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Continuous fiber-reinforced polymers (CFRPs) exhibit excellent mechanical properties and designability, offering more opportunities for achieving better structural performance through optimization. However, the high non-convexity of the concurrent optimization model may result in a suboptimal design. In this paper, a novel topology optimization method for three-dimensional CFRP structures is proposed. The light-weight optimization model with compliance constraint is formulated and solved to obtain an optimal topology and spatial fiber orientation. A local coordinate system is established based on the vectors of principal stress and fiber orientation, the interpolation method is presented to control fiber design variables during iteration, reducing the possibility of local optima. Topology and fiber orientation design variables are updated through the method of moving asymptotes (MMA) after sensitivity analysis. Numerical examples are offered to demonstrate the applicability of proposed method. The influence of different initial fiber orientations, mesh sizes and compliance constraints on the optimization results are discussed. Furthermore, the interpolation strategy is also extended to multi-loaded problems, with effectiveness evaluated through a numerical example. The proposed method offers theoretic support for light-weight design and fiber paths planning of three-dimensional CFRP structures. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites are increasingly being employed as internal reinforcement in concrete structures due to their superior mechanical properties and excellent durability. The use of FRP spirals as internal shear reinforcement in compressive concrete members can also provide significant confinement to concrete and thus improve the compressive performance of the concrete members. Compared with studies on the behavior of FRP spiral-confined concrete (FSCC) under concentric compression, the existing studies on FSCC under eccentric compression have been very limited. In the present study, therefore, an experimental program containing 30 specimens was designed and conducted to investigate the compressive behavior of glass FRP (GFRP) spiral-confined concrete (GSCC) under eccentric compression, with the main examined parameters including the FRP spiral pitch and the load eccentricity-to-diameter ratio. The test results revealed that load eccentricity could largely influence the behavior of GSCC in terms of compressive strength, stiffness, ultimate axial deformation and ultimate section curvature. On the other hand, the decrease in the FRP spiral pitch can to some extent compensate for the influence of load eccentricity. The present study sets a solid experimental basis for the future numerical and theoretical studies on the behavior of GSCC under eccentric compression. [ABSTRACT FROM AUTHOR]

The mechanical properties of unidirectional fiber-reinforced plastic (UD-FRP) are affected by a variety of micro-defects, such as random fiber arrangement, fiber misalignment and micro-voids. This study aims to investigate how these multiple micro-defects interact with each other and how they affect the strength and failure mechanism of UD-FRP by means of computational micromechanics. The composite behavior was simulated by the finite element analysis of a representative volume element of the composite microstructure in which the random distribution of fibers, the micro-voids, and the fiber misalignment are explicitly included. Both matrix and interface failure were considered for the loadings of transverse tension/compression, longitudinal compression, transverse/longitudinal shear, and their combination. It was found that these three micro-defects significantly weakened the compressive strength of UD-FRP along the longitudinal direction. Especially, the fiber misalignment magnified the effect of fiber arrangement, while the micro-voids reduce the effect. Besides, the fiber arrangement and micro-voids significantly weakened the tensile and compressive strength of UD-FRP along the transverse direction, but their interaction effect was not obvious. Moreover, transverse and longitudinal shear strength are significantly affected by micro-voids, but only longitudinal shear is affected by geometric fiber arrangement, and this effect is also weakened by micro-voids. Finally, the damage envelope under the combined longitudinal compression and transverse loads was obtained and compared with the Tsai-Wu failure criterion. The results showed that the Tsai-Wu criteria can provide an effective estimation for the failure locus under this biaxial loading condition. [ABSTRACT FROM AUTHOR]

• Effect of variations of standardized FRP-concrete bond test methods is studied. • UBoT: A device applicable to all bond tests overcomes limitations of individual methods. • Generated bond data & supplementary videos can empower industry & modeling experts. • Trilinear bond-slip is achieved, but with weaker bond in single vs. double shear tests. • Beam test is unsuitable for bond-slip models, but its average strength matches shear tests. • Mixed-mode test best mimics field scenarios; pull-off test yields most consistent results. The lack of a standardized bond test method for fiber-reinforced polymer (FRP)-concrete interfaces leads to variations in forms of the popular single-lap shear, double-lap shear, beam, mixed-mode, and pull-off tests. Recognizing the limitations of each bond test technique and the importance of analyzing all results as complementary, a detailed evaluation of these variations is essential for accurate bond behavior assessment prior to design and field deployment, to avoid subjective decisions and predictions. This study pioneers the evaluation of FRP-concrete bond test methods, offering the industry a consistent dataset for informed decision-making. Single- and double-lap shear tests yield trilinear bond-slip responses; however, the single-lap test's lack of symmetry reduces bond strength by 15% compared to the double-lap test. The beam test, unsuitable for bond-slip modeling, shows comparable average bond strength to the single- and double-lap tests. The mixed-mode test better simulates field applications, while the pull-off test provides the most consistent results. Given that each test method reflects only one field scenario, the Universal Bond Tester (UBoT) was developed. This device can convert to all FRP-concrete bond test types. It also addresses the modified double-lap shear test's limitations (e.g., inapplicability to pultruded laminate and FRP rupture in wet layup systems) and present a modified ASTM D7958 beam and mixed-mode tests cost-effectively. The UBoT captures full bond behavior and variabilities, overcoming the limitations of existing methods which fail to capture all failure modes in bond-critical applications. It reduces specimen sizes, weight, and data acquisition needs by half for most tests. This study allows test laboratories to use any preferred testing method with the UBoT. Link to video demonstrations for all tested specimens are provided in the supplementary material. [ABSTRACT FROM AUTHOR]

This study provides an experimental and numerical evaluation of the energy absorption performance of a 3D-printed star hourglass honeycomb structure with a novel design made from pure and reinforced PLA by chopped carbon fibers and continuous glass fiber. The study further investigates the energy absorption response of this structure after the shape recovery due to thermal stimuli under the quasi-static compressive loading. As an additive manufacturing process, Fused Deposition Modeling is used to produce the specimens with pure and reinforced PLA filament. The difference in the nonlinear response of PLA due to plasticity and damage in tension and compression loading directions, as a feature that helps the shape recovery, is considered in mechanical response analysis using the Finite Element approach. Then, in the obtained results distinguish constitutive laws in tension and compression mechanical properties are employed leading to a failure model using the appropriate algorithm consistent with the experiments. According to the obtained results which reveal good agreement regarding the experimental results, by designing appropriate auxetic configuration selecting suitable geometry parameters, and employing the proper material with diverse properties in tension and compression directions, it is possible to fabricate a lattice structure inherits the shape recovery after the compression deformation which exhibits acceptable energy absorption performance even the second shape recovery. [ABSTRACT FROM AUTHOR]

