Assessment of bridges by proof load testing

Throughout the world, many countries are faced with the problem of ageing bridge infrastructure that is being called upon to carry increasing loads. With the difficulties associated with gaining funding to replace or rehabilitate these bridges, asset managers must ensure that the most efficient use is made of the existing infrastructure. It has been shown that theoretical assessment of bridges by analytical means often leads to conservative estimates of capacity. Many bridges therefore have been posted with load limits which do not accurately reflect the structural capacity of these bridges. Various methods of assessing bridge capacity are adopted by. road authorities throughout the world. These forms of assessment include analytical rating, calibration of analytical models by supplementary load testing and assessment by proof load testing. Proof load testing has consistently demonstrated that bridges often have reserves of strengths in excess of that indicated by theoretical analysis. The aim of proof load testing is to determine a realistic bridge load rating which accurately reflects the load capacity of the bridge. This thesis investigates the use of proof load testing in the assessment of bridges and its application to the Australian bridge infrastructure. The procedures used in proof load testing do not vary greatly between countries but the magnitude of the loads applied and the load factors used to calculate a load rating vary significantly. The procedures and practices adopted internationally were reviewed and adapted to suit Australian bridge infrastructure and conditions. The methodology was evaluated through a series of pilot proof load tests and subsequently potential improvements were identified. One of the challenges associated with proof load testing is the determination of the proof load that should be applied. In this thesis, structural reliability methods have been used to determine the proof load required to achieve a desired level of safety after testing. These methods were extended to incorporate the expected residual life of the structure and to investigate the resulting effect on the proof load required. Reliability theory has also been used to assess the risks involved, and the benefits gained by proof load testing. These risks and benefits are expressed in terms of a decreased probability of failure or an increased safety index after a successful proof load test. The methods developed have been applied to the results of the proof load test conducted on the South Pine River Bridge