Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil and Environmental Engineering

First Advisor

R. Richard Avent


A comprehensive statistical analysis was performed on the condition data generated by a statewide underwater inspection of bridges in Louisiana. The research defined pertinent underwater structural decay characteristics and established a method for establishing a bridge's propensity for underwater deterioration based upon those relevant factors. The inspection results were reviewed to ascertain the impact of human-bias on the consistency in the bridge condition ratings. Using a set of importance factors obtained through a questionnaire submitted to a group of inspectors, the fuzzy set theory was employed to assist in the removal of data incongruities. A combination of pure fuzzy set theory and classical binary weighting was found to produce optimal results. Bridge age, material-type, and location were found to be significant in defining the rate of deterioration in Louisiana bridges. Linear least-squares, piece-wise linear least-squares, and polynomial regression curves were matched to the overall underwater condition ratings, with the piece-wise linear least-square curves providing the optimal fit for concrete and steel bent bridges and linear least-squares best describing the regression of timber bent bridges. For concrete and steel bent bridges, significant changes in deterioration rates were found at ages of 20 and 40 years. Comparisons of regression curves for neighboring states indicated reasonable consistency in results for different inspection programs if similar inspection methodologies are employed. The correlation between above-water and subsurface inspection ratings was found to be poor for concrete and steel bent bridges, but acceptable for timber bent bridges within a given age group. Additionally, a poor correlation was found between water quality data and underwater bridge deterioration rates. A methodology for determining the frequency and detail of future underwater inspection projects was developed based upon the deterioration trends and available bridge decay-defining characteristics discovered in this research.