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Reinforced concrete buildings are prone to collapse during seismic events due to the brittle shear failure of non-seismic beam-column joints (BCJ). In this study, two one-third scale reinforced concrete (RC) frames incorporating various non-seismic details were tested under lateral cyclic loading. One of the RC frames was used as control, while the other was strengthened using externally bonded carbon-fiber-reinforced polymer (CFRP) sheets in a L-Shaped configuration with particular attention to anchorage to evade debonding. For the strengthening process, L-shaped CFRP sheets were bonded to the inner face of columns, extended on beams both above and below the joint up to a hinge length. To avert debonding, the L-shaped CFRP sheets were fully wrapped with CFRP sheets around the column, both near the joint and at the end of the sheet. The sheets were also wrapped around the beam, through two slots in the slab that were adjacent to the beam-column interface and at the far end of the sheet. Test results confirmed that the installation of CFRP sheets in an L-shaped configuration altered the brittle-shear failure mechanism of the beam-column joints to a ductile failure by repositioning the hinges away from the columns. Additionally, the proposed anchorage method successfully eradicated the debonding and peel-off of the CFRP sheets. Moreover, strengthening with the CFRP sheets in the L-shaped configuration enhanced the strength and ductility of the RC frame by 45% and 43%, respectively. According to the findings of this study, the application of L-shaped CFRP sheets proved effective in strengthening RC frame structures. [ABSTRACT FROM AUTHOR]

Geopolymer concrete is a new concrete technology that emerged as an alternative to conventional concrete by replacing traditional Portland cement with geopolymer binders. Strengthening of concrete structures using CFRP composites has become an essential technique last decades. Most of the studies were conducted on conventional concrete of Portland cement. In this research, an experimental and finite element analysis has been conducted to assess the bonding properties between geopolymer concrete substrate and CFRP composites using near-surface mounted strengthening system. The program consisted of concrete prisms bonded with NSM CFRP laminate and tested using single-lap shear test set-up with different bond lengths. Bond-slip behaviour has also been evaluated. The experimental results exhibited significant bonding properties, achieving an average bonding stress between 8.97 and 15.58 relative to the bonding length. The numerical analysis showed comparable results and a good correlation with that of experimental work.

Among many manufacturing industries, civil engineering sectors have been more involved in incorporating fiber reinforced polymer (FRP) composites. These composite materials have been selected as an appropriate solution for strengthening reinforced concrete structural elements because of their excellent tensile strength, high strength to weight ratio, and simplicity of implementation. This experimental study aims to evaluate the flexural behaviors of structural light-weight reinforced concrete (SLWC) one-way slabs strengthened with different patterns of CFRP. The proposed material in the current study is using pumice aggregate as a full replacement of natural coarse aggregate. Four structural light-weight concrete (SLWC) slabs with the dimensions of 1200 mm long, 450 mm wide, and 80 mm thick were cast and tested to failure. One slab has been taken as a control and the other samples are strengthened with five strips in one layer, ten strips in two layers and full wrap CFRP. The samples are tested under a four-point load bending test setup until failure. Each of the ultimate loads, mid-span deflection, cracking loads, crack patterns, and failure modes were well evaluated. The results showed that, strengthening with CFRP composites significantly increases load-carrying capacity. Strengthening with five strips, ten strips, and full wrap with CFRP increased the ultimate capacity by 115%, 138%, and 170% respectively and decreased mid-span deflection by 43%, 58%, and 55% compared to the reference specimen respectively.

Fibre reinforced polymer (FRP) composite materials are widely used in many branches of life from aerospace and automotive, through boatbuilding, mechanical and civil engineering even to art. Thanks to their lightweight, high strength, and ease of shaping are very attractive materials. The main disadvantage of FRP composites is the possibility of defects in their structures which influence on proper work of the material. These defects can appear in the production phase as well as be caused by impact. Especially sensitive to defects/damages are the responsible structures such as those used in the aerospace industry. In this paper, the application of digital image correlation (DIC) to tracking the development of strain fields in FRP composites with different types of fibres is proposed. Thanks to the use of the DIC the finding of areas where the strain distribution (caused by loads) is different than in surroundings is possible. The presented measurement technique is vision-based, non-contact, and enables full-field measurements without disturbing structure behaviour by any additional mass. This method, in combination with other non-destructive testing is potentially applicable in damage detection of the aircraft sheathing parts. However, further research in order to its application to online monitoring is required, especially considering the minimisation of equipment, supply of energy and wireless data transmission. [ABSTRACT FROM AUTHOR]

