Polymer Grid Research Articles

Flexural performance of BFRP grid–ECC in strengthening damaged RC beams

An innovative strengthening method combining basalt fiber reinforced polymer (BFRP) grid and engineered cementitious composites (ECC) is proposed to address the shortcomings in the durability of bonded connections with FRP materials and concrete materials. In this method, the BFRP grid wraps around the original damaged reinforced concrete (RC) structure, and the outer layer is cast with ECC, which mainly acts as a binder to enhance the bonding effect. In order to verify the effectiveness of the proposed method, 10 specimens were prepared and their flexural characteristics and load carrying capacity were investigated. Some factors that may affect the effectiveness of strengthening, such as the degree of initial damage (expressed in terms of different initial damage loads), the thickness of the BFRP grid, and the method of reinforcement, were considered in the experiments. The experimental results show that the proposed strengthening method can significantly improve the bending capacity of the damaged RC beams (7%~43%) without significantly enlarging the cross-section and self-weight. In addition, during the loading tests, localized peeling between the BFRP grid–ECC layer and the RC beams occurs at the time of damage, meanwhile the BFRP grid breaks. This suggests that it is feasible to enhance the bond between BFRP grid and RC by using ECC layer instead of other materials as the bonding agents. The proposed strengthening method has a promising application in strengthening old/residual bridges. In addition, a simple formula for predicting the flexural load capacity of the strengthened beams is derived. The ratio of the proposed formula to test value is between 0.853 and 1.304. The flexural load capacity predicted by the proposed formula is in better agreement with the experimental results.

Evaluation of the shear behavior of RC beams strengthened with prestressing BFRP grids

The shear behavior of reinforced concrete (RC) beams strengthened with prestressing basalt-fiber-reinforced polymer (BFRP) grids was experimentally evaluated. Parameters, including grid type, concrete strength, and prestress direction and level, were numerically investigated. Equations for the shear capacity of prestressing grid-strengthened beams were derived. The results showed that using BFRP grids with a 30 % prestress level increased the number of mid-span flexural cracks in the strengthened beam but reduced their length. Compared to the control beam, the load capacity under the serviceability limit state was enhanced by 48 %. The strain responses of the grids exhibited a linear stage followed by a nonlinear stage due to diagonal cracks. The maximum strains of longitudinal and transverse grid tendons in the prestressed strengthened beam decreased by 15 % and 30 %, respectively, compared to the non-prestressed beam. The BFRP grids showed a comparable strengthening effect to low-modulus carbon-fiber-reinforced polymer grids. Increasing concrete strength greatly improved the shear capacity of RC beams. The enhancement effect was greater for transverse tendons with a 30 % prestress level than for longitudinal tendons with a 60 % prestress level. The derived equation accurately predicted shear capacities in experiments or simulations within an error range from −4.7–1 %.

Flexural performance of UHPC two-way slab reinforced with FRP bars

The flexural behaviors of ultra-high-performance concrete (UHPC) two-way square slabs reinforced with fiber-reinforced polymer (FRP) bars were studied experimentally. Flexural tests were conducted on eight specimens, varying in reinforcement type, reinforcement ratio and confinement condition in compressive zone. Test results showed that the bridging effects of steel fibers in UHPC can mitigate the brittle characteristics of slab experiencing punching shear failure. The failure modes of slabs shifted from tensile failure to compressive failure by increasing the tensile strength of bar, leading to an improvement on the flexural capacity and ductility. The ultimate capacity of the slab with a reinforcement ratio of 1.06 % was 15.8 % greater than that of the slab with a reinforcement ratio of 0.67 %. By incorporating a layer of basalt fiber-reinforced polymer (BFRP) grid in the compressive zone to confine UHPC, the bearing capacity and ductility index of the slab increased by 17.8 % and 56.7 %, respectively. Introducing an enhancement coefficient to account for the confinement effect induced by the BFRP grid, a method was developed for predicting the flexural capacity of FRP reinforced UHPC two-way slab subjected to a local load at the mid-span, and its prediction accuracy was well verified.

