As stated in the AASHTO Manual for Condition Evaluation of Bridges, the basic LRFR equations are as follows:
In LRFR calculations, permanent loads are separated into the three variables DC, DW, and P, because each is assigned an independent load factor ([gamma]) for each load rating limit state.
As with load factor rating, LRFR live loads are temporary loads that act on a structure.
454: Calibration of Load Factors for LRFR Bridge Evaluation, [beta] is defined as follows:
Because the LRFR live-load factors depend on average daily truck traffic (ADTT), researchers used traffic data for calibration.
To enable a smooth transition from load factor rating, the LRFR research team set a goal to make the manual practical and easy to use.
As with LRFD, LRFR promises a more uniform level of safety and a lower risk of over- or underdesigned members.
Although the general equations are similar for the current LFR and new LRFR methodologies, and the procedures are straightforward, the implementation of a new load rating method can be time-consuming and costly for State DOTs.
LRFR provides a simplified approach through the use of the HL-93 live loading as a screening check for all other legal loading.
LRFR enables bridge owners to apply traffic volume and other site-specific data when determining live-load factors for a bridge.
LRFR facilitates using the past performance of a bridge to help determine its serviceability rating.
LRFR provides procedures for load rating vehicles with loads that exceed the legal limit (or permit vehicles).