The LRFR Manual, within commentary Article C6.4.4.2.3, contains provisions for development of site-specific live load factors. In Oregon, truck Weigh-in-Motion (WIM) data were used to develop live load factors for use on state-owned bridges. The factors were calibrated using the same statistical methods that were used in the original development of LRFR. This procedure maintains the nationally accepted structural reliability index for evaluation, even though the resulting state-specific live load factors were smaller than the national standard. The first part of this report describes the jurisdictional and enforcement characteristics in the state, the modifications used to described the alongside truck population based on the unique truck permitting conditions in the state, the WIM data filtering, sorting, and quality control, as well as the calibration process, and the computed live load factors. Large WIM data sets from four sites were used in the calibration and included different truck volumes, seasonal and directional variations, and WIM data collection windows. Finally, policy implementation for actual use of the factors and future provisions for maintenance of the factors are described. For bridge rating and evaluation, notional truck models are commonly used to simulate the load effects produced by the truck population. The recently developed Load Resistance and Factor Rating (LRFR) Bridge Evaluation Manual was calibrated based on the 3S2 truck configuration as the notional model. Using GVW as the parameter for establishing live load factors to reflect load effects may not necessarily provide consistent outcomes across all bridge span lengths, indeterminacies, or specific load effects. This is because the load effects are dependent on the distributions of the axle weights, the axle spacing, and the number of axles, in addition to the span geometry and support conditions. The Oregon Department of Transportation currently uses a suite of 13 rating vehicles for evaluation of their bridge inventory. The load effects for Oregon's bridge rating vehicles have also been calculated for various span lengths and support conditions in the second part of this report. These load effects, both unfactored and factored, were compared with load effects calculated using vehicles from large sets of WIM data. Further, because no established standard of time or quantity of WIM data has previously been recognized, a separate study was conducted in order to determine an acceptable window of WIM data. The objective of this analysis was to determine if the load effects and the live load factors developed for bridge rating produced by the suite of vehicles envelope load effects produced by an acceptable window of collected vehicle data for a variety of bridge span lengths and types. Observations and suggestions are made based on the results of these analyses.

This Primer serves as an initial resource for planning and performing inspection, metallurgical testing, and strength evaluation of suspension bridge cables. Also provides an example of a simplified strength evaluation, flowcharts illustrating the inspection and strength evaluation procedures, and inspection and strength evaluation forms that can be used, or replicated, by bridge inspectors and engineers. FHWA Publication No. FHWA-IF-11-045.