Impact loads lead to the failure of structures and significantly diminish their operational lifespan. The necessity to enhance impact performance has shown gradual progress, resulting in utilising nano-fillers as an additional reinforcement within the matrix. Despite the significant number of studies that have been done on this unique hybrid material, there have only been a few reviews published that discuss the effect of production processes on mechanical properties and performance in these hybrid composites under projectile impact. There have been conflicting results obtained in experimental results from the literature. The disparity is related to the variation in dispersion, bonding states, and inconsistent fabrication processes. This work defines the pros and cons of carbon nanotube (CNT)-based composites along with a systematic representation of the development of CNT-reinforced composites under projectile impact using experimental, analytical, and numerical techniques. The potential of CNT reinforcement on fibre-reinforced polymers (FRPs) and its effect on mechanical properties have been discussed. Furthermore, different impact test setups are explored to determine the effective method to determine the impact performance of CNT-reinforced laminates. Moreover, the impact of surface treatment is discussed using different non-destructive methods, and the influence of CNT reinforcement is determined. In addition, mechanical and impact response with varying configurations of fibres is gathered from the available literature, and optimal design based on the required application is suggested. Also, analytical methods developed to determine the impact response of laminates are discussed to determine the parameters dominating the impact response of the laminate. This review will help researchers find the right combination of FRP materials for a given application.

Reinforced concrete buildings are prone to collapse during seismic events due to the brittle shear failure of non-seismic beam-column joints (BCJ). In this study, two one-third scale reinforced concrete (RC) frames incorporating various non-seismic details were tested under lateral cyclic loading. One of the RC frames was used as control, while the other was strengthened using externally bonded carbon-fiber-reinforced polymer (CFRP) sheets in a L-Shaped configuration with particular attention to anchorage to evade debonding. For the strengthening process, L-shaped CFRP sheets were bonded to the inner face of columns, extended on beams both above and below the joint up to a hinge length. To avert debonding, the L-shaped CFRP sheets were fully wrapped with CFRP sheets around the column, both near the joint and at the end of the sheet. The sheets were also wrapped around the beam, through two slots in the slab that were adjacent to the beam-column interface and at the far end of the sheet. Test results confirmed that the installation of CFRP sheets in an L-shaped configuration altered the brittle-shear failure mechanism of the beam-column joints to a ductile failure by repositioning the hinges away from the columns. Additionally, the proposed anchorage method successfully eradicated the debonding and peel-off of the CFRP sheets. Moreover, strengthening with the CFRP sheets in the L-shaped configuration enhanced the strength and ductility of the RC frame by 45% and 43%, respectively. According to the findings of this study, the application of L-shaped CFRP sheets proved effective in strengthening RC frame structures.

Materials with shielding capabilities against gamma radiation are important for nowadays applications in order to alleviate radiation damage. This study investigates the shielding characteristics of carbon fiber/epoxy composites incorporating lead nanoparticles (Pb-NP) of variable weight fractions. The composites in this experimental study are prepared using the handlayup vacuum bagging process at room temperature. Mass attenuation coefficients are calculated for composites with variable Pb-NP weight fractions based on radiation intensity measurements taken using NaI (Tl) scintillation detector. The results show that adding small fractions of lead nanoparticles to the matrix phase of the composite material leads to improving its shielding properties, including their linear attenuation coefficient, mass attenuation coefficient and the Half- Value Layer (HVL). The results also show that mass attenuation coefficients of composite material with added Pb-NPs are higher than those of pure lead. For validation purposes, the experimental results are compared to computational results obtained using MCNP5 code for the same weight fractions of Pb-NPs. The two sets of results were found to be in good agreement with a maximum relative error of ∼16%. [ABSTRACT FROM AUTHOR]

