The effects of corrosion on the reliability of steel girder bridges.

Abstract

The objective of this thesis is to develop a corrosion damage model to measure and predict the performance of corroded steel bridges. The damage model is developed from information concerning the type, location, pattern, and rate of corrosion occurring on a bridge. The most important form of corrosion, general surface loss, is considered. Additional investigation is given to corrosion fatigue. The other forms of corrosion which occur (galvanic, pitting, crevice, and stress) are identified and discussed. Structural analysis is used to evaluate the behavior of the corroded girders. The capacity of the main girders is dependent on bending, shear, and bearing. Analysis of the bearing resistance requires the formulation of a behavior model based on plate theory. Structural reliability theory is used to determine the probable distribution of corrosion, loss, member resistance, and structural safety. The resistance modes of bending, shear, and bearing are treated as a series system. The system reliability is calculated from the component reliabilities and correlations of the resistance modes. The safety of the individual modes and of the system is measured in terms of the reliability index, using a normal variable formulation. The rating of a corroded bridge is based on the st and ard procedures set forth by AASHTO. A comparison is made between the safety and capacity of simple span steel girder bridges of differing lengths. Each bridge is considered with and without a web bearing stiffener at the support. Different types of environment are also studied. The parameters which make up the corrosion damage model are investigated using sensitivity analysis. The investigation shows that a marine environment, with salt contamination, has an extremely detrimental effect on bridge performance. The rural and urban environments are not as serious. The presence of a bearing stiffener improves the lifetime performance of a corroded bridge. The most influential parameters in the corrosion model are; the corrosion loss exponent B, the web boundary conditions and stress distribution at the support, and the distribution of shear live load to the girders.