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This paper presents a new approach for damage detection in thin plates by fusing variational mode decomposition and spectral entropy (VMD-SE). In this method, after the received signal is decomposed into some intrinsic mode functions (IMFs) by variational mode decomposition (VMD), the spectral entropy ratio of the first and last IMFs is calculated for optimizing the VMD's parameters and improving its decomposition performance. Moreover, the cross-correlation coefficient between the decomposed IMFs and the reference signal is computed to separate the desired IMF, which contains more damage information. Finally, the spectral entropy of the obtained IMF is calculated as an indicator for assessing the damage's severity. The comparative analysis of the simulated signal clearly shows that only the proposed method can successfully separate the damage-related and reference signals. To verify the VMD-SE method, damage detection of two different types of damage on aluminum and composite fiber-reinforced polymer (CFRP) plates is conducted by using this new approach. The experimental results demonstrate that the parameters of VMD affect greatly its decomposition performance, and the best parameters are selected. The results also indicate that the normalized spectral entropy monotonically increases when the diameter of the through-hole or the length of the scratch increases. In addition, the correlation coefficients of the fitting lines of the plates are larger than 0.998. The experimental results of aluminum specimens demonstrate that the damage's location has an influence on the normalized spectral entropy. At last, based on the linear relationship, the severity of damage in the fourth specimen is identified. The identification results demonstrate that the relative error of the aluminum and CFRP plates is less than 7.34%, which indicates that this new algorithm by fusing VMD and spectral entropy can detect the damage size in thin plates accurately and efficiently. [ABSTRACT FROM AUTHOR]

This research systematically compares the effectiveness of Carbon Fiber-Reinforced Polymer (FRP) and Fabric-Reinforced Cementitious Matrix (FRCM) in shear strengthening of reinforced concrete (RC) deep beams featuring web openings. Through a comprehensive experimental program, six RC beams were subjected to shear tests, considering variations in the number of layers for both FRCM and FRP, employing a U-wrapping configuration. Recorded parameters include load-deflection curves, ultimate strength, cracking patterns, failure modes, and strains in steel bars, allowing a comprehensive comparison between strengthened and un-strengthened RC beams. The study compares observed shear strengths from experiments with shear capacities predicted by proposed models for RC beams strengthened with FRCM and FRP, following codes such as ACI 440.2R-17, CSA S806-12, Eurocode 2, and ACI 549.4R-20. Increasing layers enhanced shear strengths and post-elastic stiffness. The presence of substantial openings led to early shear cracks and reduced strength. CFRP improved shear strength by 13.99% (1-layer) and 18.12% (2-layer), while FRCM strengthened layers by 20.2% (1 layer) and 29.3% (2 layers). FRCM outperformed in strength and stiffness, while FRP excelled in ductility and concrete confinement. Experimental and calculated results varied based on ACI, CSA, and Eurocode, with ACI providing consistent and accurate results. CSA's calculation surpassed experiments, emphasizing its consideration of effective fabric design strain. [ABSTRACT FROM AUTHOR]

Motivated by a curiosity to explore the behavior of innovative arch structures enabled by the use of fiber-reinforced polymer (FRP) composites, this paper proposes a theoretical model built upon an enhanced formulation of the deflection method, broadening its scope to large-curvature problems. Traditionally, the deflection method approximates curvature as the second-order derivative of deflection, a simplification valid only for small curvatures. This limitation poses a challenge when applying the deflection method to problems involving large curvatures, a characteristic inherent in FRP-enabled arches where significant curvatures arise either initially or due to deformation. The enhanced formulation at the core of the proposed model addresses this challenge by incorporating a circular deflection function. This function posits that each deformed segment of the structural member can be represented by a circular arc, with its curvature and length related to the internal axial force and bending moment at the midpoint section of the segment. This feature facilitates the exact representation of curvature, offering the proposed model a unified approach capable of addressing both small- and large-curvature problems. The paper details the formulation and verification of the theoretical model, with an emphasis on its application to representative cases of FRP-enabled arches. [ABSTRACT FROM AUTHOR]

Bast fiber-reinforced polymer composites (BFRPs) are grabbing considerable research attention due to their assertive impact on the environment and excellence in biodegradability. Though BFRPs have excellent ecological performance factors, they also lack in some cases, such as lower mechanical, electrical, and thermal properties, due to the significant moisture absorption, minimal thermal stability, and inherent nature of bast fibers. BFRPs exhibit weaker fiber/matrix interfacial adhesion as compared to synthetic fiber-reinforced polymer composites, resulting in lower mechanical properties. Nowadays, a wide variety of fiber and matrix modification techniques are practiced improving the fiber-matrix interaction, which ultimately improves the mechanical properties. Among the fiber and matrix modification techniques, nanofiller integration is the most promising one. This study reviews the impacts of introducing carbon-based nanofillers, particularly graphene and carbon nanotubes (CNT), in diversified BFRPs. The influence of carbon-based nanofillers on the mechanical, electrical, and thermal behavior of BFRPs and their potential prospects are comprehensively reviewed. The paper concludes with the challenges and difficulties in composite processing, along with the techniques for overcoming them. [ABSTRACT FROM AUTHOR]

For slender FRP columns, predicting the global buckling critical loads is crucial in structural design. However, there is a lack of a consensus prediction method based on specialized domain knowledge. To address this issue, this study created a comprehensive database by collecting 365 experimental data related to global buckling of axially loaded pultruded FRP columns to predict buckling critical loads using such machine learning methods as extreme gradient boosting, artificial neural network, and support vector regression. The prediction accuracy and stability of the machine learning prediction methods were evaluated, and the interpretability of the features was analyzed in depth. The results show that the prediction accuracy of the traditional theoretical methods is low, while that of the machine learning methods is high. The contribution of geometric parameters to the buckling critical load is more than 80%. The contribution of material parameters to the buckling critical load is small, less than 20%. The cross-sectional moment of inertia has the most significant effect on the buckling critical load, while the shear modulus and compressive strength have a smaller effect. [ABSTRACT FROM AUTHOR]

The design of end zones to prevent severe cracking is a key requirement toward durable prestressed girders. Traditional approaches employ large amounts of steel reinforcement to attain this requirement, which may result in steel congestion. This paper investigates a hybrid girder concept that uses Ultra-High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) bars to enhance crack control and long-term durability in the end zones of prestressed girders. The objectives of this study are to quantify the UHPC zone lengths needed to restrain end zone cracks, eliminate or reduce the required amount of steel reinforcement, and investigate its replacement with CFRP bars. A finite element modeling (FEM) approach was developed for this purpose and its fidelity was validated with experimental data. The FEM results showed that UHPC zones with lengths below or equal to half of the girder depth can significantly reduce end zone cracking. CFRP bars can be added in the UHPC zones as a conservative measure to crack control, to ensure the long-term corrosion resistance of the girders. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites are particularly suitable for spring applications due to numerous advantages like lightweight design, intrinsic damping, or chemical resistance. Although there are many studies on the properties of FRPs and even some on springs made out of these materials, there is no holistic method for FRP spring design. Therefore, this article focuses on a new approach that combines all relevant design steps. This includes a spring-related overview of requirements and associated FRP properties, as well as recommendations regarding material and spring type selection with a specialization on polymer composite volute springs. Thereupon, a mountain bike rear suspension spring was designed and produced. These carbon fiber-reinforced polymer (CFRP) lightweight spring, which weighs only half of the metal spring, was examined in static and cyclic experiments. Important results of the tests are a lower spring rate than theoretically expected as well as a loss of stiffness of the spring of about 25% after 25,000 full deflections just before failure. Downhill riding tests were carried out and showed comparable driving characteristics as when using conventional steel springs. The research is a contribution to FRP spring design considerations as well as to extend the range of applications for composite springs, and especially volute springs, in the future. [ABSTRACT FROM AUTHOR]