• FRP-UHPC-steel tubular columns (FUSTs) exhibited ductile behaviour with remarkable strain and strength improvement. • The steel fibers in UHPC had marginal influences on the ultimate conditions of FUSTs. • A larger inner void had a general effect to lead to more localized damage for the FRP tube. • The FRP thickness was the predominant influencing factor on the ultimate conditions of FUSTs. By integrating structural steel with Fiber-Reinforced Polymer (FRP) and Ultra-High Performance Concrete (UHPC), FRP-UHPC-steel tubular columns (FUSTs) emerge as innovative composite members that offer exceptional corrosion resistance and lightweight properties. FUSTs hold significant potential for use as thin-walled tubular columns working in harsh environments, such as wind turbines and high-voltage transmission towers. To obtain in-depth understanding of key parameters including the steel fiber ratio of UHPC, the specimen void ratio and the FRP thickness, this paper tested 24 specimens to evaluate their compressive behaviour, including 18 FUSTs and 6 UHPC-filled FRP tubes (UCFFTs). Experimental results showed that: (1) FUSTs demonstrated ductile behavior with significant strain enhancement and notable strength improvement; (2) the steel fibers in UHPC had marginal influences on the ultimate condition of FUSTs; (3) a larger inner void had a general effect to lead to more localized rupture for the FRP tube; (4) the FRP thickness was the predominant influencing factor on both the general shape and the ultimate point of the normalized axial stress–strain curves. Finally, a design model was proposed, which was able to capture the general shape of the axial load–strain curves, and could generate reasonably accurate predictions for the peak load. [ABSTRACT FROM AUTHOR]

The fiber-reinforced polymer (FRP) composites have been widely used as bullet-proof materials due to their low specific gravity, high specific strength and stiffness, and excellent impact resistance. A comprehensive understanding of the energy absorption of the FRP composites during impact and penetration and accurate prediction of the ballistic limits of the FRP composites may provide valuable guidance for designing bullet-proof composites. In this review paper, various analytical and numerical research on the ballistic limits of FRP composites are outlined. Besides, the influences of various factors such as component properties and microstructure of FRP composites and impactor characteristics on the ballistic limits of FRP composites are discussed. We focus on introducing new methods and ideas that provide guidance for the design of advanced bullet-proof composites. [ABSTRACT FROM AUTHOR]

• Investigates the mechanical performance of sandwich beams with PET FRP facings and recycled PET cores. • Examines two types of PET FRP facings with bio-resin and partial bio-resin matrices. • Compares mechanical properties of beams with recycled PET honeycomb and foam cores. • Analyzes parameters like core type, thickness, orientation, and facing thicknesses. • Provides experimental data validated by finite element modelling, aiding sustainable construction practices. The objective of this paper is to assess the mechanical performance of new forms of sandwich beams predominantly comprised of recycled plastic polymers. These beams feature two types of polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) facings: one with a bio-resin matrix and the other with a partial bio-resin matrix. The core of the beams is a focal point of the study as well, comprised of recycled PET (R-PET). Fifteen different types of sandwich beams were tested, with three identical specimens from each type, totaling 45 beams. Each beam, measuring 240 mm in length, was fabricated and categorized based on its core composition: either an R-PET honeycomb or an R-PET foam core. The study investigated key parameters including the core type (honeycomb or foam), core thickness (12 mm or 15 mm), core orientation, and facing thicknesses (1 mm or 2 mm). The mechanical testing of these beams involved a four-point bending setup to assess their flexural performance. This included analyzing mid-span load–deflection, moment–curvature behaviours, and changes in tension and compression strains in the facings during bending. The results demonstrated that core density, type, and facing thickness significantly impact the beams' stability and failure modes. High-density foam cores primarily failed through core shear, while lower density cores showed both core shear and wrinkling, dependent on facing thickness and core type, highlighting the complex influence of material properties on structural behaviour. A finite element (FE) model was developed to verify the experimental findings, effectively corroborating the test results. The research data is intended as a reference for structural designers seeking to incorporate sustainable alternatives into traditional building materials, thereby promoting a more environmentally conscious approach within the construction industry. [ABSTRACT FROM AUTHOR]

Fiber-reinforced plastic sandwich structures (FRPSSs) are increasingly used in marine applications thanks to their high levels of stiffness, lightweight, buoyancy and damage resistance to penetration and impacts. This paper investigates the effect of exposure to seawater conditions on mechanical behavior of FRPSSs with various core configurations loaded with indenters with different geometries. A new in-situ acoustic emission (AE) methodology is applied to monitor the moisture evolution process, while X-ray micro-computed tomography validated its influence on out-of-plane failure modes observed in quasi-static indentation experiments. Results indicate that AE velocity can effectively monitor the moisture uptake, serving as an in situ structural health monitoring approach. It was also revealed that the core configuration had a limited effect on moisture ingress. Samples exposed to sharp indentation exhibited the greatest decrease in load-bearing capacity (in excess of 50% in some cases) while that for blunt indentation was the lowest. This can be explained by reduced penetration forces resulting from matrix plasticization and degraded matrix/fiber interface, exacerbated by a smaller contact area. Also, early damage initiation and intensified damage progression were observed for sharp indenters after the seawater exposure. The core of FRPSSs significantly influenced localized damage in samples indented with conical and flat indenters, unlike those subjected to hemispherical ones. The seawater exposure adversely affected the energy absorption and penetration performance, enhancing macroscale damage mechanisms. These findings offer valuable insights for design and optimization of FRPSSs for marine applications. [ABSTRACT FROM AUTHOR]

Quartz fiber-reinforced polymer (QFRP) is a vital non-polar material used in aviation wave-transparent structural components. Automatic characterization of delamination defects in QFRP is critical to aviation structural component safety. Terahertz time-domain spectroscopy (THz-TDS) is one of the new non-destructive testing (NDT) methods with highly accurate characterization of internal defects in non-polar material. Hence, attempts to extract features of THz time-domain signals for automatic characterization have been made by using deep learning algorithms. In this work, a Transformer-based neural network to classify the THz time-domain signals collected from a QFRP curved structure for automatic characterization of pre-embedded delamination defects has been reported. A THz-TDS system combined with a collaborative robot for collecting the THz signals from QFRP curved structure has been built. An automatic characterization method framework is developed. Results show that the precision rates of Transformer-based neural network for 1 s t delamination to 5 t h delamination are 1.0, 1.0, 1.0, 0.985, 1.0, and F 1 score of it is 0.982. During the process of testing, delamination defects inside the QFRP curved structure were visualized using pixels with different colors. Results indicate that the Transformer-based neural network can characterize all pre-embedded delamination defects while minimizing false identification of non-defective areas, performing outstanding generalization. [ABSTRACT FROM AUTHOR]

Due to their outstanding mechanical properties, fiber-reinforced polymer composite (FRPC) structures have become a prominent research topic. Yet, to surpass existing performance limits, their design potential should be expanded beyond conventional empirical methods. Moreover, because of the high manufacturing costs, the protection of FRPC structures should be considered in the design phase to extend their service life. In this paper, we introduce an innovative configuration wherein metal coatings are strategically applied to the surfaces of FRPC structures. This technique aims to protect the internal matrix and fiber materials, and to inhibit the interlaminar delamination of composite laminates. Then, a corresponding full-scale topology optimization framework is built based on a density-based method. The coating, matrix, and fiber materials are considered collectively, avoiding issues such as excessive computation, non-convex optimization, and fiber discontinuity. Furthermore, a dual variable scale filtering (DVSF) method and its simplified scheme are presented to optimize coating thickness based on the physical information obtained from finite element analysis. Meanwhile, the co-evolution of solid topology and fiber morphology, driven by algorithms, facilitates the parallel optimization of multiple geometric features. Several typical examples, including wing ribs, are provided to illustrate the effectiveness and superiority of our approach, highlighting its engineering relevance. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) materials are integral to various industries, from automotive and aerospace to infrastructure and construction. While FRP composite design guidelines have been established, the process of obtaining the desired strength of an FRP composite demands considerable time and resources. Despite recent advancements in Machine Learning (ML) models which are commonly used as predictive models, the inherent 'black box' nature of those models poses challenges in understanding the relationship between input design parameters and output strength of the composite. Moreover, these models do not provide tools to facilitate the designing process of the composite. The current study introduces an explainable Artificial Intelligence (XAI) framework that will provide understanding for the input–output relationships of the model through SHapley Additive exPlanations (SHAP) and Partial Dependence Plots (PDPs). In addition, the framework provides for the first time a designing approach for adjusting the important design parameters to obtain the desired composite strength by the designer through utilizing an explainability technique called Counterfactual (CF). The framework is evaluated through the design of a 14-ply composite, successfully identifying critical design parameters, and specifying necessary adjustments to meet strength requirements. [ABSTRACT FROM AUTHOR]

