Steel Fiber-reinforced Polymer Research Articles

Effect of steel–FRP ratio and FRP wrapping layers on tensile properties of glass FRP-wrapped ribbed steel reinforcing bars

Effect of steel–FRP ratio and FRP wrapping layers on tensile properties of glass FRP-wrapped ribbed steel reinforcing bars

Experimental research on the progressive collapse resistance of concrete beam-column sub-assemblages reinforced with steel-FRP composite bar

The progressive collapse behavior of conventional reinforced concrete frame structures caused by the loss of columns has been widely investigated over the past years. However, few papers on the improvement of the structural progressive collapse resistance accounting for the mechanical properties of the reinforcement material are reported. As a kind of reinforcement material of reinforced concrete frames, steel-FRP composite bar (SFCB) has the typical feature of controllable post-yield stiffness. This paper explored and compared the progressive collapse characteristics of concrete frames reinforced with SFCBs, steel bars and hybrid reinforcements including both steel bars and FRP bars. Scaled pushdown experiments based on the alternate load path method were conducted to study the effect of post-yield stiffness on the progressive collapse resistance of beam-column sub-assemblages. The experimental results demonstrated that the SFCB specimens experienced three mechanical actions: flexural action, post-yield stiffness plus compressive arch action (PYSCAA) and catenary action. The feature of the PYSCAA differed significantly from the second action of the specimen reinforced with steel bars. Due to the effect of the post-yield stiffness, not only was the load capacity of SFCB specimens significantly enhanced, but also the transition displacements from the PYSCAA to the catenary action were delayed. Meanwhile, the finite element method was employed to simulate the whole progressive collapse process of the specimens, and the simulation results agreed well with the experimental ones. Parametric analyses based on numerical simulations proved that the application of SFCBs was beneficial to reduce the vulnerability of progressive collapse for concrete frames. The ratio of post-yield modulus to initial elastic modulus of SFCBs was found to be the key factor affecting the characteristics of the progressive collapse resistance, and the optimal ratio of 0.30 is recommended.

Experimental and numerical studies on the flexural behavior of fibre reinforced concrete beams with innovative hybrid FRP-wrapped steel bars

ABSTRACT The durability and lifespan of concrete structures are significantly affected by the corrosion of steel reinforcement. Though epoxy-coated steel reinforcement is being used for practical applications, slight damage in the coating during the construction process is enough to initiate the corrosion process. The shortcomings in the current practices to prevent corrosion of steel reinforcement have led the researchers to look for alternatives. Innovative hybrid reinforcing elements with solid steel core and fibre-reinforced polymer (FRP) wrapping (called steel–FRP composite bars (SFCB)) can be considered as a suitable alternative to conventional steel reinforcement. In this research paper, experimental and numerical studies that investigated the flexural behaviour of concrete beam specimens reinforced with SFCB produced using glass fibres or carbon fibres are presented and discussed. Experimental study consisted of flexural testing of six concrete beam specimens with conventional steel reinforcement or SFCB with glass fibres or SFCB with carbon fibres. Two different spacings of shear stirrups were considered. Failure mode, first crack load, ultimate flexural load and load-deflection behaviour were recorded during the experiment. The test results showed that beam specimens with SFCB reinforced achieved less ultimate flexural load as compared to beam specimens with conventional steel reinforcement. The failure mode was found to be influenced by the spacing of the shear stirrups. The results of the numerical analysis were close to the experimental results. .

Mechanical behavior of steel FRP mixed beams jointed by high strength frictional bolts

Mechanical behavior of steel FRP mixed beams jointed by high strength frictional bolts

Flexural Behavior of One-Way Concrete Slabs by Hybrid Glass Fiber-Reinforced Polymer-Steel Reinforcements

Flexural Behavior of One-Way Concrete Slabs by Hybrid Glass Fiber-Reinforced Polymer-Steel Reinforcements

Ductile, durable, and reliable alternative to FRP bars for reinforcing seawater sea-sand recycled concrete beams: steel/FRP composite bars