The utilization of fiber-reinforced polymer (FRP) reinforcements in structural design is increasing due to their non-corrosive nature. However, the anisotropic features and linear elastic behavior of FRP rebars have led researchers to explore the use of hybrid combinations of FRP and steel reinforcements. Current codes and guidelines predominantly focus on the design of glass FRP (GFRP) reinforced structural elements, leaving a gap in incorporating the hybrid use of FRP-steel combinations and different types of FRP materials, such as carbon FRP (CFRP). This study conducted experimental investigations on concrete beams reinforced with GFRP, CFRP, and hybrid (GFRP-steel and CFRP-steel in combination) rebars, comparing the results with theoretical models. Ten full-scale beams were tested under monotonic loading. Test results revealed that existing codes overestimate GFRP reinforced beam displacements while underestimating CFRP reinforced beam displacements. A reduction factor is proposed for the effective moment of inertia expression given by ACI 440.11-22 to predict the deflections of CFRP reinforced and hybrid reinforced beams. The experimental data for CFRP and hybrid reinforced concrete beams align well with the predictions calculated using the proposed equations. [ABSTRACT FROM AUTHOR]

Arch action in deep reinforced concrete (RC) members has a beneficial effect on shear capacity. The Strut-and-Tie Method (STM) is one of the proposed methods for the design of steel reinforced deep beams (DBs). However, some iterations may require to obtain the optimum solution. This paper investigates the shear capacity of fiber reinforced polymer (FRP)-reinforced DBs using STM and sectional methods of Canadian Standard Association (CSA) and American Concrete Institute (ACI) design provisions. To this end, 106 FRP-reinforced DBs were compiled from the literature. It has been found that current sectional methods do not adequately account for the effects of arch. action on DBs. From this investigation, modifications were proposed in the current sectional methods to calculate the shear capacity of FRP-reinforced DBs. The proposed modifications were found to significantly improve the prediction accuracy. The sectional methods proposed by CSA and ACI were found to be better than the CSA-STM method in predicting the shear capacity of FRP-reinforced DBs.. The mean, standard deviation and coefficient of variation for the proposed CSA sectional method are 1.00, 0.28 and 28.2% and for the proposed ACI sectional method are 1.01, 0.26 and 25.6, respectively. The same for the CSA-STM method are 2.20, 0.76 and 34.4%, respectively. The proposed methods can be used to predict the shear capacity of FRP reinforced deep members. [ABSTRACT FROM AUTHOR]

The optimization of post-curing processes is crucial for enhancing the performance of epoxy-based fiber-reinforced polymers (FRP) by ensuring adequate cross-linking. This study focuses on optimizing the post-curing parameters for hybrid Ramie and Carbon fiber composites with the primary objective of improving tensile strength. Variations in post-curing temperature, post-curing time, and the number of synthetic fiber layers were systematically investigated across three levels using Taguchi design of experiments. The ultimate tensile stress was employed as the response parameter. Results indicate that post-curing temperature exerts a greater influence on tensile strength compared to post-curing time. A failure pattern of natural fiber followed by synthetic fibers was seen to happen progressively. A precise multivariable regression model was developed to predict the response for different combinations of post-curing parameters. Furthermore, employing particle swarm optimization revealed an optimal post-curing time of 12 h and an optimal temperature of 60°C. These findings contribute to the optimization of post-curing processes in hybrid fiber composites, thereby enhancing their mechanical properties. [ABSTRACT FROM AUTHOR]

The welding manufacturing process is increasingly being used as an alternative joining method to sewing for functional textiles including for medical and protective wear, high-performance reinforcement textiles for fiber-reinforced plastics, film materials, and smart textiles. Ultrasonic (US) welding technology is a universally applicable cost-effective joining method for thermoplastic membranes. A key issue with the quality of the welded seam is that many of the faults are not visible on the membrane surface. The traditional quality control of the seam cannot be performed because it is done by destructive testing methods. Therefore 100% assurance of compliance of product safety produced at a production scale is not possible. The objective of the study is to develop a nondestructive (NDT) inline testing method for the quality control of welded seams during the continuous ultrasonic welding process. Currently, the quality control of Ultrasonic (US) welded seams is performed based on sample destructive standard tests, where the quality control of complete welded seams is not ensured. The air-coupled US sensors are used to detect imperfections in the welded seam. A variety of membrane materials with base fabric made of polyester and coated with PVC coating were tested during this research. A superimposed type of seam was produced longitudinally by PVC-coated textiles with smooth surfaced anvil wheels and was welded using a welding width of 10 mm. These coated materials were provided by industrial partners and are used in diverse technical textile applications. A process-integrated NDT test method was developed. The imperfections in welded seams were identified during a continuous US welding procedure with the help of air-coupled ultrasonic sensors by developing an inline test method. A prototype to realize inline monitoring during continuous ultrasonic welding was developed and tested. Faults of different widths were artificially produced during welding. The inline monitoring of welded seams with faults was successfully performed and analyzed. The developed process can further pave the way for the development of inline monitoring of welding seams with US sensors for textile membranes joined with a continuous US welding technology. [ABSTRACT FROM AUTHOR]

Few studies combining experimental and theoretical analyses of pultruded fiber-reinforced polymer (FRP) composites are available in the literature. In this study, experimental methods and a nonlocal theoretical approach were used to investigate the flexural performance of pultruded glass-FRP (GFRP) plates. In the theoretical method used, the Eringen's nonlocal elasticity theory was adopted so that small-scale material effects on pultruded FRP composite plates were taken into account. Based on the plate theory of high-order shear deformation, the kinematic relationships of the composite plates were established. The stiffness matrix coefficients and tangential stiffness matrix were shown along with the nonlocal force vector. Also, finite element modeling was performed with the help of ABAQUS for the accuracy of experimental and theoretical results. For the analysis, a variety of laminated plate types were taken into consideration. The flexural performance was investigated utilizing flexural tests under point and distributed loads. To comprehend the behavior of the pultruded GFRP plates more fully, macro mechanical damage analyses were carried out. Numerical values were compared with experimental findings, theoretical solution results, and finite element simulation results which were found to be very similar. [ABSTRACT FROM AUTHOR]

