Amir Mofidi

Shear Strengthening of RC Beams with EB FRP: Influencing Factors and Conceptual Debonding Model

This paper deals with the shear strengthening of RC beams using externally bonded (EB) fiber-reinforced polymers (FRP). Current code provisions and design guidelines related to shear strengthening of RC beams with FRP are discussed in this paper. The findings of research studies, including recent work, have been collected and analyzed. The parameters that have the greatest influence on the shear behavior of RC members strengthened with EB FRP and the role of these parameters in current design codes are reviewed. This study reveals that the effect of transverse steel on the shear contribution of FRP is important and yet is not considered by any existing codes or guidelines. Therefore, a new design method is proposed to consider the effect of transverse steel in addition to other influencing factors on the shear contribution of FRP ( Vf ) . Separate design equations are proposed for U-wrap and side-bonded FRP configurations. The accuracy of the proposed equations has been verified by predicting the shear st...

Embedded Through-Section FRP Rod Method for Shear Strengthening of RC Beams: Performance and Comparison with Existing Techniques

Embedded through-section (ETS) technique is a recently developed method to increase the shear capacity of reinforced concrete (RC) using fiber-reinforced polymer (FRP) rods. The ETS method presents many advantages over existing methods, such as externally bonded FRP sheets (EB FRP) and near-surface mounted FRP rods (NSM FRP). Unlike EB and NSM methods where the FRP relies on the concrete cover of RC beams, in the ETS method, the FRP relies on the concrete core of the RC beam, which offers a greater confine- ment and hence improves bonding performance. Additionally, the ETS method requires less concrete preparation compared with EB and NSM methods. The objective of this paper is to present results of an experimental investigation that studies the effectiveness of the ETS method and compares the performance of the ETS method with both EB and NSM methods. In total, 12 tests are performed on 4,520-mm- long T-beams. The parameters investigated are as follows: (1) the effectiveness of the ETS method, compared with EB FRP sheet and NSM FRP rod methods; (2) the presence of the internal steel; and (3) the internal transverse steel reinforcement ratio (i.e., spacing). The test results confirm the feasibility of the ETS method and reveal that the performance of the beams strengthened in shear using this method is signifi- cantly superior compared with that of the beams strengthened with EB and NSM methods. DOI: 10.1061/(ASCE)CC.1943-5614.0000174.

Performance of End-Anchorage Systems for RC Beams Strengthened in Shear with Epoxy-Bonded FRP

This paper presents the results of an experimental investigation on the performance of full-scale reinforced concrete (RC) T-girders strengthened in shear using externally bonded (EB) fiber-reinforced polymer (FRP) U-jackets end-anchored with different systems. Debonding of FRP, particularly in shear, is a major failure mode when using FRP sheets to strengthen concrete structures. Design code provisions and guidelines related to shear-strengthening of RC beams using externally bonded FRP (EB FRP) suggest the use of end- anchorage systems to prevent FRP debonding. However, no guidelines are available for the design and effectiveness of end-anchorage sys- tems. The main objective of this study is to evaluate the effectiveness of different end-anchorage systems for RC beams strengthened using EB FRP methods. To this end, nine tests were performed on 4520-mm-long RC T-beams. Four specimens were strengthened in shear using EB FRP methods with various end-anchorage systems, and their performance was compared with similar specimens strengthened with: (1) EB FRP with no anchorage; (2) near-surface-mounted (NSM) FRP rods; and (3) embedded through-section (ETS) FRP rods. The results of this study reveal that specimens retrofitted with EB FRP methods and properly designed end-anchorage systems can achieve a superior contribution to shear resistance compared with specimens strengthened using EB FRP with no anchorage, NSM, or ETS methods. DOI: 10 .1061/(ASCE)CC.1943-5614.0000263.

