Bridges: a practical guide to loads and strengthening

Like those in the rest of Australia, Tasmaniars aging road bridge stock is expected to carry higher and higher loads over time. Even the current general access vehicles often exceed the original design standard for many bridges in service throughout the State. The increased use of high productivity vehicles and higher mass limit axle loadings means that many bridges either require strengthening or replacement in order to safely service the community and freight industry. Fortunately, there are a number of practical and relatively cost effective options for increasing the capacity of a bridge. This paper reviews the history of design loads, compares them with current loads and looks at four recent case studies where structures have been strengthened using innovative methods that allow a significant increase in vehicle loadings. The four case studies are: Mersey River Bridge; South Esk River Bridge and Pipers River Bridge; Duck River Bridge; Emu River Bridge. The result in each case was a practical and cost effective outcome that improved each bridge from an original design of a 33T truck to take a suite of vehicles including 68T B-Doubles, therefore improving the economic life of the asset.