A carbon-fiber-reinforced polymer (CFRP) sheet is wrapped around the basalt-fiber-reinforced polymer (BFRP) to develop a hybrid carbon/basalt-fiber-reinforced polymer (C/BFRP) so as to protect the basalt fibers in touch with chloride ions. Tensile testing is conducted on the BFRP and hybrid C/BFRP sheets. The effect of the durability of the fiber-reinforced polymer sheet on the behavior of the seawater–sea sand concrete (SSC) columns confined by the BFRP and hybrid C/BFRP sheets is examined using axial compression testing. The tensile strength retention and elongation at break retention of the hybrid C/BFRP sheet improve by 41% and 24% higher than those of the BFRP sheet after 12 months in seawater. The ultimate strength of the BFRP-confined SSC column decline by 40% more than those of the hybrid C/BFRP-confined SSC column respectively, after 12 months of seawater immersion, resulting from the reduction of lateral pressure provided by the BFRP and hybrid C/BFRP sheets in seawater. A formula for calculating the long-term ultimate strength and ultimate strain of the FRP-confined SSC column is proposed, and its predictions agree well with the test results. The hybrid C/BFRP sheet proves more efficient than the BFRP sheet in confining the seawater–sea sand concrete columns. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites are a class of advanced non-metallic materials featuring advantages of high strength, light weight and excellent corrosion resistance. These advantages, in conjunction with the various methods available for making curved FRP members, create a wide range of possibilities for innovating arch structures with FRP composites. However, this subject has received inadequate research attention despite the exciting prospects demonstrated by pioneer studies. This paper provides a review on this subject with the aim to build a holistic picture and engage wider research participation. The paper begins with an overview of four feasible manufacturing/forming methods (vacuum infusion, filament winding, pultrusion and active bending), with an emphasis on their capability of creating curved FRP members and potential applications in arch structures. A review is next made on previous arch projects and relevant novel concepts, which are classified into two categories (all-FRP arches and FRP-incorporating hybrid arches) with distinct functionality and targeted areas of application. On the basis of this review, directions for future development of each of the two categories are highlighted, with a number of challenges and potential solutions discussed. [ABSTRACT FROM AUTHOR]

Due to the lack of relevant research, the effect of the lateral confinement provided by stirrups and concrete cover on the bond behavior between glass fiber-reinforced polymer (GFRP) bars and concrete is ambiguous, resulting in the lack of a practical bond slip theory of GFRP bars. Therefore, it is impossible to accurately analyze the load response of GFRP-reinforced concrete (RC) structures from the stress level. In this paper, the local bond behavior of ribbed GFRP bars was systematically analyzed by the beam-end tests. The test parameters include concrete strength, stirrup spacing, and concrete cover. In addition, a bond stress-slip model considering the bonding mechanism was proposed on the basis of the beam-end tests and previous research. The results show that, the development of concrete cracks is restricted due to the existence of stirrups, and the specimens tend to fail in pull-out failure with strong confinement of stirrups. With the increase in the lateral confinement level, the failure mode of specimens transits gradually and smoothly from splitting failure to pull-out failure. Meanwhile, the peak slip of specimens with splitting failure also increases, and its maximum value does not exceed the peak slip of the corresponding specimens with pull-out failure. The confining capacity of stirrups and concrete cover was unified by a proposed parameter K. Then, a bond stress-slip model based on parameter K was established to predict the bond behavior of ribbed GFRP bars. [ABSTRACT FROM AUTHOR]

Due to increasing precipitation intensity, rising sea level, and land development, urban flooding has become a major issue in many places around the world. This research aims to develop underground storage tanks (USTs) using fiber-reinforced polymer (FRP) materials for stormwater detention, storage, and reuse. The USTs are intended to be placed underneath highway or street pavements. FRP as one of the emerging structural materials possesses several advantages including high strength-to-weight ratio and corrosion resistance. The mechanical performance of USTs has rarely been visited in the literature, the majority of which focuses on leakage issues and associated environmental problems. This paper presents detailed analyses of the mechanical performance of FRP USTs, including a laboratory test on a small-scale FRP UST and a verified finite element (FE) analysis on full-scale FRP USTs. The influences of various factors on the mechanical performance of the USTs were examined, including wall thickness, water storage, interfacial roughness between FRP and soil, and tank sizes. Both results from experiments and FE studies agree satisfactorily and reveal that (i) underground FRP UST developed tensile axial strains at the top surface at the mid-span of the tank and the side surface at the mid-height; (ii) compressive axial strains developed in most of the cap region; and (iii) large compressive circumference strains developed in the FRP UST in most locations. Insights gained from the laboratory test and the FE analysis are expected to provide a general guidance on the design of FRP USTs under road pavements for urban flooding mitigation and stormwater harvesting. [ABSTRACT FROM AUTHOR]

Considering sustainable environmental problems due to waste and the enormous potential of natural plant resources in producing natural fibers has encouraged researchers to make environmentally friendly composite materials reinforced with fibers. Several articles on using natural fibers as composite reinforcement have been collected and studied to produce this article. This article aims to comprehensively describe the physical properties, chemical composition, factors that affect fiber quality, and their relationship with mechanical properties. In the first section, we introduce the general classification of plant fibers and summarize the annual production and category of fiber origin used for fiber-reinforced composites. It then presents the parts of plants and plant species for fiber, including fruit, leaf, and seed fibers, and discuss their characteristics. Further describes the chemical compounds and physical and mechanical properties based on fiber sources. Based on our discussion, this review shows that plant fibers are very suitable as an alternative to polymer-based reinforcement materials due to low cost, renewable, and environmentally friendly composites. However, compatibility with synthetic polymers, dimensional stability and processability must be actively considered to replace synthetic fibers in various applications. [ABSTRACT FROM AUTHOR]

This paper provides an experimental study of a new fiber-reinforced polymer (FRP)-high strength concrete (HSC) hybrid beam, which consists of a glass FRP (GFRP) I-shaped profile beam strengthened with a layer of HSC on top and carbon FRP (CFRP) sheets on the web. In this study, a total of two GFRP I-shaped profile beams, two GFRP I-shaped profile beams strengthened with CFRP sheets on the web and nine FRP-HSC hybrid beams were tested under four-point bending loading. The test parameters varied for the existence of CFRP sheets, the flange width of the GFRP profile, the width of the HSC slab, the type of shear connectors and the interfacial connection method. The test results indicated that bonding CFRP sheets, increasing the flange width and HSC slab width all showed positive effect on the ultimate bearing capacity and initial rigidity. Compared with U-shaped GFRP shear keys and inverted T-shaped GFRP shear keys, the hybrid beams using steel bolts had the highest ultimate load capacity and initial rigidity. The hybrid beams using the composite-bond interface (CB) performed better than the hybrid beams using wet-bond (WB) and dry-bond (DB) interfaces. [ABSTRACT FROM AUTHOR]

