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To determine the load at which FRPs debond from concrete beams using global-energy-balance-based fracture mechanics concepts, the single most important parameter is the fracture energy of the concrete–FRP interface, which is easy to define but difficult to determine. Debonding propagates in the narrow zone of concrete, between the FRP and the (tens...
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Context 1
... rapid development of microcracks followed by stable widening of a critical macrocrack was observed in the tests [24]. Thus, the shape of the softening curve has been approximated by using bilinear [24] and polynomial [25] models with f t and w tip_c as the key parameters (Fig. ...
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... bilinear models, the coordinates of the kinking point (f 1 , w 1 ), and w tip_c are required to determine G CI (Fig. 8a). It has been reported that f 1 is about 1/3 of f t [24], and a range of values between 0.03 and 0.04 mm were quoted for w 1 [23,24]; these values are assumed in the present study. The stress transfers between the crack surfaces, and hence, w tip_c , depend upon d a of the mix. The CEB-FIP model code [13] recommends typical w tip_c ...
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... to the simplified models and the empirical model discussed above. Since the softening models can only be used to estimate G CI of concretes with crushed aggregates, the G CI of the mixes with rounded aggregate were estimated using the empirical model only. When using the bilinear models, the coordinates of the kinking point (f 1 , w 1 in Fig. 8a) were assumed to be 0.33f t [24] and 0.03 mm [25] respectively, for all concretes. The values of f t were obtained from Eq. (3). The values for the w tip_c of concretes with 10 and 20 mm crushed aggregates were assumed to be 0.130 and 0.175 mm respectively, based on the typical values recom- mended in the CEB-FIP model code ...
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Citations
... Some researchers assumed that the cohesive strength and the fracture energy were identical in normal direction and tangential direction (mixed-mode ratio = 1) [25,26,29]. However, the cohesive strength and fracture energy in shear direction was found to be significantly higher than that in normal direction due to the interlocking between aggregate and surrounding normal mortar [72,73]. According to the literature, the mixed-mode ratio for cohesive strength can be in a range between 3 and 6 [74], while the mixed-mode ratio for fracture energy highly varied among different studies [75,76]. ...
Waste glass has become one of the most attractive candidates for replacing natural aggregate in mortar/concrete. Although researchers have conducted extensive experiments to investigate the macroscopic behaviour of mortar/concrete containing glass aggregate, certain mechanical behaviours are difficult to capture. These include damage initiation and propagation, and the effects of the intrinsic characteristics of glass aggregate, which are important in building applications. In this study, a two-dimensional meso-scale model was developed to numerically investigate the macroscopic and mesoscopic behaviour of glass mortar under uniaxial compression loading. Glass mortar was modelled as a three-phase composite including the surrounding normal mortar, glass aggregate and interfacial transition zone. The developed model was validated using experimental observations of the behaviour of glass mortar under uniaxial compression loading. Two prominent physical characteristics of glass aggregate were reflected in the developed meso-scale model, namely the angular aggregate shape and weaker interfacial transition zone. Based on the simulation results, it was found that both characteristics affected the mechanical response, while the aggregate shape was observed to be less significant. A comprehensive sensitivity analysis was performed to investigate the effects of various aggregate's properties, including random distribution, volume fraction, particle size, and elongation ratio, on the mechanical response of mortar. Overall, the developed meso-scale model for glass mortar is expected to provide a better understanding of the failure mechanisms of glass mortar/concrete under uniaxial compression loading.
... On the other hand, crack growth due to repeated loading that is generally applied to structures is an issue that, without considering it in the design, it is possible to significantly reduce the useful life of the structure. In recent years, a number of researchers investigated the nature of the separation mechanism between FRP sheet and concrete by using fracture mechanics and determining the obtained energy [1][2][3][4]. Taljesten [5] presented a linear equation to calculate the bearing capacity of reinforced concrete with FRP sheet. under tensile axial load and based on it, the maximum load and ultimate load is a function of fracture energy (GF), modulus of elasticity and thickness of FRP sheet Yashiza et al. [6,7] succeeded in determining the fracture energy and the stress-strain relationship by conducting a one-way shear test on reinforced concrete samples with FRP sheets. ...
... The first part of the diagram is assumed to be elastic up to the corresponding limit stress. The amount of this stress is considered equal [4]. where is the compressive strength of concrete. ...
... Strain is equal to stress. Young's modulus is also calculated based on [4] and Poisson's ratio is considered equal. The second part of the diagram, which has a parabolic shape, starts from the point with the limit stress and continues until reaching the highest compressive strength of concrete. ...