These elements are innovative and of interest to many researchers for the reinforcement of wooden elements. For the reinforced beam elements, the effect of the reinforcement factor, FRP and steel elastic modulus or FRP and steel arrangement of the reinforcement on the performance of the flexural elements was determined, followed by reading the load-displacement diagram of the reinforced beam elements. The finite element model was then developed and verified with the experimental results, which was mainly related to the fact that the general theory took into account the typical tensile failure mode, which can be used to predict the flexural strength of reinforced timber beams. From the tests, it was determined that reinforced timber beam elements had relatively ductile flexural strengths up to brittle tension for unreinforced elements. As for the reinforcements of FRP, the highest increase in load-bearing capacity was for carbon mats at 52.47%, with a reinforcement grade of 0.43%, while the lowest was for glass mats at 16.62% with a reinforcement grade of 0.22%. Basalt bars achieved the highest stiffness, followed by glass mats. Taking into account all the reinforcements used, the highest stiffness was demonstrated by the tests of the effectiveness of the reinforcement using 3 mm thick steel plates. For this configuration with a reinforcement percentage of 10%, this increase in load capacity was 79.48% and stiffness was 31.08%. The difference between the experimental and numerical results was within 3.62–27.36%, respectively. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites have gained increasing recognition and application in the field of civil engineering in recent decades due to their notable mechanical properties and chemical resistance. However, FRP composites may also be affected by harsh environmental conditions (e.g., water, alkaline solutions, saline solutions, elevated temperature) and exhibit mechanical phenomena (e.g., creep rupture, fatigue, shrinkage) that could affect the performance of the FRP reinforced/strengthened concrete (FRP-RSC) elements. This paper presents the current state-of-the-art on the key environmental and mechanical conditions affecting the durability and mechanical properties of the main FRP composites used in reinforced concrete (RC) structures (i.e., Glass/vinyl-ester FRP bars and Carbon/epoxy FRP fabrics for internal and external application, respectively). The most likely sources and their effects on the physical/mechanical properties of FRP composites are highlighted herein. In general, no more than 20% tensile strength was reported in the literature for the different exposures without combined effects. Additionally, some provisions for the serviceability design of FRP-RSC elements (e.g., environmental factors, creep reduction factor) are examined and commented upon to understand the implications of the durability and mechanical properties. Furthermore, the differences in serviceability criteria for FRP and steel RC elements are highlighted. Through familiarity with their behavior and effects on enhancing the long-term performance of RSC elements, it is expected that the results of this study will help in the proper use of FRP materials for concrete structures. [ABSTRACT FROM AUTHOR]

• A new analytical approach to predict the bond behaviour of mechanically anchored FRP-to-substrate joints is proposed. • The end anchorages of the bonded joints are simulated through a spring with a linear behaviour. • One unique function is used to predict all the stages that the interface undergoes until complete debonding. • The Finite Element Method is used to validate the proposed analytical approach. • The good accuracy obtained in all studied joints suggests that the proposed analytical solution covers a wide range of cases. Fibre-reinforced polymers (FRP) are often externally bonded (EB) to concrete, steel or timber structures for structural strengthening purposes. In the EB reinforcement system, the bond between materials is critical for the success of such a bonding system. However, the system is prone to debond at an FRP strain level much lower than its rupture value. For this reason, it is often necessary to use end anchorages in FRP-strengthened beams to delay or avoid this premature debonding of FRP from the beams. To better understand the debonding process of mechanically anchored FRP-to-substrate joints, the present work proposes a new analytical approach that considers an elastic end anchorage, which can simulate, through a spring, the slips developed in an end anchorage such as an FRP U-wrap jacket, FRP spike anchor, steel plate anchorage, among others. This new approach can also simulate the bond performance of FRP-to-substrate joints with no end anchorages by assuming that the stiffness of the end anchorage is zero. Expressions for defining the load-slip curves, FRP strains, interfacial slips, and bond stresses developed throughout the bonded length are derived and validated against the results from the Finite Element Analysis (FEA). In the end, the model was used to simulate several experimental tests on mechanically anchored FRP-to-substrate joints available in the literature. Despite its simplicity, the proposed analytical approach covers wider situations that no other known similar approach can deal with. [ABSTRACT FROM AUTHOR]

