Journal of Composites for Construction

In this paper, the results of tests that will be carried out on beams strengthened in shear with polybenzoxazole fabric–reinforced cementitious matrix (PBO-FRCM) composites will be presented and compared with the results of theoretical calculations. Tests will be carried out on 12 RC T beams strengthened in shear with anchored or unanchored PBO-FRCM stirrups with different widths and spacing. Strain gauges and the digital image correlation (DIC) method will be used to measure the deformation of the composite. The mechanisms of failure of the beams will be analyzed and described. The shear capacity will be calculated based on the characteristics of the materials and the specimens used in the tests. The results of the calculations that are based on the latest standards and theoretical modeling showed that the shear capacity of the T beams with transverse steel reinforcement and anchorage were significantly underestimated. The results and differences between the experimental and analytical results will be discussed.

Fiber-reinforced polymer (FRP) systems are commonly used in the flexural strengthening of reinforced concrete beams. However, concrete cover separation (CCS) is one of the main debonding failure modes that negatively impact the strengthening efficiency. This premature failure mode occurs at a lower fraction of tensile strain capacity of the longitudinal FRP reinforcement. Placing FRP U-wrap anchorage at the end regions of FRP longitudinal plates appears to be a promising technique that could mitigate or prevent CCS. This study characterized, experimentally, the effect of FRP U-wraps in enhancing the strengthening efficiency by mitigating CCS in FRP-strengthened RC beams. The study included full-scale RC beams strengthened in flexure using FRP sheets and anchored at their ends using FRP U-wraps. The beams were simply supported and tested under four-point bending. The test variables were the width and layout of the FRP U-wraps. The test results indicate the effectiveness of FRP U-wraps in preventing CCS once the required area of U-wrap is provided. The paper also presents a proposed design method for quantifying the minimum area of FRP U-wrap anchorage required to prevent CCS. The proposed design method was verified using the test results obtained from this study and also from a database of beams reported in the literature. Based on the findings of the study, recommendations are suggested for the design of a FRP U-wrap anchorage system that is capable of preventing CCS in FRP-strengthened RC beams.

This paper presents results of a first-ever experimental study on the axial compressive behavior of large-scale square reinforced concrete (RC) columns confined with polyethylene naphthalate (PEN)/terephthalate (PET) fiber–reinforced polymer (FRP) composites, which is a new type of FRP with a large rupture strain (LRS) of over 5%. In total, 10 large-scale square RC columns were tested under axial compression, including 8 LRS FRP–wrapped RC columns and 2 RC columns, which served as control specimens. The key experimental parameters were the sectional corner radius and the thickness and type of LRS FRP. The test results show that the effective confinement stiffness ratio of an FRP jacket, as determined by the corner radius and FRP thickness, has a significant effect on the axial compressive behavior of LRS FRP–jacketed large-scale square RC columns. Based on the experimental results, this paper presents an evaluation of two existing LRS FRP–confined concrete models for noncircular columns. Finally, based on the test findings, a refined model for LRS FRP–confined large-scale square columns is presented to provide more accurate predictions of the compressive behavior of these columns.

Fiber-reinforced polymer (FRP) confinement has shown promise as an alternative method aimed at enabling the structural use of recycled brick aggregate concrete (RBAC) in columns. To facilitate practical applications, an existing stress–strain model for FRP-confined normal concrete is modified in this paper to extend its applicability to FRP-confined RBAC. The modification was based on a rigorous approach involving a direct examination of the path-independent assumption, which was made possible by conducting companion tests on actively confined and FRP-confined RBAC. Comparisons of the stress–strain and dilation responses obtained from the two confinement schemes showed that the axial strain of RBAC can be considered path-independent while the axial stress of RBAC tends to be path-dependent. The underlying cause is probably that the weak resistance of recycled brick aggregate (RBA) makes itself a medium for crack propagation. The effect of path dependence is accounted for in the modified model by purposefully weakening the stress–strain response of actively confined RBAC to correct the overestimate found in the axial stresses of FRP-confined RBAC, which originates from adopting the path-independent assumption.