Since the parameters affecting the strengthening of cracked beams and their failure behavior after strengthening are very important, this research is devoted to the numerical investigation of the failure behavior of cracked concrete beams reinforced with steel sheet. The investigated beams have an initial crack in the middle of the span and are reinforced with a steel layer under the beam. Using the finite element method and non-linear static analysis, the bearing capacity of the samples, the growth and opening of the crack opening have been evaluated. First, in order to evaluate the accuracy of the modeling, the results obtained with the data obtained from the existing laboratory work were compared, and after ensuring the correctness of the modeling, the effect of changing various parameters, including sheet thickness, mechanical characteristics of concrete, initial crack length, was investigated. The results show that the load-opening diagrams of the crack openings have two maximum load points, the first and second maximum points increase with the increase of concrete strength and sheet thickness, and due to the increase in the initial crack length, the first maximum point decreases, while the maximum point The second remains almost unchanged.
... Bond capacity was estimated as a function of various factors including the stiffness and tensile strength of adhesive material [14,[16][17][18], the uniaxial stiffness and tensile strength of FRP composite [14,[16][17][18][19][20], FRP width to member width ratio [11,16,21], the compressive and tensile strength of concrete [14,16,[22][23][24][25][26][27], FRP materials [19,28], bond length [14,19,29], and dominant loading modes [30,31]. Attaining the full capacity of FRP composite in external reinforcement of concrete structures requires an appropriate surface preparation for eliminating or postponing premature FRP composite debonding [32][33][34][35][36][37][38][39][40][41][42][43]. To solve this problem, Mosto nejad and Mahmoudabadi suggested a novel method called the grooving method (GM) [44], in which interfacial stress was transferred into rmer layers of beams by creating grooves on the tensile face of the beams. ...
In recent decades, the externally bonded reinforcement (EBR) method has been recognized as a desirable and established choice to strengthen reinforced concrete (RC) structures with fiber-reinforced polymer (FRP) composites. The major weakness of this method is the premature debonding of FRP composites from concrete substrates. The grooving method (GM) has been introduced to prevent or postpone premature debonding. This study aims to review the previous studies on strengthening structural members by the grooving method. More specifically, it sought to examine the studies addressing the behaviors of strengthened beams, slabs, columns, and beam-column joints with FRP composites by grooving methods. The effects of groove dimensions as well as the properties of concrete and FRP materials on the performance of the grooving method were evaluated. The enhancements of flexural, shear, compressive, and seismic behaviors of strengthened RC members by grooving method were assessed and their efficiency was compared with the EBR method. The results showed the considerable efficiency of the grooving method in enhancing the performance of all structural concrete members by postponing or preventing premature debonding. Additionally, this method could considerably decrease the amount of consumed material.
... With an increase in service time, when the GFRP-RC beam structure failed, the maximum CMOD of the AS group at 30 Thus, in the same alkaline corrosion conditions, the APS group with prefabricated cracks is more likely to fail due to the propagation of cracks in the structure. The resistance to deformation of the APS group with a pre-crack is inferior to that of the AS group, indicating that the crack has a great influence on the stability of the GFRP-RC beam structure. ...
... Interfacial fracture energy is an essential indicator of interface fracture performance of a material, and can be used to describe the resistance of a material to crack propagation [5,[28][29][30]. The concept of material fracture energy was first proposed by Griffith [31]. ...
The development trend of glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) beams partially or entirely replacing reinforced concrete beams has gained acceptance. However, related research on long-term fracture durability is insufficient. This paper aims to investigate the long-term fracture durability of GFRP-RC beams, 36 GFRP-RC beams under the alkaline corrosion environment and sustained load for eight years were subjected to three-point eccentric loading experiments. The load crack opening distance (P-CMOD) curve and the corresponding fracture energy were obtained. The results show that the bearing capacity and residual fracture energy retention (ER) of GFRP-RC beams with working cracks in the APS (alkaline + pre-cracks + sustained load) group were 18.71% and 26.38% lower, respectively than those in the AS (alkaline + sustained load) group. After analyzing the critical CMOD curves for each service period with failure probabilities of 60% and 85%, a long-term crack growth failure probability model for the service time t and the critical CMOD was proposed, which provide a non-destructive damage assessment method for GFRP-RC beams in actual service.
