A probabilistic framework to optimize the target proof load for existing bridges

Many existing bridges suffer from resistance deterioration due to environmental or operational attacks and thus may rate under the anticipated performance requirements. The proof load testing is a commonly used approach to evaluate whether the bridge would have the capacity of carrying a certain load. The magnitude of proof load will determine the safety level of the proven bridge. A proof load test, if not designed properly, may potentially cause structural damage and even collapse to the bridge. This implies that the load testing should be oriented by a probability-based framework in an attempt to control the failure probability of the bridge. However, the current engineering practice insufficiently considers the risk control of proof load testings. This paper presents a reliability-based framework to guide and optimize the proof load testing for existing bridges. A mathematical model is developed to compute the target proof load, where two types of constraints are considered simultaneously: the acceptable structural safety level and the economic costs. A numerical example is presented to demonstrate the applicability of the proposed method. The framework developed in this paper can be used in practical engineering as an auxiliary decision-making tool for bridge load testings.