The kapok fibre (KF) contains impurities like wax and oily substances on its surfaces, making it incompatible for composite fabrication at the interface. To enhance the mechanical and electrical properties of the KF/epoxy composites, the structure of the KF is modified by dewaxing. Using the correlation function derived from SAXS Intensity, the macromolecular parameters of the KF are assessed. The XRD study confirmed the cellulose Iβ structure of the KF. The FTIR spectra confirm the partial removal of hemicellulose, lignin, wax and hydrophilic -OH groups from the KF after dewaxing, which helped in better chemical linking between the KF and the matrix at the interface. The dewaxing enhanced the flexural, tensile, impact strength and storage modulus of the FRP composites by 40 %, 38 %, 25 % and 55 % respectively, possibly due to strong interfacial binding and interlocking between the KF and epoxy. The removal of -OH groups from the KF and hindered molecular motion of polymer chains at the interface between the KF and matrix, resulting from better binding by dewaxing, led to the lower dielectric constant (ε ′), dielectric loss (tan δ) and ac conductivity (σ ac) of the FRP composites. [Display omitted] • The macromolecular structure of KF is modified by dewaxing. • Dewaxing on KF enhanced interfacial chemical and mechanical bonding. • Flexural, tensile and impact strength increased by 40 %, 38 % and 25 % respectively. • T g and E ′ of the composites increased after fibre treatment. • DKFRPC showed low ε ′ , tan δ and σ ac. [ABSTRACT FROM AUTHOR]

Two methods of enhancing the mechanical performance of glass fiber reinforced polymer (GFRP) composites, namely the formation of an interpenetrating polymer network (IPN) of two thermoset polymers (epoxy and vinyl ester) and the addition of nanofillers (nano Al2O3) have been implemented simultaneously. The content of nano Al2O3 (0.1, 0.4, and 0.7 wt% of the polymer matrix) in the glass fiber reinforced epoxy‐vinyl ester IPN (GEVIPN) composite significantly affected its mechanical performance. Incorporation of 0.1 wt% nano Al2O3 in GEVIPN composite exhibited 17.69% and 27.64% improvement in flexural strength and toughness, respectively. Additionally, when the composites were subjected to elevated temperature testing, their mechanical performance was drastically affected. However, the test results revealed that nano Al2O3/GEVIPN composites possessed significantly improved mechanical degradation resistance at elevated temperatures. This new composite material could be utilized as structural materials in the civil, automotive, and marine industries. Dynamic mechanical thermal analysis was performed to assess the composites' thermomechanical behavior. Fractography analysis of tested samples revealed the underlying phenomena, which dictate the mechanical performance at each testing temperature. A constitutive deformation model assessed the reliability of this new material at ambient and elevated test temperatures. [ABSTRACT FROM AUTHOR]

The principal objective of this study is to employ non-destructive broadband dielectric spectroscopy/impedance spectroscopy and machine learning techniques to estimate the moisture content in FRP composites under hygrothermal aging. Here, classification and regression machine learning models that can accurately predict the current moisture saturation state are developed using the frequency domain dielectric response of the composite, in conjunction with the time domain hygrothermal aging effect. First, to categorize the composites based on the present state of the absorbed moisture supervised classification learning models (i.e., quadratic discriminant analysis (QDA), support vector machine (SVM), and artificial neural network-based multilayer perceptron (MLP) classifier) have been developed. Later, to accurately estimate the relative moisture absorption from the dielectric data, supervised regression models (i.e., multiple linear regression (MLR), decision tree regression (DTR), and multi-layer perceptron (MLP) regression) have been developed, which can effectively estimate the relative moisture absorption from the dielectric response of the material with an R¬2 value greater than 0.95. The physics behind the hygrothermal aging of the composites has then been interpreted by comparing the model attributes to see which characteristics most strongly influence the predictions. [ABSTRACT FROM AUTHOR]