Glass-fiber-reinforced polymer (GFRP) bars have been widely used as a reinforcement in concrete, and glass fibers are susceptible to reacting with alkali ions in concrete pores. Thus, carbon fibers are wrapped around GFRP bars to produce carbon/glass hybrid fiber-reinforced polymer (HFRP) bars so as to promote the durability of the internal GFRP bars in concrete. This work studies the durability of the interfacial bond between GFRP bars/HFRP bars and concrete using pullout tests. The specimens are tested after immersion in distilled water for 0, 150, 255, and 544 days. The failure of the GFRP bar–concrete composite is due to damage to the GFRP bar, while the HFRP bar–concrete composite fails because of a combination of the scratching of the HFRP bar and the failure of the concrete. Both HFRP and GFRP bars are scratched as the immersion period extends. Further, the strength of the bond between the HFRP bar and concrete is lower than that of the bond between the GFRP bar and concrete, while the bond stiffness of the HFRP bar–concrete composite is higher than that of the GFRP bar–concrete composite. The bond strength of the HFRP bar–concrete and GFRP bar–concrete composites increases in the early immersion periods but decreases after 544 days of immersion in water. The retention of the bond strength of the HFRP bar–concrete composite is superior to that of the GFRP bar–concrete composite. The carbon fiber coat is proven to improve the durability of the bond between HFRP bars and concrete in water. A formula for predicting the bond strength of HFRP bar–concrete and GFRP bar–concrete composites in water is also developed. Finally, the modeling results demonstrate that the bond strength retention of the HFRP bar–concrete and GFRP bar–concrete composite is 76% and 46% after 50 years of service time, respectively. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites have been used tremendously to repair and rehabilitate timber structures due to their formability, ease of use, and high specific strength. The bond quality between FRP and timber substrate is critical for complete composite action. In this paper, a comprehensive set of linear and nonlinear ultrasonic methods was performed to investigate the bond between carbon-FRP (CFRP) and timber. For this purpose, 126 specimens of reinforced timber were prepared. Two techniques were considered to bond CFRP and timber: (1) externally bonded reinforcement (EBR), and (2) externally bonded reinforcement on the groove (EBROG). The effect of the number of CFRP layers, adhesive types, the extent of artificial surface defects, and the depth of the groove were contemplated. By analyzing linear methods, differences in stiffness and modulus of elasticity of CFRP and timber led to velocity variation and attenuation phenomena. Higher-order harmonics were also used to investigate the nonlinear behavior of ultrasonic waves at the bond. The second harmonic generation detected surface damage at CFRP and timber bond. Single-lap shear tests were employed to determine the bond strength of CFRP and timber and evaluate the accuracy of the linear and nonlinear methods. Finally, using the linear and nonlinear features extracted from the ultrasonic response signals and available physical parameters, three artificial neural networks (ANNs) were developed to predict three important CFRP-to-timber bond characteristics quantitively: (1) to predict the groove depth, (2) to predict the volume of voids, and (3) to predict the CFRP-to-timber bond strength. The three proposed models achieved an average R 2 of 0.95, 0.96, and 0.92 in predicting the groove depth, voids volume, and bond strength, respectively. [ABSTRACT FROM AUTHOR]

To solve the instability of the compression bars in the space truss composed of GFRP tubes, a composite column with high-strength concrete (HSC) confined by glass fiber-reinforced plastic (GFRP) tube was proposed. High-strength self-compacting micro-expansive concrete with a slump greater than 255 mm was produced under normal-temperature curing conditions and confined by GFRP tubes. A mechanical performance test of the GFRP-confined HSC short column under axial compression was performed. The effects of GFRP tube types, concrete expansion agent, constraint effect, ultimate load capacity, and failure mode of the composite structure were discussed and analyzed through the test. A model of the stress-strain response of the GFRP confined HSC column was proposed. The results show that the 45° fiber-wound GFRP tube has a significant restraining effect on the HSC. The stress-strain relationship increases quadratically in a linear fashion. When the composite column was damaged, the GFRP fiber was broken and the concrete was crushed. The ultimate strength was about 1.5 times that of unconstrained HSC columns, and the loading method has less influence on the results. The expansion agent has a significant effect on the deformation performance of the composite column, and its ultimate strain was about 1.4 times that of the composite column without expansion agent. [ABSTRACT FROM AUTHOR]

Successful experimental and theoretical studies have promoted fiber-reinforced polymer (FRP) as an innovative strengthening material for metal columns in structural engineering, highlighting the necessity for an effective and reliable calculation method for such strengthened members. Here, based on existing experimental data, an advanced method using an artificial neural network (ANN) is developed to predict the axial compression bearing capacity (ACBC) of FRP-strengthened hollow section metal (FSHM) columns, where FRP strengthening includes wrapping/bonding FRP sheets/laminates; this method considers realistic conditions, incorporates a variety of parameters, and produces accurate and fast predictions. First, a multilayer perceptron (MLP) neural network was applied. By studying the optimization algorithm, learning rate, hidden vector and activation function, an optimal ANN model was established, which yielded better predictive accuracies and safety than existing calculation methods. Using the validated model, an prediction program was developed that promptly generated predictions of ACBC with a high reliability. Finally, a sensitivity analysis was performed to further assess the effects of key parameters on the behavior of FSHM columns to provide practical recommendations for their design. [ABSTRACT FROM AUTHOR]

Recent studies have proven the possibility of polymer sheet forming by incremental sheet forming (ISF) process, while there are limited studies on ISF of polymer matrix composites. Fiber-reinforced polymers (FRP) are significantly useful in industries due to their unique properties. In the current study, owing to the merits of ISF and the wide applicability of FRP, single point incremental forming (SPIF) of polyamide 6 (PA6) sheets reinforced by glass fibers (GF) is taken into account at various forming temperatures. In this regard, a fixture equipped with a ceramic infrared heating element was designed. The effect of some important parameters such as the volume fraction and orientation of fibers and the forming temperature on the formability, the thickness distribution, and the dimensional accuracy of PA6 and PA6/GF sheets is investigated. According to the results, an improvement in the formability of the composite sheet can be obtained using SPIF by increasing the forming temperature and decreasing the volume fraction of fibers. The formability of the composite sheet with the fiber orientation of [0/90] is far less than the one with unidirectional fibers. In the most of the successfully formed samples, the transverse compaction and the fracture of fibers at the part bottom, the buckling of fibers at the edge of the backing plate, and the draw-in of the sheet along the main direction of fibers can be detected. The thinning of the composite sheet is most affected by the volume fraction and orientation of fibers, while the forming temperature has the least effect. Moreover, the feasibility of SPIF of a circular flange with a wall angle of 90° from the composite sheet is assessed at elevated temperature. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) reinforcement is known to be extremely susceptible to deterioration of mechanical properties when exposed to fire. FRP grids encased with polymer mortar have received much attention lately as an efficient and fire-resistant technology for strengthening concrete structures. An experimental investigation was undertaken to examine and document the performance of carbon-fiber-reinforced polymer (CFRP) grids strengthened reinforced concrete beams under the sustained service load and the standard fire. Tests results on fire indicated that, even without any insulation, the CFRP grids strengthened beam can achieve a satisfactory fire endurance of more than 2 hours. The polymer mortar layer allows the strengthened beam to have longer fire endurance time than the un-strengthened beam, while under larger service loads. Moreover, this paper also presents a residual strength study of fire-tested beams. It has demonstrated that, if the FRP grids are able to maintain below the decomposition temperature when exposed to fire, the FRP grids strengthening system will be able to retain almost full effectiveness after cooling down. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) diaphragms play a fundamental role in seismic resistance of RC buildings. In addition to transferring the gravity loads to the beams and columns, diaphragms need to be sufficiently rigid with high shear capacity to resist and distribute the earthquake loads to the lateral force resisting system. Despite the large building inventory with under designed diaphragms to resist the shear loads from earthquakes, the number of studies investigating possible approaches to increase the in-plane shear capacity of diaphragms is limited. External equally distributed narrow strips of fiber-reinforced polymers (FRP) providing additional shear strength for RC diaphragms is proposed in this study. Five full scale RC diaphragms with overall dimensions of 4.5 m long by 1.5 m wide by 0.1 m thick were built and tested under cyclic shear loading. One out of the five specimens was tested as a reference with no strengthening, while the remaining four were strengthened with external glass or carbon fiber-reinforced polymer (GFRP or CFRP) composites. The test results showed that the FRP strengthening system effectively enhances the in-plane shear capacity of the RC diaphragms. Compared to the reference specimen, the FRP layout used for testing increased the shear capacity by up to 40%. This paper presents the test specimens, strengthening systems, and in-plane shear response of tested diaphragms in terms of failure modes, strength, and deformation. The experimental results were also compared to theoretical values determined according to the evaluation criteria in the International Code Council (ICC)-Evaluation Services (ES), Acceptance Criteria (AC) 125. [ABSTRACT FROM AUTHOR]

