FRP Sheets Research Articles

The Seismic Performance of Infill and Retrofitted Structural Walls under Earthquakes

To account for the effects of infill walls, the Iranian Code reduces the period of the structure. As a result, filler walls in the plane of structural frames result in significant changes in the properties they possess; therefore, the resistance, stiffness, ductility, distribution of internal forces, and other characteristics of such a frame with an empty frame differ greatly. In this research using 7 far-field earthquakes, a nonlinear time history analysis was performed on reinforced concrete frames with and without masonry infill walls. The maximum relative displacements between the stories were determined. Also, to evaluate the seismic performance of structural masonry walls, the fragility curve of unreinforced masonry walls retrofitted with FRP sheet based on different scenario under the effect of earthquake loads has been investigated by the finite element method. According to the results, the presence of infill walls reduces the number of plastic hinges as well as the maximum relative displacement between the stories. Furthermore, by increasing the number of FRP sheet layers and the reinforced area of the FRP sheet to the entire wall of an unreinforced structural wall, the seismic behaviour of the wall is more effective than other reinforcement patterns and damages the wall less.

Performance of Reinforced Concrete Flat Slabs Having GFRP Gratings

A thorough study of the literature indicated that there is not much relevant research on the application of GFRP gratings. Otherwise, extensive study has been done on FRP bars, laminates, sheets, strips, and rods. This study proposes a novel approach to improve the punching shear resistance of flat slab column connections by inserting GFRP gratings across the slab thickness. The results of seven specimens tested under vertical static loading are presented, considering the influence of the grating’s characteristics. All specimens were tested as simply supported slabs under one point of static loading. Experimental results, including crack patterns, slab deflection, concrete compressive strain, tensile steel strain, GFRP grating strain, and failure load, were recorded using extensive electric instrumentation. Test results revealed an enhancement in the failure load ranging between 9.03% and 27.67% for the specimens provided with the GFRP grating. In addition, a nonlinear finite element numerical model analysis was carried out using the ANSYS 15 program. Correlational studies based on the load-deflection response and crack patterns were utilized, resulting in a good agreement between numerical simulations and experimental results with differences ranging from 1.0% to 8.0%.

Flexural Behaviour of FRC Beams Wrapped With FRP

Structural elements such as beams, slabs and columns may require strengthening during their service life period. A concrete structure may need strengthening for many reasons such as to increase live load capacity, to add reinforcement to a member that has been unsigned or wrongly constructed. The FRPs have various advantages like, high strength to weight ratio, corrosion resistance and ease of installation and flexibility in its use. FRP material which are available in the form of sheet are being used to strengthen a variety of RC elements to enhance the flexural, shear and axial load carrying capacity of these elements. The objective of this experiment is to strengthen the RC beams using fibres and FRP sheets in flexure. In this experimental program CFRP and GFRP sheets were applied to the bottom surface and sides of the concrete beam with different configuration and their performance in flexure were studied. In this experimental program eight RC beams of size 1500 x 150 x 200mm were casted with two 10mm dia. bars as tension zone, two 8mm dia. bars as compression zone and 8mm dia. bars @ 200mm c/c spacing as shear reinforcement. The experimental result shows that the flexural strength of FRP wrapped beams were increased in the range of 23.49% to 67.9% in comparison with the flexural strength of the control beam (unwrapped). The flexural strength of the beam wrapped with the single layer CFRP at the soffit and around the sides (for full depth of the beam) and beam wrapped with the single layer GFRP at the soffit and around the sides (for full depth of the beam) exhibits better performance compared with other FRP beams and increase in flexure was 67.9% in comparison with the capacity of the control beam.

