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 infrastructure, 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 destroying 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 consistently 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 experience 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 requirement 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 training, 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 application 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 members to detect cracks that could cause a bridge to collapse. Beyond the performance of a routine visual inspection, as required by the federal government, the Utah DOT includes NDT in the procedures for NSTM and comparable specialized inspections.

Similarly, New York has one of the best state bridge inspection requirements. Over the past twenty years, the New York State Department of Transportation (NYSDOT) incorporated more NDT training into the state’s inspection standards for bridges. In the development of its Bridge Inspection Manual of 2017, which remains the current standard used by NYSDOT personnel, New York requires the performance of NDT to assess the condition of assets integral to the health of the structure, such as approach slabs, as well as diving inspections. Load testing is a recognized practice, at the discretion of bridge engineers, for use as part of routine inspection contracts. NYSDOT also administers a certification program for UT. Program applicants must meet the minimum requirements as outlined in ASNT-TC-1A (2016), a collection of recommended practices by the American Society for Nondestructive Testing (ASNT) for NDT certification employer-based programs, for a UT level II technician, a minimum of 2 years of field experience prior to taking the exam, as well as passing an exam that includes written and practical components.

While NDT methods have been incorporated into NSTM and specialized underwater inspection, they have value throughout the bridge’s lifespan during routine inspections as well. Introducing NDT to bridge inspection during the bridge’s initial construction can lead to lower lifecycle costs, ensuring the bridge is built according to the original plans and specifications where NDT can yield great benefit as a tool of quality control. Similarly, NDT is very useful at the later stages of the bridge’s life to plan appropriate corrective actions while problems are still small before they can be seen with the naked eye and can therefore prioritize the funding for effective asset management.  In either case, NDT can be a powerful tool in bridge inspections when properly executed by trained and accredited personnel who follow well developed testing and evaluation procedures and protocols. Its value is increased when state departments of transportation mandate its use. Differing state regulations result in the reality that NDT is overlooked as an essential component of inspection regimens. Whereas in other more heavily regulated industries such as aviation & aerospace and oil & gas, NDT is a non-negotiable essential service in the lifecycle of an asset. 

Federal standards also must be bolstered to ensure practices across state DOTs and the industry are uniform and consistently applied. Furthermore, state DOTs need to increase the application of NDT testing in inspection protocols by adopting regulations that require it be used in bridge inspection, where appropriate, to prevent the future costs associated with bridge failures and closures. These measures will increase the longevity of the bridges, allowing for better and more efficient use of the public’s money.

The Federal Highway Administration has laudably developed a program to showcase different NDT methods to state DOT officials through the National Highway Institute. The one-day, demonstration-based seminar, started originally as a one-day course supplementing NYSDOT annual refresher training, educates bridge inspection personnel on the primary NDT tools for this purpose and teaches them how to perform NDT effectively in bridge inspections. However, it only touches the surface of these methods and by no means qualifies independent execution of NDT on bridges.

In the interest of implementing best practices, bridge owners would also do well to adopt the use of advanced technologies, such as drones and passive sensor based structural monitoring, to improve testing efficiency and reduce the risk of human injury. Proactive efforts to use NDT and monitoring methods to recognize deterioration before it becomes critical to plan maintenance work would be instrumental in preventing the high expenses that accompany emergency work, postings, and full replacements. Without more stringent regulation, proper NDT based inspections may increasingly be set aside as a cost saving measure or inconsistently applied, even though full replacement is exponentially more expensive than preventive maintenance, not to mention much more disruptive.

As technology in the NDT industry advances, owners along with regulators bear a responsibility at the state and federal levels. Professionals in the field must consistently update their training and accreditation in NDT methods as required by their individual state guidelines. ASNT, the largest technical society for NDT professionals, offers certification and standards programs to NDT personnel. Despite the fact that the majority of states require inspectors to attend regular training courses, the value of certification from ASNT cannot be minimized. ASNT’s certification and standards programs as well as its professional development programs, provide the foundation for expanded awareness of advancements in NDT technology. While ASNT itself does not produce standards that describe how to perform NDT inspections, those standards are available through ASTM International and other organizations. They also are highlighted in the codes and standards involved in NDT industry.

The improvement of bridge inspection practices could detect and address poor construction to dangerous structural defects before a worst-case scenario presents itself. We should learn from our past and become more proactive and less reactive in our approach to bridge management. We regularly perform diagnostic tests on our planes, cars, and even our own bodies. Why should we tolerate anything less for the structures that are the lifeline of our economy?

Marybeth Miceli, C.Eng. has been a member of ASNT for over 20 years. Throughout the years, she has served as chairperson on different committees and councils, including the Board of Directors and the Infrastructure Committee. Ms. Miceli also led many of the Women in NDT committee initiatives in ASNT to supports women’s advocacy in the NDT field.
Sreenivas Alampalli, P.E. PhD is a Senior Principal at Stantec, focusing on NDT and Structural Monitoring areas. He is a Fellow of ASNT, ASCE, the Structural Engineering Institute (SEI), and the International Society for Structural Health Monitoring of Intelligent Infrastructure (ISHMII).