The combination of seawater, sea-sand and recycled concrete aggregate (RCA) to make the so-called seawater sea-sand recycled concrete (SSRC) is a promising alternative to mitigate the shortage of raw construction materials, e.g. river sand, freshwater and crushed stone. Although equipped with anti-corrosion and high strength, the reduced ductility due to the linear elastic nature of conventional fiber-reinforced polymer (FRP) bars hinders their application scope in civil engineering. Inherited the advantages of FRP bars, steel fiber-reinforced polymer composite bars (SFCBs) are also characterized by good ductility and stable post-yield stiffness, which can potentially be ideal reinforcement for concrete structures made with un-desalted corrosive raw materials. This paper presents experimental and theoretical investigations on the flexural performance of SFCB reinforced SSRC beams. Test results indicate that the displacement ductility factor of almost all the SFCB reinforced SSRC beams are in a range from 3.7 to 4.9. The ratios of peak load-to-yielding load of SFCB reinforced SSRC beams varied from 1.5 to 3.1, indicating a remarkable post-yield behavior. Compared with the counterparts with natural aggregates, SSRC beams show slightly reduced flexural strength and comparable ductility. Theoretical models were proposed to predict the load-deflection responses of SFCB reinforced SSRC beams, which paves the way for the design of such members.

Bond Behavior Between Steel Fiber Reinforced Polymer (SRP) and Concrete

Steel fiber reinforced polymer (SRP) composite materials, which consist of continuous unidirectional steel wires (cords) embedded in a polymeric matrix, have recently emerged as an effective solution for strengthening of reinforced concrete (RC) structures. SRP is bonded to the surface of RC structures by the same matrix to provide external reinforcement. Interfacial debonding between the SRP and concrete is a primary concern in this type of application. This study aimed to investigate the bond characteristics between SRP and concrete determined by single-lap direct shear tests with different composite bonded lengths and fiber sheet densities (cord spacings). Specimens with medium density fibers failed mainly due to composite debonding, whereas those with low density fibers failed due to fiber rupture. Results of specimens that exhibited debonding were used to determine the bond-slip relationship of the SRP-concrete interface and to predict the full-range load response, which was in good agreement with the experimental results. A database of SRP-concrete direct shear tests reported in the literature was also established. Four analytical equations derived for fiber reinforced polymer (FRP)-concrete debonding were evaluated based on the database results and were found to predict the maximum load within approximately 15% error on average, however, they all underestimated the effective bond length.

Steel-FRP Reinforced Concrete Moment-Resisting Frames under Lateral Loads: Numerical Investigation

This paper suggests using a combination of steel and fiber-reinforced polymer (FRP) reinforcements to introduce sustainable reinforced concrete moment-resisting frames (RC-MRFs) characterized by damage-controlled seismic performance, cost-effectiveness, and postearthquake recoverability. The aim of this study is twofold. First, according to a predefined seismic performance of RC-MRFs, this study introduces the optimum replacement ratio of the longitudinal FRP reinforcement of FRP RC-MRFs with steel bars. Second, this study investigates the application of FRP-steel reinforcement details to alleviate damage in the plastic-hinge zones of the beams. A detailed three-dimensional finite-element model (3D-FEM) of an RC-MRF is developed and validated against the experimental results of a large-scale, two-bay, two and half story MRF entirely reinforced with FRP rebars and stirrups. Results indicate that compared with FRP RC-MRFs, for a replacement ratio of FRP reinforcement ≤42%, the serviceability state of the proposed steel–FRP RC-MRFs is characterized by a controlled deformability, and the ultimate state is characterized by an acceptable residual lateral strength ensuring safe exit of the structure from its functionality. Furthermore, when steel reinforcements are only provided at the ends of the beams, the frame lateral deformability is based on the development of two sequential plastic hinges at each end of the beams, leading to higher deformability and lower damage levels.

