تحلیل مدل‌های پیوستگی لغزش-تنش برای میل‌گردهای تقویت کننده FRP در بتن

ABSTRACT Evaluation of bond stress-slip models for FRP reinforcing bars in concrete

In recent years, fibre reinforced polymer (FRP) has been widely used in reinforced concrete structures due to its superior material properties, such as high tensile strength, excellent electrochemical corrosion resistance and cost effective fabrication, over the traditional steel reinforcements. Despite the obvious advantages of FRPs, they are not without drawbacks, and one major disadvantage is the comparatively weaker bond strength of FRP reinforcing bars (rebars) in concrete compared with traditional steel rebars.

In fact, bond between concrete and the reinforcing bars plays an important role in stress transferring from the former to the latter, and debonding has become one of the thorny issues in analysis of reinforced concrete structures. Bond between FRP reinforcing bars and the surrounding concrete is complicated and various factors may influence the bond characteristics of FRP reinforcements to concrete. For example, geometry and surface conditions of FRP rebars, concrete compressive strength, confinement pressure, rebar diameter and the position in the cast and specimen, embedment length, temperature changes and environmental conditions [1] will all affect the bonding capability between FRP rebars and the concrete.

So far, numerous experimental studies have been conducted to investigate the bond strength of FRP rebars in concrete as well as the influences of parameters, such as fibre type, surface treatment, bar diameter and temperature, on the bond characteristics of FRP rebars [2–6]. However, very few studies have been carried out to determine the bond stress-slip constitutive law for FRP rebars, which is essential to finite element analysis of FRP-reinforced concrete structures. Therefore, perfect bonding was assumed in most of the numerical studies of FRP-reinforced concrete structures [7–12], resulting in non-realistic and imprecise predictions of the structural behaviour. In order to obtain a more accurate structural analysis, the bond-slip behaviour of FRP rebars in concrete should be considered in the numerical model. However, only several FRP bond stress-slip models have been reported so far, and the suitability and capability of these models for numerical modelling of FRP reinforced concrete structures have not been justified yet.

This paper aims to give a review of the currently available bond stress-slip models for FRP rebars in concrete, as well as some models for traditional steel rebars which may be suitable for numerical analysis of FRP-reinforced concrete structures. Then the appropriateness and capability of the most promising and often used bond stress-slip models are investigated for FRP rebars. The paper is structured as follows. A brief review and introduction of the currently available bond stress-slip models for FRP rebars in concrete is given in Section 2, and both their merits and demerits are discussed. A few bond stress-slip models for steel rebars in concrete are presented in Section 3. In Section 4, three bond stress-slip models, i.e. the Eligehausen, Popov and Bertero (BPE) Model [13], the BPE Modified Model [1], and the Cosenza, Manfredi and Realfonzo (CMR) Model [14], which have been often used and seem to be the promising FRP bond stress-slip models for numerical analysis, are discussed in more details, and their appropriateness and capability are evaluated via finite element analysis of FRP-reinforced concrete beams by implementing them in a newly developed finite element model [15]. In addition, the appropriateness of two bond stress-slip models, which were proposed by Harajli et al. [16] and Haskett et al. [17] for steel rebars, for finite element analyses of FRP-reinforced concrete structures is also evaluated in Section 4. Section 5 presents a parametric study using the most suitable bond stressslip model for FRP rebars, and the effect of different rebar surfaces on the structural behaviour is investigated. Conclusions are drawn in the final section.