Bridge load rating is the process by which the continued health and capacity of bridges are determined by state authorities. This process was established after the collapse of the Silver Bridge over the Ohio River due to overloading resulted in 46 deaths and has been federally mandated since 1968. NCDOT currently uses 29 legal vehicles to load rate bridges, of which 16 are generated by NC general statutes. Most states have successfully optimized their rating vehicles to fewer than five legal vehicles for the same purpose. The work presented in this thesis provides a proposed methodology to optimize the number of legal vehicles used by NCDOT. Values were calculated for maximum bending moment, lowest operating weight, and lowest posting weight for the current legal vehicles. Steel girder bridges with spans ranging between 19.5 ft. and 162.9 ft. were tested at varying levels of effectiveness and section modulus loss. The resulting values for the vehicle operating weights of the legal vehicles were then used to determine the impact of degradation on the controlling posting vehicles. This process showed that seven of the sixteen vehicles used to load rate non-interstate bridges were redundant in the load rating process for steel girder bridges. Additionally, a computer program was developed to generate potential legal vehicles that comply with North Carolina general statutes determining maximum vehicle weights. This can be utilized by NCDOT to replace the current legal vehicle representing cotton trucks, which was found to be non-compliant with the general statute.