The adoption of fiber-reinforced polymer (FRP) bars in lieu of traditional steel reinforcement for concrete structures has gained prominence. Nevertheless, prevailing international standards have not incorporated provisions to assess the significant contribution of FRP materials to the axial capacity and deformability of compression members. This study investigates the impact of Basalt (BFRP) ties on the axial performance of full-scale concrete columns reinforced with BFRP and Glass (GFRP) rebars, alongside traditional steel longitudinal rebars. Ten columns were subjected to concentric loading, with parameters including the type of longitudinal rebars (BFRP, GFRP, and steel), spacing of BFRP ties (180 mm, 120 mm, and 60 mm), and diameter of steel rebars (16 mm and 20 mm). Varied steel rebar diameters aimed to discern the influence of axial stiffness on column behavior. Results indicate an 18 % to 26 % higher axial load capacity in steel-reinforced concrete (RC) columns compared to FRP-RC columns. Both types of FRP rebars contributed approximately 12 % to the axial capacity. Reducing BFRP tie spacing from 180 mm to 60 mm significantly increased deformability by up to 250 % in FRP-RC columns and ductility by up to 14 % in steel-RC columns. The study highlights conservative predictions in existing design equations (ACI 440.11–22 and CSA S806-12) for the axial load capacity of BFRP and GFRP RC columns, underestimating by 14 % to 20 %, as they neglect the contribution of FRP rebars. Utilizing a concrete crushing strain of 3,000 µε and 3,500 µε as the ultimate FRP compressive strain produced predictions closest to the experimental axial load capacity. [ABSTRACT FROM AUTHOR]

Although fiber-reinforced polymer (FRP) reinforcements have become popular, the post-pultrusion bending leads to significant deficiency in bent portions of FRP hoops and spirals. This study adopts flexible carbon FRP (CFRP) grids as stirrups, and investigates the shear behavior of circular short columns reinforced with GFRP bars and CFRP grid stirrups. Six specimens with different shear reinforcement ratios, axial load ratios and types of stirrups (CFRP grids and steel hoops) were tested to shear failures. The failure modes, crack and strain developments, and shear load-horizontal displacement responses were presented for discussion. All specimens experienced shear-compression failures, and the critical diagonal crack widths increased approximately linearly with shear loads. The typical shear load-horizontal displacement curve consisted of three branches: a linear elastic branch, a cracking branch with progressive slope deteriorations, and an almost flat failure branch. Increasing CFRP grid stirrup ratio could not only enhance strength and ductility performance, but also alleviate the slope degradations, while increasing axial load ratios could enhance the initial cracking loads, restrain crack propagations, and reduce the lateral displacements. In terms of strength performance, steel hoops could be replaced by CFRP grid stirrups even with smaller stirrup ratio. Additionally, analytical investigations suggested that the effective stresses and strains of CFRP grid stirrups at failure may be lower than code limits. [ABSTRACT FROM AUTHOR]

• 6.0 % RCWTB provided longitudinal load-bearing capacity under a compression load. • RCWTB increased transverse fracture strain and removed yield step under compression. • Concrete exhibited load-bearing capacity from 3.0 % RCWTB in deflection terms. • 6.0 % RCWTB provided load-bearing capacity when applying indirect-tensile stresses. • Any RCWTB amount enhanced absorbed energy per unit of strength and carbon footprint. End-of-life wind-turbine blades undergo non-selective crushing to produce Raw-Crushed Wind-Turbine Blade (RCWTB), which can be recycled as a raw material in concrete. RCWTB contains fibers from glass fiber-reinforced polymer that can add ductility and load-bearing capacity to concrete. Concrete mixes with percentage additions of between 0.0 % and 6.0 % RCWTB by volume are produced to analyze their compressive stress–strain performance, their deflection under bending forces, and their deformability under indirect-tensile stresses. Higher RCWTB contents increased deformability in the longitudinal direction under compression, the concrete material absorbing energy levels that were up to 111.4 % higher, even though additions of only 6.0 % RCWTB were sufficient to strengthen the load-bearing capacity. RCWTB fiber stitching effect was most noticeable in the transverse direction under compression, as it reduced elastic deformability and failure strain, removed the yield step caused by vertical-splitting cracking, and increased the fracture strain by up to 94.4 %. With regard to deflection, RCWTB fibers conditioned concrete compliance at advanced ages without any dependence on the modulus of elasticity, and percentage additions from 3.0 % provided load-bearing capacity. This advantage was also noted in indirect-tensile stresses for 6.0 % RCWTB. In summary, RCWTB successfully increased the ductility and load-bearing capacity of concrete per unit strength and carbon footprint. [ABSTRACT FROM AUTHOR]

• The first-ever systematic experimental program on the transverse tension tests of PGFRP profiles using non-standard short coupons was presented. • Size effects on transverse tensile properties in terms of coupon width and gauge length were examined. • Finite element models were developed to provide a better understanding of the failure mechanisms of the transverse short coupons under tension. • Recommended short coupon configuration for transverse tension tests of PGFRP profiles was eventually proposed. Pultruded glass fiber-reinforced polymer (PGFRP) profiles, manufactured via a pultrusion process, are increasingly used in civil engineering. However, due to the anisotropic nature, their transverse material properties are weaker than the longitudinal ones, necessitating robust material characterization methods for transverse properties. Commercially available PGFRP profiles often have insufficiently large cross-sections for standard-sized transverse tensile tests, prompting the need to investigate the effect of coupon size on transverse tensile properties and propose a feasible shorter coupon size. This paper therefore aims to examine the coupon-size effects and propose suitable short coupon geometries for transverse tensile tests. Standard material characterization tests were conducted on channel-section PGFRP profiles, followed by transverse tensile tests on six types of non-standard short coupons. The effects of coupon width and gauge length on transverse tensile properties were evaluated and compared across six aspects, with potential failure mechanisms further explored using finite element analysis (FEA). The paper concludes by proposing a feasible short coupon configuration for transverse tensile tests. [ABSTRACT FROM AUTHOR]

