Search

In this study, polyethylene terephthalate (PET) was substituted for 10%, 20%, and 30% of the sand volume in concrete. Compressive, splitting tensile, and flexural strength tests were applied to the concrete samples and stress–strain graphs were obtained. It was observed that PET substitution caused a decrease in the mechanical properties of the concrete. For this reason, the concrete with the best PET substitution rate (10%) was reinforced by wrapping it with carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP), and the same experiments were repeated. It was observed that a 10% PET substitution reduced the strength of the reference concrete by about 6%. However, wrapping the PET-substituted concrete with CFRP and GFRP increased the strength by about 1.9 and 1.5 times, respectively, surpassing that of the reference sample. In addition, this study provides a comprehensive database by bringing together experimental data from studies in which PET was used as a substitute by volume or weight instead of fine aggregate in concrete. The models proposed in this study, along with previous models, were tested for applicability. Similarly, the model suggestions in the literature for fiber-reinforced polymer (FRP)-confined concrete were tested with the experimental data in this study, and their suitability for PET-substituted concrete was discussed. [ABSTRACT FROM AUTHOR]

Fiber-reinforced cementitious composite (FRCC) and fiber-reinforced polymer (FRP) have been widely applied in infrastructures. Their mechanical behavior and innovative applications are examined in this article. Firstly, the mechanical behaviors of FRCC and the corresponding improving methods are elaborated. The bond behavior of the FRP–concrete interface, which has a significant effect on the strengthening effect of FRP, is reviewed. A proposed method to enhance the bond behavior is also introduced. In addition, the effectiveness of FRP is demonstrated in terms of improving the load-bearing capacity, stiffness, crack resistance, fatigue resistance, and other behaviors of existing structures. Furthermore, the feasibility of fibers or FRPs in new constructions is also validated. Finally, the future prospects of the research and applications of FRCC and FRP are discussed. [ABSTRACT FROM AUTHOR]

Pultruded glass fiber-reinforced polymer (GFRP) materials are increasingly recognized in civil engineering for their exceptional properties, including a high strength-to-weight ratio, corrosion resistance, and ease of fabrication, making them ideal for composite structural applications. The use of concrete infill enhances the structural integrity of thin-walled GFRP sections and compensates for the low elastic modulus of hollow profiles. Despite the widespread adoption of concrete-filled pultruded GFRP tubes in composite beams, critical gaps remain in understanding their flexural behavior and failure mechanisms, particularly concerning design optimization and manufacturing strategies to mitigate failure modes. This paper provides a comprehensive review of experimental and numerical studies that investigate the impact of key parameters, such as concrete infill types, reinforcement strategies, bonding levels, and GFRP tube geometries, on the flexural performance and failure behavior of concrete-filled pultruded GFRP tubular members in composite beam applications. The analysis includes full-scale GFRP beam studies, offering a thorough comparison of documented flexural responses, failure modes, and structural performance outcomes. The findings are synthesized to highlight current trends, identify research gaps, and propose strategies to advance the understanding and application of these composite systems. The paper concludes with actionable recommendations for future research, emphasizing the development of innovative material combinations, optimization of structural designs, and refinement of numerical modeling techniques. [ABSTRACT FROM AUTHOR]

To promote the application of molybdenum tailings as the fine aggregate in concrete in construction engineering and verify the feasibility of fiber-reinforced polymer (FRP) material for strengthening molybdenum tailings concrete columns, this study takes a short circular molybdenum tailings concrete column reinforced by glass FRP (GFRP) as the research object. The influences of the molybdenum tailings content (0%, 25%, 50%, 75%, and 100%), the concrete grade (C30, C40, and C50), and the layer number (0, 1, and 2) of the GFRP sheet on the axial compressive capacity of the molybdenum tailings concrete column are investigated. The experimental phenomena and failure modes of the unreinforced and GFRP-reinforced columns are analyzed. The axial compressive strengths of the unreinforced and GFRP-reinforced columns are then compared. The load–strain curve and load–displacement curve of typical molybdenum tailings concrete columns are presented. Subsequently, six classical strength models for FRP-reinforced concrete are used to calculate the axial compressive strength of the confined specimens. The results show that the best classical model has a predictive accuracy with an absolute relative deviation (ARD) of 8.5%. To provide a better prediction of the compressive strength of the GFRP-reinforced molybdenum tailings concrete column, the best classical model is further improved, and the ARD of the modified model is only 5.87%. [ABSTRACT FROM AUTHOR]

The objective of this study was to systematically evaluate the effects of different repair methods to determine optimal strategies for enhancing the load-carrying capacity of damaged reinforced concrete beams. During construction or rehabilitation, some openings may be created in structural members for various reasons, either intentionally or accidentally. While creating these gaps, damage may occur to the lower reinforcement of the beam. Within the scope of this paper, the effects of these openings were studied, and the different techniques to be used in the repair of damaged reinforced concrete beams were investigated. This study discusses an experimental analysis of ten beams under bending loads. An opening gap was formed at the lower mid-span of all beams except the reference beam, with the main reinforcement in these openings being cut. The damaged beams were then repaired with various techniques, including fiber-reinforced polymer (FRP) sheets and different reinforcement bars. The experiments of all beams were carried out by applying the four-point bending test model. The results showed that all repaired beams had significant enhancements in behavior and load, stiffness, ductility, and energy consumption capacities compared to the damaged beam. [ABSTRACT FROM AUTHOR]

The utilization of bio-based materials for the manufacturing of fiber-reinforced polymer composites is gaining importance under the sustainability paradigm. The identification of suitable process parameters and limited process reproducibility remain among the major challenges to enhance the industrial application potential of bio-based composites. This is especially relevant, as the manufacturing process influences composite quality, economic performance and environmental impacts. This study compares Resin Transfer Molding and Vacuum Assisted Resin Infusion for two sets of process parameters in order to manufacture a composite plate consisting of a flax-fiber textile impregnated with a partially bio-based epoxy matrix. Process quality is described through statistical analysis of processing and composite properties, and performance in terms of process replicability and reliability using performance estimates. Processing parameters were selected to depict a range of manufacturing scenarios that were suitable for the selected bio-based material system from curing for 180 min at 60 °C to curing for 30 min at 100 °C. For an identical set of process conditions, Resin Transfer Molding outperforms Vacuum Assisted Resin Infusion in terms of tensile and flexural characteristics. Conversely, the latter shows the strongest fiber-matrix adhesion and the most homogeneous impregnation. Whereas manufacturing at lower temperature leads to positive effects on composite quality, higher processing temperature with shorter curing cycles achieve highest process performance in terms of Pp and Ppk indices. An additional annealing at 120 °C neither increases composite quality nor reduces manufacturing-induced variability. Results depend on processing differences and indicators to determine process performance, as well as methodological choices. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymers (FRPs) are increasingly recognized in sustainable materials research due to their potential environmental advantages. This study presents a focused bibliometric review of the sustainability research on FRPs. An initial search of the Web of Science (WOS) database identified 803 documents, which were refined to 749 relevant articles, reviews, and proceedings. A co-authorship analysis highlights the significant contributions of the USA and India, with European countries forming regional collaborations. The research output has steadily increased since 2011, peaking in 2022 and 2023. The multidisciplinary nature of the research spans materials science, engineering, and environmental sciences, with journals such as *Polymers*, *Sustainability*, and the *Journal of Cleaner Production* emphasizing sustainability themes. This analysis covers key aspects such as keyword co-occurrence, overlay visualizations, co-authorship networks, and the distribution of publications by year, research area, and journal. The findings underscore the evolving research landscape of sustainable FRPs and highlight the ongoing need for life cycle assessments and interdisciplinary collaboration. [ABSTRACT FROM AUTHOR]

