Testing the viability of timber bridges is becoming increasingly important as replacement of this type of infrastructure is notoriously difficult.
Recent surveys show that there are in excess of 40,000 bridges in Australia and an estimated 27,000 of these are timber bridges.
Many of these timber bridges are at least 70 years old and located predominantly on regional roads. The most common type of timber bridge uses round girders fabricated from native hardwood spaced at 1000mm to 1500mm centres, transversely overlaid with decking planks.
The problem with the traditional timber bridges is that they were not designed for modern axle loads, which are typically three times greater than the loads expected at the time of construction.
The load test that has historically been used involves placing a legally-loaded vehicle with known axle loads and fixed geometry onto a bridge deck and measuring the deflections of the girders.
A team at the Centre for Built Infrastructure Research at University of Technology in Sydney, led by Keith Crews, has developed a new procedure for testing timber bridges.
The testing method measures the dynamic frequency of a deck for unloaded and slightly loaded (2 to 5 tonnes) conditions to obtain the same global stiffness and then the data is analysed by a computer program to determine the safety of the bridge.
The project, which originally ran between 2003 and 2005, was funded by the Commonwealth Department of Transport and Regional Services Grants in collaboration with IPWEA and a number of local councils in NSW.
“We are talking to Keith about how IPWEA might be able to deliver training to councils across NSW,” IPWEA Manager Roads and Transport Directorate Mick Savage.
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