Numerical simulation of post fire-behaviour of high strength lightweight reinforced concrete beams strengthened with basalt fiber-reinforced polymer grid and engineered cementitious composites jacket

Numerical simulation of post fire-behaviour of high strength lightweight reinforced concrete beams strengthened with basalt fiber-reinforced polymer grid and engineered cementitious composites jacket

Study on Flexural Performance of Reinforced Concrete Beams Strengthened with FRP Grid–PCM Composite Reinforcement

To study the flexural performance of fiber-reinforced polymer (FRP) grid–polymer cement mortar (PCM)-composite-strengthened RC beams, the finite element numerical simulation of FRP grid–PCM composite RC beams is carried out using ABAQUS to analyze the effects of the amount of FRP grid reinforcement, the type of FRP grid material, and the geometry of FRP grid on the flexural performance of reinforced concrete beams and to establish the flexural capacity calculation formula of FRP grid–PCM-reinforced RC beams in case of debonding failure, based on analysis of the influencing factors. The results show that increasing the reinforcement of the FRP grid and increasing the stiffness of the FRP grid can improve the flexural bearing capacity of RC beams, and the change of FRP grid geometry has little effect on the flexural bearing capacity of RC beams. The established formula for calculating the flexural bearing capacity of FRP grid-reinforced concrete beams can better predict the flexural capacity of reinforced concrete beams under peeling failure.

Shear behavior of pre-damaged RC beams strengthened with UHPFRC-CFRP grid layer

Ultra-high performance fiber reinforced concrete (UHPFRC), incorporating recycled tyre fibers, and carbon fiber-reinforced polymer (CFRP) grid were utilized to strengthen the pre-damaged reinforced concrete beams caused by coupling action of sustained loads and marine environment. The failure modes, characteristic loads, deflection features, and strain behavior of the strengthened beams with various types of UHPFRC, thicknesses of UHPFRC layers, CFRP grid ratios, and CFRP grid layout angles were investigated. The results indicated that they exhibited the typical shear failure, and their characteristic loads increased by 102 %–205 % compared to the undamaged beam. By increasing the thickness of the UHPFRC layer and the CFRP grid ratio, and adopting 45° CFRP layout angle, the cracking stiffness, energy absorption capacity, and shear force sharing ability would be further improved, while adopting the UHPFRC incorporating recycled tyre fibers would decrease the ductility. Moreover, analytical models were developed to calculate the ultimate loads, manifesting reasonable accuracy.

Flexural behavior of reinforced concrete beams externally strengthened with ECC and FRP grid reinforcement

To prevent premature delamination of FRP sheets in strengthened concrete structures, this study explores a novel method of laying a composite layer of fiber reinforced polymer (FRP) grid reinforced with engineering cementitious composite (ECC), designated as FGRE, and applied at the soffit of reinforced concrete (RC) beams to improve its flexural performance. Experimental studies were conducted on RC beams with different strengthening configurations to validate the effectiveness of the proposed strengthening method. In addition, analysis on the working mechanism and a parametric analysis were performed for the composite strengthened beam using nonlinear finite element modeling. The experimental results showed that FGRE composite layers can significantly improve the bearing capacity of RC beams. Compared with the control RC beam, the FGRE composite strengthening technique significantly increased the cracking load, yield load, and ultimate load of the beam specimens up to 28, 11, and 12 %, respectively. The ECC grout layer maintained a good bonding performance with the concrete substrate until beam failure. The flexural capacity of RC beams with the proposed FGRE strengthening systems is determined by the thickness of the ECC layer. In addition, the effect of strengthening on the flexural capacity was more significant when the yield and tensile strength of the steel reinforcement were lower. Moreover, the prediction deviation from the experimental data of the FE models and analytical models for the ultimate load-bearing capacity were less than 2 and 7 %, respectively. It can be concluded that the proposed FGRE system is a viable solution to enhance the flexural capacity of RC beams.

Numerical Analysis on Flexural Shear Behavior of Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer Grid and Engineered Cement Composites

Numerical Analysis on Flexural Shear Behavior of Reinforced Concrete Beams Strengthened with Fiber-Reinforced Polymer Grid and Engineered Cement Composites

Flexural behavior of pre-damaged RC beams strengthened with UHPFRC-CFRP grid layer