This study proposes a relation for the failure strain of externally bonded reinforcement on groove (EBROG) joints derived through multivariate regression analysis on the experimental results. In addition to the conventional parameters of concrete compressive strength and groove dimensions studied as independent variables, a novel descriptor variable of great effect, called width of fiber-reinforced polymer (FRP) sheet on a single groove, is also introduced for the first time. Using these descriptors and their variations, 27 specimens are strengthened via the EBROG method and subsequently subjected to the single lap-shear test. First, the proposed relation is assessed with respect to its goodness of fit using certain statistical indices, which reveals a good agreement between estimated and measured values. The relation is also verified in terms of its efficiency and accuracy through a comparison with a previous model using 65 specimens in three groups previously reported in the relevant literature. The comparisons indicate the superior accuracy of the proposed relation in estimating the failure strain of EBROG joints and its higher generality as compared to the rival model.

In this study, nonlinear finite-element analysis (FEA) will be employed to investigate textile-reinforced mortar (TRM) jackets for shear strengthened reinforced concrete (RC) beams. FEA models of TRM shear strengthened RC beams will be developed and validated against experimental study from the literature. Subsequently, a parametric study will be conducted on the validated FEA models to examine the effect of various beams’ depths, load distributions, and orientations and stacking sequences of the textile’s mesh layers. The results of the parametric study show that increasing the cross section depth improved the load capacity of the shear strengthened RC beams and reduced the shear contribution of TRM. In addition, the shear influence of TRM was more dominant when the beams were subjected to a uniformly distributed load. However, the strengthening the beams with one or three layers of textile mesh that had a 45° orientation was the most effective configuration to improve the shear capacity (V_R). For stacking sequences, the improvement in the shear strength of all models compared with the control were between 68.6% and 77.4%, which indicated that the ply sequences had an insignificant impact on the RC beam’s V_R.

This paper proposes a novel method for strengthening existing timber beams that can effectively improve the deformability of beams. As high-performance engineered bamboo, bamboo scrimber was attached to the bottom tensile area of a timber beam together with carbon fiber–reinforced polymer (CFRP) layers. The CFRP was used to improve flexural strength, and the bamboo scrimber was used to enhance the flexural stiffness and strength of the original timber beams. Fourteen timber beams were tested to study the flexural behavior of the reinforced timber beams. The main test parameters included the bamboo scrimber thickness and the number of CFRP layers. The results showed that the stiffness and bending strength of the beam increased with the increasing thickness of the bamboo scrimber, but no noticeable effect was observed with the addition of the CFRP layers. The cross-sectional stiffness at the serviceability limit state and ultimate bending strength increased by approximately 70%–130% and 50%–90%, respectively. A stable and durable platform segment was observed for most reinforced beams, which displayed excellent deformability. The large deformable behavior was mainly due to the fact that the addition of bamboo scrimber delayed the tensile failure of the wood, and timber under compression parallel to the grain showed plastic behavior. By considering the simplified stress–strain relationship for the constituent materials and force equilibrium in the cross section, an analytical strength model was developed for predicting the flexural capacity of timber beams reinforced with bamboo scrimber.

Tensile tests on fabric-reinforced cementitious matrix (FRCM) coupons are used to evaluate the tensile mechanical properties of the composite. Bond tests, typically single-lap shear tests, are used to characterize the interfacial properties between the FRCM composite and the substrate and to identify the interface at which debonding takes place. Some FRCM composites exhibit debonding at the fiber–matrix interface, which is characterized by a cohesive material law (CML) that can be obtained from bond tests. The authors have shown that for these composites, the CML can be fed into an analytical model to predict the results of tensile tests. In this paper, the same model is used to highlight some critical aspects of the clevis-grip tensile test. In particular, it will be shown that the length of the gripping devices, the length of the specimen, and the gauge length adopted to measure the deformation of the specimen have a strong influence on the results of the tensile tests. In addition, an analogy between the clevis-grip tensile test and single-lap shear test will point out that the tensile test is a bond test and can be used to determine the bond capacity rather than the tensile properties, which will be proven to be non-uniquely defined by this test.

