A proof load formula is proposed for highway bridge evaluation through proof load testing to determine target proof load and load rating. This formula is based on a target structural safety index 13 of 2.3, which is consistent with current bridge evaluation practice and also with an evaluation method of load and resistance factors under development. It is demonstrated that the proposed formula will ensure a relatively uniform level of bridge structural safety and that possible changes in input data and probability distribution assumptions in the reliability models will not affect the results obtained. This formula can be applied to highway bridge evaluation by proof load testing, and the resulting rating· can be directly input to the current national bridge rating inventory. The formula may be included in specifications for highway bridge evaluation by proof testing.

According to FHW A, about 40 percent of this country's highway bridges are considered either structurally deficient or functionally obsolete. Some 68 percent of New York State's bridges fall into these categories, representing the highest percentage among the states. Funds necessary to replace and rehabilitate them will not be available in the foreseeable future. Major factors contributing to this serious situation are age of the infrastructure, increases in both volume and weight of vehicular loads, environmental contamination, and inadequate maintenance (1).