U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-HRT-09-013
Date: May 2009
The topic of advancements in bridge inspection drew nearly 200 participants to a bridge inspection Web conference held by the Federal Highway Administration's (FHWA) National Highway Institute (NHI) on March 11, 2009. The conference was sponsored by NHI Innovations, a free monthly Webinar series held in partnership with FHWA's Highways for LIFE program. Technologies highlighted during the conference included fatigue crack detection using electrochemical fatigue sensors (EFS) and video inspection of bridge decks.
Webinar participants represented State transportation agencies, Local Technical Assistance and Tribal Technical Assistance programs, FHWA, and the private sector. Seventy-two percent of participants indicated they had not used the highlighted technologies before, while nearly 99 percent of participants noted they would like to see more Webinars discussing bridge inspection topics.
Helene Bowman of FHWA's New Jersey division office described how EFS was used in 2006 to detect cracking on the Route 72/Manahawkin Bay Bridge in Ocean County, New Jersey. Built in 1959, the 731-m-long (2,400 ft) bridge has 17 spans and a continuous, cantilevered steel girder system with pin suspended spans. A major retrofit of the bridge was performed in 1995. In recent years, cracks caused by out-of-plane distortion have been occurring in floorbeams and connection angles. EFS is a nondestructive method for detecting fatigue cracking that uses sensors, an electrolyte, and a voltage-inducing data collection device. The technology includes analysis software.
The New Jersey Department of Transportation (NJDOT) used EFS at 17 locations between spans 2 and 12 of the Route 72 bridge. Five locations on the Route 72 bridge showed little to no crack growth during the EFS evaluation, while the remaining 12 locations had active growth. A close visual reinspection was conducted in 2007, with results from the EFS evaluation correlated in 14 locations. In two locations, crack growth not predicted by EFS was occurring, while crack growth that had been predicted by EFS was not occurring in one location. FHWA's Turner-Fairbank Highway Research Center in McLean, Virginia, is conducting an independent evaluation of the EFS technology, with field tests to be held this summer. NJDOT has indicated that it would use the technology again, though no applications are currently planned.
Jody Bywater of the Washington State Department of Transportation (WSDOT) discussed the agency's use of video cameras to perform bridge deck inspections. The video cameras are contained in a specially designed vehicle that takes digital images of the bridge deck, with each image covering an area roughly the width of a lane, 3.8-m-wide (12.5 ft) by 8.04-m-long (26.4 ft). Hairline cracks are the smallest crack size that can be detected in the final processed digital images. After reviewing the video images, signs of distress such as open cracks and spalling in the deck surface or superstructure are triggers for conducting a more indepth inspection of the deck.
The initial cost of the inspection vehicle was $750,000. However, the vehicle belongs to WSDOT's pavement management office and is essentially rented at hourly rates for the purpose of video deck inspection at a much smaller cost. The benefits of the technology include savings on manpower and equipment, improved quality of inspections with less impact from weather conditions, and reduced impact to the traveling public. The video technology also limits the exposure of bridge inspectors to hazardous traffic conditions.
|The Washington State Department of Transportation's specially designed vehicle uses video cameras to perform bridge deck inspections.|
Michael Brokaw of the Ohio Department of Transportation (ODOT) described ODOT's use of a pocketultrasonic thickness (Pocket UTTM) gauge to assess gusset plates on bridges. The Pocket UT gauge has allowed ODOT to gather thickness data faster and better detect areas of corrosion. "The device has saved time and money and given us better confidence in the data," said Brokaw. In March 2008, ODOT used the Pocket UT gauge to inspect a three-span deck truss bridge near Columbus. Using the pocket gauge reduced inspection time by about 25 percent, while also cutting costs by about 25 percent. Brokaw noted that while the gauge cost $17,000, "it has already paid for itself."
Also featured during the Web conference was an initiative to improve the reliability of bridge inspections in Oklahoma. Calvin Karper of FHWA's Oklahoma division office detailed how the Oklahoma Department of Transportation (ODOT) has established a systematic quality assurance (QA) approach. In 2002, ODOT formed a Bridge Ratings Team (BRT) to manage the QA process. The team includes ODOT team leaders and program managers, an FHWA bridge engineer, county bridge coordinators, and an ODOT data manager. In 2003, the BRT had all staff involved in bridge inspection at ODOT inspect the same three bridges. The results were highly variable. After the BRT also experienced difficulty in coming to consensus on the bridge ratings, team members recommended changes to Oklahoma's State Bridge Inspection Manual, including adding photographs to help explain condition states and better defining terms such as "impending pothole" and "deep pitting."
This new process has continued, with the bridge inspection exercise conducted in odd numbered years and the State Bridge Inspection Manual updated the following year to include recommendations resulting from the exercise. Karper noted that "this process has dramaticallyimproved the quality of our inspections and data."
To download an audio file from the bridge inspection Web conference, visit www.nhi.fhwa.dot.gov (click on "Register for NHI Innovation Series" and then select the March 11 "Bridge Inspection" seminar).
The Transportation Research Board (TRB) also recently sponsored a Webinar on the "Importance of Bridge Inspection and Management." Held on March 29, 2009, Webinar topics included "Bridge Inspection Practices," "Monitoring Scour Critical Bridges," and "Guidelines for Implementing Quality Control and Quality Assurance for Bridge Inspection." To download slides from the Webinar, visit onlinepubs.trb.org/onlinepubs/Webinars/InspectingBridgesSlides.pdf (PDF - 7 MB).
"Bridge inspection has been in the spotlight since the collapse of the I-35W bridge in Minneapolis. Through events such as the recent FHWA and TRB Webinars, we are spreading the word about some of the more advanced technologies and practices that are in use today," says Tom Everett of FHWA.
For more information on bridge inspection, contact Tom Everett at FHWA, 202-366-4675 (email: email@example.com). FHWA is in the process of updating all of its bridge inspection training courses offered through NHI. As the new courses become available, Focus will provide updates in future issues.