Experimental and numerical investigation for the flexural strengthening of RC beams using near-surface mounted steel or GFRP bars

In this paper, the effectiveness of NSM bars as a means of restoring or upgrading the flexural capacity of RC beams is experimentally and numerically investigated. The studied parameters included type of NSM bars: steel versus GFRP, and NSM reinforcement ratio (number and diameter of inserted NSM bars). A total of eight groups of 16 beams were tested under four-point bending. The two beams of the first group were reinforced with three main steel bars and were used as control specimens. The two beams of the second group were reinforced with three main GFRP bars and were utilized for comparison with control specimens. Assuming that one of the three main steel bars in the control specimen had corroded, three groups of six beams were designed in which one NSM steel or GFRP bar was inserted in the tension side. Yet, with the assumption of the corrosion of two main steel bars in the control beam, the last three groups of six beams were planned in which two NSM steel or GFRP bars were planted in the tension side. For NSM-upgraded beams, special type of epoxy paste was used as bonding agent. Test results showed that by using NSM steel or GFRP bars to compensate the difference in the main reinforcement, the original load capacity of the control beam was successfully restored. The ultimate capacity of the beams was predicted using the ACI 318-11 code and ACI 440.1R-06 guidelines. A numerical investigation utilizing nonlinear finite element (FE) analysis was also carried out using LS-DYNA software. A comparison was made between the experimental and numerical results and good agreement was obtained. Based on the validation of FE results, the numerical analysis was extended to include additional cases to study the effect of FRP reinforcement ratio on the flexural performance of NSM-upgraded beams.

► The worth of NSM bars for upgrading the flexural capacity of RC beams is investigated.
► A total of eight groups of 16 beams were tested under four-point bending till failure.
► The ACI 318-11 code and ACI 440.1R-06 guidelines were used for peak load prediction.
► Nonlinear finite element analysis was conducted using LS-DYNA software.
► NSM bars were found to be successful at upgrading the flexural capacity of RC beams.