FRP Grids Research Articles

Axial compression performance of underwater columns reinforced with stainless steel tube-FRP grids

Stainless steel tubes have excellent plasticity and ductility, and FRP grids have favorable advantages for application in specific structural reinforcements. For systems including underwater construction without drainage, underwater columns reinforced with stainless steel tube-FRP grids are proposed using nondispersive mortar (NDM) as the reinforcement layer to best leverage the material properties of all elements. This paper carried out axial compression tests on 18 underwater columns reinforced with stainless steel tube-FRP grids (SS-FGWCs), 6 columns reinforced with stainless steel tube-FRP grids on land (SS-FGLCs), 3 underwater columns reinforced with stainless steel tubes (SSWCs), and 3 unreinforced concrete columns. The research parameters include the number of FRP grid layers, the types of FRP grids, and the reinforcement layer mortar pouring environments. The test results showed that FRP grids can be combined with stainless steel tubes (SSs) and nondispersive mortar (NDM) to reinforce concrete columns in underwater construction without drainage. In addition, compared with those of the SSWC specimens, after the BFRP grid and CFRP grid were built in, the ultimate stresses of the specimens increased by 13.4% ∼ 20.8% and 19.5% ∼ 25.4%, respectively, and the ultimate strains increased by 6.8% ∼ 31.7% and 21.8% ∼ 59.1%, respectively. Compared to BFRP grids, CFRP grids provide better reinforcement of the underwater columns. Existing prediction models were evaluated for ultimate stress calculations, the calculation methods for the ultimate stress and ultimate strain applicable to the SS-FGWCs and SS-FGLCs were revised, and a calculation model for the FRP grid failure point was proposed. Finally, a corresponding full stress–strain curve model was established.

Axial Compression Performance Test and Bearing Capacity Calculation of RC Square Column Strengthened by FRP Textile Grid-reinforced ECC

In order to investigate the strengthening effect of FRP textile grid reinforced ECC composite (abbreviated: TRE) restrained RC columns, this study conducted experimental and theoretical studies on the axial compression performance of TRE strengthened RC square columns with RC square columns as the research object. The effects of the chamfer radius of the original column, the type of FRP grid and the number of layers of the grid on the axial compression performance of the TRE-strengthened RC square column were considered. The axial compression tests showed that the strengthened layer exhibited excellent crack control, the reinforced column cracked as a whole without breaking when it was damaged, and the strengthened layer adhered well to the core concrete. Compared with unstrengthened specimens, the compressive strength, ductility and deformation capacity of the RC square column under TRE restraint were significantly higher. The increase of chamfer radius of square column makes the TRE restraint effect better. Increasing the number of grid layers can significantly improve the ultimate bearing capacity and ductility of the strengthened specimens. The effects of TRE strengthening methods with different FRP grids differed, with the same number of grid layers, the ultimate bearing capacity of the specimens strengthened with CFRP grid reinforced ECC was higher, and the cracking load of the specimens strengthened with BFRP grid reinforced ECC was higher. A model for calculating the ultimate bearing capacity of the TRE-constrained RC square column was established, and the validity of the model was verified by comparing the results of this test.

Finite Element Analysis of a Concrete Beam Reinforced with FRP Grids

Finite Element Analysis of a Concrete Beam Reinforced with FRP Grids

Experimental evaluation of concrete confined with hand laid carbon FRP grids

In many cases structures serve in highly corrosive environments and as a result the service life of the elements is significantly reduced. An alternative could be the use of fiber reinforced composites. The skepticism behind using this material has to do with the lack of ductility. A different approach must be followed in the design of such structures to achieve a behavior similar to regular reinforced concrete. In this case failure should initiate and end in concrete with confinement providing ductility. This paper investigates concrete confinement through experimental testing of concrete specimens utilizing embedded custom made, hand laid carbon FRP (CFRP) grid. The grid was formulated into the shape of a tube and embedded in concrete specimens to evaluate the grid tube effect on concrete properties. Typically, the FRP material is applied externally using an adhesive. In this case the hand laid CFRP grid was pre-manufactured and was embedded into concrete. Standard sized cylindrical specimens were manufactured using hand laid CFRP grid. Some of the specimens were made using plain concrete and served as reference specimens. The specimens were loaded axially in compression. This allowed the evaluation of the extent to which the hand laid tubular shaped grid positively affected the ultimate capacity and deformation of concrete. This application is unique and its confinement effectiveness needs to be investigated and evaluated. Experimental results show a very significant change in the maximum capacity and deformability for confined concrete. Depending on the amount of CFRP reinforcement in the grid strands the enhancement in strength was between 42 % and 58 %. The deformability of the specimens with the hand laid CFRP grid was between 134 % and 196 % higher compared to the reference specimens, with higher values associated with higher amounts of the CFRP grid.

