Search Results (191)

The application of fiber-reinforced polymer bars has been considered an alternative for the non-metallic reinforcement of concrete structures. Basalt fiber-reinforced polymer (BFRP) is a new composite used to reinforce concrete structures. However, the main drawback of BFRP is its low modulus of elasticity. Therefore, hybrid reinforced fiber polymers, in which carbon fibers replace part of the basalt fibers, might be considered as a relatively “simple” modification that can increase the modulus of elasticity. The literature data suggest that modification of the epoxy matrix with nanosilica particles can positively influence resistance to high temperatures. Besides the mechanical characteristics of FRPs, the evaluation of alkali resistance is necessary for technical approval for construction applications. This paper focuses on testing the alkali resistance of basalt fiber-reinforced polymer (BFRP) bars and its modification through the partial substitution of basalt fibers with carbon fibers (HFRP) and the addition of nanosilica to the epoxy binder (nHFRP). The alkali resistance was tested based on the most common method described in ACI report 440.3R-04—part B6. This method consists of three procedures carried out at 60 °C on the specimens immersed in an alkaline solution, both with and without load. The changes in the mass and tensile strength of the bars are examined after 1, 2, 3, 4, and 6 months. The test procedures are time-consuming and expensive, particularly Procedures B (in alkaline solution) and C (in concrete cover), in which longitudinal tested specimens must be immersed in alkaline solution and subjected to constant strain at an elevated temperature for a 6-month period. Therefore, this study proposes a test setup to achieve a less time-consuming and cheaper assessment of the alkali resistance of FRP bars. Additionally, the usefulness of the shear strength test for the evaluation of alkali resistance of FRP bars is also discussed. The results (Procedure A) indicate that modification of the composition of BFRP did not decrease the resistance to the alkaline environment in the case of HFRP (5% lower than in the case of BFRP). Under the same conditions, the decrease in the tensile strength of nHFRP was 40% higher than in the case of BFRP. This indicates that additional modification of the composition by adding nanosilica to the epoxy binder did not provide the expected stability of tensile properties at elevated temperatures. The results of the evaluation of alkali resistance according to Procedure B show that the device proposed for maintaining constant strain during the seasoning is promising. At this stage, the device makes it possible to conduct the tests at ambient temperature and yields a significantly lower decrease in tensile strength (10–14%) after 6 months, demonstrating a significant effect of temperature on the results of the FRP alkali resistance test. Full article

The shear behavior of basalt fiber-reinforced polymer (BFRP) bars is crucial for their applications in geotechnical reinforcement and composite structures. In this study, double-side direct shear tests were conducted to investigate the progressive failure mechanism of BFRP bars. The results reveal a three-stage process: initial matrix-dominated vertical shear, followed by fiber-bridging dominated oblique tension-shear, and finally formation of a “brush-like” fracture surface with significant residual strength. The average peak shear strength of the ten specimens was 204.04 MPa with a coefficient of variation of 7.25%, while the initial shear modulus averaged 3.37 GPa with a coefficient of variation of 11.82%. Based on statistical damage theory, a shear constitutive model incorporating fiber bridging and residual strength is established. Parameter analysis indicates that the shape parameter m governs the post-peak softening rate, while the residual strength τ_res essentially determines the height of the residual plateau. The model achieves a goodness-of-fit (R²) exceeding 0.98 for most specimens, accurately describing the mechanical behavior from linear elasticity, damage-induced hardening, peak softening, to the residual stage. This study provides theoretical and experimental support for the engineering application of BFRP bars under complex stress states. Full article

