The strengthening of deteriorated reinforced concrete (RC) structures with externally bonding fiber-reinforced polymer (EB-FRP) composites has become a popular method for upgrading structural performance over the past two decades. For this application, there are many advantages of FRP composites, including light weight, high tension strength, good corrosion resistance and ease of applying in strengthening applications. However, there are still a number of issues that need to be further explored and investigated, especially in the area of FRP shear strengthening technique. In this thesis, the effects of shear span-to-effective depth ratio (also known as shear span/depth ratio) on the mechanical behavior of RC beams strengthened in shear with EB-FRP strips are systematically studi...[ Read more ]

The strengthening of deteriorated reinforced concrete (RC) structures with externally bonding fiber-reinforced polymer (EB-FRP) composites has become a popular method for upgrading structural performance over the past two decades. For this application, there are many advantages of FRP composites, including light weight, high tension strength, good corrosion resistance and ease of applying in strengthening applications. However, there are still a number of issues that need to be further explored and investigated, especially in the area of FRP shear strengthening technique. In this thesis, the effects of shear span-to-effective depth ratio (also known as shear span/depth ratio) on the mechanical behavior of RC beams strengthened in shear with EB-FRP strips are systematically studied. In particular, focus is placed on the effects of shear span/depth ratio on the failure mode, strain distribution of FRP strips and FRP shear contribution of shear-strengthened RC beams.

For better understanding of existing studies, the literature on beams strengthened in shear with EB-FRP is reviewed first. Besides summarizing the general properties of shear strengthened members, the literature review specially covers the following aspects: (a) effect of shear span/depth ratio on mechanical behavior of shear-strengthened RC beams; (b) existing shear strength models for FRP composites, and (c) existing data analysis and the use of finite element (FE) approaches for beams shear strengthened with FRP composites. Based on these reviews, limitations of existing studies are highlighted to set the stage for the thesis research.

An experimental study on RC beams strengthened in shear with two different configurations (i.e., the full-wrapping and U-wrapping FRP strips) is then discussed. In this experimental study, eighteen RC beams (six beams as control beams without FRP strengthening, six beams each strengthened in shear with full-wrapping and U-wrapping CFRP strips, respectively) are tested in four-point bending method. Mechanical behavior of specimens is studied extensively and discussed in depth. The specific issues include: (a) failure modes of un-strengthened and strengthened RC beams; (b) effect of shear span/depth ratio on the shear contribution of FRP; (c) the strain development of FRP during the loading process; (d) effect of shear span/depth ratio on the strain distribution of FRP strips, and (e) comparison between the shear behavior of RC beams strengthened with full-wrapping and U-wrapping FRP configurations. The experimental investigation indicates that the shear behavior of RC beams shear strengthened with FRP in both full-wrapping and U-wrapping configurations is significantly affected by the shear span/depth ratio. When the shear span/depth ratio increases from 1.0 to 3.5, the trend of FRP shear contribution shows a near-parabolic shape with the maximum contribution obtained at medium span/depth ratio. Also, for different shear span/depth ratios, the FRP strain distributions along the critical shear crack are found to exhibit different shapes.

Data analysis to evaluate the effect of shear span/depth ratio on the FRP shear contribution of strengthened RC beams is carried out in the last part of the thesis. The data analysis is based on a large number of available experimental data collected from existing investigations. Furthermore, the FRP shear contribution predicted from various design guidelines is compared with our own experimental results as well as those in the literature. The investigation indicates that the shear span/depth ratio can significantly affect the accuracy of predictions from various design guidelines, and hence should be taken into account. Based on the traditional truss model, an advanced strength model for FRP shear contribution which includes the effect of the shear span/depth ratio is proposed. The proposed model is shown to improve the accuracy of predicting FRP shear contribution in the comprehensive range of a_v/d ratio from 1.0 to 3.5.

Key Words

Fibre-Reinforced Polymer (FRP); Shear-Strengthening Technique; Shear Span-to-Effective Depth Ratio; Shear Behavior of Reinforced Concrete; Shear Strength Model