... Achintha and Burgoyne [18] employed fracture mechanics theory concerning the global energy balance, so as to estimate the load level at which the FRP sheet is debonded from the concrete substrate. They realized that the key factor pertained to fracture energy at concrete-FRP interface, and that the FRP sheet debonded in concrete at the tension reinforcement location. ...
The current study presents numerical and experimental approaches in the assessment of fracture behavior of self-consolidating concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) lamina. The failure modes, mid-span displacement, and the load-bearing capacity of specimens with initial notches at mid-span are analyzed by varying the notch length and the beam height. Furthermore, the effects of variations in CFRP and concrete mechanical properties, bond strength, and notch location are examined by using the non-linear finite element analysis. Findings reveal that stress concentration in concrete and CFRP, in the vicinity of initial notch, as well as the failure of specimens occur as a result of CFRP debonding and crack extension. Moreover, it is observed that load- mid-span displacement curves are characterized by two peak load points strength. At the first stage, the applied load increases up to one peak value and then at the second stage there is a drop in the load-caring capacity. The applied load is then improved to another peak value due to the relatively high cohesive effect of the CFRP sheet at the third stage. Among different variables, the second peak load shows higher sensitivity to variations of the elastic modulus of CFRP, and bond strength at interface. As the notch approaches the beam support, and hence the relative distance from mid-span changes from 0 to 2/3, the two peak loads are respectively escalated by 116 and 58%, and thus the inclined crack propagates toward mid-span.
... If τ is too low, the transfer of load from matrix to fiber will also be low. This results in a low micro-cracking stress, low ultimate strength and less effort on fiber pullout [27][28][29]. ...
The incorporation of recycled papers, paperboards and Tetra Pak as filling materials in brittle matrices presents an interesting approach in the utilization of waste materials for building construction. This paper examines the compressive strength and microstructure of gypsum-bonded wastepaper-based composites. Recycled wastepaper of various types (office paper, magazine paper and newspaper), cardboards, paper boxes and Tetra Pak were shredded to short length strips of about 4 × 18 mm. The shredded materials were used as filling materials in natural gypsum in a ratio of 1:3 (v/v), and water was added to the mix. The paste was formed in cylindrical samples measuring 10 cm in length and 5 cm in diameter. Seven different types of composites were produced depending on the material used. The composite products with newspaper and magazine paper had significantly lower density and compressive strength (p < 0.05) than the others. However, the differences were small to have any practical importance. The density values ranged between 1.26 and 1.34 g/cm3, and compressive strength was the lowest (4.48 N/mm2) in the gypsum–magazine paper composites and the highest (6.46 N/mm2) in the gypsum–Tetra Pak I composites. Since the samples produced in this study exhibited adequate compressive strength, the products could be suitable for such applications as interior walls in building constructions. Scanning electron microscopy (SEM) examination of the fractured surfaces revealed needle-like structures of gypsite crystals surrounding the fibers, which indicates good adhesion between the hydrophobic matrix and lignocellulosic fibers.
... Research studies on the different aspect of FRP composites specification is going on [1][2][3] and a wide array of empirical, analytical, and numerical models of bond strength and effective bond length have been so far developed by researchers [4][5][6][7][8][9][10][11][12][13][14][15][16] and adopted by different national codes [10,17,18] to simplify structural strengthening design procedures for members prepared via EBR technique. Fracture mechanics approaches have been investigated in an attempt to predict the debonding behavior of RC members strengthened with externally-bonded FRP [4,12,[19][20][21][22][23]. ...
The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) off the concrete substrate in retrofitted structures. In FRP application, the effective bond length is defined as a length over which the majority of the bond stress is transferred and the maximum load-bearing capacity is obtained. The present study endeavors to develop an original empirical model of the effective bond length of FRP sheets applied on concrete via the EBROG technique. For this purpose, an experimental program is conducted in which 95 specimens prepared through the EBROG and EBR techniques are subjected to the single lap-shear test. The effective bond length is evaluated by analyzing the strain and stress fields on the FRP bond area using the image processing technique of particle image velocimetry (PIV). A model is then developed based on a nonlinear regression analysis along with a probability study performed on the results obtained from the experiments; and the goodness of fit to the data is confirmed. In this model, the effects of groove dimensions, concrete compressive strength, as well as FRP sheet width and stiffness are taken into account. The feasibility of the well-known existing models developed for EBR method was investigated in the EBROG technique and the prediction accuracy was compared with the proposed model.