Ultra-high performance fiber reinforced concrete (UHPFRC) using recycled tyre fibers and carbon fiber-reinforced polymer (CFRP) grid were combined to strengthen the pre-damaged reinforced concrete (RC) beams caused by coupling action of sustained loads and marine environment. The flexural tests were conducted to investigate failure modes, characteristic loads, deflection features, and strain behavior of the strengthened RC beams with different configurations. The results showed that they exhibited the typical bending failure without interfacial debonding, and their cracking, yield, and ultimate loads increased by 64.7 %−152.9 %, 105.7 % to 192 %, and 65.4–131.2 % compared with that of the RC beam (B0). By increasing the thickness of the UHPFRC layer and adopting the Y-type UHPFRC (using recycled tyre fibers), the stiffness, ductility, and synergistic performance among the main materials would be further improved, while the increase of the CFRP grid layers would decrease the ductility. Furthermore, analytical models considering the coupling action of sustained loads and marine environment were developed to calculate the characteristic loads, manifesting reasonable accuracy. The proposed UHPFRC-CFRP grid strengthening method has excellent mechanical and durability performance, cost-effectiveness, and environmental benefits, which can serve as a valuable reference for the innovation and development of structural strengthening technology.

Characterization of Bond Mechanism between Concrete and Cabon Fiber Reinforced Polymer Grids: Experimental Study

Characterization of Bond Mechanism between Concrete and Cabon Fiber Reinforced Polymer Grids: Experimental Study

Numerical analysis of reinforced concrete beams enhanced in shear with external polymer cement mortar‐bonded FRP grid

AbstractThis paper presents a finite element (FE) modeling approach to assess the performance of reinforced concrete (RC) beams strengthened in shear using external polymer cement mortar (PCM)‐bonded basalt fiber‐reinforced polymer (BFRP) grids. The study begins with an experimental program and FE modeling of a double shear bond test, simulating the bond behavior between the BFRP grid and RC beams with PCM. Subsequently, a FE model for BFRP shear‐strengthened beams explores key parameters, including shear span to depth ratio, bonding agent type (PCM and epoxy resin), and angles between BFRP grid bars and the beam axis. Comparative analysis with experimental results verifies the accuracy of the FE models. Additionally, a critical parameter, the BFRP reinforcement ratio, is numerically investigated, revealing that achieving a ratio between 1.33% and 1.55% enhances both maximum load and deflection in beams strengthened with externally bonded composite reinforced mortar.

Axial compressive behavior of fire‐damaged RC column strengthened with ECC‐CFRP grid

AbstractTo study the axial compressive performance of fire‐damaged reinforced concrete (RC) columns strengthened by engineered cementitious composites (ECC) combined with carbon fiber reinforced polymer (CFRP) grids, eight RC columns were designed and fabricated to analyze the effects of fire exposure time, thickness of the strengthening layer, incorporation of the CFRP grid, and subjecting the strengthening layer to direct compression on the axial compressive performance of the strengthened columns by conducting fire and compressive tests. It was found that the ECC‐CFRP grid strengthening significantly increased the axial compressive load and axial deformation of the columns; the bearing capacity of the strengthened column subjected to fire for a longer period of time was lower under the same strengthening condition; when the thickness of the strengthening layer was increased, the load‐carrying capacity and axial deformation of the column were enhanced; the addition of CFRP grids could further improve the mechanical properties of the repaired column; when the strengthening layer was directly compressed, the axial deformation was significantly reduced, although the bearing capacity would be further increased. An analytical model of the strengthened column was established using the ABAQUS software, and a formula for calculating the bearing capacity of the strengthened column was derived.

Tensile behavior of ultra-high-performance concrete (UHPC) strengthened with fiber reinforced polymer (FRP) grid

