System for Detection of Defects in Cables of Bridge Structures

Abstract

Over the last 75 years, many cable-supported bridges have been built in America, Europe, Asia and other parts of the world. However, over the years these bridges have aged and been exposed to environmental conditions such as rain, snow, de-icing and harmful chemicals. These conditions cause various levels of deterioration in bridges, particularly corrosion. Corrosion causes a loss of cross-section in the steel, adversely affecting the bridge's capacity to carry its service loads, and can possibly cause bridge failures. Although many methods have been attempted to inspect these bridges, most have offered limited success. In the recent years, it has been shown that the Magnetic Flux Leakage (MFL) method, may offer the performance and practicality needed to inspect similar structures such as post-tensioned (P-T) tendons in segmental concrete bridges. This thesis offers a design for an NDE system based on the MFL method to inspect the entire length of the cables of cable-stayed bridges. The thesis also addresses the feasibility of integrating a secondary NDE method, the Magnetostrictive (MS) method, with the MFL system to provide a complete assessment of these bridges including the anchorage area. As a part of this study, prototype models of the MFL and MS systems were built. Past experimental results on a real P-T bridge cables have shown that the MFL is capable of detecting as small as 1% of the cross sectional loss in bridge cables due to corrosion. Experiments carried out on a simulated anchorage area of 13 strands showed that the MS test is capable of detecting steel defects from single to several broken strands. Furthermore, based on simulation and experimental results, a more practical magnet design has been proposed to enhance the bridge cable inspection in future.