In this study, in-service conditions were evaluated to estimate the service life of concrete and metal culverts. The Ohio Research Institute for Transportation and the Environment (ORITE) and a private consulting company proposed new inspection methods and rating procedures for concrete, metal and thermoplastic pipes; concrete and metal culverts are addressed in this study. The inspection activities were developed in culverts located in Ohio Department of Transportation (ODOT) Districts 9 and 10 since the aggressive environmental conditions found in these portions of the state of Ohio.
Before each field trip, culverts were selected to meet requirements of location, material, and dimensions. For dimensions, screening criteria were than 42 inch span and rise dimensions, and a maximum length of 150 feet.
From each culvert, basic information was gathered from the inventory data provided by ODOT and in the field. The data gathered from the inventory and the field work was statistically analyzed to identify significant factors that contribute to material deterioration. The rating scales proposed by the ORITE and ODOT were employed in the statistical regressions as outcome variables, to measure the effectiveness and accuracy in predicting the remaining service life. Multivariable linear and nonlinear regression models were proposed to estimate the remaining service life of existing metal and concrete structures with similar conditions in the state of Ohio.
Results for concrete culverts show that the multivariable linear regression results showed that pH and resistivity of water were significant for the ODOT and ORITE rating scale but the linear model is not since the age is not included in the regression. While, the multivariable non-linear regression results indicated that pH of water, age and span were significant based on the ODOT rating scale.
For metal culverts, the multivariable linear regression results showed that rise, span, age, level of abrasion, thickness of the plate, slope, velocity, and depth of the flow were significant based on the ODOT rating scale. And, age, soil cover, level of abrasion, pH of water, thickness of the plate, slope, flow velocity, and depth of flow were all significant for the ORITE rating scale, both models are not practical in estimating the deterioration of metal pipes. Non-linear regression did not generate more reliable results in predicting the service life of metal culverts.