Fitness-for-purpose evaluation of bridges using health monitoring technology

Evaluation of in-field performance of bridges is dependent on many assumptions. Those associated with the analytical model (boundary conditions, influence of curbs, membrane action, the model, etc.) and the resistance model (material properties, condition, fatigue damage, etc.) are commonly recognized as the sources for the differences between theoretical strength and in-service strength as demonstrated by proof load testing worldwide. Likewise there are many assumptions associated with the loading model and the related load factors. Bridge health monitoring technology is providing the opportunity to monitor the in-service performance of bridges. A methodology is presented for undertaking a fitness-for-purpose evaluation (FPE) of bridges based on health monitoring and theoretical data. The methodology is set in the context of limit state codes and illustrated by four case studies, two from Australia and two from New Zealand. Each of the bridges is steel, lowly rated theoretically, and located on relatively low-trafficked routes. The outcome of the FPEs indicates that the structures are safe to remain in service under current loading conditions although interventions are suggested in the relatively short term. Health monitoring was also able to identify the reasons for the significant differences between the theoretical and the health monitoring results. Many of the reasons are related to the specific loading conditions at the site and could not readily have been identified using theoretical approaches, behavioral testing, or proof load testing. Although this technology has its limitations, it is providing better information for those involved in the decision-making process and helping to target actions based on risk.