Non deterministic approaches in current structural codes for assessing the safety and reliability of bridges

The main goal of bridge agencies is to ensure the safety of the traveling public and the health of the economic cycle by maintaining a safe bridge network system and extending its useful life at minimal life cycle cost. To achieve this goal, bridge agencies select an appropriate bridge management approach that may include bridge instrumentation for health monitoring purposes. The implementation of such monitoring systems requires the availability of damage assessment models to evaluate the degree of structural degradation that would trigger a warning mechanism when a bridge reaches a critical state. Health monitoring systems include instrumentations for the non destructive evaluation of materials, load testing, corrosion detection, and analytical models for using the collected information for load rating. To this end, appropriate criteria are needed to identify threshold values that separate the damage state into critical and noncritical stages. Different approaches exist for assessing the performance of bridges. The most commonly used method of bridge evaluation is the so called condition rating method. But recently, reliability assessment methods based on non deterministic concepts have also been widely recommended in the literature and in bridge codes. The condition rating and the reliability-based performance assessment techniques serve the same purpose but have different theoretical bases and completely different formulations. The object of this paper is to present an overview of current code-specified criteria for assessing the safety and reliability of bridges.