To investigate the cyclic behavior of FRP-reinforced steel fiber reinforced concrete (SFRC) composite walls, this paper proposes a section-based finite spring calculation method (FSCM) to reliably predict the cyclic response of such walls under seismic loads. The proposed model accounts for the bond-slip effect of FRP bars and the confining action of transverse reinforcement in the boundary elements. Numerical calculations were conducted on six composite wall specimens with varying longitudinal bar types, fiber volume fractions, concrete strengths, and axial compression ratios. The results indicate that the established calculation method efficiently characterizes the “pinching” effect induced by the linear-elastic properties of FRP bars, and the obtained hysteretic curves are in good agreement with experimental data. Furthermore, the model accurately predicts the load-bearing capacity and residual displacements of the FRP-reinforced SFRC composite walls. Specifically, the average error of peak load calculation for all specimens ranges from −3.36% to 7.36%, and the predicted residual displacements correlate well with the experimental data. These findings demonstrate the applicability of the proposed model for key seismic performance indicators and provide a reliable basis for the research and engineering application of FRP-reinforced SFRC composite walls. Full article

Fiber-reinforced polymer (FRP) pipes are increasingly used in pressure piping systems due to their corrosion resistance and favorable mechanical performance; however, the direct experimental validation of design assumptions adopted in international standards remains limited. The objective of this study is to experimentally validate the mechanical response and stress distribution of filament-wound GFRP pipes under representative loading conditions and to assess the consistency of the measured behavior with the allowable-stress design framework of ISO 14692 and complementary ASME and BS codes. In this study, the mechanical behavior of filament-wound glass fiber-reinforced polymer (GFRP) pipes is investigated through a combined experimental program including tensile, bending, and full-scale internal pressure tests. Electrical resistance strain gauges were applied in axial and circumferential directions to directly measure deformation under internal pressure up to 31 bar, allowing experimental stresses to be derived using orthotropic laminate relationships. The results demonstrate a predominantly linear elastic response within the service range, followed by progressive damage initiation at higher load levels, with circumferential stresses consistently exceeding axial stresses, confirming a hoop-dominated response. At the maximum applied pressure of 31 bar, axial and circumferential strains reached approximately ε_a ≈ 1.30 × 10⁻³ and ε_h ≈ 1.60 × 10⁻³, corresponding to experimentally derived stresses of σ_a^exp ≈ 15.3 MPa and σ_h^exp ≈ 18.8 MPa, without catastrophic failure. The novelty of this work lies in the direct integration of full-scale strain gauge measurements with standardized allowable-stress design assumptions, enabling an experimental validation of ISO 14692 that is rarely addressed in existing studies. The experimentally derived stress–strain data show good agreement with theoretical models and provide a direct link between measured behavior and the allowable stress philosophy and design equations defined in ISO 14692 and complementary ASME and BS design codes. The findings validate the applicability of standardized design approaches and provide experimentally grounded support for engineering design decisions in FRP piping systems. Full article

In this paper, the bond performance of tensile lap-spliced Glass and Basalt Fiber-Reinforced Polymer bars is investigated in high-strength concrete. Eighteen large-scale GFRP-reinforced concrete beams were fabricated and subjected to four-point loading. Key parameters explored included bar diameter and splice length for both GFRP and BFRP reinforcement. The results indicate that the flexural capacity of GFRP-reinforced beams was comparable to that of BFRP-reinforced beams, though BFRP bars exhibited marginally superior bond and strength with concrete. The bond strength of spliced FRP bars was directly proportional to the splice length. This study also determined that characteristics of development lengths necessitate splice lengths that exceed the bar diameter 40 times to mitigate bond stress. Critical splice lengths, derived from experimental findings, were compared with existing models and code-based equations, specifically, Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer Bars (ACI 440.1R-15) and Canadian standard that provides comprehensive guidelines for incorporating Fiber-Reinforced Polymer reinforcement in concrete structures (CSA S806-12). Both codes were conservative in splice length prediction for GFRP and BFRP bars, with ACI 440.1R-15 showing greater accuracy for BFRP bars with a larger diameter. A modification factor, based on hyperbolic functions, is proposed to enhance the accuracy of ACI 440.1R-15 in predicting splice lengths for various FRP bar diameters. Full article

