Predicting First Time Reaching Deficiency Status (FTRDS) for Steel Bridges in Oklahoma

Abstract

The need of an accurate model to characterize deficiency time for bridges is an important issue for bridge owners to ensure an adequate maintenance schedule. The main objective of this research is to create a simple, rational statistical model that characterizes bridge conditions in Oklahoma. Thus, this research focuses on addressing the influence of age on bridge components including deck, superstructure, and substructure. This was done by tracking historical data for steel bridges built between 1992 and 2015. In this study, condition ratings of 2,145 steel bridges were analyzed to determine the First Time Reaching Deficiency Status (FTRDS). Four well-known statistical distributions (gamma, Weibull, lognormal, and log-logistic) were investigated to predict each bridge component’s First Time Reaching Deficiency Status (FTRDS). The goal was to identify the best distribution that fits Oklahoma’s steel bridges to obtain the probability for the FTRDS. Based on the Anderson-Darling test for the goodness of fit test process, the Weibull distribution was the most appropriate distribution that characterized the effect of age on bridge components. The Weibull parameters, scale and shape factors were estimated to calculate the FTRDS probabilities based on bridge ages from the year built to the point that bridge reached deficiency status for the first time. Results show that data for superstructure and substructure elements were useful to calculate FTRDS while the deck element was excluded due to insufficient data. Finally, these models will be helpful in assisting agencies such as Oklahoma Department of Transportation (ODOT) in monitoring the condition of their bridges and to develop more reliable maintenance and rehabilitation plans.