Roving engineers monitoring safety of bridges, lighting towers
Robert J. Connor, a Purdue assistant professor of civil engineering, seated, works with research engineer Ryan Sherman in a new roving research vehicle that is dispatched to sites around the nation to assess the condition of bridges and steel lighting towers located along interstate highways. The mobile field office and workshop, a Sprinter 3500 van customized by Purdue engineers, is equipped with computers, safety equipment, flashing lights, and air horns, and is stocked with tools, equipment and sensors before being dispatched. (Purdue University photo/Andrew Hancock)
WEST LAFAYETTE, Ind. - Civil engineers at Purdue University have created a roving research vehicle that is dispatched to sites around the nation to assess the condition of bridges and steel lighting towers located along interstate highways.
The mobile field office and workshop, a Sprinter 3500 van customized by Purdue engineers, is equipped with computers, a warning strobe light and air horns and is stocked with tools, equipment and sensors before being dispatched.
"We are able to respond quickly," said Robert J. Connor, an assistant professor of civil engineering. "We load our luggage and roll, a fast-response capability that's unusual in academic settings."
Connor also has been involved in numerous steel bridge failure investigations, the most recent being the 2007 I-35W Mississippi River bridge collapse in Minneapolis.
Researchers have driven the mobile field facility as far as California to install sensors on structures. The sensors transmit data by wireless high-speed modem, much like signals for portable consumer electronics, and can be monitored by engineers back at Purdue's Robert and Terry L. Bowen Laboratory for Large-Scale Civil Engineering Research.
The Purdue researchers will use the mobile facility on Wednesday (March 24) to test a bridge on Interstate 465 in Indianapolis, work aimed at learning whether an explosion and fire in a 2009 propane-tanker accident resulted in any long-term effects. The tanker overturned Oct. 23, exploding and bursting into flames under the I-465 overpass at Interstate 69.
Connor and his team installed instruments on the bridge in December and have been continuously monitoring it since. He and Amit Varma, an associate professor of civil engineering, traveled to the scene the night of the accident and are helping the Indiana Department of Transportation evaluate the structure and conduct materials testing. Researchers at Purdue, working with INDOT, have tested samples from the bridge, and results indicate no apparent damage.
However, further tests will be conducted through the Joint Transportation Research Program at Purdue and INDOT to evaluate fatigue and performance and to learn whether the structure might require additional long-term maintenance, Connor said.
He and his students will use sensors called strain gages to see how the bridge responds when heavy trucks are driven over it. The work, scheduled for about midnight when traffic volume is low, will take about two hours and require the closure of two lanes of traffic on the three-lane highway in the proximity of the bridge.
The mobile field facility is being used extensively on a National Cooperative Highway Research Program project intended to develop fatigue design specifications for towering highway lighting poles, some of which approach 180 feet tall.
"The students gain valuable career experience, but it's also good for educational reasons," Connor said. "The students feel that they are equal partners of something important. They bring a lot to the table, especially graduate students. They are really working engineers."
The Purdue research includes the installation of monitoring systems on eight "high-mast lighting towers" around the nation.
The lighting towers are located where visibility is critical such as the intersections of two interstate highways. Wind-related stress sometimes causes fatigue cracks to form at the base of the towers, and the towers sometimes collapse.
Ten states have reported at least one high-mast lighting tower collapse in the past decade, and three of those states have had several collapses, Connor said. Two structures near Rapid City, S.D., collapsed in November and April 2005. After these collapses, officials ordered a statewide inspection of all remaining 136 towers. As a result of this inspection, an additional 11 were removed from service.
"Given the proximity of these structures to the motoring public, the safety of motorists becomes one of great concern," Connor said. "We have specifications that say how to design the poles, but these specifications obviously need to be improved if poles are cracking and falling over."
The civil engineers are monitoring lighting towers in Barstow, Calif.; Creston Junction Wyo.; Rapid City; Bismarck, N.D.; Hays, Kan.; Erie, Pa.; and Henryetta, Okla.
New data are automatically downloaded to a central computer every four hours.
"Some poles have failed in only a year and a half, yet others will last over 20 years," Connor said. "By monitoring several poles around the country for a period of time we will learn how they respond. The goal is to develop loading criteria and national specifications for the American Association of State Highway and Transportation Officials that companies will use when designing the towers."
Another key part of the research involves using a wind tunnel to study a complex phenomenon called "vortex shedding," which results in unusual vibrations that heighten fatigue damage.
Steven Collicott, a professor of aeronautics and astronautics, leads the wind-tunnel portion of the research.
The researchers also are testing a 35-foot-tall pole segment using a hydraulic apparatus that constantly pushes the pole to simulate the effect of strong winds over time. The experiment at the Bowen Laboratory is funded by the state of South Dakota. Research findings will help the engineers devise how to properly retrofit the damaged poles with a jacket of steel plates to reinforce the cracked portions at the base.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Sources: Robert Connor, 765-496-8272, rconnor@purdue.edu
Amit H. Varma, 765-496-3419, ahvarma@purdue.edu