Nondestructive Testing: The Key to Bridge Longevity
By Marybeth Miceli and Sreenivas Alampalli
The unfortunate reality of time is that all things age. Hopefully with age comes wisdom, and with wisdom comes the decision of making healthy choices that increase longevity and functionality. If you go for an annual physical and the doctor declares that you are healthy without checking your vitals, you might be a little thrown off. As we get older, recurring blood tests and other diagnostics are critical to finding concerns early so that proper corrective measures can be taken immediately to maintain your health. Similarly, regular health examinations of infrastructure, especially bridges, are vital to ensure a long and healthy lifespan. More than just landmarks, bridges play a critical role in the daily lives of all Americans. There are over 600,000 highway bridges in the United States. According to the most recent American Society of Civil Engineers' (ASCE) Report Card for America’s Infrastructure , about 7.5 percent of bridges (45,000 in all) are considered to be in poor (structurally deficient) condition. While bridges in poor condition are generally safe for the traveling public, they likely could use some corrective measures to repair advanced deterioration and damage. This would improve safety, maintain uninterrupted utility, and better the competitiveness of the United States economy by avoiding long detours for trucks. This abundance of vulnerable, aging bridges highlights a need for more regular and thorough examination of our nation’s highway bridge in - frastructure, in addition to a need for data-driven decision making to use the limited funds available in the most responsible way possible. While many factors play a role in reducing the number of poor bridges and structural failures, regular and proactive quantitative assessment followed by consistent maintenance can go a long way to ensure the longevity and integrity of such vital infrastructure. Among the most effective evaluation techniques is nondestructive testing (NDT). NDT is the process of thorough evaluation without de - stroying the serviceability of the asset. Today, NDT can be utilized to discover potential defects and deterioration not only in bridges, but in innumerable other structures from pipelines to nuclear plants to rockets. While there are multiple NDT methods, one most often used on bridges is visual inspection (VI). VI is one of the oldest applications of NDT. Whether using ropes for access or, increasingly, drones, VI enables engineers with specialized and comprehensive training to conduct and evaluate a bridge to identify anomalies for closer study supplementing other NDT methods such as magnetic particle (MT), ultrasonic testing (UT), dye penetrant testing (PT), or ground penetrating radar (GPR). Sonar based methods are gaining traction to supplement underwater inspections where visibility is low or unsafe for divers.
Unfortunately, research has found that NDT methods are not as consis- tently applied in the inspection of bridges as their proven effectiveness would lead us to imagine. Studies like the 2014 Performance Testing of Inspectors to Improve the Quality of Nondestructive Testing found that the performance tests of bridges by technicians from other industries were not up to snuff. At least one of the reasons was that inspectors as well as other NDT technicians were not always specifically trained, tested, and certified in NDT for bridge infrastructure. Their knowledge of the practice was derived in other industries and sectors and therefore lacked some of the bridge-specific behavioral understanding and expe - rience critical to effective inspections. Further, regulations and guidelines that require bridge inspectors and their testing skills to meet high levels of performance are few and far between. While it is true that bridge safety inspections in the US are regulated by the National Bridge Inspection Standards (NBIS), one of the major flaws in these regulations is the absence of a require - ment to use NDT personnel specifically trained in bridge inspections. Inspection guidelines do not call for check-ups to be conducted using technology more sophisticated than VI, which is only truly effective if the defects are not hidden and if inspectors have the right train- ing, knowledge, and experience. Similarly, the Federal Highway Administration recently released updated standards with mandatory requirements for inspection personnel but excluded the requirement for NDT certification. Such lenient federal regulations allow discrepancies to exist in state inspection practices. While some states exemplify the best practices of effective and thorough bridge inspection, other states fall short. With the fewest structurally poor highway bridges in the country, Utah has one of the best inspection and testing strategies among all 50 states. In its manual of state standards for bridge management inspections, the Utah Department of Transportation intentionally outlines the applica- tion of NDT in different types of inspections. NDT is recommended, for example, in a Fracture Critical Member (FCM) inspection (now known as non-redundant steel tension member inspection (NSTM)), in which personnel conduct a hands-on inspection of steel tension mem- bers to detect cracks that could cause a bridge to collapse. Beyond the performance of a routine visual inspection, as required by the federal
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