The ultimate load-carrying capacity of concrete-filled steel tubular (CFST) columns exposed to monotonic loadings can be greatly increased by strengthening those columns, and the occurrence of the steel tube's outward buckling can be postponed. The current research aims to study the possibility of improving the structural characteristics of CFST columns exposed to cyclic loadings in terms of lateral load capacity and absorbed energy by strengthening them with different patterns of fiber-reinforced polymer (FRP) sheets. The ABAQUS software was used to create a three-dimensional (3D) non-linear finite element model (FEM) to simulate the behavior of FRP-strengthened CFST columns exposed to monotonic and cyclic loadings. After ascertaining the accuracy of the proposed model's results in successfully predicting failure patterns and lateral loads compared to the experimental results of tested specimens available in the literature, the model was used to create a parametric study. The parametric study focused on the impacts of the thickness, location, and length of the strengthening sheets on the failure pattern, lateral load-carrying capacity, stiffness, cumulative energy, absorbed energy, and viscous damping factor of the CFST columns exposed to cyclic loadings. The results revealed that the un-strengthened specimen displayed a maximum lateral load of 185 kN and a viscous damping factor of 45.2% at a lateral drift of 5.7%. On the other hand, strengthening the CFST column using five layers of FRP sheets exhibited the highest lateral load of all investigated columns (50% more than the un-strengthened specimen). Additionally, at a lateral drift of 5.7%, the decrease in viscous damping factor of CFST specimens due to strengthening using 1, 2, 3, 4, and 5 layers of FRP sheets with respect to the control specimen was 7.9%, 14.9%, 20.8%, 27.7%, and 30.3%, respectively. [ABSTRACT FROM AUTHOR]

A sufficient understanding of the failure mechanisms that govern the mechanical behavior and failure modes of natural fiber composites is essential. In this regard, acoustic emission (AE) is a potential technique to monitor the mechanical behaviour and to provide the required information about the failure mechanism of natural fiber-reinforced polymer composites. The purpose and novelty of this study is to investigate for first time, the fracture behaviour of banana/ramie/epoxy composites under a 3-point bending test. During the test procedure, the AE parameters were recorded to evaluate the crack growth from the initial crack to the final fracture of the specimen and to determine the damage locations. AE parameters, such as amplitude, frequency, cumulative hits, and AE energy distributions, were used to identify the failure mechanisms associated with matrix cracking, delamination, fiber-matrix debonding, and fiber breakage. Based on these findings, the cumulative effect of AE events (counts/hits) represents the stress risers that cause failure in the specimen. Because natural fiber composites are brittle materials, they weaken when subjected to tensile loads. For this reason, the outermost bottom layer experienced more failure than the compressive layers during the bending of the specimen. The failure modes were studied using scanning electron microscopy. It was observed from the AE activity that the stress level at the crack initiation is 10–15% higher than the stress magnitude at the fracture stage. [ABSTRACT FROM AUTHOR]

The development of eco-friendly materials is a challenging one in the research field. Natural fibers are more accessible, biodegradable, inexpensive, and less dense. They offer fewer health risks and are eco-friendly compared to synthetic fibers. Natural fiber-reinforced polymer composites are new, eco-friendly materials with excellent mechanical and practical applications. Adding biofillers to composites improves strength and will replace synthetic materials. Utilizing cellulose as a filler for a natural starch matrix is an effective way to reduce the environmental impact of non-biodegradable materials. This study covers the influence of natural Borassus flabellifer flower microcrystalline cellulose (BFF MCC) fillers on banana fiber-reinforced polymer matrix composites. Fourier-transform infrared spectroscopic peaks at 2357, 1730, and 1245 cm-1 were absent. This indicates that the amorphous proportion of banana fiber mat/BFF MCC-reinforced hybrid composites decreased. At 1% BFF MCC, thermogravimetric examination revealed an increase in the peak temperature of maximum degradation (389.6 °C). The hybrid banana composite's tensile strength (31.36 ± 4.39 to 39.83 ± 3.07 MPa) and flexural strength (71.05 ± 2.66 to 82.4 ± 1.66 MPa) were also improved after adding 3% BFF MCC as filler material. The primary objective is to evaluate the suitability of fiber-reinforced hybrid polymers with natural fillers for future engineering applications such as automotive parts, construction materials, 3D printing, etc. In addition, this study investigated how the reinforcement of microcrystalline cellulose can result in a material with enhanced performance as well as its mechanical characteristics (XRD, FTIR, TGA, and SEM characterization). [ABSTRACT FROM AUTHOR]

Among national infrastructure facilities, electric power facilities are very important sites that must maintain their functions properly even during a natural disaster or during social crises. Therefore, seismic design is required when necessary for major electric power facilities that have a significant impact when damaged in the event of an earthquake. In electric power facilities, bushings are generally installed in devices or structures. Therefore, ground acceleration can be amplified through devices, such as transformers, or sub-structures. Among various electric power facilities, cable terminations are representative cantilever-type substation facilities consisting of a bushing, a sub-structure, and support insulators. The bushings of cable terminations are generally made of porcelain or fiber-reinforced plastic (FRP) materials, and they may have different dynamic characteristics. This study attempted to estimate the acceleration amplification ratio in the main positions of cable terminations considering the materials of bushings. For two cable terminations with different specifications and bushing materials, three-axis shake table tests were conducted in accordance with IEEE 693, which includes a seismic performance evaluation method for a power substation facility. The acceleration amplification ratios at the top of the bushing, mass center, and top of the support structure were estimated using the acceleration responses of each cable termination. They were then compared with the acceleration amplification factors presented in design standards. Consequently, the acceleration amplification ratio of cable termination with an FRP bushing was lower than that of the cable termination with a porcelain bushing. [ABSTRACT FROM AUTHOR]

Among the many methods of joining different materials, gluing is characterized by its most specific nature. In comparison with, for example, welded, screwed, or overlapped connections, a glued connection depends on the largest number of factors. Many of them are related to the phenomenon of adhesion, which is complicated by definition. It has many shapes and forms, and its existence determines not only the durability of such a joint but also the possibility of its execution. Epoxy polymers are among the most commonly used adhesives. Their extremely good parameters can be easily modified by additives in the form of fillers. Compatibility between the filler and the adhesive allows for further improving the adhesive parameters in the glued joint. However, in order to effectively combine the adhesive and the filler, different, often specific mixing methods must be used. The following study presents the results obtained in an experimental research program, the aim of which was to increase the adhesion of epoxy resin to a properly prepared concrete substrate. As a method to increase the final adhesion, the addition of microsilica and carbon nanotubes in an experimentally determined amount was selected. The use of sonication as a mixing method together with cavitation allowed for improving the parameters which determine the final adhesion of the adhesive to concrete. The parameters which were selected to describe the course of changes in the adhesion of the adhesive to the concrete substrate were the viscosity, free surface energy, surface parameters, adhesion, and SEM images of the tested resin in various modification configurations. The obtained results make it possible to form stronger and more durable adhesive joints during the reinforcement of concrete structural elements using fiber-reinforced polymer (FRP) composites. [ABSTRACT FROM AUTHOR]

