Abstract
Numerous studies on the size effect have been devoted to reinforced concrete (RC) beams. They have shown that increasing the beam size leads to a decrease in ultimate shear strength (stress) at failure. This is reflected in the design model of most current international codes and guidelines, where the size effect is taken into consideration by reducing concrete contribution to the shear resistance (force). In contrast, the size effect of RC beams strengthened with externally bonded (EB) fibre-reinforced polymer (FRP) is not fully documented, and very few experimental studies have been devoted to the phenomenon. The objective of this study was to evaluate the accuracy of the current code and guideline models in terms of the size effect on the EB-FRP contribution to shear resistance. To this end, a database of experimental findings on the size effect in EB-FRP-strengthened beams was built based on the reported literature, as well as our own experimental tests. The data were analysed and compared with the predictions of six current codes and design guidelines to assess their accuracy. Experimental results clearly revealed the presence of a size effect related to EB-FRP as well as the existence of interaction between internal stirrups and EB-CFRP. Based on analysis of the collected experimental test results, the study clearly revealed that the predictions of current codes and guidelines overestimate the contribution of EB-FRP systems to shear resistance. The size effect tends to exacerbate this overestimation as the effective depth (d) of the beams increases. Therefore, until the size effect for RC beams strengthened in shear with EB-FRP is captured by the prediction models, current codes and design guidelines are to be used with caution.
Highlights
The size effect on the shear behaviour of conventional reinforced concrete (RC) beams is well established
The present study aims to examine the size effect in RC beams strengthened in shear with externally bonded (EB)-fibre-reinforced polymer (FRP) and to assess the accuracy of the design models of some leading codes and design guidelines as well as the influence of size effect to the contribution to shear resistance attributed to EB-FRP of these models
Because these two specimens were of the same size, this result reveals a significant decrease in EB-CFRP shear gain due to the presence of steel stirrups
Summary
The size effect on the shear behaviour of conventional RC beams is well established. There is a size effect when there is a difference in shear strength at failure between beams of different sizes, but with similar geometry. The gap revealed by several experimental investigations is still not accounted for in the prediction models This is the case for many major parameters, such as: (1) the interaction between internal transverse steel and external FRP, which reduces the performance of EB-FRP as reported by [18]; (2) shear strength decrease with increasing beam height, as reported by [11]; and (3) modification of the web cracking pattern by a shear-strengthening system that modifies the anchorage conditions of EB-FRP, as reported by [19]. The present study aims to examine the size effect in RC beams strengthened in shear with EB-FRP and to assess the accuracy of the design models of some leading codes and design guidelines as well as the influence of size effect to the contribution to shear resistance attributed to EB-FRP of these models. The six codes and design guidelines used in this study for the design of shear-strengthened RC beams with EB-FRP were: ACI-440.2R-17 2017 [20]; CSA-S619 2019 [21]; CSA-S806-12 2012 [22]; fib-TG5.1-19 2019 [23]; fib-TG9.3-01 2001 [24]; JSCE 2001 [25]
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