SHEAR STRENGTHENING OF REINFORCED CONCRETE BEAMS WITH NEAR SURFACE MOUNTED FRP REINFORCEMENT

Abstract

During the last two decades, increasing the shear capacity of the existing reinforced concrete (RC) elements, such as RC beams has become an important issue around the world. The use of Near Surface Mounted (NSM) strengthening technique has contributed significantly in achieving that. However, the theoretical shear contribution of this technique in RC beams is still not yet fully achieved, and there is not a final design guidance to estimate this contribution accurately. Therefore, this dissertation aims first to study the effects of different parameters on the effectiveness of this technique in shear strengthening of RC beams, evaluating the current theoretical models. Finally, this dissertation aims to propose a modified analytical model to compute the theoretical shear contribution of NSM technique in RC beams accurately. The study of the impacts of various parameters, such as the type and material of the NSM reinforcement, angle of orientation, spacing, and percentage of existing steel stirrups, percentage of composite materials, concrete strength and the anchorage of the FRP reinforcement, on the effectiveness of such strengthening technique is first considered in this dissertation. From examining these influences using the findings of the previous experimental tests, it was discovered that these factors play an important role in the effectiveness of this technique. In fact, it was found that, they can contribute significantly in increasing the efficiency of NSM technique by means of shear strengthening technique in RC beams. Furthermore, experimental database was generated in this project using all the available technical papers in the field of NSM shear strengthening of RC beams. This was then used to evaluate the current theoretical models. Only three of the current theoretical models, which are the ones that proposed by A.K.M Anwarul Islam, (Dias and Barros) and T.C. Triantafillou, were selected and evaluated in this dissertation because of the complexity of some models and data availability. The evaluation of these three models are not only in terms of the accurate estimation of the analytical values of the shear contribution of NSM technique in RC beams, but also in terms of the considered parameters in the development of them, and their degree of sophistication. The evaluation results of the models showed that the first evaluated model is not that reliable to be used and modified. These results also demonstrated that Dias and Barross’ model is more reliable compared to the first evaluated model. Finally, the evaluations of the three models illustrated that the model of T.C. Triantafillou is the best one among the others. Based on the final evaluation results of the three models, T.C. Triantafillou’s model is modified in this dissertation using the generated database. By modifying and introducing new safety factors to this model, 94% of the considered beams of the database are in the safe side. However, since this model was originally designed for RC beam strengthened in shear using externally bonded FRP laminates, the predictive performance of this modified model is assessed. This is achieved by comparing the obtained results from the modified T.C. Triantafillou’s model with the results, which were obtained from using the three original models before carrying out any modification processes. In addition to this, Dias and Barross’ model is modified in this project, and the obtained results of the two modified models are compared. The assessment results proved that the modified T.C. Triantafillou’s model is a sufficient model, which can predict the theoretical shear contribution of NSM technique in RC beams accurately with sufficient agreement with the experimental results. Thus, this model has been adopted to be used as a design-oriented equation in RC beams strengthened in shear using NSM technique. A maximum limit to the effective FRP strain for each type of FRP reinforcement is also defined in this dissertation to maintain the aggregate interlock, and control the shear cracks in the NSM shear strengthened beams.