... A number of studies have been carried out experimentally (Cao et al. 2007;Mazzotti et al. 2008) and theoretically (Dai et al. 2006;Ferracuti et al. 2007) to address the behaviour of FRP bonded to concrete substrates. Many studies have been conducted (both theoretically and experimentally) to predict the initiation of debonding in retrofitted concrete beams, and also the ultimate load that the composite layers can resist prior to debonding (Achintha and Burgoyne 2013). However, different failure modes when FRP is externally bonded to timber have not been fully investigated and limited attempts have been made to investigate the bond behaviour of FRP to timber joint (D'Ambrisi et al. 2014) and the developed theories to date mostly cover FRP-to-concrete joint (Chen and Teng 2001;Dai et al. 2005). ...
... However, in comparison with some materials such as glass, concrete fracture process zone is considered large, usually with the width of very greater than aggregates and around 300 mm length [27]. Thus, the concrete-FRP interface model could not be developed using the linear elastic fracture mechanics (LEFM) approaches [28]. ...
... The model could be derived in two way for an intended beam; (i) crack length (which causes failure of beam at the design load), and (ii) failure load (a known length of a beam with an existing crack). In addition, test data which is reported by previous researches matched well with predictions of this model and adopted in the analysis based on this concept [28]. [28] In this research, fracture properties and debonding failure of (i) notched un-retrofitted concrete, and (ii) retrofitted notched concrete specimens (beam) was provided after performing the test and final results was compared by previous works [1,28]. ...
... In addition, test data which is reported by previous researches matched well with predictions of this model and adopted in the analysis based on this concept [28]. [28] In this research, fracture properties and debonding failure of (i) notched un-retrofitted concrete, and (ii) retrofitted notched concrete specimens (beam) was provided after performing the test and final results was compared by previous works [1,28]. Furthermore, the test that was made in this work is a three-point bending test with couple of notches instead of one notch, and the outcomes for fracture parameters was shown for finding out the differences between previous researches that was generally made by four-point test with single notch. ...
The effects of FRP retrofitted concrete specimens with couple of notches on the fracture behavior have been investigated during an experimental and analytical test program in this study. This paper represents the fracture characteristics and parameters for three point bending tests on two distinguish retrofitted and plain condition for both intact and notched (couple notches) specimens. The experimental test results find out in the laboratory tests indicated that for intact concrete specimens, there would be approximately 285% increase in ultimate flexural strength tests. The experimental results also represents that for the tested couple notched concrete specimens, there might be approximately 318% increase in ultimate flexural strength. Based on the analytical study, it is found that the near failure behavior of the notched specimens have been significantly improved using FRP retrofit of such specimens. The system`s global energy balance and failure load prediction of FRP debonding are the couple of consideration by a developed fracture mechanics based model which made by energy dissipation major mechanisms characterizing while debonding. Model verification is provided using previous researches experimental data from literature. In addition, fracture mechanics parameters were found out for three point bending test in this paper for better understanding on fracture behavior and fracture properties of intended specimens.
... Mostofinejad and Shameli [25] reported that several attempts have been made to improve the performance of FRP techniques to eliminate or postpone debonding failure of the FRP attached to concrete. Fracture mechanics-based models have been developed (both theoretically and experimentally) by many researchers to predict the initiation of debonding in retrofitted concrete elements and the peak load that the composite layers can resist before debonding [26][27][28][29]. However, performance of FRP composite externally bonded to timber, considering debonding and failure modes, has not been fully investigated [30] and to date, limited attempts have been made to investigate the bond behaviour of FRP to timber beams. ...
Despite a large number of studies on estimating the effective bond length from the characteristics of the component materials, key parameters governing the effective bond length for FRP-to-timber joint have not been suggested by any of the current Codes and developed theories to date mostly cover FRP-to-concrete joints. Also, most theoretical bond strength models have been derived based on effective bond length. Therefore, to achieve a satisfactory bonded joint, the effectiveness of bond length is required to be accurately considered. This research study investigates 136 FRP-to-timber joints subjected to pull-out tests in order to determine the stress and strain distribution profiles along the interface and subsequently analyses the results to undertake direct measurement of the effective bond length. In addition, a modified test set up has been developed and is presented. A novel theoretical model has been established through regression analysis of bond length data and accordingly a new predictive model for effective bond length for FRP-to-timber joints has been developed. A comparative analysis between the results of the experimental pull-out tests results and those predicted from the analytical model indicates a satisfactory correlation is achieved between measured and predicted effective bond length, verifying the validity of the new model.