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper. [ABSTRACT FROM AUTHOR]

The application of near-surface mounted (NSM) fiber-reinforced polymer (FRP) for shear strengthening of RC beams has attracted abundant research in the past few decades, and a number of strength models for predicting the contribution of NSM FRPs to the shear capacity of strengthened beam have been proposed. In the first of these two companion papers, a total of 12 strength models of NSM FRP shear strengthened RC beams collected from the existing literature have been comprehensively reviewed, while the present paper aims to provide an objective assessment of these models. To this end, the experimental results of 196 RC beams strengthened in shear with NSM FRP bars/strips are collected from the existing literature, as the database for the assessment. The comparisons between the experimental results and predictions by these strength models reveal that the existing strength models all fail to give accurate predictions. The reasons for the inaccurate predictions of these models are also analyzed. [ABSTRACT FROM AUTHOR]

A novel seismic retrofit technique, known as the section reduction (SR) technique, was proposed for reinforced concrete (RC) frames to realize the strong column and weak beam hierarchy. The SR technique involves the removing a portion of concrete at the bottom zone of the beam near the joint, along with shear strengthening of the weakened area using fiber-reinforced polymer (FRP). Preliminary experimental studies on RC beams with locally reduced cross sections (i.e., a gap) have demonstrated that the inclusion of a gap can effectively weaken the negative bending capacity of a T-shaped RC beam. However, there was no finite element (FE) approach for predicting the behaviour of such RC beams. Therefore, this paper aims at establishing a reliable FE approach for T-shaped RC beams with a gap. A total of five gap sizes were examined, including three small gap sizes and two large gap sizes. The applied FRP-strengthening system consisted of the CFRP U-jackets below and on both sides of the gap. In the proposed FE approach, two concrete cracking models available in ABAQUS/Explicit, including the concrete damaged plasticity (CDP) model and the brittle cracking (BC) model, were examined. Moreover, two tensile damage models were considered. The FE results showed that the CDP model with a power law tensile damage model is suitable for specimens that failed in a flexural mode, while the BC model with secant modulus of concrete adopted is suitable for specimens failing in a shear mode. The FE results also verified that increasing the gap height reduces the negative bending capacity of the beam more effectively than increasing the gap length, and the application of the FRP-strengthening system can enhance the ductility of the weakened beam. The proposed FE approach can be used for the subsequent proposal of strength model and design method of such beams. [ABSTRACT FROM AUTHOR]

A modified rotating-angle softened truss model (RA-STM) is proposed for analyzing the torsional behavior of fiber-reinforced polymer-reinforced concrete (FRP-RC) members under pure torsion. In the modified model, a generalized tension stiffening model is developed with consideration of discrepancy in the modulus of reinforcement. Furthermore, a robust numerical model is developed by refining the RA-STM as a system of nonlinear equations instead of a trial-and-error technique, which can significantly improve computational efficiency. The proposed model is verified against the experimental results of FRP-RC members, yielding an average test-to-predicted torsional strength ratio of 1.04 with a coefficient of variation of 11.66%. Moreover, the predicted torque-twist response, reinforcement strain, concrete strain, and failure modes can closely agree with the experimental results. At last, the adapted model is utilized in a parametric study to investigate the influence of key variables on the torsional behavior of FRP-RC members. Nonlinear regression analyses are performed to propose a semiempirical strength prediction formula and balanced stirrup ratio for the FRP-RC members under pure torsion. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the bond-slip behavior and model of sand-coated deformed glass fiber-reinforced polymer (GFRP) bars embedded in ultra-high-performance concrete (UHPC). For this purpose, a total of 24 pull-out specimens were tested to failure, varying embedded lengths (2d b ,3d b ,4d b and 5d b , where d b represents the diameter of the bar) and steel fiber volume fractions (1% and 2%). It was observed that as the embedded length or fiber volume fraction increased, the failure mode changed from progressive pull out of GFRP bars (pullout failure) to rupture of GFRP bars (rupture failure). Both modes of bond failure experienced damage at GFRP-UHPC interface due to the delamination of the outside layer of GFRP bars. The bond-slip response of GFRP bars exhibited four stages: micro slip stage, ascending stage, descending stage, and residual stage. The bond strength of GFRP bars embedded in UHPC exhibited an increasing trend with the fiber volume fraction, while it demonstrated a declining trend with the increasing embedded length. For specimens with fiber volume fraction of 1% and 2%, the bond strength decreased by 24.4% and 8.0%, respectively, as the embedded length increased from 2d b to 4d b . In addition, a database consisting of 200 bond specimens including 24 test specimens from this study was established to statistically derive a bond strength equation for GFRP bars embedded in UHPC. Furthermore, a bond-slip model was proposed to describe the bond-slip behavior of sand-coated deformed GFRP bars embedded in UHPC. [ABSTRACT FROM AUTHOR]

Sustainability and durability in construction are vital considerations that involve using environmentally friendly materials and implementing efficient design and construction techniques to minimize the environmental impact. This research study investigated the structural behavior of one-way solid slabs incorporating basalt fiber-reinforced polymer (BFRP) reinforcement and geopolymer concrete to develop an environmentally sustainable and durable structural member. Six full-scale BFRP-reinforced geopolymer concrete one-way slab specimens were prepared and subjected to four-point loading tests to assess their out-of-plane shear performances. The considered experimental parameters were compressive strength of concrete (i.e., 30, 40 and 50 MPa) and longitudinal tensile reinforcement ratios (i.e., 1.20% and 2.18%). The structural performance of the slabs was carefully investigated in terms of crack patterns, failure modes, load-deflection relationships and load-strain relationships. The obtained shear resistances from tests were compared with predicted results from the Codes of Practice and design guidelines. A two-dimensional (2D) finite element (FE) analysis was conducted, considering the bond-slip relationship between BFRP rebar and geopolymer concrete. It was found that all tested specimens were governed by shear failure and had similar shear resistance for the chosen values of considered parameters. The JSCE shear design method provided the closest prediction of shear resistance of BFRP-reinforced geopolymer concrete one-way slab. The developed FE models predicted the out-of-plane shear performance with reasonable accuracy and revealed that the slip distribution of the BFRP rebar presents a sawtooth shape owing to concrete cracking. [ABSTRACT FROM AUTHOR]

Hybrid fiber-reinforced polymer (FRP)-steel reinforced concrete (RC) beams exhibit various flexural failure modes depending on different equal-stiffness reinforcement ratios, the post-yield stiffness ratio, and the bond-slip behavior. This study first develops a model for the tensile behavior of hybrid Basalt FRP (BFRP) -steel reinforced concrete chords, considering the modified Bertero-Popov-Eligehausen (mBPE) bond-slip model. The rationality of the tensile stiffening model was validated through comparisons with existing experimental tests on the axial tension of chords. Subsequently, a beam deformation correction calculation method considering ‘rigid-rotation’ was proposed. The corrected theoretical calculation of the beam’s peak load shows an error of 5.0% compared to the experimental value, while modified ultimate deformation exhibits an error of 4.7%. As the bond weakens, the theory proposed in this paper is more suitable for predicting the deformation capacity of hybrid reinforced beams. ACI 440.1R-15 underestimate deformations by approximately 77.8%, limiting the normative evaluation of deformation calculations for hybrid reinforced concrete beams considering bond slip. Finally, the influence of bond-slip parameters (τm, sm and α ) and reinforcement configurations (equal stiffness reinforcement ratio, steel/BFRP reinforcement ratio, and post-yield stiffness ratio) on beam deformation and crack width was investigated. The results indicate that the peak bond strength is a key parameter affecting crack width and deformation of the beam. The exponential rise segment parameter α and the slip sm corresponding to peak bond strength mainly influence the load level corresponding to cracking. [ABSTRACT FROM AUTHOR]

