Public Roads Magazine

Collaboration in Nondestructive Evaluation of Bridges
"They have all this development going on, but they sometimes don't have the ideal bridges on which to test these procedures or equipment. And we had the bridges but not the testing capability. So, it seemed like a mutually beneficial thing to bring the two together," said John Thiel, EFL's bridge inspection program coordinator.

The RD&T/FLH relationship is characterized by cooperation as well as collaboration. Thiel cited an example, "When it comes to scheduling these tests, [RD&T] has been very flexible. Some of our dates are set a year in advance, and they have been willing to work within our schedule."

FLH also has demonstrated some flexibility. Nat Jansen, an EFL civil engineering technician, recalled a joint project, "We wanted RD&T to conduct an ultrasonic test to verify that pin connections on the bridge were good. [RD&T] also had some clamp-on gauges they wanted to evaluate. Sometimes, we have one specific test in mind, but they also want to test other things as well."

Dr. Paul Fuchs, a consultant to RD&T's Infrastructure Inspection and Management Team, described the relationship between EFL and RD&T's Nondestructive Evaluation Validation Center (NDEVC), and he pointed out some other advantages of the interoffice partnership.

"The EFL bridge inspection program has always been supportive of [the use of] new NDE [nondestructive evaluation] techniques. In particular, John Thiel has seen the importance of supplementing standard visual inspection with NDE methods. EFL has been willing to experiment and provide opportunities for testing," Fuchs said.

"Given that NDEVC is working on newly developed techniques and instruments, not all of our field tests are successful. EFL is a good partner in this case because not all external organizations are patient with failures. While a large portion of our tests with EFL have been successful, unsuccessful tests also help NDEVC better understand the capabilities and limitations of our systems," explained Fuchs.

"The ability to have access to bridges local to NDEVC is very important. NDEVC has a very active field test program and is always looking for places to test equipment," Fuchs said.

"One of the goals of NDEVC is to help train and instruct state departments of transportation on NDE techniques and instruments. EFL has always been interested in learning more about NDE methods and has made inspectors available for training and education," said Fuchs. "We put together a system that Federal Lands could use to rate [the load-bearing capability of] their bridges themselves, and we trained them to use it."

FLH offers another benefit to RD&T. "We [FLH] conduct routine bridge inspections the same way that the states do; so, by observing us, RD&T gets to see how these inspections are actually done," said Jansen.

Fuchs agrees. "EFL provides a good source of feedback on the type of instruments needed by bridge inspectors. This feedback helps NDEVC to focus on tools that will be of use to bridge inspectors in general all over the country."

By working together, RD&T demonstrated some ways to instrument structures to test capabilities and, in the process, recognized applications for technologies developed at RD&T's Turner-Fairbank Highway Research Center (TFHRC).

In recent years, the two offices have collaborated on several bridge inspection projects.

One of these projects was conducted at the Vicksburg Military Park in Vicksburg, Miss. The park contains several concrete arch bridges built in the early 1900s, and visual inspections of these structures by EFL raised concerns about the bridges. The U.S. Park Service wanted to maintain the existing structures because of their historical value; however, because large buses are used to transport some tourists through the park, the safety of the bridges was the primary concern.

For this test, EFL coordinated testing with the Park Service. The Park Service provided loaded vehicles and traffic control. NDEVC provided the instrumentation and performed the load tests.

Steve Chase (right) of RD&T operates a wireless data acquisition system used to load-test a concrete arch bridge in the Vicksburg Military Park, Miss. John Thiel of EFL positions a load truck on the bridge.

In collaboration with EFL, NDEVC load-tested four of these bridges to help determine if any repairs or retrofits were necessary. This testing provided an opportunity to use a wireless data acquisition system currently under development at NDEVC. The system allowed the bridges to be load-tested rapidly with minimal effect on the traffic in the park.

This test was beneficial to EFL because the load test provided more information about the bridges than is possible with just visual inspection. The data also helped the Park Service to determine the appropriate course of action to properly maintain the bridges in the park.

After the load test in Vicksburg, EFL wanted to test other bridges on their inspection schedule. To assist EFL, RD&T developed an instrumentation kit for load-testing bridges and trained EFL engineers to use the instruments so that the EFL bridge inspectors could perform the testing by themselves.

During the development of a laser-based instrument that is used to measure bridge deflections for the purpose of load rating a bridge, NDEVC needed to test the instrument on an actual bridge. EFL provided the prestressed concrete Carderock Bridge over the Clara Barton Parkway along the Potomac River in the Maryland suburbs northwest of Washington, D.C.

An NDEVC laser system and wireless data acquisition system are used to load-rate the Carderock Bridge on the Clara Barton Parkway near Washington, D.C.

"Testing helped determine the lateral load distribution from loaded vehicles - the actual load that each beam receives rather than the theoretical load based on equations," said Thiel.

EFL has many prestressed concrete bridges in their inspection inventory, and information on the load ratings of structures helps EFL better assess the conditions of its bridges. For this testing, EFL provided access to the structure and helped with traffic control. NDEVC provided the loaded vehicles and instrumentation for the load test.

EFL currently inspects a fracture-critical pin-and-hanger bridge in Rocky Mountain National Park in Colorado. A pin-and-hanger connection is a type of bridge detail that joins two bridge spans and accommodates thermal expansion. Corrosion problems in this detail often lead to cracks. A fracture-critical bridge is a structure that does not contain redundant elements. For example, a two-girder steel bridge is considered fracture-critical because if one of the two girders were to fail the structure would likely collapse.

Because of the fracture-critical nature of the bridge, EFL asked NDEVC to perform an ultrasonic inspection of the bridge pins. During the inspection, the NDEVC engineers instructed EFL inspectors on the use of the ultrasonic instrumentation. The results of the ultrasonic inspection helped EFL to determine the appropriate recommendations for the bridge. For this test, EFL supplied a bridge inspection truck and coordinated testing with the Park Service. NDEVC provided instrumentation for the test.

Glenn Washer (left), NDEVC program manager for RD&T, and Nat Jensen, EFL civil engineering technician, perform an ultrasonic inspection of a bridge pin on the Big Thompson River Bridge in Rocky Mountain National Park, Colo.

HERMES Ground-Pentrating radar system is tested on the GW Parkway near Washington, D.C.

HERMES ground-penetrating radar system is tested on the George Washington Parkway near Washington, D.C.

NDEVC assisted in the inspection of pins on an iron truss bridge in Williamsport, Md. This test provided an opportunity for NDEVC to train EFL inspectors in the use of ultrasonic instruments under actual field conditions.

EFL was interested in learning more about currently available ultrasonic instrumentation for bridge inspection, and so, NDEVC demonstrated the use of this type of instrumentation on the Arlington Memorial Bridge over the Potomac River. This bridge was selected because it is the responsibility of EFL to inspect this bridge and because of the bridge's close proximity to TFHRC and the EFL division office.

NDEVC recently completed a very large study on the reliability of the visual inspection technique for bridges. Part of this testing involved a series of inspection trials on actual bridges by bridge inspectors from 25 states. Prior to the testing with the state inspectors, an EFL bridge inspector conducted a practice run through the test sequence. This practice testing provided important information that assisted NDEVC in the setup of the field trials.

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