Structural response of high strength concrete beams using fiber reinforced polymers under reversed cyclic loading

This paper investigates the response of high strength concrete (HSC) beams subjected to reversed cyclic loading using carbon fiber-reinforced polymer (CFRP), glass fiber-reinforced polymers (GFRP), and hybrid FRP/steel bars as bottom tensile reinforcement. Five HSC beams with a rectangular cross-section were prepared and poured using with a 28-day concrete compressive strength of 60 MPa (8.7 ksi). A displacement-controlled reversed cyclic loading has been applied to all the beams. The test setup has been designed to represent seismic effect on structures. Flexural capacity, concrete and reinforcement steel strains, cracking behavior, and ductility results were obtained. The hybrid steel/FRP has shown an improved performance in terms of flexural capacity, strains, and ductility. While the inclusion of FRP grids reduces the flexural capacity, this can be improved by adding more layers of FRP. Overall, the nominal moment of the hybrid sections were the highest between all beams. The ACI 318 code’s empirical equations showed close results in terms of the tensile strength of the FRP. The ACI 440R has shown overestimated nominal moment values compared to the experimental results.

Flexural behavior of seawater sea-sand concrete beams reinforced with BFRP bars/grids and BFRP-wrapped steel tubes

This paper presents an investigation of a new type of seawater sea-sand concrete (SWSSC) beam which consists of BFRP bars/grids and BFRP-wrapped steel tubes (BWST). The transversally placed basalt fiber-reinforced polymer (BFRP) grid units act as shear stirrups, while the longitudinal BWST near the bottom area is used to improve the tension resistance. The flexural behavior of the hybrid SWSSC beams under different BFRP reinforcement ratios with or without the BWST were experimentally tested and compared. In addition, a finite element model (FEM) was established and a parametric study was conducted to show the influence of key parameters. The results showed that the placement of the BWST could significantly improve the mechanical properties of the hybrid beams, especially in terms of improving the flexural stiffness and reducing crack width. In addition, the full-length embedded BWST could shorten the height of the vertical cracks developed along the FRP grids, and denser diagonal cracks developed in the shear span.

Experimental Study on Eccentric Compressive Performance of Concrete Column Strengthened with CFRP Grid Reinforced ECC Matrix

Carbon‐fiber‐reinforced polymer (CFRP) grid and engineered cementitious composite (ECC) were combined in this study to strengthen concrete columns. The influences of the number of layers, the overlap length of CFRP grids, and the eccentricity on the bearing capacity and rigidity of reinforced concrete columns were determined. The results show that the principal failure of the reinforced column was debonding of external ECC from FRP grids at the compressive area, edges, or sides. Significant enhancement in the ultimate bearing capacity and rigidity of eccentrically loaded columns was observed after they were externally reinforced by CFRP grids and ECC; such enhancement increased with the number of reinforced layers. Eccentricity made little difference to the enhancement rate of bearing capacity when the number of reinforced layers was the same. At different eccentricities, the composite layers at the tensile area and the compressive area had different contributions to the bearing capacity. An effective bond and efficient stress transfer could be ensured as long as the overlap length between CFRP grids reached 120 mm.

Axial Compressive Behavior of Square-Section Concrete Columns Transversely Reinforced with FRP Grids

Abstract Using grid-type stirrups as transverse reinforcements in reinforced concrete (RC) columns can not only provide higher confinement of the concrete core but also lead to an improved concrete...

Shear strengthening of RC beams with FRP grid-reinforced ECC matrix

Fabric reinforced cementitious matrix (FRCM) composites are increasingly used for flexural and shear strengthening of reinforced concrete (RC) beams. This paper presents the results from an experimental study on the effectiveness and performance of a new FRCM system made of FRP grid-reinforced ECC matrix (referred to as “FGREM” for brevity) for shear strengthening of RC beams. A total of twelve shear-critical RC beams were constructed and tested. The parameters varied between the tests included the type of FRP grids, the type of cementitious matrix, the installation method of the shear strengthening system (prefabricated or cast-in-place), and the shear span-to-depth ratio of the beams. The crack patterns of all the tested beams were monitored using the digital image correlation (DIC) technique. Test results indicated that interfacial debonding of the shear strengthening layer and separation of the concrete side covers were two typical failure modes for the beams strengthened with the cast-in-place method and the prefabricated method, respectively. The gains in the shear capacity of the strengthened beams ranged from 50.9% to 160.6% with respect to the reference beams. Compared to the cast-in-place installation method, the prefabricated FGREM was demonstrated to be more efficient for shear strengthening of the RC beams.

Flexural strengthening of RC beams with CFRP grid-reinforced ECC matrix

This paper investigates the flexural performance of a series of RC beams externally bonded with carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composite (ECC) matrix. A total of 15 RC beams, including three control and twelve strengthened, were prepared and tested. The test variables included the longitudinal reinforcement ratio, the strengthening configurations that consisted of different cementitious matrices (ECC versus epoxy mortar), different installation methods (prefabricated versus cast-in-place), and different stiffness of CFRP grids. The test results showed that ECC is an ideal cementitious matrix for the strengthening applications where FRP grids are used as the external reinforcement. The flexural strengthening configuration using the epoxy adhesive to bond prefabricated CFRP grid-reinforced ECC plate proved to be the most efficient solution. For such configuration, the plate-end debonding can be avoided and the mid-span debonding can be almost suppressed. Flexural capacity analysis was conducted and demonstrated that the plane section assumption is valid and the full strength composite action can be nearly achieved for the strengthening system. The average ratio of the predicted peak loads to the experimental ones of the strengthened RC beams was 1.05.