• ML-aided two-step homogenization framework of short fiber-reinforced plastics is proposed. • Series–parallel artificial neural networks were developed to 12 pseudograins from a fiber orientation tensor. • ANN model and Mori–Tanaka & Voigt homogenization were implemented into user material subroutine. • The accuracy of the proposed framework was validated with an error of about 3%. Decomposing the representative volume element (RVE) of short fiber-reinforced plastics (SFRPs) into several pseudograins (PGs) is essential for understanding its effective mechanical behavior. However, conventional PG decomposition methodologies are limited by their high computational costs due to iteration-based algorithms. To address this, we propose a machine learning-assisted PG decomposition procedure that utilizes a series–parallel artificial neural network (ANN) system to facilitate the time-consuming decomposition process. To validate the effectiveness of our proposal, we implemented a two-step homogenization framework of SFRP that consists of the series–parallel ANN system, Mori-Tanaka model, and Voigt model into ABAQUS user material subroutine (UMAT). The elastic modulus values predicted by the UMAT are found to be in good agreement with both DIGIMAT-MF and experimental values, while also maintaining low computational time. [ABSTRACT FROM AUTHOR]

• The effect of bond length of NSM FRPs was examined on the performance of strengthened RC beams. • The effect of mechanical grooves was examined on the performance of strengthened RC beams. • An advanced FE model was developed to optimize the bond length of NSM FRPs. The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) technique is effective for enhancing the load carrying capacity of strengthened reinforced concrete (RC) beams. However, this technique significantly reduces the deformability of strengthened RC beams. To overcome this, the present study combines the NSM strengthening method with the partial bonding technique: the strengthening FRP reinforcement is partially bonded onto the concrete substrate). Six full-scale 4.3 m long RC beams strengthened with NSM FRPs using various bonding patterns were tested. The results indicated that mechanical interlocking grooves slightly improve the load carrying capacity, but have a negligible effect on the deformability of the strengthened beams. A decrease in the bond length increased deformability by 27.2 %, with only a 7.6 % drop in load capacity compared to that of the beam with full bonding. An advanced finite element model was developed and validated to confirm an optimal bond length of 930 mm for maximum flexural performance. [ABSTRACT FROM AUTHOR]

3D printed concrete has become increasing popular in research and industry communities, while it faces a lack of effective internal reinforcement. Fiber-reinforced polymer (FRP) reinforcement, which has been used widely as reinforcement for concrete structures, has also been adopted to enhance the performance of 3D printed concrete structures. However, conventional FRP manufacturing processes such as pultrusion does not allow on-site forming of the products, leading to difficulties in construction. This paper aims to solve the above issues by developing a novel form of 3D printed continuous fiber reinforced thermoplastic polymers (CFRTPs) reinforcement for 3D printed concrete structures. An experimental program on tensile behavior of 3D printed CFRTP bars and grids was conducted. Then the CFRTP reinforcement was used for 3D printed high-performance concrete to explore the effectiveness of the reinforcement. Twenty-two 3D printed concrete plates were tested to explore the effects of the loading direction and fabrication type on the flexural behavior of FRP reinforced high-performance concrete plates. Results show that the performance of the 3D printed HPC plates can be considerably enhanced owning to the FRP reinforcement and the CFRTP reinforcement are comparable to conventional FRP reinforcement with similar dimensions. This study identifies further research needs on CFRTP reinforcement for construction and will pave the way for studies on 3D printed reinforced concrete structures with both concrete and FRP reinforcement being printed simultaneously. [ABSTRACT FROM AUTHOR]

Many research studies have been conducted to evaluate confinement-induced enhancements on the mechanical properties of FRP (fiber-reinforced polymers)-confined plain concrete elements subjected to axial compressive loading, leading to the development of extensive predictive models. Nevertheless, experimental stress–strain results for FRP-confined RC columns (FCRC) have demonstrated some behavioural features that cannot be simulated accurately through this kind of model, developed exclusively for FRP-confined concrete columns (FCC). In this paper, a new design-oriented stress–strain model is proposed for the prediction of load-carrying capacity versus axial strain relationship of FCRC. For this purpose, a new parabolic stress–strain expression is developed for calculating the first branch of FCRC's response up to the transition zone, followed by a linear function. New formulations are proposed to determine the first branch's stress–strain gradient, transition zone-related information and the second branch's slope, calibrated using a large test database of FCRC. The proposed design-oriented model is capable of simulating accurately the combined influence of the dual FRP and steel confinement on load-carrying capacity versus axial strain relationship of FCRC. Lastly, the capability of this model is validated by comparison to existing experimental data of FCRC and those obtained from some of existing models in the literature. [ABSTRACT FROM AUTHOR]

Spurious damage modes in continuum damage mechanics models for fiber-reinforced polymer composite materials based on the effective stress tensor can be generated when large strains occur. A methodology to prevent this spurious phenomenon is developed in the present work. The longitudinal damage activation functions are based on the effective stress tensor, however, nominal stresses are used on the transverse damage activation functions. The proposed method can be straightforwardly implemented on previously-developed constitutive models which use the effective stress tensor, an explicit implementation of the proposed constitutive model is presented. The enhancement of the predicted failure mechanisms obtained from the present constitutive model, with respect to the models which use the effective stress tensor, is demonstrated. The proposed constitutive model presents a good agreement of the predicted failure pattern obtained from open-hole compressive experimental tests, as well as on the predicted failure strength. [ABSTRACT FROM AUTHOR]

Hybrid construction is proposed to decrease costs in lightweight structures using fiber-reinforced plastics (FRP) composite materials. Minimum weight, minimum strain energy (stiffness), and minimum energy variability of the structural system response are the objectives of the robust design optimization approach applied to composite shell structures with stiffeners. The trade-off depends on given stress, displacement, and buckling constraints imposed on composite structures considering non-linear geometric behavior. The design variables are ply angles and ply thicknesses of shell laminates, the cross-section dimensions of stiffeners, and the variables related to the selection of materials and their distribution at the laminate level and subsequently of the laminates along the structure. A Multi-Objective Memetic Algorithm (MOMA) applies multiple learning procedures exploring the synergy of different cultural transmission rules. An enlarged virtual population with a dual age-dominance nature captures and updates the Pareto curve. The concept of memeplex controls the meme selection and their propagation along the hybrid genetic and cultural evolution path. The success of memetic learning procedures is analyzed by measuring each meme's relative and absolute success events according to different approaches, depending on the reference time used in evolutionary history. Results show that MOMA is promising in multi-objective optimization of composite hybrid structures. [ABSTRACT FROM AUTHOR]

Pultruded fiber-reinforced polymers have been increasingly applied in engineering structures, and previous studies have focused on their axial behaviors. However, the axial load borne by the components of engineering structures is not ideal. This study presents an investigation of the behavior of I-section pultruded glass fiber-reinforced polymer (GFRP) columns subjected to eccentric loads via experiments and finite element analysis. The effects of load eccentricity around the major axis, as well as the slenderness ratio on the load-carrying capacity, were investigated. The results show that the load-carrying capacity of the GFRP column is dominated by column buckling followed by material crushing, and an increase in the eccentricity and slenderness ratio causes a decrease in the load-carrying capacity, with a progressive rate of decrease. The load-carrying capacity reduction coefficient was fitted considering the slenderness ratio and eccentricity within the scope of this study. The coefficient of determination (R2) for the fitted formula was 0.86. This study provides valuable references for designers in this field. [ABSTRACT FROM AUTHOR]

Concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars combine the advantages of both FRP and steel. The corrosion resistance and service-life are improved by placing the FRP bars, while steel bars will provide better serviceability through the higher elastic modulus and better ductility through yielding. However, there are no design provisions for hybrid FRP/steel-RC members, and the design models were evaluated over limited experimental data. This study presents a statistical and reliability evaluation for designing hybrid FRP/steel-RC beams under flexure over a worldwide experimental database. The database comprises 136 hybrid FRP/steel-RC beams tested under flexure. Theoretical balanced failure states have shown the ability to correctly predict the failure mode of the specimens. Two specimens were classified inaccurately in terms of failure mode, which is attributed to the variability in the materials' properties. Statistical evaluation for moment predictions for specimens with failure mode 2 (steel yield-concrete crushing) showed a mean, standard deviation, and coefficient of variation of 1.143, 0.169, and 14.7 %, respectively. Additionally, a reliability analysis is conducted to calibrate and recommend the strength reduction factor for the ACI 440 provisions. Targeting a reliability index of 3.5, a strength reduction factor of ϕ = 0.80 is selected as the appropriate. [ABSTRACT FROM AUTHOR]

In the present work, a unified phase field-based cohesive zone model (PF-CZM) has been utilized to predict bulk fracture and most importantly interfacial delamination in carbon fiber-reinforced polymer composites (CFRP). The formulation is based on the classical phase-field approach of energy minimization, with a rational degradation function and a polynomial-type crack geometric function. Incorporation of those provides the PF theory to integrate various traction–separation behaviors by choosing optimal constitutive functions and makes the theory capable of predicting the quasi-brittle type of fracture. Since the interfacial delamination in composites occurs either due to adhesive failure or decohesion between stacked lamina, the PF-CZM model is used to predict such failure by exploiting the cohesive zone flavor of the model. Further, the model inherently incorporates the strength of the material without any additional calibration. Various standard simulations are performed considering CFRP geometry where delaminations due to adhesive failure or interface decohesion occur in a mode-I and mode-II fashion. The model is observed to predict mode-I and mode-II separation accurately. To test the accuracy of the model an experimental validation is also performed. In addition to the delamination, open hole tension (OHT) simulations of CFRP lamina for different fiber orientations are considered to validate the anisotropic crack growth predictions, and the results are compared with experiments. [ABSTRACT FROM AUTHOR]

Abstract The integration of functional material, such as actuator material, is an essential aspect for the multi-functionality and resource efficiency of fiber-reinforced plastics (FRPs). By integrating a textile-based actuator into reinforcing fabrics during the production process, single axis and intrinsic adaptive FRPs can be produced, and these can change their form according to requirements. However, this paper presents the effect of thickness ratio and integrated weft yarn column number in shape memory alloys on the deformation behavior of adaptive FRPs. In order to achieve this aim, shape memory alloys were converted into hybrid yarn in the form of a core-sheath structure before being textile-technologically integrated into the reinforcing fabrics using weaving technology. The thickness variation was achieved by the warp as well as weft yarn density and the type of interlacement. These preforms were infused by a thermosetting resin system. The adaptive FRPs were tested electro-mechanically with respect to their maximum deformation. Results reveal that the maximum deformation of adaptive FRPs is enhanced by increasing the thickness ratio and the integrated weft yarn column number in shape memory alloys. [ABSTRACT FROM AUTHOR]

Abstract There are several methods for predicting experimental results such as empirical methods, elasticity and plasticity theory. Among these methods, the use of soft computing has been expanded due to good capabilities and high accuracy in predicting the target. Soft computing contains computational techniques and algorithms to provide useful solutions to deal with complex computational problems. In this study, three methods including Artificial neural networks, Group method of data handling and Gene expression programming are utilized to predict the compressive strength of columns confined with FRP. Total of 95 experimental data were selected to form the model. The height of the column, the compressive strength of unconfined concrete, the elastic modulus of FRP, the area of longitudinal steel, the yield strength of longitudinal steel and confinement pressure provided by FRP and transverse steel were considered as input parameters, while the compressive strength of FRP-confined columns was considered as the target. The proposed methods are compared with the existing models and provide great accuracy in predicting the results. Among the utilized methods, the ANN model showed the highest accuracy. [ABSTRACT FROM AUTHOR]

Abstract The response behavior of shear critical reinforced concrete beams was large investigated, and many studies were presented in literature. However, several issues, like the strain level of FRP at the shear failure, and the interaction between internal and external reinforcement, remain not completely understood. This paper presents an analytical model for the response behavior of reinforced concrete beams strengthened in shear with FRP. The proposed procedure has been based on the Modified Compression Field Theory and can reproduce the whole load-displacement curve. The stress and strain fields have been rigorously calculated for each load step. The effective failure strain of FRP reinforcement has been investigated by applying two different approaches. The reduction of the stirrups stress level in the presence of the external composite reinforcement has been alternately both neglected and taken into account, thus to obtain a comparison of the numerical predictions. The accuracy of the proposed model has been assessed using a database of 71 specimens reinforced with FRP. The results have showed that the proposed model has yielded accurate results and the influence of key parameters on the predictions has been highlighted. Furthermore, a simplified formulation for the evaluation of the shear strength has been derived. [ABSTRACT FROM AUTHOR]

Abstract This research investigates experimentally the effects of adding different types of fibers to the concrete mixes on the flexural behavior of concrete beams reinforced longitudinally with BFRP bars. The main aim is to study the feasibility of using newly developed basalt microfibers to improve the concrete response. Twelve beams were prepared and cast using plain, basalt fibers, and synthetic fibers-reinforced concrete (FRC) with a 40 MPa target compressive strength. Basalt fibers of two different lengths of 24 mm and 12 mm were considered. Flexural tests were conducted on each of the BFRP-FRC beams using a four-point test setup. The test matrix also included FRC beams reinforced with GFRP bars as well as conventional steel rebar for comparisons. Results showed that introducing basalt fibers to the concrete increased curvature ductility of these beams. A noticeable improvement in the flexural capacities was also recorded due to the delay in concrete failure strain (beyond 0.003) at the compression zone, which helped the BFRP bars attained a higher ultimate strength. The opening of cracks and their deep propagation was effectively restrained by the bridging effect of the basalt fibers, which kept the crack widths lower than the allowable limit of 0.7 mm at service. [ABSTRACT FROM AUTHOR]

Abstract This study investigated the usability of hybrid sandwich structures as facade panels. The explored sandwich structure was made of mineral-glass fibre reinforced polymer (GFRP) skins and a GFRP truss core, fabricated by means of a novel manufacturing method. The compressive and shear specific strengths of the panels were assessed and compared with a few common lightweight structures to verify that the manufactured truss core had comparable values. Three-point bending tests indicated that the polyurethane foam used (required for the manufacturing process) had negligible mechanical contribution. Full-scale panels were tested under a distributed load. The tests were simulated using the three-dimensional finite element method to predict the pressure at which mineral cracks appeared in order to avoid their occurrence in the design phase. The simulation results exhibited good agreement with experimental data, and the model was validated in terms of deflection and strain responses. The occurrence of cracks and their propagation were numerically reproduced using the concrete-damage plasticity model. The link between the connector and crack positions in the mineral skin was highlighted in this study. [ABSTRACT FROM AUTHOR]