Extensive experimental and theoretical studies of large rupture strain (LRS) fiber-reinforced polymer (FRP)-confined concrete columns have been conducted based on small-scale columns, mostly with a diameter of 150 mm. This paper presents the first-ever study on the axial performance of LRS polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) FRP-confined large-scale concrete columns. Twenty PET FRP-confined circular concrete columns and 20 PEN FRP-confined square concrete columns were loaded concentrically. The cross-sectional diameter or side length ranged from 100 to 400 mm. The effects of specimen size and FRP volume ratio on the failure mode, axial stress–strain relationship, and dilation behavior were investigated. The load-carrying capacity and ductility of LRS FRP-confined concrete increased with an increase of the FRP volume ratio. As the specimen size increased, the confinement efficiency of the FRP decreased, resulting in a lower strength enhancement. The accuracy of existing size-dependent strength models was also evaluated using the residual error. Furthermore, a modified size-dependent model for LRS FRP-confined circular/square concrete columns was developed, which was shown to have a more satisfactory performance than the existing models. The proposed model can serve as a basic model for the seismic analysis of strengthened reinforced concrete (RC) columns with LRS FRP, with the possible size effect duly accounted.

In this research, low cyclic loading tests were conducted on 10 polyvinyl chloride (PVC) carbon fiber–reinforced polymer (CFRP)-confined concrete column–ring beam exterior joints (PCRBEJs) and one PVC tube-confined concrete column–ring beam exterior joint. The effects of ring beam reinforcement ratio (ρ_r), CFRP strip spacing (s_f), ring beam width (b), frame beam longitudinal reinforcement ratio (ρ_b), and axial compression ratio (n) on seismic behavior were examined. The test results demonstrated that the specimens with a low ρ_b value failed in flexure in frame beams. In contrast, specimens with a high ρ_b value were damaged by shear failure in ring beam joints. The increase in ρ_r, b, or n augmented the cracking and peak loads, whereas the impacts of s_f and ρ_b on these loads were marginal. The effects of the investigated variables on the strains in ring reinforcement, ring beam stirrups, and frame beam longitudinal reinforcement were analyzed in detail. Considering the effect of b, the yields nonuniformity coefficients of ring reinforcement and ring beam stirrups (ω_rs and ω_ss, respectively) were introduced, and a formula for conveniently estimating the flexural capacity of PCRBEJs under low cyclic loading was proposed. The formula was validated by the good agreement between its results and experimental data.

This paper presents test results of eccentrically loaded concrete columns reinforced with steel fiber–reinforced polymer (FRP) composite bars (SFCBs) subjected to chloride corrosion. The first stage of the experimental work explored the tensile and compressive tests of various reinforcements (SFCBs with different cross section, steel, and FRP bars) used in the large reinforced-concrete (RC) columns after chloride corrosion with or without sustained stresses. The results showed that the tensile and compressive stress–strain relationships of SFCBs are characterized by stable secondary (post-yield) stiffness. The second stage of the testing investigated the structural performance of RC columns with various amounts and types of reinforcements, slenderness ratio, applied load eccentricity, and chloride corrosion rate. The results showed that the effect of reinforcements on eccentric compression behavior is significant. The deformation and crack width of SFCB-RC columns, respectively, decreased by 12.2%–52.6% and 8.5%–71.0%, while the load capacity improved by 0.9%–18.8%, when compared with the corresponding FRP-RC columns having the same eccentricity and reinforcement ratio. The use of SFCBs as the reinforcement of RC columns, especially with high reinforcement ratio or SFCBs having high area ratio of inner steel to SFCB, is beneficial to reducing the deflection and crack width as well as improve the bearing capacity utilization coefficients under a serviceability limit state.