Seismic Performance of Multistorey Masonry Structure with Openings Repaired with CFRP Grid

FRP composites have been used for strengthening RC and masonry structures for decades. However, the researches on repairing multistorey masonry structures using FRP grids were relative less. In the present paper, an experimental study on the seismic performance of multistorey masonry structure with openings repaired with CFRP grid is introduced. Specifically, a 1/3‐scale three‐floor masonry wall with window openings was tested under quasistatic action to simulate the seismic damages. The damaged masonry wall was then repaired by externally bonding CFRP grids to the areas where the cracks intensively occurred. The repaired masonry wall was retested under the same loading to investigate the seismic resistance and assess the recovery attributed from the CFRP grid repairing. The findings of this study showed that CFRP grid repairing could effectively postpone or even prevent the occurrence and development of cracking. The seismic resistance of the masonry, including shear capacity, energy dissipation capacity, deformability, stiffness degradation, and ductility, was restored. The application of CFRP grid may shift the failure mechanism of the multistorey masonry wall. The recommendation of repair scheme for the similar structures was also proposed in accordance with the findings of the present work.

Retrofitting of squat masonry walls by FRP grids bonded by cement-based mortar

Retrofitting of squat masonry walls by FRP grids bonded by cement-based mortar

Ageing Problems of GFRP Grids Used for Masonry Reinforcement

In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on GFRP (Glass Fiber-Reinforced Polymer) grids. The physic-mechanical properties of different types of glass FRP grids were investigated. GFRP specimens were subjected to environmental agents including freeze-thaw, high relative humidity, high temperature. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; GFRP grids are sensitive to alkaline attack when resin does not provide adequate protection to fibers.

FRPグリッドを用いたPCM吹付け工法によるトンネル補強手法に関する解析的評価

Degradation of lining concrete happens naturally in the tunnels that have been commissioned for several decades, which require proper maintenance to ensure their safety and effective functions. The PCM shotcrete method by means of FRP grid, with the characters of high strength, low weight, high workability, strong resistance to corrosion, and negligible influence on the existing structures, has been used in tunnel maintenance to repair the damaged lining of some aged tunnels. Up to now, the construction cases are still few, and the design routine of this method based on quantitative evaluation on the reinforcement effect has not been established. In this study, the shear bond strength and the shear stiffness of typical FRP grids were estimated by conducting direct shear tests on FRP-PCM specimens. Those parameters were input into a numerical model of tunnel to quantitatively estimate the displacement control effect of the FRP-PCM method on tunnel lining. The experiment and numerical simulation results show that the FRP-PCM method has good reinforcement effect on tunnel lining and has high potential to be applied extensively in the maintenance of aged tunnels.

Kinematic FE limit analysis homogenization model for masonry walls reinforced with continuous FRP grids

A homogenization model for periodic masonry structures reinforced with continuous FRP grids is presented. Starting from the observation that a continuous grid preserves the periodicity of the internal masonry layer, rigid-plastic homogenization is applied directly on a multi-layer heterogeneous representative element of volume (REV) constituted by bricks, finite thickness mortar joints and external FRP grids. In particular, reinforced masonry homogenized failure surfaces are obtained by means of a compatible identification procedure, where each brick is supposed interacting with its six neighbors by means of finite thickness mortar joints and the FRP grid is applied on the external surfaces of the REV. In the framework of the kinematic theorem of limit analysis, a simple constrained minimization problem is obtained on the unit cell, suitable to estimate – with a very limited computational effort – reinforced masonry homogenized failure surfaces. A FE strategy is adopted at a cell level, modeling joints and bricks with six-noded wedge shaped elements and the FRP grid through rigid infinitely resistant truss elements connected node by node with bricks and mortar. A possible jump of velocities is assumed at the interfaces between contiguous wedge and truss elements, where plastic dissipation occurs. For mortar and bricks interfaces, a frictional behavior with possible limited tensile and compressive strength is assumed, whereas for FRP bars some formulas available in the literature are adopted to reproduce the delamination of the truss from the support. Two meaningful structural examples are considered to show the capabilities of the procedure proposed, namely a reinforced masonry deep beam (0°/90° continuous reinforcement) and a masonry beam in simple flexion for which experimental data are available. Good agreement is found between present model and alternative numerical approaches.

Concrete Slabs Reinforced with FRP Grids. II: Punching Resistance

Concrete Slabs Reinforced with FRP Grids. II: Punching Resistance

Closure to “Concrete Slabs Reinforced with FRP Grids. II: Punching Resistance” by Stijn Matthys and Luc Taerwe

Closure to “Concrete Slabs Reinforced with FRP Grids. II: Punching Resistance” by Stijn Matthys and Luc Taerwe