| Modern Highway Bridges are designed and built to last at least 75 years. Once a Bridge is designed and constructed, it is open to the traffic and it starts carrying actual vehicle loads. However, because of environmental factors (i.e. corrosion) and increase in traffic load, deterioration of bridge members are usually observed before the bridge reaches mid-life. Therefore the design cannot guarantee a life long safety. In order to insure the safety of the bridge under operating conditions, bridge condition must be evaluated periodically.;Currently there are three methods available to evaluate the capacity of existing bridges: Allowable Stress Rating (ASR), Load Factor Rating (LFR) and Load and Resistance Factor Rating (LRFR). The most commonly used method in the past three decades has been the LFR. However, in 2001 AASHTO introduced LRFR, based on the reliability theory and actually used by most bridge evaluators. Using this new method the performance of a given bridge or its component can be estimated based on its reliability index. By taking into account the variability in load and resistance of the component, this reliability index increases public safety. |