In the last decade, synthetic fiber, as a reinforcing specialist, has been mainly used in polymer matrix composites (PMC's) to provide lightweight materials with improved stiffness, modulus, and strength. The significant feature of PMC's is their reinforcement. The main role of the reinforcement is to withstand the load applied to the composite. However, in order to fulfill its purpose, the reinforcements must meet some basic criteria such as: being compatible with the matrix, making chemical or adhesion bonds with the matrix, having properties superior to the matrix, presenting the optimal orientation in composite and, also, having a suitable shape. The current review reveals a detailed study of the current progress of synthetic fibers in a variety of reinforced composites. The main properties, failure modes, and applications of composites based on synthetic fibers are detailed both according to the mentioned criteria and according to their types (organic or inorganic fibers). In addition, the choice of classifications, applications, and properties of synthetic fibers is largely based on their physical and mechanical characteristics, as well as on the synthesis process. Finally, some future research directions and challenges are highlighted. [ABSTRACT FROM AUTHOR]

The research investigates the effect of using external fiber-reinforced polymer (FRP) –composites to strengthen the alkali-silica reaction (ASR)-damaged reinforced concrete (RC) beam-column joints. The nonlinear finite element analysis (NLFEA) method has been used to achieve the aims of this paper. Before experimenting, the B-C beam model has been verified following accredited previous experimental. Afterward, the experiment was extended to include the impact of the column’s axial load level and the ASR damage stage. For these purposes, the levels of the axial load were set at 0%, 25%, 50%, and 75%, while the stages of the ASR damage were: stage 0 (un-damaged), stage 1 (45 days), stage 2 (80 days), and stage 3 (120 days). Some of the models were strengthened with FRP, while the others were not. The evaluation of the models' structural performance was conducted by monitoring: the failure mode, distribution of stresses, degradation of stiffness, dissipation of energy, displacement ductility, pulling-pushing ultimate load capacity, and correspondent displacements, in addition to the horizontal load-displacement hysteretic loops and envelopes. The achieved results from this work indicated that the strengthened-with-FRP of ASR damaged RC B-C joint models showed an enhancement in their cyclic performance, as they showed: higher load capacity, more significant horizontal displacement, more displacement ductility, more dissipation of energy, and less secant stiffness degradation. It was also noticed that the higher the stage of the ASR damage, the better the efficiency of FRP composites. Further, strengthening the joint models with FRP transformed their failure mode from brittle mode to ductile, by forming a plastic hinge in the beam side at a column axial load exceeding 25%. On the other side, applying a column axial load below 25% only improved the ultimate deflection and corresponding axial load capacity.

This paper details the development and experimental assessment of a friction-type connector, designed to transfer shear flow between the top flange of a fiber-reinforced polymer (FRP) tub girder and a composite concrete deck for bridge applications. In contrast with previously used bearing-type connectors, this system relies on a deformed FRP surface to transfer shear via direct interlock with the concrete deck. The connector is materially efficient, simple to fabricate, can be used with lower-grade structural or stainless-steel fasteners, and provides a high degree of interface stiffness. Six compression-shear specimens were tested to assess the connector fatigue resistance and ultimate connection strength. Additionally, two short beam specimens were tested in three-point bending, one of which was subjected to fatigue loading. Based on the compression-shear tests and short beam tests, the connection exhibited strength exceeding that predicted by AASHTO for frictional concrete-concrete connections. The connection strengths were significantly greater than the factored demand required by AASHTO for a typical model FRP bridge girder. The cyclic loading of the connection in both compression-shear and beam bending showed that connection stiffness and strength do not significantly degrade, due to the application of 1 × 106 to 6 × 106 cycles of traffic-induced factored fatigue load. [ABSTRACT FROM AUTHOR]

Fiber Reinforced Polymer (FRP) composites are used extensively in aerospace, marine and civil engineering. High stiffness-to-weight and high strength-to-weight ratios make these materials suitable for modern wind turbine blade manufacturing industries. In the present study, glass, carbon and glass-carbon composite materials are studied to determine their tensile properties at elevated temperatures as this is an important design consideration for wind turbines operating in warm climates. Specimens were tested in a range of temperatures to investigate thermal effects on their mechanical, thermal and failure behaviors.Experimental and FEA results show that tensile strength and heat flow of specimens decrease with increasing temperatures. Hybridization of two materials changes failure mode behaviors. Tensile strength test data was analyzed using chi-square goodness of fit statistical model. Results were correlated by using linear regression analysis. Normal, lognormal and 2-parameter Weibull statistical approaches were used to quantify the degree of variability in tensile strength of specimens.

