•FRP and FRCM composites were effective in increasing the shear strength of RC beams.•Internal-external reinforcement interaction was less pronounced for beams with FRCM composite.•Measured fiber ...strains were higher than those computed using available models.•Effectiveness of the FRCM composite varied with internal shear reinforcement ratio.
This paper presents the results of an experimental campaign carried out to investigate the behavior of reinforced concrete (RC) beams strengthened in shear with externally bonded composites. Two different types of composites were studied: Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) composites. In addition, different types of fiber (carbon and steel) were employed, and the influence of internal transverse steel reinforcement ratio and the presence of composite anchors were investigated. Internal-external shear reinforcement interaction, i.e. reduction of the stirrup strain due to the presence of the composite, was observed for both FRP and FRCM strengthened beams, but the interaction was less pronounced for those with FRCM composites. The anchors employed in this study did not affect the shear strength of the beams, but changes in the concrete crack pattern, mid-span displacement, and failure mode were observed. For FRCM strengthened beams, strains measured in the fibers showed higher exploitation ratios, i.e. the ratio between the maximum measured fiber strain and the rupture strain, for beams with carbon FRCM than those with steel FRCM. Effective strains computed using available models were considerably lower than the maximum measured fiber strains.
•Debonding occurred at the matrix–fiber interface.•A global width effect was not observed.•After the onset of debonding friction contributed to the increase of the load.•The effective bond length ...leff due to bond was estimated to be 255mm.•Cohesive material law and fracture energy were obtained from strain profiles.
The results of single-lap shear tests, conducted on specimens with fiber reinforced cementitious matrix (FRCM) composite strips bonded to concrete blocks, are presented in this paper. The FRCM composite was comprised of polyparaphenylene benzobisoxazole (PBO) fibers and polymer-modified cement-based mortar. This study indicates that in PBO FRCM–concrete joints debonding mainly occurs at the matrix–fiber interface. Friction between fiber filaments and between fibers and matrix is observed after the debonding process initiates. The experimental data suggest that a width effect does not exist among the fiber bundles, and an effective bond length can be defined and is approximately 260mm. Axial strain profiles along the bonded length are analyzed to investigate the stress-transfer mechanism at the matrix–fiber interface.
AbstractFiber-reinforced cementitious matrix (FRCM) composites represent a newly developed promising technique for strengthening RC structures. The FRCM composites are comprised of high-strength ...fibers applied to the concrete substrate through an inorganic cementitious matrix. In this work, single-lap direct-shear tests were carried out on FRCM strips, comprised of one layer of fiber net embedded within two layers of matrix, bonded to a concrete block. The weakness of FRCM-concrete joints was observed to be the debonding at the matrix-fiber interface. The experimental results indicated that the role of each matrix layer is different. The stress-transfer mechanism between the fiber filaments and the matrix layers on either side of the fiber net was studied by means of a fracture mechanics approach, and three models of the interfacial cohesive material law were proposed for each matrix-fiber interface.
•A database of RC beams strengthened in shear with FRCM composites is developed.•FRCM composites provide increase in the shear strength of RC beams of 3%–195%.•Possible internal-external transverse ...reinforcement interaction is observed.•Different failure modes are observed depending on the strengthening configuration.•Further work is needed to develop more accurate and reliable design models.
This paper summarizes the state of research on the topic of shear strengthening of RC beams using externally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the literature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the properties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment.
•Fatigue failure is caused by rupture of the fibers within the bonded area.•The combination of high amplitude and high mean value implies greater damage.•Load frequency affects the fatigue ...response.•A fracture mechanics approach is used to describe the intermediate fatigue range.•The effect of cycles on the quasi-static post-fatigue behavior is investigated.
Fiber-reinforced cementitious matrix (FRCM) composites may represent a valid alternative to the use of traditional techniques for strengthening and retrofitting existing reinforced concrete (RC) and masonry structures. Although FRCM composites appear to be an effective strengthening technique for RC structures, limited work is available in the literature. In this paper the behavior of FRCM-concrete joints subjected to fatigue and post-fatigue quasi-static monotonic loading is presented and discussed. The single-lap direct-shear test set-up was adopted in this study. The fatigue loading protocol was designed to investigate the effects of different frequencies and different load ranges on: (a) the interfacial slip; (b) the dissipated energy during cycles; (c) the stiffness degradation of the interface; and (d) the post-fatigue quasi-static monotonic behavior. In general, it was observed that different combination of amplitude and mean value of the load range implies different damage measured in terms of slip, energy dissipation, and stiffness degradation. A fracture mechanics approach was proposed to describe the intermediate range of the fatigue crack growth for different frequencies.
