Static and fatigue behavior of reinforced concrete beams strengthened with steel plates for flexure

The strengthening of existing concrete structures is a major concern in recent years as the number of degraded structures increases. The purpose of this paper is to investigate the static and fatigue behavior of reinforced concrete (RC) beams strengthened with steel plates. Toward this end, a comprehensive test program has been set up and many series of strengthened beams have been tested. The major test variables include the plate thickness, adhesive thickness, and the shear-span-to-depth ratio. The test results indicate that the separation of plates is the dominant failure mechanism even for the full-span-length strengthened beams with steel plates. The actual measured load capacities for strengthened beams are found to be smaller than the theoretical ultimate load capacities which are based on the full composite action of a concrete beam and steel plate. The strengthened beams exhibit more dominant shear cracking as the shear-span-to-depth ratio decreases. The ultimate capacity of strengthened beams increases slightly with the increase of adhesive thickness, which may be caused by the late initiation of plate separation in the beams with thicker adhesive. The present study also indicates that the strengthened beams exhibit much higher fatigue resistance than the unstrengthened beams at the same fatigue load level. The increase of deflections of strengthened beams according to the number of load cycles is much smaller than that of unstrengthened beams. The present study provides very useful results for the realistic application of the plate-strengthening method in RC structures.