Bridges

Since the introduction of the limit state design method for Australian bridge design in the Austroads Bridge Design Code in 1992, there has not been an associated limit states timber bridge design code. The last applicable code was the working stress design version in the 1976 NAASRA Bridge Design Specification, which invoked AS 1720:1975 SAA Timber Structures Code.

The RTA is constantly under pressure to replace or significantly upgrade the remaining timber bridges on NSW roads, because they do not meet current loading standards and because of the large maintenance burden they impose. Many of these bridges employ truss designs that are of heritage significance, and are listed on the State Heritage Register. It has long been recognised that AS 1720 is particularly conservative when it is applied to the design of compression members in RTA timber truss bridges.

For this reason, a research and testing program was conducted at UTS in order to develop guidelines to allow reasonable prediction of compression strength of timber members in these bridges. The four primary areas that were studied are bridge timber properties, shear capacity of spacers, creep effects and buckling modes. From this testing, new guidelines have been developed.