Advancing Shear Capacity Estimation in Rectangular RC Beams: A Cutting-Edge Artificial Intelligence Approach for Assessing the Contribution of FRP

Shear strength prediction in FRP-bonded reinforced concrete beams is crucial for ensuring structural integrity and safety. In this extensive investigation, advanced machine learning algorithms are harnessed to achieve precise shear strength predictions for rectangular RC beams reinforced with FRP sheets. The aim of this research is to enhance the accuracy and reliability of shear strength estimation, providing valuable insights for the design and assessment of FRP-strengthened structures. The primary contributions of this study lie in the meticulous comparison of various machine learning algorithms, including Xgboost, Gradient Boosting, Random Forest, AdaBoost, K-nearest neighbors, and ElasticNet. Through comprehensive evaluation based on predictive performance, the most suitable model for accurately estimating the shear strength of FRP-reinforced rectangular RC beams is identified. Notably, Xgboost emerges as the superior performer, boasting an impressive R2 value of 0.901. It outperforms other algorithms and demonstrates the lowest RMSE, MAE, and MAPE values, establishing itself as the most accurate and reliable predictor. Furthermore, a sensitivity analysis is conducted using artificial neural networks to assess the influence of input variables. This additional research facet sheds light on the critical factors shaping shear strength outcomes. The study, as a whole, represents a substantial contribution to advancing the development of accurate and dependable prediction models. The practical implications of this work are far-reaching, particularly for engineering applications in the realm of structures reinforced with FRP. The findings have the potential to transform the approach to the design and assessment of such structures, elevating safety, efficiency, and performance to new heights.

Experimental Study on the Impact of Using FRP Sheets on the Axial Compressive Performance of Short-Circular Composite Columns.

This paper conducts an experimental study on the axial compressive performance of FRP-steel-concrete composite columns. Nine short columns were produced and evaluated in the study, comprising of three concrete-filled steel tube reference columns and six FRP-steel-concrete composite columns, respectively denoted as "reference columns" and "composite columns". Two categories of failure modes, including shear failure and waist drum, were observed from the experiments. The failure mode may trend toward waist drum from shear failure as more FRP layers were used. The number of FRP layers had a direct effect on the level of compressive strength attained, with a greater number of layers resulting in a greater increase in compressive strength. Moreover, a greater tensile strength and higher elastic modulus of CFRP sheets are more effective at improving the compressive stiffness of the columns. Finally, a four-stage confinement mechanism for FRP-wrapped steel tube concrete composite columns is proposed and discussed, through which the damage mechanisms of the composite structures are more rationally characterized.

A state-of-the-art review on reinforced concrete slabs strengthened by frp sheets under monotonic, impact and repeated loading

Composites made of fiber-reinforced polymer (FRP) have gained popularity as new high-performance material for concrete buildings in now days. The advantages of FRP composites include high strength, lightweight, and corrosion resistance. This paper’s primary objective is to assess the affect of FRP strips on the strengthening and repair of plain and reinforced concrete slabs. under the monotonic, impact, and repeated loading. According to studies’ observations, applying FRP strips to RC slabs significantly affects the final load and deflection. The number and positioning of FRP sheets improve the performance of slabs. The failure load magnitude of strengthened slabs would increase as slab thickness, concrete compressive strength, and sheet thickness increase. The ultimate load capacity was increased by (27-52%), depending on the FRP strengthening strategy used. GFRP sheets could be employed for improving or enhancing the impact strength of concrete structures. Externally attached GFRP sheets gave good resistance for reinforced concrete slabs against typical explosive blast.

Calibrating equations to predict the compressive strength of FRP-Confined columns using optimized neural network model

A procedure based on machine learning algorithms is used to develop design equations for the compressive strength of FRP confined columns. The procedure involved training and optimizing an Artificial Neural Network (ANN), and using the parametric variation of each input of the ANN to investigate nonlinear relationships between input parameters and model output. Results of the parametric study were illustrated using Partial Dependence Plots (PDP), and a polynomial regression model (PRM) was calibrated to offer a simple equation to calculate compressive strength of columns confined with FRP sheets. The ANN and PRM developed using this method provided more accurate and precise estimates of compressive strength of retrofitted columns than other models found in the literature. Moreover, investigating the relationships between each input variable and the output of the ANN model and coupling effects between pairs of input variables on the output of the ANN model using Partial Dependent and contour plots revealed that confined compressive strength was insensitive to the elastic modulus of the composite layers with the thicknesses of 2 mm or less. A new equation was recalibrated for specimens with composite layer thickness greater than 2 mm, which provided very accurate estimates of confined compressive strength for this empirical subset.

