Bridges

Theoretical assessments of a bridge network to AS5100.7 identify many bridges operating at margins smaller than those embodied in AS 5100.7. The cost of strengthening these bridges is unpalatable and the consequences of restricting access are unacceptable. Inspections of these bridges in most cases indicate they are performing satisfactorily leading one to question the plausibility of the assessments.

A review of Australian and international assessment practice suggests that Australian bridge assessment, as set out in AS 5100.7 provisions for bridge assessment, contains a number of conservative assumptions that could be refined. While AS5100.7 adopts a design based philosophy, international bridge assessment standards adopt both a reduced reliability index and reference period for assessment compared to design. This risk-informed approach results in less conservative parameters for assessing operational bridges compared to the design of new bridges that are added to the bridge inventory. In essence, the parameters used to remove bridges from service differ significantly from those used to add bridges to the inventory.

The paper discusses the assessment of a group of bridges that remain operational but lie outside the assessment parameters of AS5100.7. The risk-informed management of these bridges includes bridge specific Structure Management Plans to help ensure the refined assumptions are consistent with the operational conditions.

The paper sets out the key Operational Parameters for consideration. These include the adoption of system parameters consistent with the observation that a more conservative approach is appropriate for bridges that lack redundancy, ductility or inspectability compared to those that do. The result is riskinformed management that provides an opportunity for asset managers and planners to optimise network development while risks are being managed.