The Nondestructive Evaluator
Reinforced concrete, first invented in the mid-nineteenth century, combines the bendable strength of steel with the compressional strength of concrete. Wedded together, the pair offers a perfect bridge-building material that will support both its own weight and the weight of the traffic that travels from one end of its span to the other.
Enter the forces of nature. Besides the beating bridges take from traffic, fluctuating temperatures, high winds, excessive rain, and subsequent flooding all take their toll on the structures that are necessary to get us from here to there.
“Visual evaluation done at two-year intervals is the traditional method for bridge inspection,” said Glenn Washer, an assistant professor in civil and environmental engineering in the University of Missouri–Columbia’s College of Engineering. “Two years is a long period of time between inspections, so using sensors to monitor bridge performance makes sense. But it’s difficult to find the right application.”
For the past decade and a half, Washer has made a search for the right application the primary focus of his career. His quest, beginning at the Federal Highway Administration as a research engineer, and now as a faculty researcher at Mizzou Engineering, has earned him recognition as one of the nation’s leading experts in the field of nondestructive evaluation of bridges. As such, the MU News Bureau sent out a national “for expert comment” media advisory quoting Washer the morning after the I-35 bridge over the Mississippi River collapsed last August.
As of Oct. 1, the advisory had generated 299 “hits,” which means that nearly three hundred television, radio or print outlets had used or quoted the information. News Bureau Senior Information Officer Kevin Carlson said it was easily one of the most successful releases the office had ever done. Washer appeared on the NBC Today Show and had to turn down a number of national appearance requests due to time constraints.
On behalf of the American Society of Civil Engineers, Washer traveled to Washington, D.C. in late October to provide expert testimony at congressional hearings on nondestructive evaluation of highway bridges.
Washer has received funding from the National Academy of Sciences (NAS) as well as a number of state highway departments for his work to develop a long-term remote bridge sensor system. “Missouri has been interested in this project all along, and more now after what happened in Minnesota,” said Washer.
“The general idea that I’ve worked on since the 1990s involves using a variety of sensors and methods to better understand the condition of bridges, and to better understand bridge behavior,” Washer explained.
His current research project involves arraying a variety of tilt sensors around a structure, which can then be read from a remote location. The use of multiple sensors ensures sensor agreement, minimizing the risk of erroneous readings in the event one of them is damaged.
“Another application we’re looking at is the use of sensors during extreme weather events. Missouri lost hundreds of bridges when piers were undermined by water in the floods of the 1990s,” said Washer.
Cooperating with both the Missouri and Tennessee Departments of Transportation, Washer says that his research team is working on a sensor system that will register changing temperatures at the base of bridge piers as the earth is scoured away by raging floodwaters.
In addition, the national Transporta-tion Pooled Fund — specifically the Departments of Transportation in Missouri, Texas and New York — is supporting Washer’s research to detect defects in concrete with infrared thermography.
A concrete test block with defects embedded at different levels within the concrete has been constructed on a nearby test site. An infrared camera trained on the structure will generate thermal images every hour for a year. “We are testing to find out under what conditions — time of day, temperature, weather — the contrasts are optimized,” said Washer.
He hopes the data will eventually allow for the development of a handheld thermographic tool that could be used by bridge inspectors in the field.
Washer also works with NASA’s technical discipline team on non-destructive inspection for space vehicles and aircraft, and is doing research on the application of Raman spectroscopy as a new nondestructive inspection tool.
“The condition assessment of existing structures and components is a rapidly expanding field that cuts across many industries and technical disciplines,” said Washer.
At his current rate, Washer just might have a hand in all of them.