Rating of timber bridges in New South Wales: a simplified method of determining the priority for replacement of timber bridges

There are about 980 timber beam and 93 timber truss bridges in New South Wales for which the department is financially responsible. Over the past years, maintenance expenditure on timber bridges has been in the order of $8 million per annum. This expenditure is expected to increase in the near future unless the present rate of replacement of the timber truss and beam bridges with new structures is accelerated. In the stringent economic climate funds are not available to replace all these timber bridges. Priority for replacement has to be determined by taking into consideration the inadequacies of the bridge and its immediate approaches, together with a number of other factors. A simplified method of rating timber bridges was therefore developed, which rated the three most commonly given reasons for bridge replacement (that is, high repair cost, inadequate carriageway width and poor alignment) and also considered other relevant factors such as volume of traffic, flooding, heavy load movement and availability of alternative routes. The rating method allowed the bridges to be ranked under three categories, viz, replacement in the short term, replacement in the medium term and replacement in the long term. The ranking, together with route strategy for the particular road, is used to finally determine the priority for replacement of the bridges (a).