Showing papers in "Journal of Composites for Construction in 2022"

Enhancement of Bond Performance of FRP Bars with Seawater Coral Aggregate Concrete by Utilizing Ecoefficient Slag-Based Alkali-Activated Materials

Abstract: To effectively utilize marine resources on reefs or islands and to improve the bearing capacity and serviceability of fiber-reinforced polymer (FRP) reinforced seawater coral aggregate con...

Enhancement of Bond Performance of FRP Bars with Seawater Coral Aggregate Concrete by Utilizing Ecoefficient Slag-Based Alkali-Activated Materials

Abstract: To effectively utilize marine resources on reefs or islands and to improve the bearing capacity and serviceability of fiber-reinforced polymer (FRP) reinforced seawater coral aggregate concrete (CAC) structures in marine environments, this paper investigates the applicability of using alkali-activated materials (AAMs) as substitutes for ordinary Portland cement (OPC) in FRP reinforced CAC structures. Three types of FRP bars, i.e., carbon-FRP (CFRP), glass-FRP (GFRP), and basalt-FRP (BFRP) bars, with different bond lengths (L = 50, 70, and 100 mm) were selected to determine the bond characteristics of FRP bars in alkali-activated seawater coral aggregate concrete (AACAC), as well as in cement-based CAC, which was chosen as the reference. Moreover, a scanning electron microscope (SEM) was employed to detect the microstructure characteristic at the interfacial transition zone (ITZ) between the coral aggregates and the paste matrix. The results indicated that the AACAC specimens contained a stronger mechanical bite force at the paste–aggregate interface and exhibited a higher splitting tensile strength (approximately 6.7% improvement) than those of the CAC specimens. Additionally, the ultimate bond strength and the initial slope of the bond–slip curves at the ascending branch (i.e., initial bond stiffness) were significantly improved by utilizing AAMs. Improvements of approximately 26.6%, 26.8%, and 16.9% were achieved in the bond strength for the specimens with CFRP, GFRP, and BFRP bars, respectively. It was concluded that the utilization of AAMs as alternatives for OPC was an effective method in improving the mechanical interaction at the paste–aggregate interface and promoting the anchorage capacity of FRP bars in CAC, which may represent a promising approach for applying AAMs in FRP reinforced CAC structures or members.

Assessment of Diagonal Macrocrack-Induced Debonding Mechanisms in FRP-Strengthened RC Beams

Abstract: This study presents a numerical model to characterize the fracture process of a reinforced concrete (RC) beam strengthened with fiber-reinforced polymer (FRP) in detail. A numerical model based on the application of cohesive elements was developed. Mixed-mode constitutive models were proposed to characterize the mechanical behavior of the FRP–concrete interface, the concrete potential fracture surfaces, and the rebar–concrete interface. The normal separation of the interface and its coupling effect on the shear behavior were considered in the constitutive model. In addition, the friction effect was explicitly considered in the constitutive model. Three different typical cases of FRP-strengthened RC from other experimental research were selected to validate the numerical model developed in this paper. Finally, the influence of different constitutive models on the simulation accuracy was analyzed.

Mechanical Behavior of Concrete Columns Confined with CFRP Grid-Reinforced Engineered Cementitious Composites

Abstract: Using fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composites (ECC) for strengthening reinforced concrete columns and beams has been stirring structural research ...

Mechanical Behavior of Concrete Columns Confined with CFRP Grid-Reinforced Engineered Cementitious Composites

Abstract: Using fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composites (ECC) for strengthening reinforced concrete columns and beams has been stirring structural research interest in recent years. The objective of this research was to extend the application of this technique, using carbon-fiber-reinforced polymer (CFRP). The authors used compression tests on short concrete columns strengthened with CFRP-ECC to investigate the mechanical behavior of strengthened columns by considering the unconfined concrete strength and reinforcement layers of CFRP grid. Test results show that the failure mode of most strengthened columns lies in the rupture of the embedded CFRP grid. The lateral strains corresponding to peak stresses were close, and their average value was almost equal to the ultimate axial tensile strain of the CFRP-ECC. Meanwhile, with an increased number of reinforcement layers, the peak stress and strain of the strengthening columns increased significantly for low-strength core concrete. However, there was no significant enhancement for the high-strength core concrete. In addition, the cracking stress of CFRP-ECC had obvious effects on the yielding stress, peak stress, peak strain, and the axial–lateral strain relationship. Most importantly, a better understanding of the stress–strain relationship for CFRP-ECC confined columns was established, and the feasibility of this model was verified by the analysis results.

