Development of State-Specific Load and Resistance Factor Rating Method

Recognizing the limitations of the generic truck weight data and conservative assumptions made during the calibration of live load factors for bridge rating, the AASHTO load and resistance factor rating (LRFR) manual for bridge evaluation provides sufficient flexibility and allows state agencies to adjust the live load factors based on their individual conditions and site-specific or state-specific information. This paper describes a reliability-based process that can be followed to perform such adjustments and illustrates its application using an example in which the procedure was followed during the calibration of a LRFR methodology for New York State bridges. This methodology is applied to the rating of existing bridges, posting of understrength bridges, and checking of permit trucks. The live load models used during the calibration are based on weigh-in-motion data collected from several representative sites. The LRFR live load factors developed using the proposed calibration process would provide uniform and consistent levels of bridge safety and reliability for the bridge classes and configurations targeted. The target reliability levels used during the calibration should reflect the experience gained by state bridge engineers from evaluation of existing bridges under current loading conditions.