a photo of yourself or your GPSr at the plaque or with a tree of your choice (make sure you can describe which tree according to the earlier mentioned report).

For more information, please see this page at the Heritage Register at the Engineers Australia website: https://www.engineersaustralia.org.au/portal/heritage/tharwa-bridge-murrumbidgee-river-1895