The use and disposal of traditional fiber-reinforced polymer composites is an important environmental challenge as one of the factors contributing to worsening climate change. The primary objective of this research is to synthesize thermoplastic starch (TPS) from edible banana skins which can potentially be used as a matrix to produce bio-composite films. For the synthesis of TPS, the preparation of banana peels was performed followed by plasticization to obtain the banana peels TPS. For bio-composite film fabrication, the TPS was mixed with short false banana fibers (FBF) (10-30% by weight of the film) with an electronic blender to form a uniform dispersion of the fibers in the TPS. The FBF/TPS blend was applied uniformly on the surface of the rectangular metal mold. The autoclave method has been adopted for curing and molding the bio-composite film. Then, it was hot pressed varying the temperature and pressure from 131-141 OC to 3-6 MPa, respectively, to obtain the final cured film. The specimen was then solidified or hardened at ambient temperature. Finally, optimization of process parameters, fiber content, and their interaction effects on the tear strength, tensile strength, and bending modulus of the bio composite films were conducted using response surface methodology. The results indicate that both the effects of one factor and the interaction of factors have a significant effect on the mechanical properties of composite films. The optimum processing parameters for TPS production are a temperature of 50 OC and a drying time of 24 h. The optimal result indicates that, at 30% fiber loading, the optimum processing temperature and pressure are 135.14°C and 4.33 MPa, respectively, resulting in a composite film with good mechanical properties. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) structures are commonly strengthened using externally bonded fiber-reinforced polymer (FRP) sheets. The bond between the FRP and concrete is a crucial factor affecting the strengthening effect, and debonding along the FRP–concrete interface is usually accompanied by the fracture of the underlying concrete. Therefore, it is necessary to identify the interface damage of FRP-to-concrete joints and conduct mechanical analysis. However, debonding is invisible damage that occurs inside the underlying FRP layer, which makes damage detection more difficult. To this end, this study fuses a percussion method with a deep learning framework to address the detection of such invisible lesions. Meanwhile, the visualization study provides guidance for later maintenance work. To further illustrate the hazard of the identified lesions, three-dimensional reconstruction for finite element modeling (FEM) with detected damage information based on percussion is proposed to elucidate the mechanical degradation caused by the fracture of underlying concrete. Lastly, the results of this study demonstrate that the detection, visualization, and FEM reconstruction of FRP–concrete interface damage using percussion signals has considerable application potential and is worthy of further study. [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites with nanofiller-modified polymer matrices have immense potential to improve the safety of high-risk engineering structures. These materials are intrinsically self-sensing because their electrical conductivity is affected by deformations and damage. This property, known as piezoresistivity, has been extensively leveraged for conductivity-based damage detection via electrical resistance change methods and tomographic imaging techniques such as electrical impedance tomography (EIT). Although these techniques are very effective at detecting the presence of damage, they suffer from an inability to provide precise information about damage shape, size, or mechanism. This is particularly detrimental for laminated composites which can suffer from complex failure modes, such as delaminations, that are difficult to detect. To that end, we herein propose a new technique for precisely determining damage shape and size in self-sensing composites. Our technique makes use of a genetic algorithm (GA) integrated with realistic physics-based damage models to recover precise damage shape from conductivity changes imaged via EIT. We experimentally validate this technique on carbon nanofiber (CNF)-modified glass fiber-reinforced polymer (GFRP) laminates by considering two specific damage mechanisms: through-holes (as a function of number, size, and location) and impact-induced delaminations (as a function of impact energy). Our results show that this novel technique can accurately reconstruct multiple through-holes with radii as small as 1.19 mm and delaminations caused by low velocity impacts. The reconstructed delamination shapes and sizes were shown to be in much better agreement with the actual delaminations observed using optical microscopy than is achievable by traditional EIT alone. These findings illustrate that coupling piezoresistivity with conductivity-based spatial imaging techniques and physics-based inversion strategies can enable damage shaping capabilities in self-sensing composite structures. [ABSTRACT FROM AUTHOR]

The flexural behaviour of sandwich panels with basalt fiber-reinforced polymer (BFRP) facesheets was investigated. A total of 10 sandwich panels were subjected to six-point flexural tests to simulate uniformly distributed loading conditions. The variable parameters were the core thickness (30, 50, 60 and 100 mm), core category (polyurethane [PU], extruded polystyrene [XPS], rock-mineral wool [RW]), and hybrid core (PU+RW and XPS+RW). Finally, the shear distribution coefficient of core material for sandwich panels with BFRP facesheets was modified depending on the experimental data. The experimental results showed that an increase in the PU core thickness significantly increased the flexural strength and rigidity of the sandwich panels. For different core materials, the maximum loads of the panels were positive with the shear strength of the core materials. Whereas, XPS+RW hybrid core not only can significantly decreases the costs, but also exhibits the highest bearing capacity and stiffness as compared with the PU+RW hybrid and PU cores. [ABSTRACT FROM AUTHOR]

In practical engineering, fiber-reinforced polymer (FRP) tubes have limited lengths due to fabrication and transportation constraints. It is needed to develop reliable splices for FRP-concrete composite member. This paper focuses on the flexural performance of splicing glass fiber-reinforced polymer (GFRP)-concrete-steel sandwich composite members. Seven spliced sandwich composite specimens connected by steel bars and a continuous sandwich specimen were tested under three-point bending. The steel ratio of connecting rebar, steel tube diameter and GFRP tube thickness were all investigated. The results show that the GFRP tube has an apparent restraining effect on the concrete at around 55% of the ultimate load (Pu), and the spliced beams degrade at about 75% Pu. The splicing method based on connecting rebar satisfies the demand that the bearing capacity of a splicing member is greater than that of a continuous member, and the splicing specimens show sufficient ductile behavior with an average displacement ductility coefficient of 4.51. The connection steel ratio greatly affects the failure mode and the steel ratio 3.66% is suggested as the optimal value in the splicing joint of the sandwich composite members, for it ensures splicing strength and provides an ideal failure mode. The inner steel tube diameter affects the stress characteristic of section and improves bending stiffness, bearing capacity and ductility to a large extent. [ABSTRACT FROM AUTHOR]

The seawater sea-sand coral aggregate concrete (SWCC) is believed to have a wide application prospect in the field of ocean engineering, even if research problems are still open. In this paper, the axial performance of SWCC-filled basalt fiber-reinforced polymer (BFRP) tubular columns were experimentally tested and theoretically calculated. Considering that the BFRP tubes manufactured by spiral winding impregnated basalt fiber sheets can normally only provide strength in hoop direction, a new type of integrated prefabricated BFRP tube with longitudinal BFRP bars pre-bonded on the inner wall was manufactured. Ten SWCC columns were built, instrumented, tested, and analyzed. First, the influences of the wall thickness of the BFRP tubes (i.e., 2 mm and 4 mm) and the containing of pre-bonded BFRP bars or not were compared. Then, based on the modification of existing models, a calculation model applicable to the peak bearing capacity of the new integrated BFRP tube confined SWCC was preliminarily proposed. The results showed that the integrated BFRP tube designed in this paper has good application prospects in the marine environment and the proposed equation can be used to predict the ultimate strength of this new BFRP tube confined SWCC. The established numerical model had good accuracy in predicting the stress-strain relationship and the failure modes of the proposed SWCC-filled BFRP tubular columns under axial compression. [ABSTRACT FROM AUTHOR]

