ABSTRACT

Tied-arch bridges are widely used because of its capability of providing clear load path, long span and high clearance. However, the steel elements of a tied-arch bridge are subject to corrosion, which could lead to accidental bridge failure or even collapse when coupled with other bad factors. Hanger anchors as the key elements along the load paths were usually tightly sealed in the anchorages during construction to protect them from corrosion attacks in their service life. This makes it very difficult to manually inspect the corrosion conditions of hanger anchors. Corrosion inspection of hanger anchors has been a blind spot in tied-arch bridge routine maintenance. Corrosion monitoring using a multi-array sensor system was utilized to provide bridge owners with awareness of possible corrosion of hanger anchors, allowing them to make informed maintenance decisions, thus increasing bridge operational safety.

INTRODUCTION

Rail and automobile bridges constitute essential systems in the overall transportation networks in many parts of the world. These bridges often span waterways and other geological features and aid in providing reliable access to both sides of such features. The safety of these bridges is, therefore, critical to the economic sustainability of the regions and cities where they are installed. Furthermore, these bridges also can provide a vital function in permitting safe evacuation of populations from one side to the other side of the bridge during storms and other significant events. As a result, inspecting for possible corrosion that may lead to derating of the bridge load carrying capacity or even bridge collapse is an important activity that various federal, state, and local municipalities are engaged in. Unfortunately, cases still arise in which failures still occur despite inspections having been performed.

For example, the Lowe’s Motor Speedway pedestrian bridge collapsed in May 2000 due to corrosion of the steel supports.1 The cause of this corrosion damage was attributed to the over-addition of a chemical used to aid in drying the grout that contained calcium chloride. The corrosion and subsequent collapse resulted in the injury of 107 people when they fell onto the highway below and were impacted by debris. If inspections were performed or active corrosion monitoring was installed, this event likely could have been avoided. When this type of event is extended to consider the literally hundreds of thousands of bridges deployed worldwide, many of which have been in service for decades and are now or are becoming structurally deficient, it is critical to ensure these systems are safe to use. Because it has been recognized that effective inspection is critical to ensuring the long-term, safe use of bridges, many organizations have included active online corrosion monitoring as a part of their integrity management programs.

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