Flexural Strengthening of RC Beams with Pre-stressed steel rebar

Various methods have been developed for the retrofit and strengthening of RC beams. One of the successful methods is the near-surface mounting (NSM) method. In this method, the reinforcing rebar is inserted and glued into the groove in the concrete cover. This groove is created in the tensile face of the beam. The relative protection of reinforcing materials, which are less exposed to mechanical damage, shock and fire loading is an important advantage of this strengthening method. Pre-stressing can close the cracks caused by the weak flexural strength of the member and reduce its excess deflection. The proposed strengthening method in this research was near surface mounting of pre-stressed rebars to enhance the flexural behavior of RC beams. The test program consisted of testing 5 RC beams of 200×200 ×1700 mm. One was the control sample and was tested without strengthening. Four other beams were first pre-loaded to the cracking stage and, after unloading, were strengthened by near surface mounting of the steel bars. The beams were tested under four-point bending. The applied load and the corresponding displacement in the middle of the beam were measured. In the flexural strengthening of the beams by proposed NSM method, end-anchorage and epoxy adhesive, both provided the proper bond. Tightening the end nuts with the aid of a torque meter, was the selective method to pre-stress the reinforcing bar. The results showed that this method was very effective for the flexural strengthening of RC beams, so the final load capacity of beam samples increased about twice as much as the control sample. The proposed method also led to the closure of the bending cracks and the reduction of the samples’ deflection, as well as the increase in energy absorption of the samples.