PSI - Issue 37

Sonia Djenad et al. / Procedia Structural Integrity 37 (2022) 321–329 Djenad et al / Structural Integrity Procedia 00 (2019) 000 – 000

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The wrapping of fiber-reinforced polymer as strips has become an attractive rehabilitation solution for concrete columns. Within this strengthening technique, FRP composites make à jacket around the concrete column with the fibers oriented in the strips direction (Arash Totonchi et al, 2019). Actually, the FRP stirrups can be applied discontinuously or continuously along the concrete column and thus resulting partially or fully FRP-confined concrete columns. Current researches have demonstrated that the FRP partial confining design by discrete FRP strips is a promising and economic alternative to the FRP full strengthening technique ( G. Wu et al. (2008), H. Saadatmanesh, et al (1994)). In addition, the several techniques and models of confinement with bonded FRP available in the scientific literature have confirmed that the lateral confinement pressure is related to geometric and mechanical characteristics of composites (Q. Cao, et al (2019), S. Mohammad Askari et al (2020)). Indeed, (Liang et al, 2019) reported a compressive behavior of CFRP-confined partially concrete columns under axial loading results, which show that CFRP-confined partially columns present a better mechanical performance than those without CFRP sheets confining. (Arash Totonchi et al, 2019) have demonstrated considerable improvements in the axial stress – strain behaviour. Authors confirm that, the CFRP partial or discontinuous wrapping strengthening technique tends to be at an advantage over the full wrapping strengthening method. The comprehensively investigation of (J. Yang et al, 2020) on the difference of the confinement mechanism between fully and partially FRP confined circular normal-strength concrete have showed that better performance can be achieved when predicting the ultimate conditions of partially FRP confined concrete. However, the experimental program presented by (Zeng et al, 2018) to investigate circular concrete columns partially wrapped with FRP strips has been demonstrated the effects of the clear spacing and width of FRP strips on the axial compressive behavior of partially FRP-confined concrete. In addition, (Saadatmanesh et al, 1994) proposed à technique by wrapping thin, flexible high-strength fiber composite straps around the column to improve the confinement and, thereby, its ductility. Their results indicate that the strength and ductility of concrete columns can be significantly increased by wrapping high-strength fiber composite straps around the columns. Moreover, based on results from more than 300 specimens of FRP confined concrete cylinders covering a wide range of parameters, the confinement effect and failure mechanisms are analyzed by (G. Wu et al, 2006). In this respect, the present work aims to optimize and to assess the most adequate parameters of the FRP stirrups, which allow to improve the ultimate strength of confined concrete with the same confinement rate. Therefore, finite element simulations using (ABAQUS, 2010) software is carried out on standard concrete cylinders partially confined by externally bonded FRP stirrups under compressive loading. The constituent materials are modeled according to numerical models namely: Concrete Damaged Plasticity model which allows to take into account the nonlinear behavior of compressive and tensile concrete, also, an orthotropic elastic model to predict FRP behavior is used. The proposed approach is validated by experimental data available in the literature. Finally, the predicted numerical results in terms of stresses and damages highlight in one hand, the interest of FRP composites on the global and local response of confined elements, and in other hand, the gains in terms of bearing capacity which are quantified by the confrontation of stress-strain curves. 2. Objectives and scoops Numerical investigation was conducted to study the local and global axially compressive behavior of circular columns wrapped with GFRP strips. In order to optimize the parameters of used composite bonded strips to partially confined concrete, a parametric study related to the variation of each straps design value, through simulations using ABAQUS is conducted. Several configuration of confinement rate are considered through the number of used hoops (3C and 5C GFRP Strips). For each cases the FRP Strips spacing (S), width (B) and thickness (E) were investigated. A summary of simulated cylinders considered in the case study is depicted in Fig.1. A total of 15 numerical models are carried out on confined and unconfined cylinders under axially compressive loads according to NFP18-406. For more clarity, Table 1 summarizes the geometrical characteristics of FRP Strips used for externally and partially confinement of all designated and simulated specimens. It is important to notice that the simulations were conducted in full 3D modeling, with similar conditions to physical realty of experiments. The nonlinear simulation allows us to evaluate the contribution of FRP Strips in strength, stiffness and confinement level. 3CS1 3CS2 3CS3 5CS1