Highlights • Detailed numerical analysis of S0/A0 mode conversion phenomenon on the delamination based on spectral element method. • Analysis of wavefield (including S0/A0 mode conversion) distribution through the thickness in the delaminated region. • Implementation of the model for impact damage. • Full wavefield measurements and numerical results show good agreement. Abstract In this paper results of numerical analysis of S0/A0 elastic wave mode conversion at discontinuities in glass fibre reinforced polymer (GFRP) plates are presented. Analysis of S0/A0 mode conversion effect at Teflon inserts simulating delamination (circular Teflon inserts located at a different depth, Teflon inserts with different shapes at the same depth) and impact damage with energies 5 J, 10 J and 15 J is conducted. Numerical analysis is based on spectral element method (SEM) in the time domain. Numerical model includes a composite plate, a piezoelectric transducer and bonding layer for transducer and damage. Numerical model takes also into account the influence of material damping. Numerical results are compared with experimental results based on full wavefield measurements using scanning laser Doppler vibrometry (SLDV). It is shown that based on effects of S0/A0 mode conversion it is possible to detect the damage and determine its shape and size. [ABSTRACT FROM AUTHOR]

Abstract This paper proposed to use high-strength grout and corrugated sleeves to hold FRP bars in tension zone of concrete beams, aimed at reducing crack width and improving serviceability performance. Ten large-scale simply supported beams measuring 200 mm wide, 400 mm depth, and 4000 mm length, were tested under four-point bending. One reference beam was reinforced with steel bars and four beams were reinforced with FRP bars. Other five beams were reinforced with FRP bars grouted in sleeves in the tension zone. Test results are discussed in terms of failure modes, deflection and cracking behavior. FRP-RC beams failed by concrete crushing, achieving higher flexural capacity and larger deflection than the steel-RC beam. The use of FRP bars grouted in corrugated sleeves in tension zone of beams was an effective way to reduce crack widths and improve serviceability performance. The average bond-dependent coefficient (k b) for grouted FRP bars in sleeves was 38% lower than FRP bars surrounded by concrete. The maximum crack width at service load, which accounted for variability of crack width and long-term effect of sustained load, was less than the crack width limit of 0.7 mm for beams with grouted FRP bars in sleeves but not for beams only with FRP bars. [ABSTRACT FROM AUTHOR]

Abstract This paper summarizes results on an analytical and numerical simulation of structural behavior of reinforced concrete (RC) beam-column joints retrofitted with different types of fiber-reinforced-polymeric (FRP) composite laminates and hybrid connectors. In this study, non-linear numerical simulations for the behavior of reinforced concrete (RC) beam-column joints that were evaluated in another phase of this study. The behavior of a total of eight full-scale interior RC beam-column specimens were numerically evaluated. The interior reinforced concrete (RC) beam-column joint specimens were subjected to both simulated gravity and low-frequency full-cyclic reversal loads. For repair and external strengthening applications, three systems are evaluated including high-strength carbon/epoxy composite laminates, high-modulus carbon/epoxy laminates and E-glass/epoxy external laminates. For bond-slip retrofit, the light-weight hybrid composite connector, developed by the principal author, was evaluated through large-scale tests and is molded numerically. Good correlation between numerical and experimental results is achieved. A comparison between the numerical and experimental results are also presented. [ABSTRACT FROM AUTHOR]

Abstract The strength and deformability of reinforced concrete (RC) structures strengthened with externally bonded fibre-reinforced polymer (FRP) composites can be enhanced with the addition of anchorage devices. The inclusion of anchorage can also result in a higher utilization of the desirable strength properties of the FRP by mitigating debonding. FRP spike anchors are a particularly effective type of anchorage devices as they can be applied to a wide variety of structural forms that have been strengthened with FRP composites. Experimental verification has supported the effectiveness of such anchors. However, the limited availability of design guidance is inhibiting the widespread application of anchors in practice. A critical review of the design models available in the literature is presented in addition to a design methodology for the incorporation of FRP spike anchors in RC structures strengthened with FRP composites. Exemplar designs of FRP spike anchors are also presented, to be used in combination with the design examples currently included in ACI 440.2R (2017). Finally, several knowledge gaps are identified which can be used to inform future studies. [ABSTRACT FROM AUTHOR]

Abstract Fiber reinforced polymers (FRPs) subjected to mode I fracture show important toughening due to the development of large scale bridging (LSB). Experimental studies of this phenomenon in unidirectional carbon/epoxy laminates using double cantilever beam specimens, demonstrate important differences in R-curve response for inter- and intralaminar fracture. Post fracture observation of composite's cross-section pointed out dissimilar fiber bundle size and shape, as the main origin of their differences. In the present paper, representative volume elements with the composite's constituents, based on the actual material microstructure, and homogenized 2D finite element models were developed to study the effects of microstructure on the first stage of damage leading to LSB development in carbon/epoxy composites under mode I fracture. The differences between inter- and intralaminar fracture were investigated along with the influence of fiber dispersion and the presence of interply and intraply resin-rich zones. The numerical simulations captured different microcrack morphologies for inter- and intralaminar fracture, supporting the experimental observations, while parametric studies showed the influence of the microstructure in the formation of LSB. In particular, fiber dispersion within a ply and resin rich zone between plies play significant roles in mode I fracture and can be used to control toughening mechanisms in FRPs. [ABSTRACT FROM AUTHOR]

Abstract Previous experimental studies revealed that anchorage systems were able to increase the efficiency of fiber reinforced polymers (FRP) in terms of the flexure or shear enhancements and ductility performance of the structural members. This study was conducted to investigate the suitability and effectiveness of two anchorage systems for enhancing the bond performance of fiber reinforced cementitious matrix composite (FRCM), a more recent strengthening technique using a cementitious-based binding system. In the interest of improving its flexural performance, two anchorage systems were examined here: a glass spike anchor and a novel U-wrapped anchor. The novel U-wrapped anchor is a PBO strip where its' ends had only the fabrics in the longitudinal direction that gathered and anchored into the concrete using epoxy adhesive agent. The idea behind anchoring the ends of the U-wrapped PBO strip into RC beams was to rely on the high tensile strength of the PBO strip to control the premature debonding of the FRCM composite. Real-scale simply supported RC beams were examined under the effect of strengthening with different reinforcement ratios and with and without anchorage systems engagement. Test results revealed the contribution of anchorage systems in preventing or delaying the FRCM debonding failure mechanism and enhancing the flexural performance of strengthened beams. [ABSTRACT FROM AUTHOR]

Abstract Fiber Reinforced Polymer (FRP) anchors are an effective method to increase the bond strength and/or ensure load path continuity between FRP materials and the concrete substrate when FRP materials are used as Externally Bonded Reinforcement (EBR) to strengthen and/or repair existing structures. While advances in developing a design methodology have been made on the fiber rupture and concrete cone failure modes for FRP anchors, the FRP-to-FRP bond behavior has received limited research attention. In an effort to develop design equations to calculate FRP-to-FRP bond capacity to be used by engineers, an extensive experimental program was undertaken to characterize the behavior of adhesively bonded FRP-to-FRP lap joints. Two force-based models to calculate the FRP-to-FRP bond capacity were proposed considering the influence of the critical bond length on lap joint behavior. A study to characterize the statistical properties of the experimental data was undertaken, and 95 and 99.87 percentile models were developed based on the statistical distribution of the experimental data set. Main conclusions inferred from the study and ideas for future work are also presented. [ABSTRACT FROM AUTHOR]