In the current work, the dynamic and buckling properties of hybrid fiber-reinforced polymer composite beams are investigated. The hybrid composite beam is made of polyester matrix, carbon fiber, and jute fiber. The mechanical characteristics of carbon/jute/polyester composites were examined using ASTM standards. Experimental dynamic analysis was performed on jute, carbon, and hybrid carbon/jute composite beams. The validity of a finite element (FE) model based on higher-order theory was examined, and it exhibits outstanding agreement for composite beams when compared to experiments and literature. The hybrid composite beams have a considerable impact on structural stiffness when compared to neat jute/polyester composite beams. In this work, the effects of end conditions, taper angles, and composite layers are also investigated in relation to the dynamic and buckling properties of uniform and tapered hybrid carbon/jute/polyester composite beams. The findings imply that hybrid composites can be a superior substitute material for automotive applications. [ABSTRACT FROM AUTHOR]

State‐of‐the‐art organosheets suffer from several shortcomings that limit their applicability in high‐performance materials, mainly due to the imperfect combination of glass fibers and polymer. To overcome these issues, a novel hybrid fiber is presented, in which every single filament consists of a glass core and an individual, thin, thermoplastic polymer coating. Those fibers can immediately be consolidated into organosheets, without the necessity of the critical combination step. Production is realized by an ultra‐rapid inline coating of the filaments, incorporated into a standard spinning system. This solvent‐free process is realized by coating of the fibers with a tailor‐made, monomeric precursor solution, which is radiation‐polymerized immediately after application. Within fractions of a second, the coating layer is thus solidified, before coiling of the hybrid fiber. Due to the very low thickness of the coating and specific formulation of the precursor, tackless layers can be achieved before the coiling, even at industrial spinning speeds. Highlights: Glass fibers are coated with a thermoplast via in situ polymerization.A precursor is developed which polymerizes in 100 ms.Glass fibers are coated completely with thermoplast by using a UV tunnel.Spinning velocities of about 600 m/min can be achieved.Hybrid fibers are consolidated into glass fiber‐reinforced plastics (GFRP). [ABSTRACT FROM AUTHOR]

AbstractCarbon fiber-reinforced polymer (CFRP) and engineered cementitious composites (ECC) are commonly used to reinforce structural elements, with proven effectiveness in enhancing the performance of concrete-filled steel tube (CFST) columns as shown in prior experimental studies. However, the complex interaction among the components of the reinforced columns, including CFRP, ECC, the steel tube, and the concrete core, as well as the underlying mechanical mechanisms, remain insufficiently understood. This research aims to fill these gaps by developing a 3D finite element (FE) model of circular CFST short columns reinforced with CFRP grid-reinforced ECC for comprehensive numerical analysis. Sensitivity analyses are conducted to determine the governing parameters in the numerical simulation, including mesh size and critical plasticity parameters for the concrete damage model, such as the ratio of the second stress invariant on the tensile meridian to that on the compressive meridian (Kc), and the dilation angle (ψ) for both the concrete core and ECC. The model also accounts for the effects of concrete confinement provided by the CFRP grid-reinforced ECC layer and the circular steel tube. The accuracy of the FE model is validated against existing experimental data, and the model is subsequently used to investigate the behavior of reinforced CFST columns under varying geometric and material properties. The study examines failure modes, axial load-displacement responses, stress distributions, and the contribution of each material component to the load-bearing capacity of the strengthened columns. The results indicate an increase in ultimate axial strength ranging from 13% to 20% for the reinforced CFST columns. While the compressive strength of the ECC has a moderate effect on axial resistance, increasing ECC thickness, concrete strength, and steel tube yield strength significantly enhances the columns’ load-bearing capacity. Finally, a novel design model is proposed and validated, which accounts for the confinement effects provided by the CFRP grid and ECC on the concrete core. [ABSTRACT FROM AUTHOR]

This study utilized Calamus tenuis fiber as reinforcement in fiber-reinforced polymer composites, focusing on the structural, crystalline, thermal, tensile, and morphological properties of Calamus tenuis fiber-reinforced epoxy composites (CTF/Epoxy composites). The composites were fabricated using the hand lay-up method, incorporating fiber weight fractions ranging from 0 wt% (neat epoxy) to 25 wt%, increasing in 5 wt% increments. FTIR spectroscopy identified the chemical compounds and functional groups, while XRD analysis confirmed that the crystalline structure of the composites remained unchanged with the addition of Calamus tenuis fibers. Thermogravimetric analysis (TGA) revealed that the 10 wt% CTF/Epoxy composite exhibited the highest thermal stability among the tested compositions. Differential Scanning Calorimetry (DSC) analysis indicated an increased glass transition temperature (Tg) in the 10 wt% CTF/Epoxy composite, further confirming improved thermal stability. Notably, the 10 wt% fiber content led to significant improvements in tensile properties, with tensile strength increasing from 17.5 ± 1.42 MPa to 21.08 ± 1.03 MPa, and Young's modulus rising from 2.53 ± 0.12 GPa to 2.84 ± 0.09 GPa. Scanning Electron Microscopy (SEM) demonstrated enhanced fiber-epoxy bonding, while Atomic Force Microscopy (AFM) indicated increased roughness with higher fiber loadings. Overall, the 10 wt% CTF/Epoxy composite shows substantial potential for structural and infrastructure applications. [ABSTRACT FROM AUTHOR]

This study investigated the internal stress distribution of unidirectional fiber-reinforced plastics (UD-FRP) at the micro level using principal component analysis (PCA). The composite material was simulated using a representative volume element model together with the embedded cell approach. Two fundamental quasi-static load cases, transverse and longitudinal tensile deformation, were considered. The experimental results show that mechanical failure occurred at 2.15 ± 0.06% transverse tensile strain and at 1.52 ± 0.07% longitudinal tensile strain. Furthermore, the undamaged state and a combination of matrix and interface damage, as well as fiber breakage, were simulated. From the simulations, the octahedral shear stress and octahedral normal stress were computed at the integration points of the matrix elements, constituting what is known as the octahedral stress field. A modification on the PCA to obtain mesh-independent eigenvalues is presented and was used to investigate the effects of damage events on the octahedral stress field. The results indicate that each damage mechanism had a distinct signature in the redistribution of the stress field, characterized by specific changes in the eigenvalues and orientation of the principal component (θ1). Furthermore, the PCA suggests that the accumulation of matrix damage began to be relevant at the 1% strain, while fiber breakage began at an average longitudinal strain of 0.98 ± 0.12%. Additionally, it is shown that the first principal component served as an indicator of the predominant stress state of the stress field. This investigation suggests that the PCA can provide valuable insights regarding the complex damage mechanisms of UD-FRP that may not be captured by conventional mechanical analysis. [ABSTRACT FROM AUTHOR]

High-density polyethylene (HDPE) has emerged as a promising alternative to fiber-reinforced plastic (FRP) for small vessel manufacturing due to its durability, chemical resistance, lightweight properties, and recyclability. However, while thermoplastic polymers like HDPE have been extensively used in gas and water pipelines, their application in large, complex marine structures remains underexplored, particularly in terms of joining methods. Existing techniques, such as ultrasonic welding, laser welding, and friction stir welding, are unsuitable for large-scale HDPE components, where extrusion welding is more viable. This study focuses on evaluating the impact of key process parameters, such as the preheating temperature, hot air movement speed, and nozzle distance, on the welding performance of HDPE. By analyzing the influence of these variables on heat distribution during the extrusion welding process, we aim to conduct basic research to derive optimal conditions for achieving strong and reliable joints. The results highlight the critical importance of a uniform temperature distribution in preventing defects such as excessive melting or thermal degradation, which could compromise weld integrity. This research provides valuable insights into improving HDPE joining techniques, contributing to its broader adoption in the marine and manufacturing industries. [ABSTRACT FROM AUTHOR]

