Role of load history in reliability-based decision analysis of aging bridges

Bridges deteriorate with time due to aggressive environments and are subject to ever-increasing traffic loads. This results in reduction of their reliability, which may eventually fall below an acceptable level. A successful proof load reduces the uncertainty associated with resistance of the bridge and so increases its reliability. Also, if a bridge has survived for T years of service, its resistance is higher than any of the prior imposed loads and so is influenced by its load history. Thus, the reliability of service-proven (i.e., older) bridges would increase. However, the influence of deterioration and increases in traffic loads may negate this expected increase. The paper considers the effects of load history (proof loads and prior service loads) on the reliability of aging bridges. The influence of bridge age and the magnitude of proof loads on updated estimates of bridge reliability is examined. It was found that proof load testing may not be cost effective if the casts of bridge failure (unsuccessful test) and the test itself are considered in a preliminary risk-cost-benefit analysis. The influence of prior service loads on the reliability of existing bridges significantly increased annual bridge reliabilities. The reliability-based approach presented in the paper provides an improved decision-making framework for the assessment of aging bridges.