Fiber-Reinforced Polymer Reinforcing Bars Research Articles

Theoretical and experimental investigation of the time‐dependent relaxation rates of GFRP and BFRP reinforcement bars

AbstractCracked concrete members with fiber‐reinforced polymer (FRP) reinforcement generally suffer from increased deflections compared to steel‐reinforced members due to FRP reinforcements' lower modulus of elasticity. An approach to counteract this problem can be the prestressing of the FRP reinforcement, which can significantly reduce member deflections. However, time‐dependent prestress losses occur due creep and shrinkage of the concrete and relaxation of the prestressing tendons. Within the first part of this article, mathematical approaches to determine relaxation rates from creep tests are introduced. Subsequently, short‐term and long‐term tensile tests under sustained load on glass and basalt FRP reinforcement bars are presented. Based on the experimental data and the mathematical model, relaxation rates for the investigated specimens are derived. In addition, using an approach based on logarithmic extrapolation, the relaxation rates at 1 million hours (end of service life) are calculated, and the experimentally determined residual tensile properties are evaluated.

Flexural Performance of Concrete Beams Reinforced with Hybrid FRP-Steel Bars: A mini review

Reinforced concrete beams are the most generally used structural parts in building, bridges, and many other structures. In the past two decades, many investigations have been conducted using various fiber-reinforced polymer (FRP) material types /steel bars to reinforce concrete beams under flexural test. The purpose of this paper is to review the flexural performance of concrete beams reinforced with hybrid FRP and steel bars to better understand their behavior. The main parameters addressed by researchers were dimensions of beams, FRP bar material type, and hybrid reinforcement ratio. The researchers established that the use of the combination between steel and FRP reinforcement bars improves the performance of the concrete beams. Moreover, the studies showed that the ductility of the hybrid reinforced beams increased compared to that of conventional steel reinforced beams, however, it decreased when the ratio of (Af/As) increased. The application of using hybrid FRP/steel bars in reinforcing concrete beams will further increase upon utilizing techniques for reducing the brittleness and higher cost of FRP bars. The general structure of this paper consists of presenting the formulas offered by ACI 440.1R-15 building code relating to the flexural strength calculation of concrete beams reinforced with FRP/steel bars. The paper also details some of the current experimental tests and analytical works published for concrete beams reinforced with hybrid system, and outlines research directions and identifies gaps required for additional research.

Performance of Innovative Precast Concrete Sleepers Prestressed with Glass Fiber-Reinforced Polymer Reinforcing Bars

Performance of Innovative Precast Concrete Sleepers Prestressed with Glass Fiber-Reinforced Polymer Reinforcing Bars

Tensile Properties of Basalt Fiber-Reinforced Polymer Reinforcing Bars for Reinforcement of Concrete

Tensile Properties of Basalt Fiber-Reinforced Polymer Reinforcing Bars for Reinforcement of Concrete

Deformability and Stiffness Characteristics of Concrete Shear Walls Reinforced with Glass Fiber-Reinforced Polymer Reinforcing Bars

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Splice Strength of Staggered and Non-Staggered Bundled Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete

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Experimental Study on Splice Strength of Glass Fiber-Reinforced Polymer Reinforcing Bars in Normal and Self-Consolidating Concrete

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Shear Transfer Mechanisms for Glass Fiber-Reinforced Polymer Reinforcing Bars

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Flexural Cracks in Fiber-Reinforced Concrete Beams with Fiber-Reinforced Polymer Reinforcing Bars

The use of fiber-reinforced polymer (FRP) in reinforced concrete results in excessive crack widths under service due to its generally low elastic modulus and poor bond characteristics. This study proposes that fiber-reinforced concrete (FRC) be used with FRP to reduce crack widths. Sixteen beams are tested under four-point bending with either Grade 420 (Grade 60) steel or FRP reinforcing bars, and either plain concrete or FRC. A modified Gergely-Lutz model was applied to the measured crack widths to calculate bond coefficients that were used to quantify the effectiveness of FRC in reducing crack widths. Results showed that FRC significantly reduced maximum crack widths in beams with FRP reinforcing bars. However, FRC was found to have little influence on crack width in beams with steel reinforcing bars. The use of FRC was also found to reduce bond coefficient on the order of 45-75% for FRP-reinforced beams, compared to 1-15% for steel-reinforced beams.

Mechanical Behavior of an Innovative Hybrid Beam Made of Glulam and Ultrahigh-Performance Concrete Reinforced with FRP or Steel

The main objective of the research project reported here is to develop a new hybrid glulam beam that will increase the performance of timber structures and optimize the use of wood in such structures. The hybrid beam is made by combining glulam with ultrahigh-performance short fiber-reinforced concrete (UHPC-SFR) planks with or without internal reinforcement consisting of steel- or fiber-reinforced polymer reinforcement bars. This paper presents an experimental program of tests on eight large-scale hybrid beams under four-point bending. The results show that by combining wood and UHPC-SFR, it is possible to obtain a hybrid beam with greater bending stiffness and increased ultimate load capacity.

Bond Durability of Glass Fiber-Reinforced Polymer Bars Embedded in Concrete Beams

An experimental and analytical investigation of bond durability of E-glass fiber-reinforced polymer reinforcement bars in concrete beams is presented. Beams were conditioned with sustained flexural loads in indoor, outdoor, 60°C alkaline solution, or freeze/thaw environments for up to 3 years , after which they were subjected to eccentric three-point flexure tests to evaluate bond. Experimental bar force and slip were used to draw direct conclusions on bond durability, and also to calibrate a proposed local bond–slip model that incorporates concrete cover splitting. Experimental bar force at the onset of free-end slip varied little after any of the conditionings, although the characteristic of bond failure was noted to be less ductile in the moister environments. The interfacial fracture energy associated with bond–slip did not change with conditioning time in any of the environments except freeze/thaw, where a monotonic reduction versus time was seen. The effective bond length of the bar under various co...