The fiber-reinforced polymers (FRP) bar is a promising solution to problems caused by steel rebar corrosion in concrete. To assess the service life of the FRP bar based on accelerated test results, it is crucial to have a reliable model. Here, a modified exponential (MEP) model is proposed based on the Avrami equation. The Avrami equation provides a theoretical foundation for the empirical exponential (EP) model and does not a priori fix the power of the exposure time to one. A database containing 903 data points from 74 groups of test specimens is assembled to compare the reliability of the MEP model vis-a-vis the EP, single logarithmic, double logarithmic, and power function models. The combination of Root Mean Square Error (RMSE), the Mean Absolute Error (MAE), and the coefficient of determination (R2) criteria is proposed for assessing model reliability. It is shown that in certain cases the combined criteria, versus R2 alone, significantly increase the number of test groups meeting the acceptable performance limit. Observed test data aberrations are found to have minor influence on the results of the EP model, but they significantly influence the results of the other four models. The EP model generally predicts the lowest activation energy and the smallest strength retention for similar groups of bars, while the predicted values of the other four models exhibit a relatively small difference. The difference between the predicted strength retention values of the EP and MEP models shows an increasing trend with the increase of the absolute value of (1 − n), where n is the power of the exposure time in the MEP model. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymers (FRPs) are increasingly being used as substitutes for traditional metallic materials across various industries due to their exceptional strength-to-weight ratio. However, their orthotropic properties make them prone to multiple forms of damage, posing significant challenges in their design and application. During the design process, FRPs are subjected to various loading conditions to study their microscopic damage behavior, typically assessed through scanning electron microscopy (SEM). While SEM provides detailed insights into fracture surfaces, the manual analysis of these images is labor-intensive, time-consuming, and subject to variability based on the observer's expertise. To address these limitations, this research proposes a deep learning-based approach for the autonomous microscopic damage assessment of FRPs. Several computationally efficient pre-trained deep learning models, such as DenseNet121, NasNet Mobile, EfficientNet, and MobileNet, were evaluated for their performance in identifying different damage modes autonomously, thus reducing the need for manual interpretation. SEM images of FRPs with five distinct failure modes were used to validate the proposed method. These failure modes include three fiber-based failures such as fiber breakage, fiber pullout, and mixed-mode failure, and two matrix-based failures such as matrix brittle failure and matrix ductile failure. The entire dataset is divided into train, validation, and test sets. Deep learning models were established by training on train and validation sets for five failure modes, while the test set was used as the unseen data to validate the models. The models were assessed using various evaluation metrics on an unseen test dataset. Results indicate that the EfficientNet model achieved the highest accuracy of 97.75% in classifying the failure modes. The findings demonstrate the effectiveness of employing deep learning techniques for microscopic damage assessment, offering a more efficient, consistent, and scalable solution compared to traditional manual analysis. [ABSTRACT FROM AUTHOR]

This paper presents a progressive damage model (PDM) based on the 3D Hashin failure criterion within the ABAQUS/ExplicitTM 2021 framework via a VUMAT subroutine, enhancing the characterization of the mechanical performance and damage evolution in the elastic and softening stages of composite materials via the accurate calculation of damage variables and accommodation of non-monotonic loading conditions. In the subsequent multi-level verification, it is found that the model accurately simulates the primary failure modes at the element level and diminishes the influence of element size, ensuring a reliable behavior representation under non-monotonic loading. At the laminate level, it also accurately forecasts the elastic behavior and damage evolution in open-hole lamina and laminates, demonstrating the final crack band at ultimate failure. This paper also emphasizes the importance of correct characteristic length selection and how to minimize mesh size impact by selecting appropriate values. Compared to ABAQUS's built-in 2D model, the 3D VUMAT subroutine shows superior accuracy and effectiveness, proving its value in characterizing the mechanical behavior and damage mechanisms of fiber-reinforced polymer (FRP) materials. The enhanced 3D PDM accurately characterizes the softening processes in composite materials under simple or complex stress states during monotonic or non-monotonic loading, effectively minimizes the mesh dependency, and reasonably captures failure crack bands, making it suitable for future simulations and resolutions of numerical issues in composite material models under complex, three-dimensional stress states. [ABSTRACT FROM AUTHOR]

Based on existing experimental data and analysis, seven different fiber-reinforced polymer (FRP) bar models including carbon fiber-reinforced polymer (CFRP), basalt fiber-reinforced polymer (BFRP), aramid fiber-reinforced polymer (AFRP), glass fiber-reinforced polymer (GFRP), GFRP and CFRP combined (G–C), GFRP and AFRP combined (G–A), BFRP and CFRP combined (B–C), and BFRP and AFRP combined (B–A) were established. Finite element simulation analysis was conducted on seven different FRP bar combinations under static load bending tests. The flexural behavior of the specimens reinforced with different FRP bar combinations and their influencing factors were analyzed. The results showed that using AFRP as the reinforcement material for FRP composite bars in FRP reinforced concrete beams cannot effectively enhance the overall load-carrying capacity of the composite bars. The combination of CFRP with GFRP and BFRP bars significantly increases the stiffness of the FRP bar structure and improves the structural load-carrying capacity of the concrete beams. [ABSTRACT FROM AUTHOR]

To evaluate the axial compressive performance of the hollow sandwich GFRP-concrete-steel double-skin tubular columns (DSTC), 15 composite column specimens were produced to study the effect of various design variables. And the study presents a rational and accurate finite element (FE) model that provides a detailed working mechanism of the DSTCs, leading to the enrichment of parametric research and the creation of an extensive database. Based upon the unified strength theory of double shear, limit equilibrium theory, and superposition theory, the study evaluates and compares the effectiveness of different bearing capacity calculation models. With each added millimeter in the thickness of the GFRP tube, the ultimate bearing capacity of the DSTC specimen increased by 23.6% and 61.8%, respectively, compared to that of the 1.5 mm thick GFRP tube sample. The lower the hollow ratio of the DSTC section, the higher its ultimate bearing capacity. Specimens with a hollow ratio of 0.3 and 0.43 showed an ultimate bearing capacity 1.4 times and 1.25 times higher, respectively, than those with a hollow ratio of 0.6. The study observes a relatively high level of precision in the results of the ultimate equilibrium theory, with an average error rate of 20%. [ABSTRACT FROM AUTHOR]

Beam–column joints are critical in reinforced concrete moment-resisting frames. Adequately designed beam–column joints support the plastic hinging of the adjoining beams under seismic actions and transfer gravity loads, both of which are critical for the energy dissipation and survival of buildings during earthquakes. Beam–column joints in exterior frames of buildings are occasionally eccentric such that the axes of the beam and column are offset from one another. Previous work on eccentric joints indicates an inferior seismic behavior compared to concentric joints. Beams flush with the concrete column represent the maximum eccentricity considered in previous studies. However, beam–column joints with higher eccentricity where the beam section only partially intersects with the column exist in some buildings. The impact of this notably high beam eccentricity on the seismic performance of joints has not been documented in studies published in open literature to the knowledge of the authors. This paper presents an experimental study focused on a joint geometry characterized by a beam eccentricity exceeding half the column width. The objective is to lay the groundwork for understanding how such eccentricity affects the seismic performance of reinforced concrete beam–column joints. The experiments involved reversed cyclic testing of four large-scale beam–column cruciform assemblages. The results indicate that the joints had sufficient core capacity to develop plastic hinges in the beams. In addition, the tested assemblies exhibited highly ductile behavior and considerable postpeak energy dissipation. The inadequacies of the design documents on such joints are discussed in detail. Based on the findings, a suggestion was made to evaluate the shear strength of such joints. Finally, a strengthening scheme using fiber-reinforced polymer patching was evaluated to improve the seismic performance with minimal work on the joint. The strengthened joint showed similar behavior with a higher energy dissipation compared to the unstrengthened joints. [ABSTRACT FROM AUTHOR]

