The most common method used to strengthening, rehabilitation or repairing of reinforced concrete (RC) members is to use external carbon fiber reinforced polymer (CFRP) sheets. CFRP can greatly improve the flexural and shear capacity of deteriorated members and therefore extends their useful life. The main problem of external CFRP is the debonding of the sheets from the concrete surface at some point of loading, which negatively affects the efficiency of strengthening and may consequently lead to an unanticipated failure of the strengthened members. The major reason for this early debonding is likely due to the low accuracy of the preparation and the high stress concentration at the flat contact area exists between CFRP sheets and the concrete. The problem has been extensively discussed in the literature and some CFRP application techniques such as “Externally Bonded Reinforcement on Grooves (EBROG)” and “Externally Bonded Reinforcement in Grooves (EBRIG)” have been proposed as alternatives to the conventional application methods. Although some research has been carried out, there have been few experimental investigations that provided quantitative discussion of the efficiency of the new developed techniques. This research was aimed to experimentally assess the efficiency of grooving techniques and to provide a quantitative data regarding the behaviour of bonding between CFRP and concrete. The effects of shape and direction of the grooves and CFRP layers on the load carrying capacity, mid-span deflection and failure mode of thirteen RC beams have been investigated and discussed. In general, CFRP has significantly improved the flexural capacity of strengthened beams especially when grooving technique has been employed.

The externally bonded reinforcement on grooves (EBROG) method is increasingly recognized as an alternative strengthening method that can overcome the debonding problem. This study aims to experimentally investigate the effectiveness of EBROG as compared to the conventional externally bonded reinforcement (EBR) method in strengthening reinforced concrete (RC) beams. Twelve RC beams have been tested under four point load bending. One of these beams has been designated as a reference beam, seven beams have been strengthened with carbon fiber reinforced polymer (CFRP) sheets, and four beams have been strengthened with CFRP laminates using EBROG or EBR methods. The effect of CFRP type, number of layers, as well as the type of strengthening methods on the flexural performance have been also investigated. The load, deflection, stiffness, and failure modes were recorded and discussed intensively. Overall, test results indicated that the flexural strength and stiffness of the strengthened specimens using EBR or EBROG methods increased compared to the control beam, where the increase in the load carrying capacity of beams strengthened using the EBR method ranged between 24.8 and 48.2% and by the EBROG method ranged between 31.7 and 76.7% of the control beam. The most interesting result obtained is that the failure mode of beams has been changed from debonding of CFRP material to rupture of CFRP in some samples strengthened by EBROG, which demonstrates the superior behavior of this strengthening technique as compared to the traditional strengthening using EBR.

An adaptive neuro-fuzzy inference system (ANFIS)-based model was developed to predict the punching shear strength of flat concrete slabs without shear reinforcement. The model was developed using a database collected from 207 experiments available in the existing literature. Five key input parameters were used to build the model, which were slab effective depth, concrete strength, reinforcement ratio, yield tensile strength of reinforcement, and width of square loaded area. The output parameter of the model was punching shear strength. The results from the adaptive neural fuzzy inference model were compared to those from the simplified punching shear equations of ACI, BS-8110, Model Code 2010, Euro-Code 2, and also experimental results. The root mean square error (RMSE) and the correlation coefficient (R) were used as evaluation criteria. Parametric studies were presented using ANFIS to assess the effect of each input parameter on the punching shear strength and to compare ANFIS results to those from the equations proposed in commonly used codes. The results showed that the ANFIS model is simple and provided the most accurate predictions of the punching shear strength of two-way flat concrete slabs without shear reinforcement.

This paper presents an experimental study on the punching shear behavior of reinforced concrete flat slabs fabricated using recycled coarse aggregate (RCA) in addition to the presence of steel fibers strengthened by carbon fiber reinforced polymer (CFRP). The ratios of replacement natural coarse aggregate by RCA were (0, 35, 55, and 75%) and the volume fraction of the steel fiber used in this study was 1.2%. Two strengthening methods were used, namely, externally bonded reinforcement (EBR) and externally bonded reinforcement on groove (EBROG). 16 square slabs were cast with overall dimensions of 800 mm by 800 mm by 80 mm thickness. The slabs were designed to fail in punching shear only. All the slabs were simply supported on four edges and tested for punching via a vertical load applied through the square central column. The test results showed that the mechanical properties, ultimate loads, and first crack loads decreased with increasing proportion of RCA replacement, while the incorporation of steel fibers improved the compressive strength and ultimate loads by the ranges of 12%–17% and 16%–25%, respectively. Strengthened slabs lead to considerable improvements in the punching behavior of slabs, with an increase in punching load ranging from 22–30% compared to unstrengthened slabs when using the EBR technique, while the increase in the punching loads ranged between 40 and 55% when using EBROG strengthening technique. However, using half amount of CFRP with the EBROG method led to an increase in punching shear of 20–28%. This research indicates the particular improvement offered by the EBROG with regard to the punching shear capacity of fibrous recycled coarse aggregate concrete (RCAC) slabs compared to the EBR method. In addition, the mode of failure of reinforced concrete (RC) slabs changed from one of debonding failure to concrete cover separation when using the EBROG method.

This paper deals with reinforced concrete beams strengthened by CFRP in flexure. The debonding between CFRP and the surface of the beam is the main problem. Many researchers around the world have made extensive efforts to study the phenomenon of debonding for efficient applications. Based on these efforts and different related field applications, code previsions and various models have been proposed for predicting debonding failure. Two code previsions and three typical models are presented in the current study. ACI-440.2R 17, CNR-DT 200 R1/2013, Said and Wu, Lu et al., and Teng et al. have been used to estimate the flexural strength of RC beams strengthened by CFRP with and without grooves. Test results of eleven flexural beams strengthened by CFRP sheet/laminate using externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods were used in the current paper. The performance and accuracy of each model were evaluated based on these test results. Most of the prediction models that used in this study give a closer prediction of the flexural strength of beams strengthened by EBR compared to that of the beams strengthened by EBROG. Finally, the prediction results of CNR-DT 200 R1/2013 were the most accurate and approval with test results compared with other models in the current study