Rehabilitating bridges better

Across Wisconsin, and almost everywhere you travel, sit hundreds of aging bridges. Many are nearing the end of their useful lives. But replacing them is costly. What’s a bridge owner to do?

Civil and environmental engineering professor Lawrence Bank has come up with a solution – temporarily strengthening them by using composite strips attached to the underside of the bridge. “It has tremendous economic potential,” Bank says.

Wisconsin, for instance, has hundreds of concrete bridges that were built 60 or 70 years ago. These aren’t the long, impressive steel girder structures that cross major rivers. These are the short, stumpy bridges that cross minor streams. Many of the bridges are still functional, but are deteriorating.

From Bank’s perspective, these kinds of bridges are ideal candidates for Fiber Reinforced Polymer (FRP) plates, or strips, that can be attached to the underside of the bridge. The plates are held in place by fasteners that are shot into the concrete by a power-actuated fastening gun (similar to a pneumatic nail gun). The sheer force of shooting the fastener with a nail gun creates a bond between the fastener surface and the concrete, making for a secure connection.

A key factor in utilizing the FRP plates is a bridge’s “sufficiency number,” which is an overall assessment of a bridge’s condition. Bridges are typically assessed on measures such as the load they can hold, their width, safety features such as guardrails, and their general condition, according to Bank. A bridge with a sufficiency number below 50 is usually slated for replacement. But by utilizing the FRP plates, a bridge’s sufficiency number can be improved enough to forestall its total replacement.

City, village and town governments own many of these deteriorating bridges. For some communities, replacing more than one or two bridges at any one time could be too costly. Using FRP plates would allow local governments to spread out their bridge replacements over several years.

“It’s an economical system to bring your bridges up to an acceptable sufficiency number for three to five years,” Bank says.

Bank, along with graduate student Anthony Lamanna, has filed for a patent for the FRP plate technology with the Wisconsin Alumni Research Foundation.