FLEXURAL PERFORMANCE OF RC BEAMS BONDED WITH UV-GFRPR SHEETS

This study presents the flexural performance of reinforced concrete (RC) beams externally bonded with UV-curable glass fiber reinforced polyester resin (UV-GFRPR) sheets onto their soffit surface. UV-GFRPR sheets can be cured by UV irradiation. The UV-GFRPR sheets after hardening have about one-seventh of the yield strength of normal steel (SS400), which is lower than FRP sheets such as carbon, aramid, and glass fibers. However, the UV-GFRPR sheets are easily attached to the surfaces of substrates for repair and preventive maintenance and have excellent durability with impermeability of moisture and corrosion factors. The aims of this study are to assess the flexural performance and the strengthening effect of RC beams bonded with two and three laminated layers of the UV-GFRPR sheets in four-point bending tests. The test results showed that the ultimate load-carrying capacities of the specimens with two and three laminated layers were 1.13 and 1.37 times higher than that of the control beam. The RC beams with the UV-GFRPR sheets failed in bending due to rupture of the UV-GFRPR sheets. The load-carrying capacity and the flexural performance were also predicted using the cross-sectional analysis.

Resilience of Medium-to-High-Rise Ductile Coupled Shear Walls Located in Canadian Seismic Zones and Strengthened with Externally Bonded Fiber-Reinforced Polymer Composite: Nonlinear Time History Assessment

Coupled shear walls (CSWs) are structural elements used in reinforced concrete (RC) buildings to provide lateral stability and resistance against seismic and wind forces. When subjected to high levels of seismic loading, CSWs exhibit nonlinear deformation through cracking and crushing in concrete and yielding in reinforcements, thereby dissipating a significant amount of energy, leading to their permanent deformation. Externally bonded fiber-reinforced polymer (EB-FRP) sheets have proven to be effective in strengthening RC structures against various loading and environmental conditions. In addition, their high strength-to-weight ratio makes them an attractive solution as they can be easily applied without significantly increasing the structure’s weight. This study investigates the effectiveness of using EB-FRP sheets to reduce residual displacement in CSWs during severe earthquake loadings. Two series of 15-story and 20-story CSWs in Western and Eastern Canadian seismic zones, which serve as representative models for medium- and high-rise structures, were evaluated through nonlinear time history analysis. The numerical simulation of all CSWs and strengthened elements was carried out using the RUAUMOKO 2D software. The findings of this study provided evidence of the effectiveness of EB-FRP sheets in reducing residual deformation in CSWs. Additionally, significant reductions in the rotation of the coupling beams (CBs) and the inter-story drift ratio were observed. The results also revealed that bonding vertical FRP sheets to boundary elements and confining enhancement by wrapping CBs and wall piers is a very effective configuration in mitigating residual deformations.

Proposing the combined MARS–PSO and ELM–PSO models for estimating the compressive strength of circular concrete columns wrapped with FRP sheets

Proposing the combined MARS–PSO and ELM–PSO models for estimating the compressive strength of circular concrete columns wrapped with FRP sheets

3D printing functionally graded metamaterial structure: Design, fabrication, reinforcement, optimization

The current study introduces a novel class of bio-inspired and 3D-printed metastructures called functionally graded lattice metamaterial beams (FGLBs). These lightweight lattice metastructures offer several benefits, including a high stiffness-to-weight ratio and excellent energy absorption efficiency. Therefore, their mechanical properties reinforced with AL-FRP (fiber-reinforced polymer) face sheets are aimed to examine through experimental testing and finite element simulation in the present work. An improved FGLB is also raised to expose the failure characteristics of graded metamaterial beams. The deformation mode, failure mechanism, and energy absorption of several 3D-printed graded metamaterial beam constructions were carefully explored. The results show that the bending behavior of the novel lattice beam is promoted mainly due to the reinforced structure, especially under mixing reinforcement of FRP and Al face sheets. Additionally, it is discovered that the geometrical parameters and metamaterial core graded direction have a substantial impact on the failure process and energy absorption of FGLB structures. Lastly, multiobjective optimization is used to identify the ideal FGLB design parameters. These accomplishments open the possibility of creating new classes of high-performance metamaterial structures by combining gradient design with additive manufacturing.