Flexural Performance of Steel\u2013FRP Composites for Automotive Applications

The design of hybrid structure offers an attractive solution to enhance strength and structural stiffness as well as to achieve lightweight effect and cost reduction. The applications of steel–FRP (fiber-reinforced polymer) composites in transportation and civil engineering have been comprehensively reviewed. In order to apply hybrid structures to car body parts such as B-pillar, flexural performance of steel–FRP composites is investigated by means of three-point bending test in this study. An analytical model is deduced to calculate the initial stiffness, the bending load and the energy absorption of steel–FRP composites. Steel–CFRP (carbon fiber-reinforced polymer) and steel–AFRP (aramid fiber-reinforced polymer) composites are experimentally studied and discussed. The results demonstrate that the steel–FRP composites exhibit significantly higher load-carrying capabilities and initial stiffnesses along with larger energy absorptions in the bending process compared to the single steel sheet.

Experimental study of concrete beams reinforced with hybrid bars (SFCBs and BFRP bars)

This paper presents the flexural performance of new hybrid concrete beams reinforced with steel fiber-reinforced polymer composite bars (SFCBs) and basalt fiber-reinforced polymer (BFRP) bars. Ten concrete beams reinforced with hybrid SFCBs, BFRP bars, and steel bars were constructed and tested. The main parameters were the reinforcement ratio and the ratio of FRP and steel content. The new hybrid-RC beams (with SFCBs and BFRP bars) exhibited good serviceability and ductility compared to the traditional hybrid-RC beams (with steels and BFRP bars), and the proposed model can accurately predict the moment capacity, deflection and crack width of all types of hybrid-RC beams (with SFCBs, BFRP bars and steel bars) based on the experimental results and the predictions.

Flexural performance of concrete beams reinforced with steel–FRP composite bars

Flexural performance of concrete beams reinforced with steel–FRP composite bar (SFCB) was investigated in this paper. Eight concrete beams reinforced with different bar types, namely one specimen reinforced with steel bars, one with fiber-reinforced polymer (FRP) bars and four with SFCBs, while the last two with hybrid FRP/steel bars, were tested to failure. Test results showed that SFCB/hybrid reinforced specimens exhibited improved stiffness, reduced crack width and larger bending capacity compared with FRP-reinforced specimen. According to compatibility of strains, materials’ constitutive relationships and equilibrium of forces, two balanced situations, three different failure modes and balanced reinforcement ratios as well as analytical technique for predicting the whole loading process are developed. Simplified formulas for effective moment of inertia and crack width are also proposed. The predicted results are closely correlated with the test results, confirming the validity of the proposed formulas for practical use.

Width Effect in FRP–Concrete Debonding Mechanism: A New Formula

This paper presents the results of an experimental work aimed at determining the effect of the width of a steel fiber-reinforced polymer (FRP) composite on the load-carrying capacity of a composite–concrete interface. Single-lap shear tests were performed in which the main parameter was the width of the composite strip. Steel FRP strips were applied to three different faces of each concrete prism and it was observed that the load-carrying capacity is strongly related to the face to which the composite is applied. In addition, a few tests were carried out at a displacement rate, used to control the test, equal to ten times the rate employed for the majority of the specimens. A great influence of the rate on the load-carrying capacity was observed, although the number of tests was limited. The authors argue that most of the width effect formulas available in the literature use data from different sources without taking into account the face of application and the rate. A new width effect formula is proposed, which takes into account the most recent articles on this subject.

Evaluation of fatigue performance of ballastless track slabs reinforced with basalt-FRP and steel-FRP composite bars

The objective of this research was to present a method for the mid-span deflection and crack width prediction of ballastless track slabs under fatigue loading. All nine ballastless track slabs were reinforced with steel fibre-reinforced polymer (FRP) composite bars (SFCB), basalt FRP bars and traditional steel bars. The main parameters were the loading level and loading sequence. Three theoretical models for mid-span deflection were used and compared with the test results. The present study indicates that Lovegrove and El Din's model can predict the deflection more accurately for the SFCB slabs and traditional reinforced-concrete slabs, with the load level ranging from 0·45 to 0·6, and 0·5 to 0·6, respectively. To predict the crack width, the proposed regression equations showed satisfactory accuracy for both constant and variable fatigue loading, with the load levels ranging from 38% to 67·5% of the ultimate load.

