Simple Procedure for Load Rating Reinforced Concrete Slab Bridges without Plans

Abstract

In New Mexico, bridges without plans are currently an issue as in other states in the US. Standard techniques cannot be used for load rating due to the lack of design plans that contain necessary information such as material properties and the amount and location of mild steel reinforcement. In this study, state departments of transportation were surveyed regarding their load rating policies and procedures for planless bridges. Many states reported a significant number of bridges without plans, in particular reinforced concrete bridges, and the rating approaches for such bridges vary from state to state. This project was conducted for the New Mexico Department of Transportation (NMDOT) to develop an effective method to load rate reinforced concrete slab bridges without plans and obtain more representative estimates of load-carrying capacity. In New Mexico, 46 reinforced concrete slab bridges (simple and continuous span) were load rated and evaluated using simple analytical and nondestructive testing techniques. The procedure includes field measurements of the bridge dimensions and geometry, Windsor Probe testing of the concrete strength, scanning of the embedded steel reinforcement, generation of the as-built drawings, and modeling the bridge with a load rating software. The procedure provided the NMDOT with as-built plans as well as more realistic load rating results for their reinforced concrete slab bridges without design plans. The rating results for the 46 New Mexico bridges are presented in this paper and comparisons are made with other state policies to illustrate the differences in the load ratings.