The cohesive material law (CML), i.e., relationship between the interfacial shear stress and slip between a fiber reinforced composite and the substrate, is a fundamental tool to model the structural ...behavior of composite-strengthened elements. A crucial problem that researchers working in the field of strengthening applications with fiber reinforced cementitious matrix (FRCM) composites face is how to obtain the CML. A direct method to determine the CML could be applied if the longitudinal strain is measured along the bonded length. However, since the critical interface for some FRCM composites appears to be the interface between the fibers and matrix, measuring the fiber strain in FRCM composites is a difficult task due to the presence of the matrix that embeds the fiber textile. To overcome this difficulty, an indirect method is proposed in this paper. The parameters of the CML are determined by fitting experimental data in terms of peak load measured for different composite bonded lengths. The procedure is applied to single-lap shear test results previously published by the authors. The CML obtained shows good correlation with the CML obtained from direct calibration of strain profiles measured along the bonded length and is able to predict the experimental load responses.
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•The proposed indirect method to calibrate the cohesive material law of FRCM-concrete joints does not require strain measurements.•Indirect calibration of the CML is performed simply by employing peak load versus bonded length plot.•Peak strain and corresponding slip versus bonded length and analytical load responses compare well with experimental data.
This paper presents the results of an investigation on the bond behavior and stress-transfer mechanism of polyparaphenylene benzobisoxazole (PBO) fiber-reinforced cementitious matrix (FRCM) ...composites bonded to a concrete substrate using double-lap and single-lap shear tests. Results of double-lap shear tests with different composite bonded lengths and widths are presented and compared with those from single-lap shear tests previously reported by the authors. The idealized load response developed from single-lap shear tests is found to characterize the response of the composite in double-lap shear tests, although with a few key differences. With the double-lap shear test, load redistribution among the composite strips influences the post-peak response if debonding does not occur equally in both strips. Values of the ultimate (peak) stress determined using double-lap shear tests are generally consistent with, although slightly lower than, those determined by single-lap shear tests when the bonded length is longer than the effective bond length.
Composite materials are increasingly used in applications of civil infrastructure and building materials. The new generations of two-part thermoset polyurethane resin systems are desirable materials ...for infrastructure applications. This is due to high impact resistance, superior mechanical properties, and reduced volatile organic compounds when compared to the conventionally used resin systems such as vinyl ester and polyester. Glass fiber-reinforced two-part polyurethane composites and low-density polyurethane foam are used to design and manufacture composite structural insulation panels using vacuum assisted resin transfer molding process for temporary housing applications. Using these types of composite panels in building construction will result in cost-efficient, high-performance products due to inherent advantages in design flexibility. Use of core-filled composite structures offers additional benefits such as high strength, stiffness, lower structural weight, ease of installation and structure replacement, and higher buckling resistance than the conventional panels. Energy efficiency is known to be inherently better with the core-filled composite panel than in a metallic material. The panels can be designed to resist the required loads, and the study aims to evaluate the ability of lab scale tests and models to predict part quality in full-scale parts. Furthermore, it discusses the manufacturing challenges. Flexural tests and energy consumption evaluations were performed on these structural components. Finite element simulation results were used to validate the flexural experiment findings.
AbstractThe bond behavior of fiber-reinforced cementitious matrix (FRCM) composites applied as externally bonded reinforcement is the most critical concern in this type of application. FRCM–concrete ...joints are generally reported to fail because of debonding (slippage) of the fibers from the embedding matrix. However, depending on the characteristics of the composite and substrate used, failure may also occur as a result of detachment of the composite strip at the FRCM–support interface, interlaminar failure (delamination) of the matrix, or tensile failure of the fibers. In this paper, a three-dimensional (3D) numerical model is developed to reproduce the behavior of polyparaphenylene benzo-bisoxazole (PBO) FRCM–concrete joints. The numerical model accounts for the fracture mechanics mixed Mode-I and Mode-II loading condition observed in single-lap direct shear tests by means of nonlinear damaged contact law associated with different interfaces considered in the analysis. The numerical results obtained are compared with those obtained by experimental tests of PBO FRCM–concrete joints. The model is capable of predicting the different failure modes, and it correctly reproduces the experimental load responses including the contribution of friction to the applied stress.
This paper presents a non-contact measurement approach, based on digital photogrammetry, applied to the experimental study of the bond behavior of fiber reinforced cementitious matrix composite ...to concrete joints tested in single-lap direct shear tests. The use of digital photogrammetry techniques and traditional contact measurement approaches for determining displacement and strain are investigated and compared. The results show that measurements of strain in the fiber bundles determined using the image correlation system (ICS) correlate well with those obtained from electrical strain gauges. However, differences of 38–52% were observed between the maximum strain measured with either ICS or electrical strain gages attached to the fiber bundles and the maximum strain in the fiber bundles computed from the maximum applied load. ICS is also used to measure slip and strain of bare fiber bundles, and results show that the load distribution among fiber bundles is non-uniform. The proposed measurement approach shows higher spatial measurement resolution and increased accuracy compared to traditional contact approaches by enabling measurements in each fiber bundle and overcoming the need to attach additional elements to the tested specimen.
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