OFBG-Based Smart Double-Skin Tubular Confined-Concrete Column with Basalt FRP-Steel Composite.

Fiber-reinforced polymer (FRP) composites have been widely employed to design advanced structural columns such as the hybrid FRP–concrete–steel double-skin tubular column (hybrid DSTC) with potential benefits. To date, the safety and self-monitoring of the hybrid DSTCs are still a challenge to overcome due to the complex damage scenarios. This paper investigates the self-sensing performance of a newly developed smart double-skin tubular confined concrete column (smart BFST-DSTC) made of basalt FRP–steel composite with built-in optical fiber Bragg grating sensors (OFBGs). The design of the smart BFST-DSTC and sensing principle are firstly addressed, followed by an experimental investigation on the basic mechanical properties and strain-based sensing performance of ten scaled specimens under axial compression. The outcomes reveal the enhancement of the proposed column in terms of load-carrying capacity, confinement ratio, and axial stress-axial strain behavior, as well as failure and damage modes when compared with the hybrid DSTC. The self-sensing investigation demonstrates that the measurement range satisfies the requirement to monitor and evaluate the hoop strains of the FRP jackets and the health state of the inner tube. The smart BFST-DSTC can replace the hybrid DSTC with the ability to provide early failure warning and life cycle health monitoring.

Seismic Retrofit of R/C T-Beams with Steel Fiber Polymers under Cyclic Loading Conditions

This paper presents results of an experimental study on seismic response of reinforced concrete (RC) T-beams with shear deficiencies strengthened with externally bonded steel fiber reinforced polymer (SFRP) strips. Seven cantilever RC beams were strengthened with externally bonded uniaxial SFRP strips in a U-shape configuration and were tested under cyclic loading conditions. The two main variables examined were the strip spacing and the use of anchoring system. Among the investigated anchoring systems, one was patented, and it is studied in the present manuscript. The examination of the results leads to the conclusion that the anchoring system has a significantly more pronounced effect on the performance of the beams and the mode of failure than the type or spacing of the strips. Furthermore, SFRP strips seem to have a great potential to be used for shear strengthening, especially since the use of mechanical anchoring systems drastically improves their performance. On the contrary, the lack of mechanical anchoring results in premature delamination of the strengthening system, and thus an undesirable SFRP material performance.

Flexural behavior of concrete beams with steel bar and FRP reinforcement

ABSTRACT The purpose of this paper is to investigate the flexural behaviour of concrete beams with deformed steel bars and FRP bars for reinforcement. From experimental and analytical works, stiffness, crack, strength, and deflection behaviour was analysed and compared with ACI318 and ACI440. There were six specimens, which were tested by the variables of reinforcement combination (steel-steel, steel-GFRP, steel-CFRP) and concrete strength (40 MPa, 60 MPa). Test results showed that specimens with steel-FRP reinforcements had two times higher strength than the specimens with steel-steel reinforcements and that deflection of specimens was similar. Nominal flexural strengths of specimens by ACI318 and ACI440 were 113 ~ 142% of flexural strengths by the test. From finite element analysis, the reliability of the analysis was demonstrated by comparison between appropriate analysis model and test results.

Numerical Sensing of Plastic Hinge Regions in Concrete Beams with Hybrid (FRP and Steel) Bars.

Fibre-reinforced polymer (FRP)-reinforced concrete members exhibit low ductility due to the linear-elastic behaviour of FRP materials. Concrete members reinforced by hybrid FRP–steel bars can improve strength and ductility simultaneously. In this study, the plastic hinge problem of hybrid FRP–steel reinforced concrete beams was numerically assessed through finite element analysis (FEA). Firstly, a finite element model was proposed to validate the numerical method by comparing the simulation results with the test results. Then, three plastic hinge regions—the rebar yielding zone, concrete crushing zone, and curvature localisation zone—of the hybrid reinforced concrete beams were analysed in detail. Finally, the effects of the main parameters, including the beam aspect ratio, concrete grade, steel yield strength, steel reinforcement ratio, steel hardening modulus, and FRP elastic modulus on the lengths of the three plastic zones, were systematically evaluated through parametric studies. It is determined that the hybrid reinforcement ratio exerts a significant effect on the plastic hinge lengths. The larger the hybrid reinforcement ratio, the larger is the extent of the rebar yielding zone and curvature localisation zone. It is also determined that the beam aspect ratio, concrete compressive strength, and steel hardening ratio exert significant positive effects on the length of the rebar yielding zone.