Composite-Wedge Anchorage for Fiber-Reinforced Polymer Tendons

Abstract: A novel composite-wedge anchorage is proposed here for prestressing fiber-reinforced polymer (FRP) tendons. The composite wedge was designed and optimized in terms of the length and elastic modulus of the wedge segments via finite-element analysis. The manufacturing technologies for the composite wedge involving a molding process, are presented in detail. Static, creep, and fatigue tests on basalt FRP (BFRP) tendons with the proposed anchorages were conducted. The tensile capacity, long-term deformation, and fatigue life of the tendon–anchor assemblies were analyzed. The experimental results show that the proposed anchorage exhibits an anchor efficiency factor of up to 91%; the corresponding value for a conventional steel–wedge anchorage is only 80%. The tendon–anchor assembly displays a creep behavior similar to that of BFRP tendons. Furthermore, the system survives 200 million cycles of fatigue load at a maximum fatigue load of 0.5 Fu (Fu is the tensile capacity of the tendon–anchor assembly) and a load range of 0.05 Fu. Wedge–sleeve and tendon–wedge sliding under a sustained load or cyclic load cannot cause considerable prestress loss in practical engineering. The results validate the effectiveness of the proposed anchorage under service loads and demonstrate the application prospects of this anchorage.

Seismic Behavior of Repaired and Externally FRP-Jacketed Short Columns Built with Extremely Low-Strength Concrete

Abstract: Short columns with deficiencies of low-strength concrete and large spacing of transverse reinforcement are quite common in construction practice in many developing countries in seismically active regions. Therefore, it is important to retrofit this type of column to avoid negative consequences in the case of severe damage. External fiber–reinforced polymer (FRP) jacketing is one of the most practical methods to retrofit reinforced concrete (RC) frame members against shear actions. However, knowledge of the seismic behavior of FRP-retrofitted RC short columns is still limited. Thus, the aim of this study was to investigate the seismic response of FRP-retrofitted low-strength RC short columns with and without predamage through the testing of 11 short column specimens representing old and deficient RC buildings. Accordingly, the results of a research program on the seismic behavior of such columns and on their repair and FRP retrofitting, covering experimental and analytical phases, are presented. In the experimental phase, test results obtained for short columns, FRP-retrofitted short columns, and repaired and retrofitted short columns are documented. Test results provide important knowledge about the effects of extremely low-strength concrete, and of different levels of predamage on the behavior of FRP-retrofitted substandard short columns. In the analytical phase, the performance of relevant design documents in predicting the shear strength of such columns retrofitted with FRP jacketing was tested through the comparison of predicted and experimental results.

Data-Driven Flexural Stiffness Model of FRP-Reinforced Concrete Slender Columns

Abstract: Predicting the nominal axial capacity of slender fiber-reinforced polymer (FRP) reinforced concrete (RC) columns is dependent majorly on their flexural stiffness. However, the current design provisions do not incorporate design equations to estimate the flexural stiffness of slender FRP-RC columns yet due to the limited research work on this aspect. Although limited research studies proposed flexural stiffness models for slender FRP-RC columns, these models show inaccurate results with large discrepancies. This study, therefore, compiles and analyzes a surveyed database of 53 tested slender FRP-RC columns found in the literature to construct a simplified and accurate model to predict the flexural stiffness of the slender FRP-RC columns. In this approach, the experimental-based flexural stiffness values of the tested specimens were used to build a nonlinear regression flexural stiffness model and examine the influence of the critical design parameters affecting this value. As a result, the proposed model showed a strong agreement with the experimental flexural stiffness values evidenced by having the least root mean square error (RMSE) compared to the other proposed models in the literature. Moreover, the proposed model was theoretically evaluated accounting for the second-moment order effect by which a data set of 36,000 cases were generated and compared to the results of the proposed model to increase its creditability and repeatability. Moreover, a design example was presented to quantify the difference in predicting the flexural stiffness of the slender FRP-RC columns between the proposed and available models. Accordingly, the proposed model revealed better representation of the flexural stiffness with higher accuracy compared to the available models which will help the engineers to accurately design the FRP-RC columns.