Fused deposition modeling (FDM) is a low-cost additive manufacturing method with moderate tolerances and high design flexibility. Ample studies are being undertaken for modeling the mechanical properties of FDM by using the Finite Element Method (FEM). The process technique of FDM results in anisotropic inner structures that are affected by the chosen manufacturing parameters. Moreover, composite filaments, such as fiber-reinforced polymers, have anisotropy even in filament form before FDM printing. These anisotropic effects are needed to be examined and incorporated for an adequate model. In order to speed up the design stage, we aim to prepare a practical method for simulating the mechanical properties of FDM-printed fiber-reinforced polymer composites. In this work, we computed the homogenized material properties for various fiber lengths, fiber volume percentages, and fiber orientations by asymptotic homogenization at the microscale. Then, mesoscale simulations are carried out through FEM simulations by incorporating the influences of process parameters. In this way, we demonstrate the effect of various micro- and mesostructural features on the homogenized properties step by step. [ABSTRACT FROM AUTHOR]

Conventional pultruded fiber-reinforced polymer (FRP) rod stirrups are susceptible to premature bent corner rupture and bond slip failure of overlapping legs. This research proposed a new type FRP shear reinforcement, closed-type winding GFRP (CW-GFRP) stirrups, featuring a fully closed rectangular cross-section. CW-GFRP stirrups completely avoided slip and significantly improved the strength of bent portion of stirrups. To investigate the feasibility of using CW-GFRP stirrups as shear reinforcement, shear test of 8 concrete beams reinforced with conventional pultruded stirrups and CW-GFRP stirrups was conducted. The beams were 300 mm deep and 150 mm wide, and their shear span ratio were 2.07. The effect of the material of stirrups, the spacing of stirrups, and the width of CW-GFRP stirrups were investigated. The test results showed that pultruded stirrups exhibited bond slip failure, in contrast, CW-GFRP stirrups reinforced beams prevented this failure and showed enhanced stiffness, narrower shear crack width and 1.09–1.12 times higher shear capacity. The splitting failure typical of CW-GFRP stirrups was reported, and a smaller stirrups width is expected to avoid splitting and generate greater strain at ultimate. It can be concluded that the new type of CW-GFRP stirrups is an optimized form of FRP shear reinforcement to supersede conventional pultruded stirrups. Strut-and-tie models based on ACI 318-19 and CSA S806-14 were used to predict the shear strength and produced a safe but relatively accurate prediction. [ABSTRACT FROM AUTHOR]

Interest in natural fiber-reinforced polymer (NFRP) composites is growing rapidly in the transportation sector, especially as a replacement material for metals and synthetic fiber composites. The heightened interest is directly related to a need to produce lightweight and fuel efficient vehicles. Further, stringent legislation and greater environmental awareness is forcing transportation industries to select materials with a smaller carbon footprint. In such a context, NFRP composite materials are a good choice due to their low cost, low environmental impact, and relatively equivalent properties to metals and other composites. Most prior studies have examined commodity plastics such as polypropylene, polyethylene, and epoxy as the primary polymer matrix in NFRP composites and little work has addressed engineering plastics. Engineering plastics, which includes polycarbonate, polyamides, and polystyrene, are high performance thermoplastics with superior properties but relatively higher cost than commodity plastics. It has been claimed that even after recycling, engineering plastics properties are superior to those of commodity plastics, and thus, utilization of recycled engineering plastic in NFRP composites can help reduce waste and lower composite material costs. The aim of this review article is to explore the current status of engineering plastics reinforced with natural fibers such as flax, hemp, jute, and sisal and to examine their use in automotive, aerospace, and maritime applications. Properties and processing techniques of engineering plastics reinforced with natural fibers are also studied. [ABSTRACT FROM AUTHOR]

This study proposes a practical fragility-oriented approach for the seismic retrofit design of case-study structures. This approach relies on mapping the increase of the global displacement-based ratio of capacity to life-safety demand (CDRLS) to the building-level fragility reduction. Specifically, the increase of CDRLS due to retrofitting is correlated with the corresponding shift in the fragility median values of multiple structure-specific damage states, observing that a pseudo-linear trend is appropriate under certain conditions. Accordingly, a practical approach is proposed to fit such a (structure-specific) linear trend and then use it by first specifying the desired fragility median and subsequently finding the corresponding target value of CDRLS that must be achieved through retrofit design. The validity of the proposed approach is illustrated for an archetype reinforced concrete (RC) structure not conforming to modern seismic design requirements, which has been retrofitted using various techniques, namely, fiber-reinforced polymers wrapping of columns and joints, RC jacketing, and steel jacketing. [ABSTRACT FROM AUTHOR]

The bond between glass fiber-reinforced polymer (GFRP) rebar and concrete is one of the most important parameters in the design of GFRP-reinforced structures. This study investigates the bond behavior of single and bundled high-modulus ribbed GFRP rebars with short embedment lengths in concrete. To achieve this, a total of 48 pullout specimens were constructed and tested. The effect of various parameters, including GFRP rebar embedded length, the concrete block dimensions, GFRP surface characteristics, presence of transverse reinforcement, and bundling of rebars on the bond behavior of high-modulus ribbed GFRP rebar was studied. The experimental results indicated that the failure mode changed from pullout to splitting failure as the embedment length increased. The presence of transverse reinforcement, in many cases, changed brittle splitting failure to partial splitting failure followed by pullout failure. The variation in rebar surface characteristics resulted in differences in the bond-slip behavior of GFRP rebar in concrete. The experimental findings illustrated that rebar stress at failure for specimens with bundled GFRP was generally higher than that of corresponding individual bar with approximately same cross-sectional area. This observation suggests that the equivalent area method may serve as a conservative approach for evaluating the embedment length of bundled ribbed GFRP rebars. Furthermore, the adhesion between ribbed GFRP rebars and concrete was quantified for various bar sizes. Finally, the experimental results were employed to refine and calibrate existing bond-slip models of ribbed GFRP rebar to concrete. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Evaluating shear capacity in reinforced concrete deep beams with web openings strengthened using fiber-reinforced polymer and fiber-reinforced cementitious matrix." The correction updates the funding section of the article, stating that the research was supported by the Vietnam Ministry of Education and Training. The article focuses on evaluating the shear capacity of reinforced concrete deep beams with web openings and the use of fiber-reinforced polymer and fiber-reinforced cementitious matrix for strengthening. [Extracted from the article]

Basalt Fiber Reinforced Polymer (BFRP) is an environment friendly strengthening material that can be used in several engineering applications. In this research, an experimental program was directed to investigate the BFRP strengthening adequacy of reinforced concrete beams. Eight simple-span beams were tested under the four-point bending test and were all made from the same concrete mixture. One layer of BFRP was applied on the soffit of B1, while this layer was wrapped partially along the sides of beams B2, B3, and B4 with vertical side extensions of 25, 75, and 105 mm, respectively, to evaluate the effect of vertical extension of the bottom BFRP layer on the flexural behavior of the strengthened beams. The beams B5 and B6 were strengthened with three BFRP U-strips along the flexural span without and with a bottom layer of BFRP sheet, respectively. On the other hand, the bottom and side surfaces of B7 were fully wrapped with a layer of BFRP, while B0 was kept without strengthening as a reference beam. The test results showed that strengthening with BFRP can noticeably improve the beam load capacity at cracking, yield, and ultimate stages. The ductility of strengthened beams was less than B0 by up to 33% for partial side strengthening and 45% for full side strengthening, while the toughness of all strengthened beams was higher than that of reference beam by 8–78%. The results also showed that increasing the vertical side extension of the bottom BFRP layer leads to significant load capacity increase. [ABSTRACT FROM AUTHOR]