In order to enhance the tensile strength and toughness of Ultra-High Performance Concrete (UHPC) at the macro level, this study developed Fiber-Reinforced Polymer (FRP)-reinforced UHPC composite materials. The steel fibers and FRP grids in UHPC play a reinforcing and toughening effect on UHPC at two different levels. Therefore, this paper examined, evaluated 48 FRP grid-UHPC specimens. The study includes independent parameters such as grid type (Carbon-FRP, Basalt-FRP, stainless steel wire mesh), grid size (5 × 5 mm, 10 × 10 mm, 20 × 20 mm), steel fiber content (0 %, 0.5 %, 1.0 %, 1.5 %, 2.0 %), grid layers (1 layer, 2 layers, 3 layers, 4 layers), and the fiber bundle impregnation status. Based on the test results, a simplified tensile stress-strain relationship for FRP grid-UHPC was proposed. The test results show that when the steel fiber content is less than 1 %, the FRP grid does not exert its reinforcing effect. The FRP grid-UHPC composite material exhibits strain-softening behavior. However, when the steel fiber content is greater than 1 %, the FRP grid-UHPC specimens all exhibit strain-hardening phenomena. Compared to other grids type, the enhancement and toughening effects on UHPC are more pronounced when using CFRP grids. Specifically, when using a 20 × 20 mm CFRP grid, the tensile stress can be increased by 30.36 %. Regardless of whether dry grids or impregnated grids are used, increasing the grid layers greatly improves the peak strain and stress of UHPC. Compared to dry grids, impregnation with epoxy resin further improves the stress state between fiber filaments in FRP grids, resulting in a more significant improvement in the tensile performance of FRP grid-UHPC composite materials. Finally, based on experimental data, a tensile stress-strain model for FRP grid-UHPC considering different mesh ratios was proposed and validated against experimental results. These conclusions and findings are of great significance for understanding and optimizing the performance of FRP grid-UHPC composite materials, providing valuable references for the future research and application of FRP grid-UHPC composite materials.

Beam-Column Joint Retrofitting Using Basalt Fiber- Reinforced Polymer Grid and Cementitious Matrixes

Beam-Column Joint Retrofitting Using Basalt Fiber- Reinforced Polymer Grid and Cementitious Matrixes

Cyclic Lateral Loading Behavior of Thin-Shell Precast Concrete Wall Panels

Two precast concrete thin-shell wall panels were subjected to reverse-cyclic lateral loads to replicate wind fatigue over a 50-year design lifetime prior to loading to failure. The panels consisted of an outer wythe of concrete connected to light-gauge steel framing. Wire mesh was used to reinforce the concrete panel skin. Rivets provided a connection between the steel studs and the concrete panel. Two reinforced concrete (R/C) beams were integrated into the top and bottom parts of the panel, isolated from the concrete face by a thin sheet of extruded polystyrene (XPS) foam insulation. To connect these beams with the concrete face through the rigid foam insulation, a carbon-fiber-reinforced polymer (CFRP) grid was utilized. The aim of the experimental program was to characterize the behavior of the concrete and steel framing panel, with particular attention focused on the connections between the various structural elements of the panel. The first and second thin-shell panels survived the fatigue loading cycles and behaved elastically through failure-level lateral load cycles equivalent to 54 psf (2.6 kPa) and 66 psf (3.2 kPa) of applied uniform load, respectively. The failure mode was the separation of the top R/C beam from the concrete panel on the pull stroke of the loading cycle (when the connection between the beam and the concrete shell was in tension) for both specimens.

Behavior of 3D-printed HPC plates with FRP grid reinforcement under bending

High-performance concrete (HPC) has become increasing popular in structural engineering. Capitalizing the advanced construction technology of 3D concrete printing (3DCP) and merits of HPC, structures with various profiles could be designed and constructed easily. As the mechanical properties of 3D printed concrete may be worse than the corresponding concrete cast by the conventional technology, this study proposes to evolve flexible fiber-reinforced polymer (FRP) grid as reinforcement for 3D printed HPC plates. Twelve plates were tested to explore the effects of the loading direction and fabrication type on the flexural behavior of FRP grid reinforced HPC plates. The results showed that the performance of the 3D printed HPC plates can be considerably enhanced owning to the FRP grid reinforcement. Additionally, the μCT-scanned images show that the pores between deposition layers were elongated due to the movement of the nozzle during printing, and the pores were stretched in the printing direction. The flexible FRP reinforcement may allow 3D printing of FRP reinforced concrete elements in the future.

Development of theoretical model for predicting flexural behavior of GFRP reinforced concrete beams with CFRP grid‐reinforced ECC

AbstractGlass fiber reinforced polymer (GFRP) concrete beams reinforced by carbon fiber reinforced polymer (CFRP) grid reinforced engineering cementitious composite (ECC) have excellent flexural performance and corrosion resistance in marine environments. However, the lack of a reliable theoretical model for predicting the flexural behavior of the hybrid beams makes it challenging apply them in the practical engineering. To address this issue, a series of numerical models were established to investigate the effects of key parameters on the flexural behavior of the hybrid beams, including the peak load, the neutral axis height, and the sectional stress distribution. Subsequently, based on the influence of the failures of different materials on the flexural performance of the hybrid beam, the loads of four feature points were calculated in the theoretical model to predict the entire load–displacement curve. Finally, the application range of the theoretical model was given based on the neutral axis height. The results showed that the cover thickness of the ECC, the GFRP reinforcement ratio and the cross‐sectional area of the CFRP grid were the key factors affecting the flexural performance of the hybrid beams. The theoretical model established in this study can predict the load–displacement curve accurately and can provide a reference for the subsequent design of the hybrid beams.