Characterization of Textile-Reinforced Mortar: State of the Art and Detail-Level Modeling with a Free Open-Source Finite-Element Code

Abstract: The research addressed in the paper is aimed at calibrating a numerical model developed by using a free open-source finite-element code for the assessment of the structural performances of historical masonry buildings strengthened using the textile-reinforced mortar (TRM) technique. TRM is a near-surface-mounted system, which couples inorganic matrices with fiber-based textile or meshes. The main purpose is to develop a multiple-level numerical approach, starting with the detailed modeling of components and interfaces, followed by a computationally efficient intermediate level model, using layered elements, for the calibration of a lumped plasticity-based model suitable for the global analysis of structures. In this paper, the first research results are presented. In particular, a broad literature review concerning the mechanical characterization and analysis of TRM systems is collected. Then, the calibration of the numerical model, the validation through comparison with the results of experimental characterization tests available in the literature (tensile, shear bond, and in-plane shear tests) and a sensitivity analysis are reported. Nonlinear static analyses were performed, considering the nonlinearity of the composite material components and interfaces. The model was capable of accounting for the main parameters affecting the behavior of the composite material, such as the reinforcement ratio and orientation, the mortar characteristics and the wire–mortar interaction and proved to be a valid tool to investigate the optimization of TRM applicative details.

Tensile Testing of FRCM Coupons for Material Characterization: Discussion of Critical Aspects

Abstract: 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.

Improving the Mechanical Performance of Timber Railway Sleepers with Carbon Fabric Reinforcement: An Experimental and Numerical Study

Abstract: This paper proposes an externally bonded carbon fabric system to mitigate the causes of timber sleeper deterioration. Therefore, three methods of carbon fabric application for timber sleep...

Theoretical Analysis and Design of Prestressed CFRP-Reinforced Steel Columns

Abstract: This paper theoretically analyzes the symmetrical global buckling behavior of imperfect prestressed carbon fiber-reinforced polymer (CFRP) laminate-reinforced steel columns (PCRSCs) with two hinged supports under axial and eccentric compression loadings. First, the causes of the buckling of the component are revealed; either the steel yields or the CFRP becomes slack. Therefore, four buckling cases are found, and a theoretical calculation method for the buckling capacity is established. On this basis, a theoretical calculation method for the optimal CFRP initial prestressing force and maximum buckling capacity is built from physical explanations. The results of the theoretical method fit well with the test and finite-element results. Finally, a design method of PCRSCs is proposed for engineering applications, followed by a design example, by which the optimal reinforcing efficiency is realized.

Mixed-Mode FRP–Concrete Bond Failure Analysis Using a Novel Test Apparatus and 3D Nonlinear FEM

Abstract: This study introduces a novel test apparatus that can be used to test the adhesive bond between fiber-reinforced polymer (FRP) laminate and concrete in both double shear and mixed mode (shear/peeling). It was deployed to evaluate the behavior of carbon FRP (CFRP)–concrete interfaces at six peel angles. The apparatus is usable with any servohydraulic load test frame and requires only one-half of the traditional concrete block specimen used in both double shear and mixed-mode tests. Experimental results revealed a decrease in bond capacity as peel angle increased. The reduction is quantified using a power-law relationship with respect to the tangent of the peel angle. A three-dimensional (3D) finite-element model utilizing a cohesive zone model to characterize the FRP–concrete interface was developed to corroborate experimental results and carry out parametric studies. The percentage increase in CFRP–concrete bond capacity resulting from an increase in the FRP modulus or its thickness declined as the peel angle increased.