Splicing glass fiber–reinforced polymer (GFRP)-concrete–steel double-skin tubular column (DSTC) is to set connection component at the joint of two or more separated GFRP tubes, and then pour concrete in the double-tube interlayer to form a continuous composite member. In this paper, the splicing DSTC composite members based on steel bar connection were designed and tested under axial compression to determine its mechanical performance. The main parameters include the connection steel ratio, the hollow ratio, and the thickness of GFRP tube. The results show that the GFRP tube presents apparent constraint effect on the concrete at about 60% of the ultimate load. The failure of splicing specimen occurred in the non-splicing section at a certain distance from the splice joint, and the stirrups at the splice joint provide effective constraint effect on the internal concrete. The proposed DSTC splicing method based on steel cage connection can satisfy the strength requirements of splice joint. Nevertheless, the increase of axial steel bar ratio cannot improve the bearing capacity of the splicing column, and the steel ratio of 2.44% is suggested for the splice joint of DSTCs under axial compression. The axial bearing capacity of splicing DSTCs significantly increases with the increase of GFRP tube thickness, but the amount of stirrups should be increased properly when a larger tube thickness is used. Two models were selected to calculate the bearing capacity of splicing members and it is found that Yu's model is more accurate in predicting splicing DSTCs. [ABSTRACT FROM AUTHOR]

Alkali-activated materials (AAMs) are considered an eco-friendly alternative to ordinary Portland cement (OPC) for mitigating greenhouse-gas emissions and enabling efficient waste recycling. In this paper, an innovative seawater sea-sand concrete (SWSSC), that is, seawater sea-sand alkali-activated concrete (SWSSAAC), was developed using AAMs instead of OPC to explore the application of marine resources and to improve the durability of conventional SWSSC structures. Then, three types of fiber-reinforced polymer (FRP) bars, that is, basalt-FRP, glass-FRP, and carbon-FRP bars, were selected to investigate their bond behavior with SWSSAAC at different alkaline dosages (3%, 4%, and 6% Na2O contents). The experimental results manifested that the utilization of the alkali-activated binders can increase the splitting tensile strength (f t) of the concrete due to the denser microstructures of AAMs than OPC pastes. This improved characteristic was helpful in enhancing the bond performance of FRP bars, especially the slope of bond-slip curves in the ascending section (i.e., bond stiffness). Approximately three times enhancement in terms of the initial bond rigidity was achieved with SWSSAAC compared to SWSSC at the same concrete strength. Furthermore, compared with the BFRP and GFRP bars, the specimens reinforced with the CFRP bars experienced higher bond strength and bond rigidity due to their relatively high tensile strength and elastic modulus. Additionally, significant improvements in initial bond stiffness and bond strength were also observed as the alkaline contents (i.e., concrete strength) of the SWSSAAC were aggrandized, demonstrating the integration of the FRP bars and SWSSAAC is achievable, which contributes to an innovative channel for the development of SWSSC pavements or structures. [ABSTRACT FROM AUTHOR]

This paper investigates the static and dynamic performances of sandwich plates with magnetorheological elastomer (MRE) core, in which the MRE core includes two copper wire layers, two inner metal layers, and one MRE layer. First, based on the complex modulus method, the Jolly theory and the pre-defined magnetic coefficients, the dynamic moduli, and loss factors of MRE are assumed as a function of magnetic induction intensity. Furthermore, a theoretical model of the MRE sandwich plates (MRESPs) is proposed, which considers the internal magnetic field excitation and four types of panel materials, namely fiber-reinforced polymer (FRP), fiber-reinforced polymer with carbon nanotubes (CNT-FRP), metal and fiber-metal hybrid (FMH) panels. After the deformation and energy equations are derived to solve the static bearing stiffness, dynamic stiffness, and damping parameters, some literature results are employed to provide the initial validation of the model developed. Subsequently, four MRESP specimens with the FRP, CNT-FRP, metal, and FMH panels are fabricated and measured to further verify the model as well as to evaluate the mechanical performance. The influence of critical geometric and material parameters related to MRE on static and dynamic properties is also discussed to summarize some practical conclusions for engineering applications. [ABSTRACT FROM AUTHOR]

Exposure of buildings to fire is one of the unexpected events during the life of the structure. The heat from the fire can reduce the strength of structural members, and these damaged members need to be strengthened. Repair and strengthening of concrete members by fiber-reinforced polymer (FRP) composites has been one of the most popular methods in recent years and can be used in fire-damaged concrete members. In this paper, in order to provide further data and information about the behavior of post-heated circular concrete columns confined with FRP composites, 30 cylindrical concrete specimens were prepared and subjected under four exposure temperatures of 300, 500, 700, and 900. Then, specimens were repaired by carbon fiber reinforced polymer composites and tested under axial compression. Results indicate that heating causes the color change, cracks, and weight loss of concrete. Also, with the increase of heating temperature, the shape of stress–strain curve of FRP-retrofitted specimens will change. Therefore, the main parts of the stress–strain curve such as ultimate stress and strain and the elastic modulus will change. Thus, a new stress–strain model is proposed for post-heated circular concrete columns confined by FRP composites. Results indicate that the proposed model is in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Southcentral Alaska, the most populous region in Alaska, was violently shaken by a Mw 7.1 earthquake on 30 November 2018 at 8:29 am Alaska Standard Time. This was the largest magnitude earthquake in the United States close to a population center in over 50 years. The earthquake was 46 km deep, and the epicenter was 12 km north of Anchorage and 19 km west of Eagle River. The event affected some 400,000 residents, causing widespread damage in highways, nonstructural components, non-engineered and older buildings, and structures on poorly compacted fills. A few isolated serious injuries and partial collapses took place. Minor structural damage to code-conforming buildings was observed. A significant percentage of the structural damage was due to geotechnical failures. Building stock diversity allows use of the region as a large test bed to observe how local building practices affected earthquake damage levels. The prevailing peak ground acceleration (PGA) was 0.2–0.32 g, causing shaking intensity at most sites of 50%–60% of the ASCE 7-16 design basis earthquake acceleration. Thus, the seismic vulnerability of building stock in the region was not truly tested. Reinforced concrete buildings had minor structural damage, except in a few cases of shear wall and transfer girder shear cracking. Fiber-reinforced polymer (FRP)-retrofitted buildings performed satisfactorily. Concrete-masonry-unit (CMU) masonry buildings experienced serious structural damage in many cases, including relatively newer buildings. The earthquake caused widespread structural damage in non-engineered buildings (primarily wood and CMU masonry) that exist widely in the region, especially in Eagle River. Of these, non-engineered single-family wood buildings had the heaviest structural damage. No structural damage could be observed in steel buildings. The aftershock sequence, which included 7 M5+ and 50 M4+ events, exacerbated structural damage in all types of buildings. The present study is based on the EERI field reconnaissance mission conducted by the authors following the earthquake. Based on the observed damage and structural performance, seismic risk mitigation recommendations are suggested. [ABSTRACT FROM AUTHOR]