Behavior of Reinforced Concrete Beams Strengthened in Shear Using L-Shaped CFRP Plates: Experimental Investigation

This paper presents the results of an experimental investigation on reinforced concrete (RC) T-beams retrofitted in shear with prefabricated L-shaped carbon fiber–reinforced polymer (CFRP) plates. Shear strengthening of RC beams with L-shaped fiber-reinforced polymer (FRP) plates has proved effective. In this method, grooves are made throughout the beam flange to fully embed the vertical leg of the L-shaped CFRP plate perpendicular to the longitudinal axis of the RC beam and in the RC beam web surface. However, in some cases, drilling grooves in the concrete flange might not be feasible because of the presence of obstacles such as longitudinal steel in the flange of the RC beams. Therefore, the main objective of this investigation was to evaluate the performance of the RC beams strengthened in shear with externally bonded (EB) L-shaped plates as affected by the embedment length of the L-shaped FRP plates. In total, six tests were performed on 2,500-mm long T-beams. Three specimens were strengthened in shear using epoxy-bonded L-shaped CFRP plates with different embedment lengths in the RC beam flange. One specimen was shear-strengthened with fully embedded CFRP plates in the concrete beam flange. The second specimen was strengthened with partial embedment of the L-shaped CFRP plate. This specimen is representative of the case where full penetration of the CFRP plate is not feasible because of an obstacle. In this specimen, the embedment length was set to 25 mm to simulate the minimum concrete cover thickness in RC beams. The third specimen was shear-strengthened with L-shaped CFRP plates with no embedment in the concrete beam flange. In addition, the performance of the beams strengthened with L-shaped CFRP plates was compared with that of a similar specimen strengthened with EB FRP sheets without embedment. Results show that the performance of the specimens strengthened with partially and fully embedded L-shaped CFRP plates in the beam flange was superior to that of the beams strengthened with EB FRP sheets and L-shaped CFRP plates with no embedment.

Investigation of Near Surface–Mounted Method for Shear Rehabilitation of Reinforced Concrete Beams Using Fiber Reinforced–Polymer Composites

AbstractThis paper presents the results of an investigation of reinforced concrete (RC) T-beams retrofitted in shear with near-surface mounted (NSM) fiber-reinforced polymer (FRP) rods. Six full-scale 4,520-mm-long RC T-beams were tested to study the effects of important parameters such as the presence of NSM FRP rods, the presence of steel stirrups, and the steel stirrup ratio. This paper provides an insightful and comprehensive description of the behavior of strengthened T-beams under increasing load, from the formation of the first crack to ultimate failure. The results of this study and those gathered in the presented database show that existing steel stirrups and strengthening NSM FRP did not diminish each other’s effect when failure modes unrelated to shear resistance of RC beams were prevented. The experimental results of this study and those in the database were used to verify a newly proposed model to predict the shear contribution of NSM FRP rods and laminates in RC beams strengthened in shear. T...

Reinforced-concrete beams retrofitted in shear with externally-bonded fibre-reinforced polymer: development of a design model

This paper presents the results of a theoretical study of the parameters that affect the contribution of fibre-reinforced polymer (FRP) composite to the shear resistance of reinforcedconcrete (RC) beams retrofitted in shear. To assess and analyse the variables that have the most signifi cant effect on the shear resistance of RC members strengthened with externally-bonded (EB) FRP, the results of available studies reported in the literature are used. In addition to variables related to the mechanical properties of FRP and internal transverse steel reinforcement, the following influential parameters on the shear contribution of FRP are assessed in this study: (i) the shear span ratio; (ii) the longitudinal-steel reinforcement ratio; (iii) the compressive strength of concrete; and (iv) the failure mode of RC beams shear-strengthened with EB FRP. This study shows that the effect of steel stirrups on the shear contribution of FRP is significant. However, the steel stirrups effect is not taken into consideration in existing codes and guidelines. In this paper, a design method is proposed that considers the effect of steel stirrups in addition to other influential parameters on the contribution of FRP to the shear resistance. Comparison with current design guidelines reveals that the proposed model achieves a better correlation with experimental results than current design codes and guidelines.

Shear Strengthening of RC Beams with EB FRP: Evolutive Model versus Code

This paper deals with the shear strengthening of reinforced concrete (RC) beams using externally bonded (EB) fiber-reinforced polymers (FRP). The parameters that have the greatest influence on the shear behavior of RC members strengthened with EB FRP and the role of these parameters in current design codes are reviewed. The effect of transverse steel on the shear contribution of FRP was found significant and yet is not captured by any existing codes or guidelines. Therefore, a new design method is proposed, which considers the effect of transverse steel as well as to other influencing factors on the shear contribution of FRP (Vfrp). The accuracy of the proposed equations is verified by predicting the shear strength of experimentally tested RC beams using data collected from literature.