Estimating the Future Condition of Highway Bridge Components Using National Bridge Inventory Data

The accurate prediction of the future condition of bridge components is an important part of any bridge management system. Past bridge inspection data along with information on any repair and/or retrofit can provide a baseline for predicting future conditions of bridge components. As expected, such data are subject to a rather large uncertainty, primarily due to the variation in the inspection process. This uncertainty is also caused sometimes by unrecorded repairs and/or replacements conducted on various parts of the bridge. If not properly considered in the bridge data analysis, the uncertainty may result in an erroneous prediction for future bridge conditions. To develop a reasonable estimate for future bridge conditions, this paper discusses two possible methods. In these methods, discrepancies inherent in bridge condition ratings, that may have been due to unrecorded improvement works, are removed to arrive at more consistent estimates for future bridge conditions. In one method, the adjustment in condition ratings is done based on the notion that unless there is evidence of improvement work, the condition rating cannot be larger than previous ratings. In the other method, the duration between consecutive inspections is used as a means to construct deterioration curves. These methods are applied to rating data collected from 2,601 Illinois bridges in the period of 1976–1998. The results obtained by applying the two methods are presented in the form of bridge deterioration models, compared with one another and discussed in the paper.