Double-skin tubular columns (DSTCs) are promising modern columns with concrete sandwiched between fiber-reinforced polymer (FRP) and steel skins. Typical concentrated and localized failure modes in DSTCs can be constrained or delayed when stiffened inner steel tubes are used. DSTCs with circular cross sections are better investigated in the literature than scarcely studied square shapes, especially with variations of stiffened inner steel tubes. This study examined the nonlinear confined concrete behavior in stiffened DSTCs with square-shaped glass FRP as outer skins and stiffened steel tube as inner skins. The documented test results on 26 DSTCs were used to formulate a new analysis-oriented, axial stress–strain model for confined concrete. Primary model-formulation parameters were evaluated using a genetic algorithm (GA)–driven error minimization. A detailed parametric study was then performed on square DSTCs by incorporating the proposed stress–strain constitutive relationship for confined concrete in nonlinear finite-element analysis. The variations used in the parametric study included the shape of the inner steel tube (circular versus square), unconfined concrete strength, and flat-stiffener geometry characteristics (i.e., quantity, configuration in terms of thickness versus the number of stiffeners for similar total cross-sectional area, and its cross-sectional dimensions). Analytical results were finally used to propose a new load-bearing equation for estimating the axial load capacity of square DSTCs having stiffened inner steel skins of circular or square shapes. The proposed formulation showed better accuracy (about 2% on average and 14% maximum disparity with refined ultimate axial load capacities of DSTCs used in this study) than the existing prediction models. [ABSTRACT FROM AUTHOR]

Iran is located in a seismically active region, which poses a significant threat of destructive earthquakes. Given the dense populations they support and their structural importance, schools demand resilience across various dimensions. In this study, we aimed to evaluate the seismic performance of schools in Khorramabad, Lorestan, Iran, by obtaining resilience curves. The research involved a thorough analysis of retrofitting options for a specific school, identified through a review of data from Lorestan province. Three retrofitting options were considered: (1) bracing, (2) friction dampers, and (3) utilization of fiber-reinforced polymers (FRP) in the columns. The structure was modeled and designed using suitable software before and after implementing the retrofitting options. Incremental dynamic analysis (IDA) was conducted using recommended ground motions (including 10 ground motions for near and far fields). Subsequently, a risk analysis of the study area was performed, and a comparison was made between damage and fragility curves under different conditions; this included an assessment of potential damage in future earthquakes. The results demonstrated the efficacy of the analysis method in evaluating the seismic performance of buildings. Last, the study highlighted the building's response under different earthquake intensities and confirmed that the maximum capacity determined closely corresponded to findings from other nonlinear analyses. This approach was proven to be highly effective in assessing a building's behavior and ultimate capacity in the face of earthquakes. [ABSTRACT FROM AUTHOR]

Steel plate girders are susceptible to web buckling due to slender web. This phenomenon creates an undesirable failure mode and limits their ultimate load capacity. The use of fiber-reinforced polymer (FRP) composite materials offers a good prospect of strengthening the slender web of plate girders to avoid web buckling. This paper presents the details of experimental testing of steel plate girders with nonrigid end posts. These girders were tested in three-point bending. The end shear panels of the girders were strengthened by glass FRP (GFRP) pultruded section stiffeners or glass fiber fabric composite. GFRP stiffeners were applied either vertically or along the compression diagonal in the shear panel. All strengthened panels failed by web shear buckling associated with a breakdown of the employed strengthening scheme. It was found that the shear capacity of the panel remained unchanged by replacing the steel stiffener with GFRP stiffeners in the end panel. The critical buckling load of the strengthened panels increased up to 44% compared to the unstrengthened panel. The shear capacities of the panels strengthened by the glass fabric composite and diagonal GFRP pultruded section were the highest and similar to each other. Both these panels resisted a 50% larger shear compared to the unstrengthened panel. The positions of the plastic hinges in all tested panels were the same due to the same ratio of panel length and depth of the web. [ABSTRACT FROM AUTHOR]

This paper presents a finite element (FE) model of reinforced concrete two-way slab strengthened using fiber-reinforced polymer (FRP) sheets. This model was validated against experimental data from the literature and it showed acceptable prediction accuracy. Although carbon-FRP (CFRP) is the most commonly used composite in repairing and strengthening reinforced concrete structures, it is important to consider other types of FRP composites such as the eco-friendly basalt-FRP (BFRP) and the newly developed polyethylene terephthalate-FRP (PET-FRP). Therefore, the validated FE model was utilized to perform a parametric study for slabs having different values of concrete compressive strength (ranging from 20 to 80 MPa) and strengthened with other types of FRP. The results show that CFRP provides the highest strength enhancement with a 34.5% increase in the ultimate load, while PET-FRP provides the lowest improvement with an increase of 11.2%, compared with unstrengthened slab. The results also show that the concrete compressive strength (fc') has moderate influence on the ultimate load. For example, increasing fc' from 20 MPa to 80 MPa increased the predicted ultimate load for CFRP-strengthened slab from 15% to 62%. The FE model provides a suitable prediction for the ultimate strength and deformability of the strengthened two-way slabs that helps in better understanding of the performance of strengthened slabs and allows engineers to optimize design parameters. [ABSTRACT FROM AUTHOR]

This study examines the pull-out behavior of timber elements connected using dowelled joints (type 1) and axially loaded screws (type 2), focusing on numerical predictions and experimental validation under various conditions. Different screw diameters, configurations, material properties, and corrosion resistance are examined. Pull-out tests demonstrated that type 2 connections, particularly using 10 mm and 14 mm screws, outperformed traditional dowelled joints in terms of load capacity. Numerical analysis based on Eurocode 5 showed close alignment with experimental results, particularly for screws with actual thread diameters of 5.2 mm and 6.2 mm, with minor deviations attributed to material variability. The finite volume method (FVM), implemented using the Geodict ElastoDict software, provided additional insights into the mechanical behavior of the connections. Corrosion resistance tests confirmed the long-term durability of fiber-reinforced polymer (FRP) components in saline environments, with negligible material degradation after 28 days of exposure. The 10-90-6 screw configuration was identified as the most efficient, balancing load capacity, displacement, and material cost. These findings highlight the effectiveness of both Eurocode 5 and FVM-based approaches for predicting screw behavior and emphasize the importance of accounting for material heterogeneity in timber connection design. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effect of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) strengthening materials on the static and dynamic behavior of reinforced concrete (R/C) beams subjected to progressive damage. Four identical beams, each strengthened with either GFRP or CFRP, are tested under a cyclic quasi-static loading pattern. Impact hammer tests are performed for undamaged states and various damage levels of the beams. The dynamic test data are analyzed using the Enhanced Frequency Domain Decomposition (EFDD) method to estimate the dynamic characteristics of the beams. In this context, the first three vibration modes in both vertical and horizontal directions are considered. Strengthening is applied to both pre-damaged and undamaged beams, enabling a comparison of their performance before and after the strengthening procedure. Beams strengthened with CFRP exhibit a higher load-bearing capacity and stiffness but also fail at lower displacement levels compared to those strengthened with GFRP, which demonstrate more ductile behavior. Furthermore, the modal frequency ratios indicate that the first vibration mode is more sensitive to damage than the second and third modes. This study highlights the effectiveness of both strengthening materials in enhancing the structural performance of both undamaged and damaged beams. [ABSTRACT FROM AUTHOR]