As fiber reinforced polymer (FRP) composites become ever more established construction materials in the marine industry sector the influence of the harsh environmental operational conditions and its consequence on failure prediction of such structures is an imperative. Coupons of epoxy/glass and polyester/glass with various fiber layout configurations have been submerged under the sea for prolonged periods (6 and 12 months) in order to assess the impact on mechanical behavior of the material exposed to real marine environment as opposed to the more commonly adopted artificially produced laboratory sea environment and accelerated testing. Changes in mass, marine microbiology growth, tensile strength and morphological structures were analyzed after submersion and compared with samples exposed to room environment. All coupons have shown mass increase due to seawater absorption and microorganism growth in the organic resins matrices. The dynamic and level of change in tensile strength proved to be dependent on the fiber layout configuration. Optical and scanning electron microscopical investigation performed showed significant matrix morphological changes primarily due to salt crystal formation and the impact of sea microorganisms embedding in the resin. The collected experimental data will be used to develop a more realistic environmental input parameters for structural modeling of marine structures. [ABSTRACT FROM AUTHOR]

Limited information is known about the effects of bond strength degradation during installation on the bond's quality and performance between fiber-reinforced polymer (FRP) reinforcement and substrate material. This research study's primary focus is to investigate the efficiency of the external FRP composites in rescuing the structural performance and controlling the mode of failure of the reinforced concrete (RC) beam-column joint with different bond strength degradation percentages nonlinear finite element analysis (NLFEA). Firstly, the RC beam-column model was validated against the published experimental results and then was expanded to consider the effect of the degradation percentages in bond strength between concrete and FRP composite (0 % (Fully bond), 10 %, 20 %, 30 %, 40 %, 50 %, 60 %, 70 %, 80 %, 90 %, and 100 % (control or un-strengthened joint). The structural performance was evaluated in terms of failure mode, stress distribution, pulling and pushing ultimate load capacity and corresponding displacement, horizontal load-displacement hysteretic loops, horizontal load-displacement envelopes, displacement ductility, energy dissipation, stiffness degradation, and equivalent hysteretic damping factor. The NLFEA results showed that the FRP strengthening technique with bond strength degradation percentages less than 30 % enhanced the cyclic performance (higher load capacity, larger horizontal displacement, higher displacement ductility, higher energy dissipation, and slower secant stiffness degradation). Also, the utilized FRP method with bond strength degradation percentage less than 30 % performed well in eliminating any surface debonding or buckling in the FRP composite because of the proper lateral support provided for the strengthening sheets. Finally, the bond strength degradation percentage less than 30 % could significantly enhance the deficient joints' seismic performance under strong beam-weak column conditions by changing its behavior to a more ductile one, including the beam flexural hinging. Moreover, the relocation of a plastic hinge in the beam provided more lateral strength for the joint specimens.

Regarding the high interfacial shear stresses at end-plate, and end-plate cover separation in externally bonded methods, bar end-interfacial debonding and bar-end cover separation in near-surface mounted technique, a hybrid strengthening method called combined externally bonded near-surface method was proposed. In this method, the externally bonded and near-surface mounted techniques complement each other and mutually overcome their limitations. The purpose of this study is to numerically investigate the flexural strengthening efficiency of reinforced concrete beams with combined externally bonded FRP sheets and near-surface mounted FRP rods. The numerical analyses were conducted with finite element software ABAQUS 6.11, which can accurately simulate the experimental investigations on the flexural behavior of reinforced concrete beams strengthened with FRP composites. Validation of finite element simulation was confirmed first by making a comparison with the experimental study presented in the literature for both un-strengthened and strengthened beams with FRP materials. The verified model of the un-strengthened beam, which serves as a control beam, was used to simulate reinforced concrete beam strengthened with externally bonded FRP sheets and combined externally bonded near-surface mounted technique. The numerical results of mid-span bending moment deflection, ultimate bending moment, failure deflection, and ductility index were reported. Based on the results of this study, it is concluded that the developed finite element models for the externally bonded, near-surface mounted, and combined externally bonded near-surface techniques can be used by structural engineers as an alternative solution in design-oriented parametric studies of strengthened reinforced concrete elements. The performance of the combined externally bonded near-surface mounted technique was confirmed by making the comparison between the results of the intended method with other strengthening techniques.

