Design Approach to Determine Shear Capacity of Reinforced Concrete Beams Shear Strengthened with NSM Systems

Abstract

This paper present a design approach to predict the shear capacity of reinforced concrete (RC) beams strengthened with fiber reinforced polymer (FRP) laminates/rods applied according to the near surface mounted (NSM) technique. The new approach is based on the simplified modified compression field theory (SMCFT) and considers the relevant features of the interaction between NSM FRP systems and surrounding concrete, like debond and concrete fracture. In the SMCFT model, the shear strength of a RC element is a function of two parameters: the tensile stress factor in the cracked concrete (), and the inclination of the diagonal compressive stress in the web of the section (). However, this approach is not a straightforward design methodology due to its iterative nature. A sensitivity analysis is carried out to assess the relative importance of each input parameter that mostly affect the shear capacity of RC beams shear strengthened according to the NSM technique. Taking into account the obtained results, equations to determine  and  without recurring to an iterative procedure are derived. The experimental results of 112 beams shear strengthened with NSM FRP are used to appraise the predictive performance of the developed approach. By evaluating the ratio between the experimental results and the analytical predictions, an average value of 1.14 is obtained, with a coefficient of variation of 13.1%, being safe estimations 87% of the predictions.

Shear behavior of concrete beams reinforced exclusively with longitudinal glass fiber reinforced polymer bars: Analytical model

“…The axial strain, ε x , can be obtained from the following equation (limited to the yield strain, ε l , y ): where f l , E l , and ρ l are the stress (limited to the yield stress, f l , y = E l ε l , y ), the modulus of elasticity, and the ratio of the longitudinal reinforcement, respectively. The procedure to calculate the shear strength of an RC beam, according to the SMCFT, is summarized as follows:…”

“…The development of a relatively simple design approach for predicting the shear capacity of reinforced concrete (RC) beams with good accuracy is still a challenging topic due to several and complex resisting mechanisms involved in shear such as (a) shear resistance assured by the uncracked concrete in the compression zone; (b) interface shear transfer by aggregate interlocking in the cracked concrete; (c) dowel action of the longitudinal reinforcement; and (d) resistance provided by transverse reinforcement, when existing …”

Design‐oriented approach to predict shear strength of reinforced concrete beams

“…For the New Baghi and Barros (NBB), ACI, SMCFT, and SBBB approaches, the obtained values of V ana . are compared with V exp.…”

“…The sum of squares due to error (SSE), R 2 , and root‐mean‐squared error (RMSE) for this fitted surface are 465, 0.56, and 0.03, respectively, which indicate the good fit of the model to the generated samples. More information about these goodness‐of‐fit statistics can be found in Reference .…”

“…Recently, Baghi and Barros developed a new method based on the SMCFT and Bianco et al approach to predict the shear capacity of typical building RC beams shear strengthened according to the near surface mounted (NSM) technique with fiber reinforced polymer (FRP) laminates. This model takes into account the relevant features of the interaction between NSM FRP systems and surrounding concrete, like debonding of FRP laminate/rod and fracture of concrete surrounding the FRP, by considering the inclination of the CDC .…”