Improving the Mechanical Performance of Timber Railway Sleepers with Carbon Fabric Reinforcement: An Experimental and Numerical Study

Abstract: Abstract This paper proposes an externally bonded carbon fabric system to mitigate the causes of timber sleeper deterioration. Therefore, three methods of carbon fabric application for timber sleep...

Innovative and Eco-friendly Solutions for the Seismic Retrofitting of Natural Stone Masonry Walls with Textile Reinforced Mortar: In- and Out-of-Plane Behavior

Abstract: The application of textile-reinforced mortars (TRM) on masonry walls constructed with natural stones was studied through a set of medium-scale experiments. Fourteen experiments were carried out in total, including in- and out-of-plane cyclic tests as well as two different strengthening configurations. The first consisted of a TRM made of a natural hydraulic lime (NHL) mortar, combined with a natural flax-fiber textile, while for the latter, a novel alkali-activated material (AAM) geopolymer mortar combined with basalt textile was employed. The use of such low-carbon footprint materials instead of conventional ones makes these systems environmentally friendlier, in line with the modern requirements for lowering CO2 emissions. Both solutions led to a substantial increase of the load-bearing capacity, up to 70% for both in- and out-of-plane experiments. Stiffness and energy dissipation characteristics of the masonry elements were improved as well. If some durability related issues of both configurations and feasibility ones of AAMs are addressed, they could provide good candidates for application in real-life structures.

Large Rupture Strain FRP-Confined Concrete Columns of Different Sizes: Experiments and Stress–Strain Models

Abstract: 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.

Innovative and Eco-friendly Solutions for the Seismic Retrofitting of Natural Stone Masonry Walls with Textile Reinforced Mortar: In- and Out-of-Plane Behavior

Abstract: The application of textile-reinforced mortars (TRM) on masonry walls constructed with natural stones was studied through a set of medium-scale experiments. Fourteen experiments were carrie...

Externally Bonded CFRP for Flexural Strengthening of RC Beams with Different Levels of Soffit Curvature

Abstract: This paper reports a comprehensive study on the behavior of concavely curved soffit reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) compo...

Empirical Expression for Failure Strain in EBROG-Bonded FRP–Concrete Joints

Abstract: 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.

Externally Bonded CFRP for Flexural Strengthening of RC Beams with Different Levels of Soffit Curvature

Abstract: This paper reports a comprehensive study on the behavior of concavely curved soffit reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) composites under static loading. The main objective of this paper is to explore the effect of surface concavity on the bond performance of externally bonded wet layup CFRP sheets and laminates. An experimental program consisting of flexural strengthening of 24 RC beams with concavely curved soffits was carried out. All specimens were simply supported RC beams tested under three-point bending. Of the 24 beams, 6 beams were flat soffit RC beams, and the remainder were fabricated with concavely curved soffits with a degree of curvature that is ranging from 5 mm/m to 20 mm/m. All tested specimens were 2,700-mm long and had a constant cross section at midspan of 140-mm wide × 260-mm deep. The experiments showed that all strengthened beams failed by intermediate crack-induced (IC) debonding of the CFRP. The experimental results were then used, together with those for other specimens in the literature to set recommendations for strengthening concavely curved RC beams.

Effect of Internal Stirrups on the Eccentric Compression Behavior of FRP-Confined RC Columns Based on Finite-Element Analysis

Abstract: Fiber-reinforced polymers (FRPs) have been widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can provide substantial lateral confinement to concrete. Conventionally, the presence of internal stirrups is neglected in the retrofitting design due to a lack of understanding on the effect of internal hoops when both external FRP and internal steel confinement exist, particularly under eccentric loading. In this study, a finite-element (FE) method is developed to investigate the eccentric compression behavior of FRP-confined RC columns. A reliable concrete plastic-damage model that accurately considers the confining stiffness ratio between the FRP and steel is proposed for the first time, which facilitates the study of a difficult problem: the behavior of RC columns with the dual confinement system under eccentric loading. The accuracy of the model is verified by test results. An extensive parametric study of various affecting factors is carried out to investigate the confinement mechanisms of the concrete columns in terms of the axial stress and confining pressure distributions, lateral principal stress ratio, local stress–strain response, and interaction between the FRP/steel hoops and concrete. It is found that the nonuniform confining pressures under eccentric compression are significantly affected by the internal stirrups. With the existence of discrete transverse steel reinforcement, the axial resistance of the concrete core is increased, thereby improving the ultimate load capacity of the columns. An ultimate axial load model for RC columns that considered combined FRP–steel confinement is subsequently proposed. More accurate results are obtained using the proposed model compared with those calculated from existing design codes.

