January 29, 2003

How Safe Are Our Bridges? — NC State Researcher Focuses on Improved Repair Systems

 

The underside of a bridge in Florida shows damage from vehicles that exceeded the height limit. (Photo by Dr. Mohsen Shahawy)		Workers apply fiber-reinforced polymer to the damaged bridge. (Photo by Dr. Mohsen Shahawy)

How many times have you sat in your car on a bridge only to feel the bridge shake and rumble beneath you as other cars pass over?  Questions about the bridge’s integrity pop into your head, but you usually just continue on your way when the light changes. 

For NC State University researcher and professor of civil engineering Dr. Amir Mirmiran, questions about the integrity of bridges are more than passing thoughts.  Part of his work addresses bridge stabilization and repair, and one current project for the National Academy of Sciences involves development of new construction specifications and a process control manual for use by the American Association of State Highway and Transportation Officials (AASHTO) Subcommittee on Bridges and Structures.

AASHTO strives to make bridges safer by developing design guidelines and procedure manuals for all U.S. state departments of transportation.  Recent development of new materials that could be used to reinforce bridges has sparked interest in the safe application of this technological advance to existing structures.  One new material, fiber-reinforced polymer (FRP), is the subject of Mirmiran’s research project.

The completed repair makes the bridge safe again. (Photo by Dr. Mohsen Shahawy)

FRP is a very strong, flexible fabric made of carbon or glass.  With a resin such as epoxy, FRP can be bonded to a concrete surface to expedite bridge repair, in many cases without even closing the bridge to traffic during the process.  Applying FRP is not labor-intensive compared with traditional methods, and heavy equipment generally is not required.  Strengthening and repairing a bridge is much faster and more economical using this new material.  Existing bridges can even be upgraded to accommodate heavier, wider vehicles.

The research project, led by Mirmiran, involves a collaboration among NC State University, the SDR Engineering Consultants, the University of Missouri–Rolla and the University of California–San Diego.  To assuage worries of the departments of transportation that FRP materials used for repairs may not be applied properly, Mirmiran’s group is creating a field guide and manual for the application of FRP in the repair and retrofit of bridges.  The manual is in the revision stage; Mirmiran hopes a final version will be ready to submit to the National Academy of Sciences this summer.

According to Mirmiran, “Eventually the manual will be a document that every bridge engineer in every state will use.”

Once the document is adopted by state departments of transportation, Mirmiran’s research group wants to develop a series of workshops for each state.  “The next phase of our work will be training state transportation engineers,” said Mirmiran.  During a two-day traveling workshop, facilitators would outline the FRP application process and teach highway workers how to use the field guide and an inspection manual.

Another aspect of the project is nondestructive testing and evaluation of the repairs, which will be incorporated into the inspection manual.  “One of the purposes of this project is not only to demonstrate the placement of this material but also to show how the material can be inspected right after the reconstruction to make sure that it has bonded properly,” said Mirmiran.  Nondestructive evaluation methods include both low-tech, such as visual and acoustic (tapping on the bridge), and sophisticated (thermographic and ultrasonic) alternatives.  Based on these evaluation methods Mirmiran has developed acceptance criteria so departments of transportation will know if a repaired bridge is safe.

Bridge safety — the ultimate goal of Mirmiran’s work — will be improved once these very practical documents are finished and distributed.

— rudd —

Media Contacts:
Dr. Amir Mirmiran, 919-513-1735, amir_mirmiran@ncsu.edu
Linda E. Rudd, 919-515-3848, linda_rudd@ncsu.edu