Influence of the Effectiveness Factors in Assessing the Shear Capacity of Rc Beams Strengthened With FRP

Abstract

Shear failure of RC beams strengthened with composite textiles is often affected by the different failure modes characterizing the FRP reinforcement. The most relevant analytical models for evaluating the shear capacity of RC beams strengthened with FRP take into account these failure modes by introducing an effectiveness factor "R", which reduces the ultimate FRP tensile stress. Moreover, the interaction between stirrups and FRP reinforcement leads to a reduced efficiency of the transverse steel reinforcement due to the brittle failure of composite textile which hinders the yielding of all the stirrups involved by critical crack. In this regard, some analytical models introduce an effectiveness factor "r", aiming at reducing the yielding stress of stirrups. The procedures to calculate the above two parameters represent the main differences characterizing most of analytical models, significantly influencing their results. For this reason, the present paper focuses on the comparison of the different procedures to assess the effectiveness factors, proposing a new procedure for each effectiveness factor by modification of already existing formulations. Influence of the arrangement of composite reinforcement on the efficacy of stirrups, affected by brittle failure of FRP, is considered by means of the ratio between effective strain of composite to yielding strain of steel. The proposed procedures are employed in a design-oriented analytical model able to calculate the shear strength of RC beams retrofitted with FRP reinforcement arranged in any direction. The model is formulated aiming at representing an extension of EN1992 shear model to beams strengthened with FRP. The efficacy of the proposed procedures is assessed by comparing the experimental results against the predictions obtained via the design-oriented model and the above-mentioned analytical models.

Perspectives and Specific Features of the Use of Composite Materials for Strengthening of Damaged Reinforced Concrete Structures

“…Significant improvement in design of composite strengthening systems can be achieved via effective modeling and calculation methods, which was covered by significant number of researches, enabling reliable assessment of the stress-strain state, strength parameters and residual source of reinforced concrete elements strengthened with composite materials (Alyaseen et al, 2022;Borysiuk et al, 2019;Karpiuk et al, 2020;Naser et al, 2021;Colajanni, and Pagnotta, 2021;D'Antino et al, 2020). Borysiuk et al in their article emphasize the need for the development of accurate and reliable calculation methods that can be adapted for practical needs and take into account operating conditions and the stress-strain state of the structure before application of strengthening system (Borysiuk et al, 2019).…”

“…Thus, different procedures for evaluating the influential parameters of the load-bearing capacity of the structure strengthened with composites were described by Colajanni, and Pagnotta. This study also proposes simplified formulation of the analytical model for evaluation of the shear strength based on the comparison of transverse forces perceived by FRP and steel reinforcement (Colajanni, and Pagnotta, 2021). Sensitivity analysis for various parameters of load-bearing capacity and holistic quantitative and qualitative assessment deformation, crack formation and destruction mechanisms were covered by study of Karpyuk et al (Karpiuk et al, 2020).…”

Influence of Cross-Section Shape and FRP Reinforcement Layout on Shear Capacity of Strengthened RC Beams

“…Case 3 (very large ω sw and ω fw values): cot θ < 1: It implies that cot θ = 1.0 must be assumed, and the failure is due to reaching the stress limit in the concrete strut and in one of the shear reinforcements. If it is assumed that β < α, then the maximum shear strength of the beam is given by the minimum value obtained via Equation (10) assuming that the FRP reinforcement attains the maximum effective strain in tension σ f = 1 or by Equation (11), considering that the yielding in the steel stirrups is attained, having σ s = 1. In Appendix B, the above three different cases are elucidated by calculation examples.…”

“…After that, the inclination of the concrete strut is calculated via Equation ( 14), which provides a value of cot θ = 2.09. Therefore, assuming σ c = σ f = σ s = 1, the shear capacity can be calculated using one of Equations ( 9)- (11), which provide a value of 272 kN.…”

“…In this connection, the brittle failure of FRP reinforcement, which can occur before the yielding of steel stirrups, can have a negative effect on the shear strength provided by the transverse steel reinforcement [11,12]. Some researchers have proved that, when members having a significant amount of steel stirrups have to be strengthened, the transverse reinforcement provides a greater contribution than the FRP because the bond between the steel and concrete is stronger than between the FRP and the concrete surface [13].…”