Under earthquake excitations, reinforced concrete (RC) columns could be subjected to lateral drift reversals and a combination of axial forces, bending moments, and torsional effects. This paper investigates the behavior of glass fiber-reinforced polymer (GFRP)-RC columns under seismic-simulated loading, including torsion, which has not been studied previously. Seven large-scale circular GFRP-RC column-footing connections were cast and tested under various combined reversed cyclic loading configurations to examine the effects of torsion-bending moment ratio (tm), transverse reinforcement ratio, and concrete compressive strength. The test results revealed that increasing the tm reduced the lateral load capacity and deformability of the GFRP-RC column, but resulted in a more symmetric torque-twist relationship. Increasing the transverse reinforcement ratio mitigated core damage and provided additional support (for example, spiral turns) for torsion-induced tensile stresses. Moreover, increased concrete compressive strength bolstered torque capacity and torsional stiffness, while, under a tm of 0.4, it resulted in decreased twist capacity. When torsion was present, increasing the concrete compressive strength had an insignificant impact on the bending-shear response, differing from findings for GFRP-RC columns subjected to seismic loading without torsion. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) bridge columns often encounter complex combinations of loads, including flexural, axial, shear, and torsional forces, during seismic events, especially in the presence of geometric irregularities such as skewed or curved bridges, unequal spans, or varying column heights. Corrosion-related deterioration in RC structures spurred the adoption of glass fiber-reinforced polymer (GFRP) as a promising alternative to steel reinforcement. This study experimentally investigates the performance of GFRP-RC circular columns under cyclic loading, including torsion with different torsion-to-bending moment ratios (tm and longitudinal reinforcement ratios. The results showed that, with the same reinforcement ratios, the addition of torsion to cyclic bending and shear significantly altered the behavior of the GFRP-RC column in terms of mode of failure, load resistance, drift capacity, and energy dissipation. The inelastic deformability hinge shifted upward with increased tm. Higher tm accelerated stiffness degradation, while increasing the longitudinal reinforcement ratio enhanced lateral load, drift, and twist capacities. [ABSTRACT FROM AUTHOR]

Flexural strength and ductility of exclusively bonded or unbonded steel prestressed concrete (PC) members are well covered and documented in the literature and codes of practice. However, current design methods are limiting the use of hybrid (that is, a combination of unbonded and bonded steel and fiber-reinforced polymer [FRP]) tendons, particularly when using brittle material such as FRP tendons. In this paper, a general procedure for evaluating the nominal moment capacity and ductility of hybrid PC members was developed using the strain compatibility approach. The procedure is applicable for members with any combination of bonded or unbonded steel and FRP tendons. Using capacity design approach based on strain compatibility, the ductility performance of several hybrid systems with different parameters were compared. The parameters included, among others, the level of "net tensile strain" in the tension reinforcement at nominal strength adopted in ACI 318-19 as a measure of ductility, concrete compressive strength, and the newly defined hybrid prestressing ratio (HPR). HPR represents the ratio of the moment contribution of the unbonded tendons to the total moment capacity of the member with hybrid tendons. Nonlinear analysis was carried out for generating the entire load-deflection and moment-curvature responses of the different systems. The accuracy of the nonlinear analysis was verified by comparing it with available experimental data, and the analysis results were used to compare traditional curvature ductility measures of the various systems against the ductility measure specified in the ACI Building Code. A design example is provided in Appendix A to illustrate the use of the strain compatibility approach. [ABSTRACT FROM AUTHOR]

Interface shear transfer is vital to maintain the structural integrity of concrete composite elements. Therefore, shear connectors are provided at the concrete joint interface to maintain such integrity. Due to its high tensile strength and non-corrodible nature, glass fiber-reinforced polymer (GFRP) reinforcement can be used as shear connectors in composite elements, particularly those in harsh environments. Fifteen pushoff specimens were constructed and tested to failure. The specimen consisted of two L-shaped concrete blocks cast at two stages to provide the cold joint interface. The test parameters were the type, shape, and ratio of shear-friction reinforcement and concrete strength. It was demonstrated that GFRP-reinforced concrete RC) specimens with reinforcement ratios of 0.36% or more could resist the shear-friction stresses similarly to their steel-RC counterparts. Also, increasing the concrete strength increased the shear-friction capacity significantly. Moreover, the design model in the Canadian Highway Bridge Design Code resulted in very conservative predictions. [ABSTRACT FROM AUTHOR]

For the past several decades, there has been an ongoing academic challenge to understand the shear-transfer mechanism in reinforced concrete (RC) members, particularly in those with small shear span-depth ratios, also known as deep beams. Analytical uncertainty regarding shear strength inevitably increases when those deep members are strengthened in shear using externally bonded fiber-reinforced polymer (FRP) composites. This study aims to investigate the complex, interrelated effects of short shear span-depth ratios and FRP composites on RC deep beam members. To this end, the fundamental formulations of the dual potential capacity model (DPCM) are extended to RC deep members reinforced with externally bonded FRP composites. The proposed model can consider the various types of FRP composites, fiber bonding configurations, and fiber layouts, and various failure modes of concrete and FRP reinforcements are also reflected. A total of 131 shear test results of RC deep and short members with externally bonded FRP composites are carefully collected, and those are added to the existing database of RC slender members strengthened with FRP composites. On this basis, the proposed approach is verified by comparing test results with analysis results, and a reasonable level of analytical accuracy is achieved. The statistical data distribution of strength ratios between the test and analytical results is consistent across a range of shear span-depth ratios from approximately 0.7 to 4.0. Overall, the proposed DPCM approach provides a useful tool for analyzing the shear strength of RC deep beam members strengthened with externally bonded FRP composites. [ABSTRACT FROM AUTHOR]

The brittle behavior of concrete under axial compressive loading has been a persistent issue. This study investigates the effectiveness of a hybrid Basalt-E-glass confinement (B-CSM) in improving the compressive behavior of concrete. The B-CSM confinement demonstrates a considerable improvement in ultimate strength and strain capacity by over 250 and 500%, respectively, making it a favorable solution for enhancing the ductility of concrete structures. Specimens at 18.43 MPa unconfined strength, confined with 3-layer B-CSM, demonstrated a 258% ultimate strength enhancement. For 24.43 MPa specimens, the same confinement resulted in a 207% increase in ultimate strength. Specimens with an initial ultimate strain of 18.43 MPa, when confined with 3-layers, showed a notable 516% increase. Likewise, for 24.43 MPa specimens, the same confinement led to a significant 395% improvement in ultimate strain. The use of B-CSM confinement is also effective in terms of cost compared to synthetic fiber-reinforced polymer jackets, and its availability is widespread. Existing analytical models for fiber-reinforced polymer confinement were evaluated, and it was found that these models could not predict the ultimate strength and strain of B-CSM-confined concrete. Therefore, this study proposes a unique regression-based approach for predicting the various points of the compressive stress vs. strain curve of B-CSM confinement. These points are then used to trace the complete stress vs. strain curve, which matches closely with experimental results. This work contributes to the development of new design recommendations for B-CSM confined concrete structures, which can enhance the performance of concrete structures and potentially reduce construction costs. [ABSTRACT FROM AUTHOR]