In this study, curved sandwich beams (CSBs) with glass fiber-reinforced polymer (GFRP) and polyethylene terephthalate (PET) foam core were initially fabricated. Experiments in three-point bending were then performed to understand the flexural behaviors including failure modes, load-bearing capacities, and load–displacement curves. The effects of various geometrical parameters including facesheets and core thicknesses, two different types of cores, and curvature radius were clarified. It was found that the utilization of PET foam in CSBs resulted in a prevention of core shearing failure and a gradual decrease in load–displacement response. Moreover, the results showed that the ultimate load-bearing capacity and stiffness of the CSBs decreased by 17.7 % and 61.8 %, with a curvature decreased from 1500 to 300 mm, respectively. An analytical model was performed to accurately estimate the experimental failure modes and load-bearing capacities of CSBs. Failure maps were also developed to investigate the various failure modes caused by different geometric parameters of curved sandwich beams. The failure maps offer valuable guidance for the design of lightweight structures. [ABSTRACT FROM AUTHOR]

• Pullout tests of macro fiber from cementitious matrix were performed. • A single macro fiber pullout model is proposed. • The bond parameters are obtained through an inverse analysis. • An improved particle swarm optimization algorithm is used in inverse identification analysis. A novel mechanical recycling method has been recently developed in the authors' group for processing waste glass fiber-reinforced polymer (GFRP) composites into macro fibers, which are then incorporated into concrete to produce green fiber-reinforced concrete (FRC). The present study has been conducted for facilitating the characterization of the tensile properties of macro fiber reinforced concrete (MFRC). A trilinear bond-slip model based on the shear-lag theory has first been refined by introducing a slip coefficient to consider different slip behaviors at the final pullout stages. Such a refined trilinear bond-slip model is suitable for describing the bond-slip behavior of the recycled macro fibers embedded in the cementitious matrix. The bond parameters are obtained through an inverse analysis, in which an improved particle swarm optimization algorithm (PSO) is used. The predicted force-end slip curves are compared with the pullout test results, and a good agreement is observed counterparts with the integral absolute error (IAE) ranging from 3.05% to 5.52%, demonstrating the feasibility of the proposed analytical model. A parametric study is finally conducted to examine the sensitivity of different parameters including the fiber geometries and bond properties on the pullout behavior of the macro fibers. [ABSTRACT FROM AUTHOR]

• A plastic injection molding process is finely optimized. • Manufacturing and structural requirements are concurrently addressed. • Accurate predictions are obtained from the optimized artificial neural network. • Considerable enhancement of structural and quality aspects is achieved. This study addresses the enhancement of an injection-molded fiber-reinforced plastic / metal hybrid automotive structure and its plastic injection molding process through the integration of the finite element method, artificial intelligence and evolutionary search methods. Experiments are conducted to validate the finite element models. The orthogonal array and Latin hypercube methods are employed to generate a database via finite element analysis. The database is then used to train artificial neural networks that accurately evaluate component distortion, manufacturing time, and structural strength. A genetic optimization algorithm is applied to identify optimal process parameters. The procedure was demonstrated to simultaneously reduce product warpage and manufacturing time by 10 and 62 %, respectively, when compared with the reference manufacturing process while strength is kept above the required levels with a reduced number of required data points. A more in-depth investigation into the causes of strength variation and deformation is also provided. The results contribute to the advance of robust composite automotive structures with superior quality, manufactured through efficient processes. [ABSTRACT FROM AUTHOR]

• Axial compression behaviour of BFRP tubes with three different cross-sections was studied. • The stress–strain curves of the BFRP tubes was classified into three stages of elastic, elastic–plastic, and plastic. • Three types of compressive failure modes were observed in the BFRP tubes. • Two design-oriented three-stage theoretical models were proposed for BFRP tubes with different cross-sections. • A stability equation was derived for predicting the compressive strength of slender BFRP tubes. This study analyzed mechanical properties and stability of pultruded basalt fiber-reinforced polymer (BFRP) tubes under compressive axial loading for large-span space and truss structures applications. This study assessed the compressive strength of BFRP tubes with three different cross-sectional shapes and investigated the failure modes under compression with slenderness ratios ranging from 20 to 150. The results demonstrated that short BFRP tubes can achieve a compressive strength of up to 122.36 MPa with a compressive elastic modulus of 40.39 GPa. Three types of compressive failure modes were observed in the BFRP tubes, including local material, critical, and overall buckling failures. Furthermore, based on the analysis of experiment results, two design-oriented three-stage theoretical models were proposed for BFRP tubes with three different cross-sectional shapes. The proposed models were able to predict both the stress–strain and load-lateral deflection curves by taking into account the post-peak softening behavior of the stress–strain curve. In addition, a stability equation was also derived for predicting the compressive strength of slender BFRP tubes and was validated by experiments. The predictions derived from proposed models were consistent with experiment results. [ABSTRACT FROM AUTHOR]

To address the cumbersome nature of mesoscale models for concrete as well as other similar materials, this paper presents an efficient and high-volume fraction mesoscale modeling framework with a novel aggregate surface tracking algorithm as well as an aggregate-cement interface interaction model to replace the interface transition zone (ITZ) in the three-dimensional space. This model could also be used in composite materials such as Fiber-reinforced polymer concrete. In this study, results are compared with the traditional 3 phases concrete models, uniaxial tension and compression models, and triaxial compression models for validation. The results show that the three-dimensional mesoscopic model can capture the detailed process of mesoscopic damage and the macroscopic behavior under different stress states while showing good agreement with the experimental results. It is demonstrated that compared with traditional methods, the new model can save up to 84 % of the preprocessing and computation time and provides a more convenient and efficient scheme for the three-dimensional mesoscopic modeling of concrete alike composite materials with good accuracy. This paper also presents several 3D mesoscale models of Fiber-reinforced polymer concrete. [ABSTRACT FROM AUTHOR]

Continuous fiber-reinforced polymers (CFRPs) have been widely applied in aerospace and other fields due to their excellent mechanical properties, which highly depends on the material distribution and fiber orientations. The designability of CFRP structures and fiber distributions provides an opportunity for achieving better physical properties through optimization. However, local optima and the dependence of initial fiber angle variables make the concurrent optimization of fiber orientation and topology a challenging problem. In this paper, the principal stress orientation interpolated continuous fiber angle optimization (PSO-CFAO) method combined with the independent continuous mapping (ICM) method is proposed to realize the design of CFRP structures with a clear macroscopic topology and microscopic fiber distribution. A sigmoid function is applied to interpolate the fiber angle variables by the principal stress orientation. The fiber angle variables are modified and a continuous fiber design is obtained during the iteration process, which reduces the possibility of a local optimum. Several examples are provided to prove the effectiveness and stability of the proposed method, and the expected results are acquired for different initial fiber angles, material parameters and mesh densities. The proposed method provides guidance for the design of CFRP structures and the planning of fiber laying paths. [ABSTRACT FROM AUTHOR]