Effect of Environmental Exposure on the Mechanical and Bonding Properties of Hybrid FRP Reinforcing Bars for Concrete Structures

Hybrid fiber-reinforced polymer (FRP) rebar has emerged as one of the most promising and affordable solutions to the brittle failure problems of ordinary FRP rebar in concrete structures. Hybrid FRP rebar stress-strain curves are linearly elastic, and contain a definite yield point followed by plastic deformation. In this study, the long-term durability performance of hybrid FRP rebar is evaluated. The mechanical properties and durability of one type of carbon FRP rebar, one type of glass FRP rebar, and two types of hybrid FRP rebars are investigated. The rebar specimens are exposed to twelve different environments, including an alkaline solution, an acid solution, a salt solution, deionized water, and repeated freezing and thawing. Short-beam, tensile, and bond tests are used to analyze the mechanical properties and durability of the rebar. The experimental results confirm the desirable resistance of hybrid FRP rebar to aggressive environments.

Effect of Sustained Load and Environment on Long-Term Tensile Properties of Glass Fiber-Reinforced Polymer Reinforcing Bars

Glass fiber-reinforced polymer (GFRP) bars are gaining popularity as reinforcement for concrete bridge deck slabs and other concrete structures. This article reports on a study of the creep behavior of GFRP bars in different environments under sustained load. Twenty GFRP bars (E-glass in vinylester matrix) 9.5 mm in diameter in four series were tested for over 417 days (10,000 h) under combinations of different sustained load levels and surrounding mediums in ambient temperature. The bars were subjected to two levels of sustained tensile stress at 25% and 38% of guaranteed tensile strength while being surrounded by either alkaline solution (pH 12.8) or de-ionized water (pH 7.0). Axial strain in the central conditioned part of the bars was monitored with time to evaluate the creep behavior. Following the extended creep test, the GFRP bars were tested in axial tension until failure for residual tensile strength, elastic modulus, and axial strain. Results showed that the tested GFRP bar performed very well under these extreme loading and environmental conditions. Creep strain in the GFRP bars is less than 5% of the initial value after 10,000 h of sustained tensile loading. The average residual tensile strength was found to be 139% and 144% of the design tensile strength for bars conditioned in de-ionized water at 25% and 38% stress level, respectively. Alkaline solution tends to have more harmful effects on the bars than de-ionized water at higher stress levels. In alkaline solution, this range was 126% and 97% at 25% and 38% stress level, respectively. More importantly, the modulus of elasticity of the bars is very stable and almost unaffected by the conditions and sustained stress levels used. The authors note that this finding is critical in the design of concrete elements reinforced with FRP bars because the modulus is directly related to the crack width, deflection, and other serviceability concerns.

Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments - Part I: Structural Scale Tests

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Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments- Part II: Microstructural Tests

In this part of a two-part paper, the authors pursue microstructural studies of glass fiber reinforced polymer (GFRP) reinforcing bars in concrete, including the nature, quantum, and mechanism of deterioration. A scanning electron microscope was used to show the changes in the microstructure. Energy-dispersive x-ray analysis (EDX) and inductively coupled plasma mass spectrometry (ICP-MS) were used to determine the chemical changes in the composite.

Punching of Two-Way Concrete Slabs with Fiber-Reinforced Polymer Reinforcing Bars or Grids

This paper presents 4 tests that compare the behavior of steel and fiber-reinforced polymer (FRP) reinforced slab-column connections. Existing test results for punching of FRP-reinforced slabs are also summarized. Two approaches for predicting punching strength of a slab-column are studied. The 1st is an empirically based fit of the available data following the same format of design equation as offered by Matthys and Taerwe (2000). The 2nd is an adaptation of an equilibrium-based model for slab-column connection behavior proposed by Alexander and Simmonds. Both methods give acceptable results when compared with available test data.

Durability of Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete Environment

Accelerated aging tests are being conducted on more than 20 types of glass fiber-reinforced polymer (GFRP) reinforcing bars, which are produced from different combinations of constituent materials, manufacturing parameters, sizes and shapes, and surface coatings. The specimens are being subjected to various sustained tensile loading (22 to 68% of ultimate strength) in three types of alkaline environments: NaOH, simulated pore-water solution, and embedded in concrete. Time to rupture or residual strength, as applicable, have been determined. Additionally, stress corrosion mechanisms were evaluated by various microstructural analyses. The results showed clearly that alkaline ions and moisture could penetrate or diffuse through the resin (or through cracks and voids) to the interphases and the fibers. For GFRP bars embedded in moist concrete under various sustained stress levels, three types of stress corrosion mechanisms have been identified: stress dominated, crack propagation dominated, and diffusion dominated.

Fiber-Reinforced Composite Bridge Decks in the USA

Highway departments across America are searching for ways to solve the nation’s bridge problems. Engineers have turned to fiber-reinforced polymer (FRP) composites as possible solutions. In West Virginia, a concrete bridge deck has been cast with FRP reinforcement bars. In Delaware, Kansas and West Virginia, several bridges have been constructed with FRP decks positioned above conventional substructures, and in Ohio and West Virginia composite material has been utilized for entire bridge structures. This paper presents a brief overview of FRP bridge construction.