Impact of load and resistance factor rating (LRFR) on TxDOT pan girder bridges

Highway Bridges when designed and built are assumed to last for at least 75 years. However, once a bridge is open to traffic and starts carrying its actual loads, it also starts to deteriorate. This is mainly because of environmental factors and increase in traffic load. For this reason bridge condition must be evaluated periodically to insure bridge safety under in-service conditions.

There are three methods to evaluate the load capacity of existing bridges: Allowable Stress Rating (ASR), Load Factor Rating (LFR), and Load and Resistance Factor Rating (LRFR). In the last 30 years LFR has been the most commonly used method. The LRFR was introduced by AASHTO in 2001 based on reliability theory. The performance of a given bridge or its component can be estimated based on its reliability index. Taking into account both the variability in load and resistance reliability index increases the public safety.

There are approximately 4,000 reinforced concrete pan girder bridges throughout the state of Texas. Many of these bridges were constructed in the 1940s and 50s. These bridges were designed with a live load less than the current AASHTO LRFD live load of HL-93. These bridges have been load rated using LFR and some are posted and some are not. The aim of this project is to apply LRFR to a randomly selected number of these pan girder bridges and to determine if there are significant changes in existing posting requirements.