Compared to reinforcing concrete with steel bars, rebars—made of fiber-reinforced plastic—have a high potential for resource savings in the construction industry due to their corrosion resistance. For the large-volume market of reinforcement elements, efficient manufacturing processes must be developed to ensure the best possible bond behavior between concrete and rebar. In contrast to established FRP-rebars made with thermosetting materials, the use of a thermoplastic matrix enables surface profiling without severing the edge fibers as well as subsequent bending of the bar. The rebars to be produced in this study are based on the process of reactive thermoplastic pultrusion of continuously glass fiber reinforced aPA6. Their surface must enable a mechanical interlocking between the reinforcement bar and concrete. Concepts for a profiling device have been methodically developed and evaluated. The resulting concept of a double wheel embossing unit with a variable infeed and an infrared preheating section is built as a prototype, implemented in a pultrusion line, and further optimized. For a comprehensive understanding of the embossing process, reinforcement bars are manufactured, characterized, and evaluated under parameter variation according to a statistical experimental plan. The present study demonstrates the relationship between the infeed, preheating temperature, and haul-off speed with respect to the embossing depth, which is equivalent to the rib height. No degradation of the Young’s modulus was observed as a result of the profiling process. Full article

This paper presents an experimental and numerical investigation of continuous reinforced concrete (RC) beams made of self-compacting concrete (SCC) strengthened with fiber-reinforced polymer (FRP) bars using the Near-Surface Mounted (NSM) method. While the majority of previous studies have focused on simply supported beams, this work examines two-span continuous beams, which are more representative of real structural behavior. Four SCC beams were tested under static loading to evaluate the influence of the FRP reinforcement position on flexural capacity and deformational characteristics. The beams were strengthened using glass FRP (GFRP) bars embedded in epoxy adhesive within pre-cut grooves in the concrete cover. Experimental results showed that FRP reinforcement significantly increased the ultimate load capacity, while excessive reinforcement reduced ductility, leading to a more brittle failure mode. A three-dimensional finite element model was developed in Abaqus/Standard using the Concrete Damage Plasticity (CDP) model to simulate the nonlinear behavior of concrete and the bond–slip interaction at the epoxy–concrete interface. The numerical predictions closely matched the experimental load–deflection responses, with a maximum deviation of less than 3%. The validated model provides a reliable tool for parametric analysis and can serve as a reference for optimizing the design of continuous SCC beams strengthened by the NSM FRP method. Full article

The embedded through-section (ETS) technique is a promising method for fiber-reinforced polymer (FRP)-strengthening reinforced concrete (RC) structures, offering higher bond resistance and reduced surface preparation compared to externally bonded or near-surface mounted FRP systems. A common failure in ETS applications is debonding at the FRP bar-to-concrete interface. However, current design standards often assume uniform bond stress and lack predictive models that account for debonding propagation and its effect on load capacity. Furthermore, a detailed analysis of interfacial stress development, including debonding initiation and progression along varying bond lengths, remains limited. To address these gaps, this study introduces an analytical model that describes the complete debonding process in ETS FRP bar-to-concrete joints, incorporating both long and short bond lengths and frictional effects. Based on a trilinear cohesive material law (CML), closed-form expressions are deduced for the load–slip response, maximum load, interfacial shear stress and strain distribution along the FRP bar. The proposed model is validated experimentally through pull-out tests on glass FRP (GFRP) bars adhesively bonded to concrete with different strength grades. The results show that the analytical predictions agree well with both the self-conducted experimental data for short joints and existing test results for long joints given in the literature. Therefore, the developed design-oriented solution enables accurate evaluation of the actual contribution of ETS FRP reinforcement to RC members by explicitly modeling debonding behavior. This provides a rigorous and mechanics-based tool for performance-based design of ETS FRP-to-concrete joints, addressing a critical gap in the future refinement of current design standards. Full article

