Rapid strengthening of reinforced concrete bridges

Abstract

An innovative technique for repairing reinforced concrete beams (or slabs) by attaching FRP (fiber reinforced polymer) strengthening strips to the underside of the beam using powder actuated fasteners and mechanical anchors was developed at the University of Wisconsin-Madison under funding from the U.S. Army Corps of Engineers. The method is known as the Mechanically Fastened (MF) Fiber-Reinforced Polymer (MF-FRP) method, to distinguish it from the traditional Externally-Bonded FRP (EB-FRP) method. This method is rapid and uses simple hand tools, lightweight materials, and unskilled labor. Unlike the conventional method of adhesively bonding FRP strips to the concrete surface, this method does not require much surface preparation and allows for immediate use of the strengthened structure. The potential to use the method as a rapid and temporary means of upgrading load-capacity deficient bridges in the State was studied. Such an option is desirable to local governments that have budget constraints and need to replace many older deficient bridges. In this research, the MF-FRP method was used to strengthen a bridge in Edgerton, Wisconsin, which was subsequently tested to failure. Additional laboratory tests on strengthened beams were conducted at the University of Wisconsin-Madison. The major finding of this research was that the MF-FRP method could be used to strengthen an existing deteriorated bridge. The Inventory Rating of the bridge strengthened was increased from an HS17 rating to HS25 rating for a unit cost of materials and manpower of approximately $12 per sq ft. The method is easy to use in the field and the level of strengthening can be predicted in advance using conventional analytical methods.