Numerical study of steel-to-FRP reinforcement ratio as a design-tool controlling the lateral response of SFRC beam-column joints

This study proposes both steel and fiber-reinforced polymer (FRP) composites as main reinforcement for modern reinforced concrete (RC) moment-resisting frame (MRF) structures. A detailed three-dimensional finite element model (3D FEM), which takes into account the material and geometric nonlinearity and the bond behavior of steel and glass FRP (GFRP) reinforcement, was created and validated against the available experimental results. 54 cases covering several combinations of steel-to-GFRP reinforcements and design scenarios (under and over reinforced design scenarios) were studied. The analysis results of steel-FRP reinforced concrete (SFRC) joints pointed to the ratio between the effective FRP reinforcement ratio and the balanced FRP reinforcement ratio (the normalized reinforcement ratio) as the main design tool that can be adopted to achieve a predefined seismic behavior. Moreover, a definition is given to the lower and upper limits of the normalized ratio. Design recommendations regarding the controllability of the serviceability state, the post-yielding state, the ultimate state, and the residual strength of SFRC joints through an appropriate design for the steel-to-FRP mixing ratio are drawn. Ultimately, a mechanical model describing the behavior of SFCR joints with different steel-to-FRP reinforcement ratios is introduced based on the general behaviors of the simulated joints.

Investigating Seismic Behavior of Reinforced Concrete Columns with SFRP Using Finite Element Method

Currently, various methods have been used for repairing and retrofitting reinforced concrete columns including Steel Fiber Reinforced Polymer (SFRP) jackets in order to improve load bearing capacity. However, the enclosure mechanism is less known by consideration of the effects of slender columns which needs much more studies. Avoiding the buckling of a slender Reinforced Concrete (RC) column against the compressive axial force using SFRP is the main aim of this research. One of the parametrical studies in this paper is the influence of the number of layers that is investigated by Finite Element Method (FEM). Accordingly, in this paper, several RC columns are modeled under the Manjil earthquake record and the force-displacement curves of each model are numerically calculated. The columns are divided into three groups: the first group is non-SFRP and the subsequent groups are reinforced by one and two layers of SFRP. At first, three-dimensional models of the columns were prepared by ABAQUS finite element software and then by applying axial load and seismic forces, the parametric effect on behavior of the columns has been investigated. The results show that the retrofitting of the column with SFRP increases the flexural and stiffness, which plays a significant role in reducing the buckling of the RC columns.

Investigation of intrinsic de-bonding in bonded concrete overlays: Material characterisation and numerical Study

© 2018 Growing Science Ltd. All rights reserved. This study investigates the evolution of intrinsic interfacial de-bonding of Roller Compacted Steel Fibre Reinforced Polymer Modified Concrete (RC-SFR-PMC) bonded on substrate Ordinary Portland Cement Concrete (OPCC), using both experimental and numerical techniques. The relative effects of evolving material inhomogeneity and composite dimensional stability during curing was studied as a function of overlay structural scale, using a 2D plane strain Interface Cohesive Zone Model (ICZM). The effects of creep coefficient on interface restraint capacity and ensuing cohesive zone length were clearly evaluated. The results showed that the applied curvature due to the measured shrinkage strain was inadequate to cause critical de-bonding. In the FEA results, while the rate of interface energy release generally varies as a function of the bi-material relative stiffness and overlay structural scale, it is also evident that the two variables lose effects as the overlay structural scale approaches 0.50. The overall indicative trend shows that the rate of energy release in compliant overlay when relative stiffness (α0. Therefore, a more compliant overlay typically exhibits less relative restraint to bending induced de-bonding.