Poly[[[μ3-3-(2-carboxyl-atophen-yl)propionato][μ2-N,N'-(ethane-1,2-di-yl)bis-(pyridine-4-carbox-amide)]copper(II)] monohydrate], a layered coordination polymer with (4,4) topology.

In the title compound, {[Cu(C10H8O4)(C14H14N4O2)]·H2O}n, the CuII cations are coordinated in a square-pyramidal fashion, with trans pyridyl-N donor atoms from two N-(2-(pyridin-3-yl-amino)-eth-yl)isonicotinamide (pein) ligands in the basal plane. The other three coordination sites are taken up by carboxyl-ate O-atom donors from three different 3-(2-carb-oxy-phen-yl)propionate (cpp) ligands. The central ethyl-enedi-amine segments of the pein ligands are disordered equally over two sets of positions. {Cu2O2} rhomboid clusters are connected into [Cu(cpp)(pein)]n (4,4) coordination polymer grids by the full span of the cpp and pein ligands. Individual layer motifs stack in an AAA pattern along the a axis by means of inter-layer hydrogen-bonding inter-actions.

Behavior of Ultrahigh-Performance Concrete Plates Encasing Steel H-Piles

Steel H-piles are exposed during their service life to wet-dry cycles in combination with salts, such as deicing, that may result in corrosion, leading to cross-sectional loss and reduction in axial load-carrying capacity. This paper proposes an innovative repair method for corroded steel H-piles using ultrahigh-performance concrete (UHPC) plates. The UHPC plates are reinforced with carbon fiber-reinforced polymer (CFRP) grids. The UHPC plates bridge the corroded segment so that the axial force bypasses the corroded segment. The UHPC are bolted to the steel H-pile using high-strength bolt connectors (HSBCs). Eleven steel H-piles bolted with UHPC plates were investigated experimentally under push-out loading to quantify the axial force that can be transferred from a steel H-pile to UHPC plates through HSBCs. The examined parameters were the UHPC plate thickness, the diameter of HSBC, and the number of CFRP grid layers. The results were compared with those predicted using different design codes and guidelines. The UHPC plates attached to the steel H-pile could transfer axial loads ranging from 35% to 98% of the steel H-piles’ ultimate axial capacity. Further, the installation of the UHPC plate on a steel pile can be completed in about 2 h with minimal equipment, making it a promising repair candidate in real-world applications.

Lattice discrete particle modeling of the cycling behavior of strain-hardening cementitious composites with and without fiber reinforced polymer grid reinforcement

Strain-hardening cementitious composites (SHCC) has become increasingly prevalent in structural design. Compared to ordinary concrete, SHCC exhibits ultra-high tensile ductility, significant strain-hardening behavior, very fine multi-point cracking, high energy dissipation, and good durability. One robust model for simulating reinforced concrete behavior is the so-called Lattice Discrete Particle Model (LDPM), and specifically LDPM-F which includes the effect of fiber reinforcement. The present cycling constitutive law implemented in LDPM and the cycling fiber-bridging law in LDPM-F though cannot accurately capture the residual tensile plastic strain, loading–unloading path, and energy dissipation of SHCC during cyclic tension. To solve these concerns, the cycling tension–compression constitutive law and the nonlinear cycling fiber-bridging law were reformulated. Further, the new model was used to simulate the cycling tensile behavior of plain concrete, SHCC, and Fiber-Reinforced Polymer (FRP) grid reinforced SHCC (FRP-SHCC). Simulation results show that the multi-point cracking, crack widths, and ultra-high ductility properties are correctly captured by LDPM-F. In addition, LDPM-F with the modified cycling constitutive model can effectively simulate the cycling tension–compression behavior, accurately reproducing the stress–strain relationship, residual plastic strain, and overall dissipated energy. Finally, the simulated failure modes agree well with the actual fracture planes of these materials under cyclic tension.