The objective of this study is to enhance the efficiency of urban air mobility (UAM) air transportation by determining the optimal design, materials, and processes of seven different manufactured fiber-reinforced plastics (FRP), and to confirm their applicability for next-generation UAM aircraft seats. Structural designs for the aircraft seat models were carried out using carbon fiber-reinforced plastic (CFRP), glass fiber-reinforced plastic (GFRP), and GFRP chop materials, employing Autoclave, Hot-press, and vacuum-assisted resin transfer molding (VaRTM) processes, resulting in a total of seven FRP configurations. It was confirmed that CFRP seats were 50% lower weight than aluminum models, while GFRP seats showed a 30% reduction. Although Autoclave processing resulted in the highest tensile strength at 985 MPa, VaRTM processing also produced strength levels comparable to Autoclave processing. Structural integrity assessments of the seat models, utilizing the Korean aviation standards (KAS), confirmed that the designed seat models exhibited no failure or deformation under the conditions required by the technical standards. This study provides insights into the potential application of the seven types of FRP materials in the design of aircraft seats, offering weight reduction benefits and meeting the structural integrity requirements outlined by KAS. [ABSTRACT FROM AUTHOR]

Web openings in deep RC beams significantly reduce the strength and stiffness of these structural elements. To overcome this, strengthening practices have been implemented by incorporating various techniques. Several studies have reported on the application of externally bonded fiber-reinforced polymer (FRP) techniques. In contrast, research on use of steel materials, such as steel plates or bars, for strengthening is limited. Therefore, this study applied a carbon fiber–reinforced polymer (CFRP), steel plates, and steel reinforcement to investigate the importance of steel in this area of strengthening. The effects of the opening configuration, installation of the strengthening material, and thicknesses of the CFRP and steel plates were investigated. The application of CFRP, steel plates, and steel reinforcement enhanced the load-carrying capacity of the RC deep beams. Strengthening via steel reinforcement resulted in the maximum improvement among all the installation techniques, except when the CFRP and steel plate thicknesses were increased. Furthermore, maximum improvement was observed when the strengthening material was applied around the outer surface of the opening, compared with the other installation techniques. [ABSTRACT FROM AUTHOR]

This study investigates a novel retrofitting technique to prevent premature axial failure and collapse of RC walls during earthquakes, attributed to inadequate compressive strain capacity in boundary regions. The technique involves fiber-reinforced polymer (FRP) confinement using laminate and anchors. To assess its effectiveness, four full-scale RC walls retrofitted with FRP and two reference walls were tested under consistent axial loads and reversed cyclic lateral loads. The experiment examined various variables, including axial load ratio, anchor spacing, anchor cross-sectional area, confinement type, number of confinement units, and confinement zone depth. The findings revealed that FRP confinement significantly enhanced the strain capacity of concrete in the boundary regions, preventing axial failure and instead causing failure controlled by reinforcing bar fracture, resulting in up to a 100% increase in wall drift capacity. Although FRP confinement had little effect on the equivalent viscous damping ratio, it substantially extended energy dissipation by improving the drift capacity. The study suggests that in design processes, FRP confinement should maintain the stress–strain condition of the boundary regions at a prepeak condition until reinforcing bar fracture occurs, to avoid axial failure. [ABSTRACT FROM AUTHOR]

Ductility is an important structural design characteristic for ensuring that any overloaded structural member or structure shows visible warnings of an incipient or impeding failure through large deformations and/or excessive cracking. At present, there is a knowledge disparity in quantifying the flexural ductility of prestressed concrete (PC) systems, particularly with the evolution of prestressing reinforcement to incorporate nonmetallic fiber-reinforced polymer (FRP) tendons. There is a need to adopt innovative prestressing technologies and new prestressing systems to facilitate the use of partially bonded, unbonded (externally and internally), and hybrid tendons in which the prestressing reinforcement may consist of bonded–unbonded steel or bonded–unbonded FRP tendons or a combination of both. With the development of new prestressing systems incorporating FRP tendons, accurate evaluation of the ductility of these systems has become a serious concern. In an attempt to converge on a rational approach for evaluating the ductility of hybrid PC members, a review of the evolution of ductility measures proposed in the technical literature is carried out, covering conventional methods and ductility measures specified in design codes. Based on a critical assessment of these measures, it was found that the concept of net tensile strain offers, at present, a most rational approach for evaluating the ductility of prestressed concrete flexural members, which can be extended for hybrid PC members. Accordingly, a simple yet accurate design-oriented method is developed for quantifying the ductility of hybrid PC members using conventional measures such as curvature ductility ratio or, more importantly, using the net tensile strain concept. Practical Applications: In this study, different methods proposed in the technical literature for evaluating the flexural ductility of prestressed concrete (PC) members were reviewed and assessed, with particular focus on the applicability of these methods to hybrid PC members—those utilizing a combination of different prestressing systems and/or prestressing materials. Based on the results of this assessment, it is concluded that the net tensile strain concept used in design codes for designing ductile structural members can be extended easily and rationally to any type of hybrid PC systems. These include systems in which the prestressed tendons consist of a combination of bonded steel–unbonded fiber–reinforced polymer (FRP), bonded steel–unbonded steel, bonded FRP–unbonded steel, and bonded FRP–unbonded FRP. In analogy with the flexural strength and analysis approach adopted in design codes, a direct design-oriented method is developed, which would allow design engineers to effectively and efficiently estimate the nominal moment capacity of any type of hybrid PC systems, quantify their ductility by means of the curvature ductility index (or ratio), and establish their maximum reinforcement limits utilizing the net tensile strain concept. [ABSTRACT FROM AUTHOR]

The near-surface mounted glass fiber–reinforced polymer (NSM GFRP) technique may encounter problems such as peeling-off and premature failure of NSM GFRP. To tackle these issues, this study explores the effects of carbon fiber–reinforced polymer (CFRP) U-wraps on the behavior of NSM GFRP retrofitted RC beams. Six RC beams were tested. One beam served as the control beam, another was retrofitted with two NSM GFRP bars without U-wraps, and four beams were retrofitted with an identical configuration but incorporated 1–4 pairs of U-wraps at each beam end. The experimental results confirmed the efficiency of the NSM GFRP retrofitting technique. The U-wraps successfully prevented peeling-off failure and forced the GFRP bars to work until rupture. NSM GFRP retrofitting moderately extended the elastic branch of the load–deflection curve in comparison to that of the control beam, increased the yield load by 22.4% and the ultimate load by 32.2%. The U-wraps significantly extended the postyield branch, improving the yield load by 28.6%–30.2% and ultimate load by 50.9%–57.5% compared with the control beam. NSM GFRP retrofitting transitioned the high ductility (7.3) to moderate ductility (2.9). Meanwhile, NSM GFRP retrofitting with 1–4 pairs of U-wraps reduced the ductility to 4.9, 4.4, 4.0 (high ductility), and 3.4 (moderate ductility). NSM GFRP retrofitting and U-wrapping negligibly increased the elastic stiffness, whereas NSM GFRP retrofitting enhanced the postyield stiffness by 380.8%–763.6% compared with the control beam. Finally, sectional analyses were performed and accurately predicted the yield moment capacity of RC beams retrofitted with NSM FRP, which can be useful for structural engineers. [ABSTRACT FROM AUTHOR]