This paper presents the efficiency of the external fiber reinforced polymer (FRP) composites in rescue the structural performance and controlling the mode of failure of the heated damaged reinforced concrete (RC) beam-column joint by nonlinear finite element analysis (NLFEA). Firstly, the RC beam-column model was validated against the published experimental results and then was expanded to consider the effect of column axial load level (0%, 25 %, 50 %, and 75 %) and elevated temperature (23 °C, 200 °C, 400 °C, and 600 °C) on the models with and without FRP composites. The structural performance was evaluated in terms of failure mode, stress distribution, pulling and pushing ultimate load capacity and corresponding displacement, horizontal load-displacement hysteretic loops, horizontal load-displacement envelopes, displacement ductility, energy dissipation, and stiffness degradation. The NLFEA results showed that the FRP strengthening technique of heated damaged RC beam-column joint with FRP composite enhanced the cyclic performance (higher load capacity, larger horizontal displacement, higher displacement ductility, higher energy dissipation, and slower secant stiffness degradation) and the efficiency of FRP composite increased with the heated damage level. Also, the FRP composite strengthening technique gave the ability to transform the joint-column regions mode of failure from brittle into a ductile mode of failure through the formation of plastic hinge in the beam only at a higher level column axial loads of more than 25 %. While the application level of column axial loads less than 25 % only enhanced just the ultimate axial load capacity and corresponding deflection.

This article describes a novel method for detecting flaws in curing FRP composite materials while they are being manufactured. Such a method can improve the efficiency of the manufacturing process by minimizing, or potentially eliminating, the need for post-manufacturing inspection. The method utilizes a Kalman filter, a heat conduction model, and surface temperature measurements from infrared thermography to identify likely locations of flaw and/or curing anomalies. Specifically, a methodology that compares a metric of the time-history of Kalman filter corrections at different spatial locations to identify anomalous curing behavior was developed. Several numerical studies were performed using a previously-validated model to determine the proficiency of the technique. Results of the verification studies indicated that the proposed method was effective at identifying resin-rich regions without any modification to the detection criteria, while identifying resin-deficient regions required a more lenient detection criterion. In the case of multiple flaws, the proposed method was always able to identify the flaw closer to the surface, regardless of flaw significance, while the deeper flaw was only identified when the flaw was more significant than the near-surface flaw. The proposed method demonstrates promise for passive IR thermography-based flaw detection performed during the manufacturing of FRP composites and can serve to both improve the efficiency of the manufacturing process and the quality of FRP composite parts. Further experimental studies are required for validation of the technique before it can be applied for industrial application. [ABSTRACT FROM AUTHOR]

Masonry structures, which are subjected to in-plane shearing, should be reinforced. The situation is often appearing in the regions, where masonry buildings are destroyed due to earthquakes. There are many methods of strengthened this kind of structures. One of them is reinforcement by FRP composites, which are linked to the masonry surface. It is not quite simple to select a place, where the composites should be to obtain the most effective work of behaviour. In the paper the topological optimization is used to meet this goal.

Some variation in the topological distribution of fibers inside the matrix phase of fiber reinforced polymers (FRP) is inevitable. Such irregularities can accelerate moisture diffusion and adversely affect the life of FRP. This paper presents a hierarchical technique for characterization of clustered microstructures and their transient moisture diffusion response. The clustering descriptors are derived for different fiber volume fractions (dilute to dense) for the quantitative definition of a given fiber matrix architecture. The metrics are normalized to remove dependence on volume fraction. The microstructures are analyzed for Fickian moisture diffusion. Suggested descriptors show a good correlation with transient diffusion response in relation to saturation time. The results can be used to predict the time-dependent moisture diffusion response of FRPs for any given fiber volume fraction.