A new and practical cohesive zone model (CZM) considering the coupling between damage mechanics and plasticity is proposed to facilitate structural-scale finite-element (FE) simulations for concrete members strengthened with fiber-reinforced polymer (FRP). The model dwells on an adaptive sub-stepping technique to overcome common convergence difficulties during mixed-mode debonding between FRP and concrete. Additionally, it automatically adjusts the computational time increment based on the convergence performance of Newton-Raphson iterations, ensuring efficiency by applying time stepping selectively to critical integration points with diverging problems. Moreover, the model introduces a transformation between effective stress and nominal stress to enhance numerical stability when dealing with complex interfacial behaviors like stiffness degradation, plastic deformation, dilation effects, and mixed-mode failure. Thus, the paper's novelty lies in the development of a stable and versatile 3D interface model achieved through advanced numerical optimization techniques. The resulting FE models have accurately reproduced various failure modes, such as FRP-concrete debonding and local buckling of FRP plates, demonstrating a high level of reliability and computational efficiency. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) beams are commonly strengthened using steel stirrups, but these materials have limitations such as added weight and susceptibility to corrosion. Fiber-reinforced polymers (FRPs) offer a promising alternative to steel stirrups with high mechanical performance, low density, and resistance to corrosion and chemicals. In particular, Intraply Hybrid Composites (IRCs), which comprise multiple fibers oriented in different directions within a single matrix, have recently gained attention in the construction industry. Cakir et al. [1] investigated the use of three types of IRCs (Aramid-Carbon (AC), Glass-Aramid (GA), and Carbon-Glass (CG)) for strengthening 2-meter-long RC beams (the ratio of shear span (a) to effective depth (d) equals 3 (a/d = 3)) against shear fractures. In this study, the effects of these IRCs on the shear strength of 1.5-meter-long RC beams (a/d = 2) without transverse reinforcement were examined. In this scope, four-point bending tests were conducted on the beams after U-shaped IRC strengthening, and the impact of IRCs on shear strength was evaluated using both digital image correlation and classical measurement equipment such as strain gauges and linear variable differential transducers. The maximum load measured in RC1.5 was 194.50 kN, while the ultimate load capacity reached 265 kN in AC1.5, 246 kN in GA1.5, and 229 kN in CG1.5 after strengthening, representing increases of 36%, 26%, and 18%, respectively, compared to RC1.5. Additionally, the maximum mid-span deflections were determined as 30.40 mm, 16.10 mm, 22.20 mm, and 36.40 mm for RC1.5, AC1.5, GA1.5, and CG1.5, respectively. Moreover, the experimental results were compared with the predictions obtained from the international codes. It should be noted that the failure modes of RC beams are directly affected by the type of IRCs used, highlighting the significant contribution these materials can make to the structural behavior of RC beams. [ABSTRACT FROM AUTHOR]

• Spatial-temporal graph convolutional networks (STGCN) based method for damage localization is proposed. • Spatial-temporal features of AE sensor networks are extracted combining with graph theory. • A new distance-based graph connectivity method is developed. • Validity of the proposed STGCN method is approved by experiments. A novel spatial–temporal graph convolutional networks (STGCN) based method for the regression task of localizing acoustic emission (AE) sources in composite panels is proposed. This is the first time that graph convolutional networks are introduced into the AE source localization task. Data generated by AE sensor networks is represented by a graph structure, in which the temporal features extracted from AE waveforms using one-dimensional convolutional neural networks (1D-CNN) and the spatial information of sensors constitute the node features. An adaptive distance-based adjacency matrix calculation method according to the geographical locations of AE sensors is further developed to represent the connectivity of the graph. Finally, the proposed method is experimentally validated on a glass fiber-reinforced plastic (GFRP) panel, and 5-fold cross-validation was carried out to evaluate the performance of the method effectively. The results show that the proposed STGCN method has a high performance in damage source localization and it significantly outperforms other methods. [ABSTRACT FROM AUTHOR]

Abstract This study developed a new method for determining the transfer length for FRP tendons in prestressed concrete. The governing equations are derived by combining the local bond-slip relationship for FRP tendons in concrete with composite beam theory. Comparisons to test data strain results demonstrate that the derived closed form solutions predict the transfer length of prestressed FRP tendons with good accuracy and efficiency. The developed method is then used to assess and discuss the difference between sequential release and simultaneous release of the tendons during manufacture of prestressed concrete members. Finally, based upon the developed theory, the key mechanical factors that influence the transfer length of FRP tendons are discussed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents test results of fifteen reinforced engineered cementitious composite (ECC)-concrete beams. The main parameters investigated were the amount and type of reinforcement, and ECC thickness. All reinforced ECC-concrete composite beams tested were classified into four groups according to the amount and type of main longitudinal reinforcement used; three groups were reinforced with FRP, steel and hybrid FRP/steel bars, respectively, having similar tensile capacity, whereas the fourth group had a larger amount of only FRP reinforcement. In each group, four height replacement ratios of ECC to concrete were studied. The test results showed that the moment capacity and stiffness of concrete beams are improved and the crack width can be well controlled when a concrete layer in the tension zone is replaced with an ECC layer of the same thickness. However, the improvement level of ECC-concrete composite beams was controlled by the type and amount of reinforcement used. Based on the simplified constitutive relationships of materials and plane section assumption, three failure modes and their discriminate formulas are developed. Furthermore, simplified formulas for moment capacity calculations are proposed, predicting good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Abstract The objective of this investigation is to assess the effectiveness of hybrid fiber reinforced polymer (FRP) strengthening on the overall behavioral improvement of reinforced concrete (RC) beams under flexure. Eight square RC beams were cast and strengthened using different FRP techniques including (i) near surface mounting (NSM), (ii) external bonding (EB) and (iii) hybrid strengthening using a combination of NSM carbon FRP laminates and EB CFRP fabric. Peak moment capacity was calculated analytically by enforcing the sectional equilibrium using the strain compatibility procedure. A micro plane based nonlinear three-dimensional finite element (FE) model was developed to simulate the behavior of the RC beams with and without FRP strengthening. Experimental results revealed that hybrid FRP strengthening could increase the strength by 160%. Moreover, the ultimate displacement of hybrid FRP strengthened beams improved significantly when compared to only the NSM technique. Only NSM strengthening improved the peak strength by 85% but had a brittle bond failure. Only EB strengthening improved the ductility of the flexural members due to confinement but did not significantly increase the strength. Predictions of the FE model correlated well with the experimental results and revealed that minimum edge distance for NSM laminates has to be ensured for preventing premature edge de-bonding failures. [ABSTRACT FROM AUTHOR]

Abstract Continuous fibre-reinforced thermoplastics offer advantages over their thermoset counterparts. Thermoplastics are often overlooked, as they must pass through the high temperature automotive paint shop for application in structural body parts. Tensile-, flexural-, and impact properties of polyamide 6, polyamide 66, and polyphthalamide reinforced with woven glass fibre fabrics were investigated. It is shown that the entire painting process mostly yielded a predominant improvement on the investigated mechanical properties of glass fibre-reinforced polyamide 6 due to a raised degree in crystallinity. There is no unanimous trend visible for glass fibre-reinforced polyamide 66. The examined shear properties of glass fibre-reinforced polyphthalamide were decreased by the painting process. [ABSTRACT FROM AUTHOR]