This article provides an overview of the load and resistance factor rating (LRFR) method and the load and resistance factor design (LRFD) method for highway bridges. As states adopt LRFD for bridge design, they are recognizing the need for a methodology such as LRFR for rating the load carrying capacity of existing bridges. Although bridge design and load rating are similar in overall approach, they differ in one crucial aspect: engineers contend with greater uncertainty in the amount of loading the structure will experience over its service life in bridge design, while they face uncertainty in the amount of structural resistance with load rating for an in-service structure. Although several states have either fully or partially adopted LRFD as their primary design method for bridges, few have adopted LRFR as their primary method for load rating. Since the methodology of LRFR is synonymous with LRFD, advancing the implementation of the latter will help with the eventual adoption of the former.
Abstract