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Experimental and numerical programs were conducted to investigate the effect of concrete cover and area of main steel reinforcement on the flexural behavior of strengthened RC beams by near-surface mounted glass fiber reinforced polymeric (NSM GFRP) bars of different lengths. Nine beams divided into three main groups were tested under four-point bending. The three beams of the first group were strengthened by different lengths of GFRP bars and having a concrete cover of 50 mm, while the three beams in the second group were strengthened in a similar manner as those of the first group but the concrete cover was 30 mm. The main steel reinforcement in the first and second groups was 2Ø10. The three beams of the third group were similar to those of the first and second group but the main steel reinforcement was 2Ø16. The 3-D FE commercial ANSYS program was used for the numerical work. The experimental results showed that decreasing the concrete cover increased the flexural capacity of the strengthened RC beams but this improvement disappeared by decreasing the NSM GFRP bar length. The numerical results showed an agreement with the experimental results.

Unfortunately, most of the previous work studying the fracture toughness of fibrous composites has deliberately ignored bridging the fiber onto the pre-crack/notch surfaces by creating such a crack as a through-thickness crack (TTC). Furthermore, no standard specifications for measuring the fracture toughness of fibrous composites have considered the fiber bridging through the pre-notch. Only a few pieces of research, no more than fingers on one hand, have addressed this problem by creating an actual crack, i.e., a matrix crack (MC) instead of a TTC. The challenge these researchers face is the inability to calculate the fracture toughness directly through the stress intensity factor (SIF) relationship because there is no geometry correction factor equation, f(a/d), for an MC. The main objective of the present work is to calculate f(a/d) and ascertain a relationship between the SIF and crack mouth opening displacement (CMOD) for an MC numerically using 3-D finite element analysis. An experimental program was also conducted to measure the fracture toughness of three types of concrete beams: high-strength concrete (HSC) beams with a TTC, HSC beams with an MC, and fiber-reinforced concrete (FRC) beams with an MC. The results showed that FRC beams with an MC have the highest fracture toughness and, subsequently, the highest resistance to crack growth. The numerical results revealed a suggested relationship between the SIF and CMOD of FRC beams with an MC. This relation was used to predict the fracture toughness of FRC with an MC by the critical value of CMOD measured experimentally.

Near surface mounted technique become the most attractive technique for strengthening RC structures. A lot of research had been conducted to study experimentally the flexural behavior of RC members strengthened with NSM technique unlike the numerical research. A numerical investigation utilizes the non-linear finite element (FE) modeling using ANSYS was performed. The developed FE model considers the behavior of the epoxy-concrete interface using cohesive zone model (CZM) which is capable of predicting the failure mode of the strengthened beams. The parametric study include the effect of different parameters such as NSM bar number, NSM bar length, end inclination angle and end inclination leg length on the flexural behavior of strengthened beams. The results showed that, The developed FE model able to predict the expected modes of failure in NSM technique, the NSM bar length was effective till 0.5 of beam span, beams strengthened with end inclined angle 45 º NSM bar gives the highest improvement in load carrying capacity, this improvement was very close in case of using end inclined angle of 60 º and 90 º .