Reliability-Based Calibration of New Design Procedure for Reinforced Concrete Columns under Simultaneous Confinement by Fiber-Reinforced Polymers and Steel

Abstract: External confinement of reinforced concrete (RC) columns with fiber-reinforced polymer (FRP) jackets and/or wraps is a technique extensively used for strengthening and retrofit of structurally deficient columns. The confinement effect produced by the externally bonded FRP acts simultaneously with the confining mechanism of the existing internal reinforcing steel, thus increasing the vertical load capacity and ductility of the member. The transverse steel confinement contribution can be significant, although it is generally ignored in existing design guidelines for FRP wrapping, potentially leading to an overconservative retrofit design. This paper proposes a modification to the design equation of FRP-confined RC circular columns subjected to axial loading that is given in the current US standards. The proposed design equation is calibrated through a structural reliability analysis approach, in which the capacity model (corresponding to the probability distribution for the axial load capacity of the columns) is generated via Monte Carlo simulation based on advanced nonlinear finite-element response analyses for multiple realistic combinations of design parameters. Under different design conditions, the newly proposed design equation provides a significantly less variable reliability index than that obtained using the current accepted design equation, which produces increasingly overconservative retrofit designs for increasing amounts of transverse steel reinforcement. A practical design procedure based on the proposed design equation is also presented.

Experimental and Analytical Study on Shear Performance of Embedded Through-Section GFRP-Strengthened RC Beams

Abstract: The structural performance of reinforced concrete (RC) beams strengthened in shear with embedded through-section (ETS) glass fiber-reinforced polymer (GFRP) bars is experimentally and analytically investigated. Three-point bending tests are performed. The investigated parameters include the number of existing steel stirrups (ρsw = 0.28%), concrete compressive strength (fc′ = 27 and 43 MPa), shear span-to-effective depth ratio (a/d = 2.4, 3.6, and 4.8), anchorage presence (with and without anchorage), and anchorage properties (steel and GFRP anchorage systems, as well as the anchorage length). The results indicate that the shear capacity and stiffness of the beams are enhanced by applying ETS-GFRP, increasing concrete strength, and decreasing shear span-to-effective depth ratio. The ETS-GFRP-strengthened beams exhibit a more ductile failure mode than the unstrengthened beam owing to concrete crushing in loading areas. The beam stiffness depends significantly on the anchorage presence and properties, and the beam shear capacities differ considerably for different anchorage systems. Anchorage with four steel nuts or two GFRP nuts at the ETS bar ends provides the highest shear resistance and stiffness for the ETS-strengthened beams. The results of this study suggest that the details and configuration of the anchorage system should be carefully considered for the development of unanimous specifications. Additionally, previously proposed shear models can be used to conservatively analyze test results with sufficient accuracy. The newly developed model for estimation of the shear strengths of ETS-GFRP-strengthened beams and the effective strains in ETS-GFRP bars agrees well with the test data.