A Comprehensive Formula to Predict the Shear Contribution of FRP Sheets in Strengthened Reinforced Concrete Deep Beams

A Comprehensive Formula to Predict the Shear Contribution of FRP Sheets in Strengthened Reinforced Concrete Deep Beams

Crack analysis and modeling in concrete beams reinforced with FRP composite sheets

In this article using the principles and relationships governing fracture mechanics and finite elements cracking in the first mode for reinforced concrete beams reinforced with FRP sheets are analyzed and modeled. In this method to simulate the crack in reinforced beams, the relations for determining the stress intensity coefficients with the presence of rebars and reinforcement sheets are developed. Here, it is assumed that a composite sheet is completely bound to the bottom surface of the beam under pure bending moment. In the proposed method beam components are divided into two categories, including components without cracks and components with cracks. In components without cracks, relations, equations, and the conventional stiffness matrix governing the beam are used, taking into account the changes in the moment of inertia caused by the presence of reinforcements and FRP sheets. In the finite component with a crack, the crack profile is simulated by creating a geometric defect in the beam section. So that the reduction in the hardness of the component with a crack is equivalent to the change in the dimensions of the discontinuity. Here, the changes in the hardness of the cracked component are calculated and presented as a function of the modified stress intensity coefficients. To ensure the correctness and accuracy of the presented method, all the analyzes are implemented in Abaqus software. The comparison of the obtained results shows that the presented method is a suitable method for the analysis of reinforced concrete structures resistant to cracking. So that it can be extended and developed for other models with proper accuracy.

Machine-learning-based models versus design-oriented models for predicting the axial compressive load of FRP-confined rectangular RC columns

To improve the prediction accuracy of axial compressive load of FRP-confined concrete columns, machine-learning techniques have been used recently. However, few studies have used machine learning to estimate the axial compressive load of FRP-confined rectangular RC columns. Therefore, this study introduces a state-of-art review of externally strengthened rectangular concrete columns with FRP composites: the influential parameters were introduced and their effects on the strength, ductility, and failure mode of FRP-strengthened columns were discussed. Hence, the critical design parameters were identified and used as input features in machine-learning modeling. From a practical point of view, special attention was paid to collecting any dataset related to steel reinforced rectangular concrete columns and externally confined with different types of FRP composites. These collected datasets were used to generate machine-learning models to predict the axial compressive load of rectangular RC columns confined by external FRP sheets, and were compared with existing design-oriented models. The proposed machine-learning models are found to be in good agreement with the test results in the datasets. In the comparison between the existing design-oriented models and the developed machine-learning models, the gradient boosting (GB) and random forest (RF) regressors are more accurate, and both methods achieved the lowest deviation value.

Presenting a strategy to prevent FRP debonding for strengthening RC connections

Defects in the beam-column connections of old RC frames significantly increase the vulnerability of exterior connections in an earthquake. One of the methods for improving the performance of defective connections in the previous studies was to use FRP. The noteworthy point in the past studies is the focus on 2D connections without considering the lateral beams and slabs. These elements in 3D connections simultaneously increase the confinement and increase the shear demand in the connection core. Therefore, considering the limited studies about the improvement of 3D weak connections using FRP, the aim of this study is to improve defective connections. On the other hand, the main challenge in using FRP is debonding. In this paper, a plan for the installation sequence of FRP sheets on 3D geometric connections presented, while avoiding the creation of holes or grooves on the concrete surface. For this purpose, five experimental specimens, including one connection with seismic details, two connections with defects, and two strengthened connections are tested in the laboratory under cyclic loading. The results show improvement in the behavior of the strengthened connections, moreover, FRP debonding was not observed.

Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets

Reinforced concrete (RC) slabs are widely strengthened in flexure by externally bonding (EB) carbon-fiber-reinforced polymer (CFRP) sheets, where debonding failure remains a critical issue. To solve the debonding problems, a self-locking device is initially proposed to enhance the anchorage at the end of FRP sheets for strengthening of RC slabs in this study. The effects on the debonding resistance and the improvement of the strengthening efficiency are experimentally investigated. Six one-way RC slabs strengthened with end-buckled and/or externally bonded CFRP sheets were prepared for the four-point bending tests. All strengthened specimens had higher ultimate loads than the reference specimen. While the slab strengthened by EB CFRP had a limited increase in ultimate load, the improvement was significant for the cases with hybrid anchored (HA) CFRP including both end-anchorage and external bonding, which was 46.2%. In this case, the interfacial stresses could be reduced and the end debonding can be avoided due to the increasingly tight anchoring effect, and the ultimate load can be increased even after partial debonding since the stress can continue to be transferred via mechanical anchorage. When the specimens were strengthened with HA CFRP, the surface treatment had a marginal influence on the strengthening effect. The strength of the slabs strengthened with HA CFRP decreased with the length of CFRP sheets, which is contrary to the trend of cases using EB CFRP. Finally, expressions were proposed to estimate the strain of the CFRP and load-carrying capacity of the strengthened members at the ultimate state, and the test results were within the range of the calculated results.

Shear Strengthening of Reinforced Concrete (RC) with FRP Sheets Using Different Guidelines

Shear Strengthening of Reinforced Concrete (RC) with FRP Sheets Using Different Guidelines

Detection of Debonding Area in Aluminium-GFRP Laminates by Electromagnetic Transducer

Electromagnetic Acoustic Transducer (EMAT) is applied to nondestructive testing of aluminum-GFRP laminates. Because of its high specific strength, laminated FRP came to be used in place of metal materials. However, once delamination is introduced by the impact force in the out-of-plane direction, the compressive strength in the in-plane direction is greatly reduced. To improve the tolerance for impact force, fiber metal laminates (FML) have been developed. Since debonding may occur at the interface of FRP and metal sheet, nondestructive detection of the debonding is required as health monitoring of the FML. In this study, GFRP laminates were molded on aluminum sheets, and we measured the distribution of standing wave amplitude in the aluminum sheets using EMAT for shear wave. In the bonded area, the shear wave is partially transmitted to the FRP on reflection at the boundary, which makes the attenuation coefficient larger than that in the debonded area. It was found that in scanning the EMAT, the standing wave amplitude starts to change when the center of the EMAT passes the boundary between bonding and debonding areas. It was also revealed that minimum size of the debonding area that EMAT can detect is comparable to its effective area. For accurate evaluation of the debonding area, resonant frequency measurement is recommended at each point.

Modeling the Nonlinear Behavior of Predamaged Reinforced Concrete Beams Retrofitted with Bonded and Jacketed FRP Sheets

Modeling the Nonlinear Behavior of Predamaged Reinforced Concrete Beams Retrofitted with Bonded and Jacketed FRP Sheets

Flexural Tests for Efficiency Evaluation of Spike Anchors on CFRP-Strengthened Concrete

Spike anchors are one of the most promising techniques to prevent or delay debonding in FRP reinforcement sheets. There are several parameters affecting the anchors' capacity, such as the embedment length and dowel angle. Regardless of the anchors' capacity, their contribution to the overall strength of the anchored joint is affected by a larger number of variables, including the bonded length behind the anchors, the number and arrangement of the anchors, and the contact surface between the anchor fan and the FRP sheet. This paper presents experimental results of 10 tests conducted on concrete beams. In the tests, anchored joints reached peak loads up to 155% of those of unanchored, bonded joints. The main finding of the research is that the bond length in front of and behind the anchors affects both the peak load and the overall behaviour, with unbonded anchored joints exhibiting a poor behaviour and premature slippage of the anchor, without achieving its failure due to fibre rupture.