The behavior of concrete structures subjected to shear forces involves the contribution of several shear force transfer actions, such as aggregate interlock, dowel action, concrete residual tensile along the fracture process zone, and transfer through the uncracked concrete. While the contribution and interaction between these actions dependt on the shape and kinematics of the critical shear crack, the prediction models available either do not consider all these actions or are based on linear or bilinear shapes for the critical crack. In this context, this paper presents a multiaction model in which the shear actions are considered in the equilibrium of forces and moments based on the shape and kinematics of the critical shear crack. The crack shape, represented by a quadratic Bézier curve, was obtained from an optimization process using a genetic algorithm. The results obtained from the model include the location, shape, and kinematics of the critical crack and the final shear strength and the contributions of each mechanism. The outcomes of the proposed approach were compared with experimental results reported in the literature for beams without stirrups and made with fiber-reinforced concrete (FRC) and fiber-reinforced polymer (FRP) or conventional steel bars. The experimental behavior was accurately simulated, especially for the critical shape and shear strength, which presented relative errors of around 1% and 7%, indicating good agreement. In addition, the model revealed that the residual tensile stress resulting from a discrete fiber action had the highest impact on the load-bearing capacity, following the same observations as the reference studies. The proposed model represents a promising methodology to predict the shear behavior of reinforced concrete beams with various combinations of materials. [ABSTRACT FROM AUTHOR]

In structural recycling of wind turbine blades, two options are often distinguished: reuse and repurpose. The latter was the main subject of the present research carried out by the authors in a research consortium with the leading Polish industry waste recycler. The main goal of the project was to develop, design, and demonstrate the first domestic footbridge made of decommissioned wind turbine blades, taking into account the review of existing ideas. This paper presents an experimental investigation to determine the material parameters and to evaluate the structural behavior of a decommissioned wind turbine blade to be adopted for a footbridge. Terrestrial laser scanning and comprehensive material testing were performed according to ASTM standards to determine the actual blade geometry, the stacking sequence, and the mechanical properties of the blade composite materials. The experimentally determined strengths, elastic moduli, and Poisson's ratios of the composites extracted from the shell and the spar cap along the blade were very high and definitely sufficient for the fiber-reinforced polymer bridge girders. Then, a four-point edgewise bending test was performed on an 11 m section of the blade to evaluate its structural behavior: stiffness, ultimate strength, global safety factor, and fatigue life. The full-scale model of the blade bridge girder behaved linearly elastic in the full load range up to 1,250 kN of the total load, did not reach the ultimate carrying capacity, and exhibited only small local damages (laminate cracking). The results of these tests revealed that the LM 29.1-type wind turbine blades were suitable to be reutilized as main girders for a footbridge. Using the presented research results, the first bridge in the world made of decommissioned wind turbine blades was designed and installed in the late fall of 2021 in Poland. [ABSTRACT FROM AUTHOR]

Shear strengthening of existing reinforced concrete (RC) members with externally bonded (EB) fabric-reinforced cementitious matrix (FRCM) composites represents an attractive solution with respect to alternative strengthening techniques. The EB FRCM could be side-bonded, U-wrapped, or fully wrapped around the beam cross section. Compared with analogous research on EB fiber-reinforced polymers (FRPs), limited work was performed to study the contribution of the EB FRCM to the shear strength of RC beams and was mainly focused on the U-wrapped configuration. Although various analytical models to estimate the EB FRCM shear strength contribution were proposed, their accuracy and the role of different parameters on the results obtained were not thoroughly investigated. In this paper, a state of the art on side-bonded and U-wrapped FRCM shear-strengthened RC beams is provided and discussed to highlight the knowledge gaps and identify the main parameters that control the member shear strength. The accuracy of the available analytical models for the U-wrapped configuration is assessed with respect to a database of experimental FRCM shear-strengthened RC beams collated from the literature. The results obtained point out the key features that the analytical model should have to provide accurate and reliable predictions. [ABSTRACT FROM AUTHOR]

In order to determine the influence of the ondulations in fabrics on the damping properties of fiber-reinforced plastics, the structural dynamic properties of fabric- and unidirectionally reinforced plastics are investigated. The free decay behavior of flat beam-like specimens is investigated under fixed-free boundary conditions. As the material damping is consistently higher in fabric-reinforced specimens compared to unidirectionally reinforced ones, a contribution of an additionally acting mesomechanic kinematic in fabric weaves is implied. Based on a degree of ondulation, it is possible to classify the enhancement of the material damping and determine the corresponding energy dissipation. The study provides valuable quantitative relations of the additional damping effect due to the mesomechanic kinematic. Compared to the unidirectionally reinforced material, plain weave enhances the material damping by 37…52% at O˜PL=0.0133{\tilde{O}}_{{\rm{PL}}}=0.0133, whereas twill weave 2/2 enhances it by 31…40% at O˜T2=0.0098{\tilde{O}}_{{\rm{T2}}}=0.0098. The consideration of the findings contributes to a deeper understanding of the visco-elastic dynamic behavior of fabric-reinforced plastics and allows further applications in research, development, and industry.

AbstractIn this work, an attempt is made to produce a ductile construction system using natural fiber-based engineered cementitious composite (ECC) beams where the conventional longitudinal steel reinforcements are replaced using glass fiber-reinforced polymer (GFRP) bars. In total, sixteen medium-scale reinforced ECC beams were tested under an un-symmetric three-point bending configuration to generate shear failure. The parameters considered as a part of the experimental program include (a) type of longitudinal reinforcement (steel or GFRP) and (b) type of natural fiber (flax, hemp, kenaf and pineapple). In addition, a detailed analytical study was performed using the Architectural Institute of Japan (AIJ) method, and a modified equation was proposed for predicting the shear behavior of FRP reinforcement using ECC beams. Test results reveal that the use of GFRP reinforcements resulted in the reduction of peak load from 33.6% to 65.4% when compared to similar steel-reinforced R-ECC beams. However, the failure mode was highly ductile due to the excellent fiber bridging mechanism, multi-crack formation and effective stress redistribution at the crack tip. The predictions obtained from the modified AIJ method improved the accuracy of shear capacity FRP-reinforced ECC sections when compared to the experiments. [ABSTRACT FROM AUTHOR]

The damage process of composite materials, such as short fiber-reinforced plastics (SFRP), is complex. Therefore, it is necessary to accurately represent the damage process in fatigue life prediction. Herein, fatigue life prediction was conducted by combining the digital image correlation method, which is a non-destructive testing technique, with a convolutional neural network (CNN), using Xception as the network architecture. High prediction accuracy was obtained when training and testing were performed on the same SFRP specimens. In contrast, using different specimens for training and testing resulted in lower accuracy. This issue may be improved by increasing the number of specimens. The regions of interest in the model were visualized by Gradient-weighted Class Activation Mapping. Notably, the model indicated the breaking point as the region of interest from the early stages of the test. The breaking point was identified at an earlier stage by the CNN than by visual inspection, demonstrating the potential for a new method of damage observation. [ABSTRACT FROM AUTHOR]

A key challenge in the utilization of waste polyester fibers (PET fibers) is the development of fiber-reinforced composites with high filler content and the improvement of fiber length retention. Herein, the effects of a two-rotor continuous mixer and a twin-screw extruder on the structure and properties of waste polyester fiber composites were evaluated. The results revealed that the mechanical properties of the composites were improved significantly with increasing fiber content, especially when processed using the twin-rotor continuous mixer. This mixer facilitated the formation of a robust fiber network structure, leading to substantial enhancements in tensile strength, flexural strength, and heat resistance. Specifically, compared to those processed by the twin-screw extruder, with 60 wt% fibers content, the tensile and flexural strengths of specimens processed by the twin-rotor continuous mixer increase by 21% and 13%, respectively. The average fiber length in specimens processed by the twin-rotor continuous mixer was 32% longer than that in specimens processed by the twin-screw extruder, attributable to the lower shear frequency and the higher tensile ratio of the former. This blending technique emerges as an effective strategy, contributing significantly to promoting the development and practical application of waste textile fiber-reinforced polymer composites. [ABSTRACT FROM AUTHOR]