Compressive Behavior of Predamaged Concrete Cylinders Repaired with Jute and Basalt FRP Composites: A Comparative Study

Abstract: Natural fibers have become a research hotspot in composite materials recently. This study investigated the axial compressive behavior of predamaged concrete repaired by jute fiber–reinforced polymer (JFRP) composites. Basalt FRP (BFRP) was also utilized to repair the predamaged concrete for comparison. Thirty FRP-jacketed concrete cylinders with a diameter of 150 mm and a height of 300 mm were designed and fabricated. Plain concrete cylinders were axially preloaded to three predamage levels, then repaired by JFRP and BFRP composites, and reloaded to evaluate the compressive behavior after repair. The results showed that the predamage of concrete had a noticeable adverse effect on the compressive behavior of JFRP- and BFRP-repaired concrete. Compared with the JFRP-jacketed intact concrete, the compressive strength and initial elastic modulus of the JFRP-repaired predamaged concrete decreased by 6%–18% and 16%–54%, respectively. However, the compressive strength and ultimate strain of the predamaged concrete were still improved by 5%–41% and 82%–291% after JFRP repair, respectively, when compared with those of the plain concrete. On the contrary, the ultimate axial strain and lateral strain capacities of JFRP- and BFRP-repaired concrete were insignificantly affected by the concrete predamage. Under similar confinement ratios, the compressive strengths of JFRP- and BFRP-jacketed intact concrete were close to each other, whereas the axial strain–lateral strain relationship and the variations of the Poisson’s ratios were highly dependent on the FRP types and the number of FRP layers. Based on the test results and data collected from the open literature, an ultimate strength model, an ultimate axial strain model, and a stress–strain relationship model were newly developed for JFRP-repaired predamaged concrete.

Cyclic Performance of GFRP-RC T-Connections with Different Anchorage and Connection Details

Abstract: This study investigated the effects of different configurations of connection reinforcement and anchorages on the cyclic behavior of glass fiber–reinforced polymer (GFRP) reinforced-concrete (RC) exterior beam–column connections (T-connections). Three full-scale GFRP-RC T-connections were tested under reversed cyclic loading. One connection was detailed with 90-degree hooked anchorage and horizontal stirrups, while the other two connections were detailed with L-shaped anchorage by placing additional Z- or U-shaped bars at the connection region. The objective of this study was to investigate the influence of the anchorage type (90-degree hook or L-shaped) at the end of the longitudinal bars of the beam on the cyclic performance (strength, ductility, and energy dissipation) of GFRP-RC T-connections. Moreover, the anchorage performances in terms of anchorage resistance, bond stress–slip of bars within the joint were evaluated and compared with each other. Test results indicated that all the connections passed a 5.09% drift ratio without any loss of strength. The addition of U-bars into the L-shaped anchorage connection significantly improved the strength, ductility, and energy dissipation compared with the other two connections.

Experimental Investigation on the Behavior of Hollow-Core Glass Fiber-Reinforced Concrete Columns with GFRP Bars

Abstract: Steel reinforcing bars, helices, and fibers in concrete columns are susceptible to corrosion, particularly in aggressive environments. This study experimentally investigated the use of corrosion-free glass fiber-reinforced polymer (GFRP) bars and GFRP helices in hollow-core circular glass fiber concrete (GFC) columns. The influence of the addition of the glass fibers, loading conditions, and pitch of the helices was investigated. The experimental program consisted of 12 circular specimens with an outer diameter of 214 mm and an inner circular hole diameter of 56 mm. Nine specimens (850 mm high) were tested under concentric and eccentric axial loading and three specimens (1,500 mm long) were tested under four-point bending. The experimental results showed that, for a similar amount of reinforcement, the GFRP bar-reinforced hollow-core glass fiber concrete (GFRP-HC-GFC) specimens achieved 12%–18% lower maximum axial load than the GFRP bar-reinforced hollow-core nonfibrous concrete (GFRP-HC-NFC) specimens under concentric and eccentric axial loadings, as evident in the P–M interaction diagrams of GFRP-HC-NFC and GFRP-HC-GFC. However, GFRP-HC-GFC specimens achieved 5%–20% higher ductility than the GFRP-HC-NFC specimens under different loading conditions. The experimental results also showed that the GFRP-HC-GFC specimens experienced a lower number of cracks and smaller crack widths than the GFRP-HC-NFC specimens under eccentric axial loading and four-point bending. In addition, the GFRP-HC-GFC specimens with 30-mm pitch of the GFRP helices achieved 2%–34% higher maximum load and 7%–55% higher ductility than the GFRP-HC-GFC specimens with 60-mm pitch of the GFRP helices under different loading conditions.