Calibration of Load and Resistance Factor Rating Methodology in New York State

Abstract

In 2003, AASHTO adopted the Guide Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges, which was calibrated to provide uniform reliability levels represented by a target reliability index β = 3.5 for inventory ratings and β = 2.5 for operating ratings. These target values were selected to remain consistent with the AASHTO load and resistance factor bridge design specifications and provide average reliability levels similar to those of the allowable stress operating ratings and load factor ratings (LFR). The calibration process was based on a generic live load database considered to be representative of truck weight and traffic spectra at typical U.S. bridge sites. Recognizing the limitations of this generic data set, the LRFR provides sufficient flexibility and allows state agencies to adjust the LRFR load factors on the basis of their individual conditions and site-specific or state-specific information. A reliability-based procedure was developed for calibrating a state-specific NYS-LRFR that would reflect current bridge loading conditions in the state of New York, including the intensity and shape of the truck weight spectra as well as measured truck traffic data. The proposed calibration would lead to bridge ratings consistent with the current practice of the New York State Department of Transportation and provide uniform and consistent levels of bridge safety and reliability. The methodology can be easily adapted by other states on the basis of their unique truck loads and traffic conditions.