To overcome the corrosion issues of conventional steel reinforcement and the brittleness of fiber-reinforced polymer (FRP) materials, steel-FRP composite bars (SFCBs) offer an innovative solution by combining the ductility of steel with the high strength and corrosion resistance of FRP. However, existing research primarily focuses on experimental investigations, with insufficient numerical simulations of SFCB-reinforced concrete beams, particularly regarding bond-slip effects at the SFCB-concrete interface—a critical mechanism governing composite action and structural performance. This study develops a finite element (FE) model incorporating SFCB-concrete bond-slip effects to analyze the influence of outer FRP layer thickness (0, 3, 5, and 7 mm) on the flexural performance of concrete beams. The FE model demonstrates good predictive accuracy, with errors in ultimate capacity and mid-span displacement within 7% and 8%, respectively. Both cracking and yield loads increase with FRP thickness, while the ultimate load peaks at 5 mm. At 7 mm, concrete crushing occurs before the SFCB reaches its ultimate strength. The ductility index decreases with greater FRP thickness due to increased elastic energy without enhanced plastic energy (fixed steel core area), thereby reducing overall ductility. These findings provide a theoretical basis for optimizing SFCB-reinforced concrete structural design. Full article

With the increasing demand for lightweight, high-strength, and ductile structural systems in modern infrastructure, the hybrid composite column has emerged as a promising solution to overcome the limitations of single-material members. This paper proposes an innovative variant of double-skin tubular columns (DSTCs), termed as square double-skin hybrid concrete bar columns (SDHCBCs), composed of one square-shaped outer steel tube, small-diameter concrete-infilled glass FRP tubes (SDCFs), interstitial mortar, and an inner circular steel tube. A series of axial compression tests were conducted on eight SDHCBCs and one reference DSTC to investigate the effects of key parameters, including the thicknesses of the outer steel tube and GFRP tube, the substitution ratio of SDCFs, and their distribution patterns. As a result, significantly enhanced performance is observed in the proposed SDHCBCs, including the following: ultimate axial bearing capacity improved by 79.6%, while the ductility is increased by 328.3%, respectively, compared to the conventional DSTC. A validated finite element model was established to simulate the mechanical behavior of SDHCBCs under axial compression. The model accurately captured the stress distribution and progressive failure modes of each component, offering insights into the complex interaction mechanisms within the hybrid columns. The findings suggest that incorporating SDCFs into hybrid columns is a promising strategy to achieve superior load-carrying performance, with strong potential for application in high-rise and infrastructure engineering. Full article

Engineered Cementitious Composite (ECC) exhibits superior tensile strain-hardening behavior and enhanced crack control due to its distinctive multiple cracking characteristic. In contrast, Steel–Glass Fiber Reinforced Polymer (GFRP) Composite Bars (SFCBs) combine the ductility of steel with the corrosion resistance of GFRP. To investigate the synergistic mechanisms for optimizing the performance of concrete structures, this study designed eight SFCB-reinforced ECC-concrete composite beams. Four-point bending tests were conducted to examine the influence of the ECC replacement height in the tension zone (hE/h = 0%, 16.67%, 33.33%, 50%) and the steel ratio in the bottom longitudinal reinforcement (As/Ab = 0%, 9%, 25%, 49%, 100%) on the flexural performance. The experimental results demonstrated the following: (1) Increasing the ECC replacement significantly improved both the ultimate bending capacity and ductility, while exerting a limited effect on flexural stiffness. Specifically, when increased from 0% to 50%, the ultimate bending strength and ductility index increased by 4.79% and 8.09%, respectively. (2) The steel ratio predominantly governed the yield behavior and crack development. Higher steel ratios resulted in increased flexural stiffness prior to yield, higher yield moments, improved ductility at failure, and superior crack control capability before yielding. (3) The synergistic mechanisms were identified: the ECC layer optimizes crack control by distributing crack-induced strains through multiple cracking, while the steel ratio within the SFCB regulates the ductile response. The findings of this study provide valuable theoretical guidance for enhancing the capacity and ductility of building structures. Full article

