Unified cyclic stress‐strain model for FRP‐confined concrete circular, square and rectangular prisms

Abstract

IntroductionIn recent years, owing to some excellent results when using FRP materials in seismic retrofits of reinforced concrete structures, many studies have been carried out to investigate the behaviour of reinforced concrete members confined with FRP composites. For concrete columns, FRP composites are used as confining jackets. FRP confinement can change the behaviour of concrete columns and enhance their strength and ductility. Thus, for proper design of concrete columns confined with FRP composites, good modelling of the monotonic and cyclic stressstrain curves of these columns is necessary. Over the past decade, extensive studies have investigated the monotonic behaviour of steel and FRP-confined concrete in circular and rectangular columns, and several models have been proposed for the monotonic stressstrain behaviour of them [1]- [21].The computational analysis of reinforced concrete structures subjected to dynamic or cyclic loadings requires realistic stress-strain material models to reproduce the real behaviour of the structure. Research on the cyclic response of concrete intends to provide efficient models capable of predicting all the hysteretic characteristics of the material subjected to cyclic loading. Thus, in recent years, some studies have been conducted on the behaviour and modelling of FRP-confined concrete columns under axial cyclic compression [20]- [28].Shao et al.[22] proposed a cyclic stress-strain model for FRP-confined concrete circular specimens. Lam et al. [23] has shown that this model is inadequate for predicting the unloading path of FRP-confined concrete under cyclic compression and is incapable of predicting the cumulative effect of loading history on the stress-strain response of concrete [23]. Lam and Teng [24] developed a cyclic stress-strain model for these specimens based on a test database that contained circular specimens confined by FRP composites. Although their model predicts all types of cyclic loading pattern, the test database that was used for the generation of their model has some deficiencies that may reduce the accuracy of the model results: 1) The unloading path of cyclic loading was not continued to zero stress so the plastic strain was obtained approximately.2) The maximum number of cycle repetitions at each prescribed unloading strain was three cycles. Thus, the effects of subsequent cycles on the stress deterioration and plastic strain cannot be determined from their test database.3) The test database of their study does not include partial unloading and partial reloading cycles.

Experimental investigation on the compressive behavior of short‐term preloaded carbon fiber reinforced polymer‐confined concrete columns

“…During the monotonic compression tests in both cases (with and without preloading), the load was strictly increased until failure, with desirable bilinear behavior in accordance with the classical formulations of the confining mechanism of circular columns. The failure of all tested specimens was reached in correspondence of the failure strain of the fibers, with an average hoop rupture strains of the FRP obtained from the compression tests smaller than the tensile strains provided from the technical sheets (in agreement with several previous studies).…”

“…A large number of experimental studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14] were performed to investigate the benefits conferred by the aforementioned reinforcement system in both cases of plain and/or RC so that a very extensive database of experimental data is available in the literature and the experimental behavior of the confined concrete can be considered widely analyzed. Moreover, many analytical formulations are able to reproduce the stress-strain behavior of confined concrete under monotonic, cyclic, and eccentric loads.…”

Experimental investigations on hybrid strengthening of short reinforced concrete column elements under eccentric compression

“…Confined concrete stress–strain concrete models have been proposed by several researchers . model is used in this study for predicting the confined concrete behavior due to its accuracy in capturing the confinement effect of externally bonded FRP system.…”

Assessment of analytical stress and strain at peak and at ultimate conditions for fiber‐reinforcement polymer‐confined reinforced concrete columns of rectangular sections under axial cyclic loading

“…Lam et al 36 subsequently improved the model by Shao et al 35 Wang et al 37,38 proposed two cyclic stress–strain models for FRP‐confined RC columns, one for square cross section and the other for circular cross section, based on large columns' tests. Hany et al 32 conducted experimental tests and proposed a model by adjusting the coefficients of the monotonic model proposed by Lam and Teng 39,40 as the envelope model, and using the unloading model proposed by Wang et al 37,38 Finally, Li and Wu, 41 Ziaadiny and Abbasnia 42 and Li et al 43 also proposed a cyclic model for circular and noncircular concrete columns respectively.…”