Rail Bridge Testing

Rail Bridge Testing

Many railway bridges currently in use are well beyond their original design life, while railway equipment loads have often increased significantly above the original bridge design values. As well, some newer bridges of welded design have experienced premature structural problems from component fatigue. Safely extending the life and maximizing load ratings of such railway bridges, while maintaining ongoing, uninterrupted train operations, is of both concern and great economic benefit to the bridge owner. Achieving such goals depends to a large extent on developing and maintaining an effective bridge inspection program.

A typical, 90+ year old steel bridge

The bridge engineer normally has access to life expectancy data, load data, structural analysis data, strain measurement data and field inspection reports. These combined data, however, still may not provide sufficient information to make the decision to repair a bridge member, to replace a span, or to leave things as they are. Although fatigue cracks develop in most bridges, in many cases they propagate only a certain distance and then become dormant due to stress relaxation. However, when propagation continues the bridge engineer must decide as to whether, or how soon to allocate funds for repair or replacement. Based on tests of nearly 200 railway bridges, TISEC and its railroad clients have developed advanced inspection techniques for interpreting and extending the findings of the trained visual inspector and providing the bridge engineer with additional information required to make critical decisions as to whether a specific fracture critical location requires no further action, that the location should be monitored or inspected more frequently or that a retrofitting procedure be immediately implemented.

An example of Acoustic Emission monitoring of a fatigue cracked member showing geometric clustering, load cycle correlation and waveform analysis

This jointly developed method relies on a logical combination of visual inspection results, strain measurements, acoustic emission (AE) monitoring, ultrasonic scanning (UT) and related types of nondestructive testing (NDT) to assess and classify the severity of fatigue cracks in fracture critical members. It also includes a technique for classifying fatigue crack activity.

TISEC uses a number of NDT techniques in bridge inspection for detecting and assessing cracks and discontinuities. These include dye penetrant tests (PT), magnetic particle (MT) tests, ultrasonic (UT) scanning and acoustic emission (AE) monitoring. Each method has its advantages. When the results of several NDT techniques are logically combined and used together with other engineering data, this approach becomes a powerful and cost-effective bridge inspection tool.

AE monitoring can play a very effective role in enhancing safety, ensuring availability and reducing the repair/refurbishment costs of railway bridges. TISEC uses techniques such as geometric clustering, load cycle correlation, waveform classification and pattern recognition as key parts of its techniques for advanced AE data analysis and interpretation. These results are then combined with additional complementary NDT to classify the extent of fatigue crack activity. A key part of an effective monitoring program is developing a comprehensive test procedure in cooperation with the bridge owner so that a test program addresses the owner’s needs.

Acoustic Emission monitoring of a coped member showing source located fatigue crack emissions.

TISEC inspector performing a detailed inspection of a cracked steel bridge member.

As a pioneer in structural integrity monitoring, TISEC has successfully integrated more than a decade of bridge testing and monitoring experience with over a quarter century of background in fracture mechanics, materials science and solid-state physics. Its test personnel have extensive field experience with railroad bridges including the application and use of the latest safety system protocols.

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