This study develops data-driven models for predicting the shear capacity of reinforced concrete (RC) beams longitudinally reinforced with fiber-reinforced polymer (FRP) bars and lacking transverse reinforcement. Owing to the comparatively low elastic modulus and linear–elastic–brittle behavior of FRP bars, reliable shear prediction remains a design challenge. A curated database of 402 tests was compiled from the literature, spanning wide ranges of beam size (width b, effective depth d), concrete compressive strength (f′c), FRP elastic modulus (Ef), longitudinal reinforcement ratio (ρf), and shear span-to-depth ratio (a/d). Multiple multivariate regression formulations—both linear and nonlinear—were developed using combinations of these variables, including a mechanics-informed reinforcement index (ρf·Ef). Model predictions were benchmarked against 15 existing expressions drawn from design codes, standards, and prior studies. Across the full database, the proposed models demonstrated consistently stronger agreement with experimental results than the existing predictors, yielding higher correlation and lower prediction error. The resulting closed-form equations are transparent and straightforward to implement, offering improved accuracy for the preliminary design and assessment of FRP-RC beams without stirrups while highlighting the influential roles of Ef, ρf, and a/d within the observed parameter ranges. Full article

Dams are currently confronted with severe risks from frequent extreme climates and expanding aging deterioration, with traditional mitigation measures struggling to balance efficient prevention/control and long-term management. As an innovative solution, fiber-reinforced polymer (FRP) composites support improved dam safety governance. To address the lack of systematic integration in existing dam-related studies, this paper promotes the development of an FRP in the dam field by comprehensively analyzing and summarizing the material properties, interfacial bonding properties of the FRP, as well as the flexural and compressive characteristics of FRP bar–concrete members and FRP sheet–concrete members while systematically organizing their practical engineering application cases. It also explores the FRP’s potential in hydraulic structures and suggests its wider application therein based on the FRP’s superior properties. Full article

Recent studies have confirmed the effectiveness of using natural fibers and fiber-reinforced polymer (FRP) composites as methods to improve the mechanical properties of timber structures. This improvement is particularly evident in static and dynamic flexural and shear performance. Moreover, there is a paucity of literature pertaining to numerical models that predict the non-linear behaviour of low-quality timber beams reinforced with natural and man-made fibers. The present article expounds upon a shear bending study of timber beams reinforced with bars in addition to other materials. The experimental study yielded the following findings: the best properties were obtained with hybrid reinforcement, in comparison to the reference beams. The enhancement of load-bearing capacity and stiffness for beams that have been reinforced with pre-stressed basalt bars was found to be the most advantageous, with increases of approximately 17% and 8%, respectively. Natural fibers exhibited slightly lower values, with an increase in load-bearing capacity and stiffness of approximately 14% and 3%, respectively, when compared to beams that had not been reinforced. Moreover, the numerical analyses yielded analogous results to those obtained from the experimental study. The numerical models thus proved to be a valid tool with which to study the influence of the reinforcement factor. Full article

Corrosion concerns motivate the use of alternatives to conventional steel reinforcement in RC beams. This review evaluates fiber-reinforced polymer (FRP) bars and hybrid steel–FRP composite bars (SFCBs) used for durability-critical applications. We conducted a structured literature search focused on 2010–2025 and included seminal pre-2010 studies for context. Experimental studies and code provisions were screened to synthesize evidence on load–deflection response, cracking, and failure, with brief notes on UHPC systems. FRP-RC offers corrosion resistance but limited ductility and an abrupt post-peak response. Steel is ductile and provides warning before failure. SFCB combines durability with steel-core ductility and yields gradual softening and higher energy absorption. Practice should select reinforcement based on stiffness–ductility–durability trade-offs. Current codes only partially cover hybrids. Key gaps include standardized bond–slip and tension-stiffening models for SFCB and robust data on long-term performance under aggressive exposure. Full article