Comparison of the effect of GFRP and steel reinforcement in concrete members subjected to compressive stress

Composite materials became more popular and commercially available as reinforcement for concrete elements. Fibre Reinforced Polymer (FRP) bar is an excellent thermal and electrical insulator with high tensile strength and low weight. These assumptions make them a possible substitution for steel reinforcement. Moreover, GFRP is not responsible to corrosion for that are suitable for structures with high humidity and unfavorable environment. GFRP is easier to handle due to its low weight. Also, it has electromagnetic neutrality. But it has some disadvantages. It has a low modulus of elasticity and sensitivity to elevated temperatures. Another drawback and uncertainty with designing is the impact of an alkaline environment, which decreases the long-term strength of GFRP bars. This paper describes a pre-experiment study of concrete elements resistance. The analysis is performed for a cross-section of 200x150 mm for a short concrete column with steel and GFRP reinforcement. The study compares P-M diagrams for steel reinforcement and GFRP reinforcement with different reinforcement ratios. Other characteristics such as tensile strength and modulus of elasticity must be considered to design the GFRP reinforced concrete element. The study also considers the contribution of GFRP reinforcement in compression. The analysis has shown, the shape of interaction diagrams of steel and GFRP reinforcement are significantly different.

Parametric Study of Concrete Members with GFRP Reinforcement Subjected to Bending and Axial Force

The paper deals with the possible replacement of steel reinforcement by GFRP reinforcement for concrete elements subjected to bending moment and compressive axial force. For the last 15 years, Fibre Reinforced Polymer (FRP) bars became more popular and commercially available as reinforcement for concrete elements. Composite FRP materials are still new in construction and many engineers are not familiar with their properties and behaviour. FRP has certain advantages over steel reinforcement. It is a durable material that is not subject to corrosion, does not conduct heat, is an electrical insulator and conducts electrical current, and is non-magnetic. In contrast, FRP also has certain deficiencies such as sensitivity to higher temperatures, alkaline environments, and reduction of mechanical properties at high levels of long-term stress. In the case of FRP reinforcements, the plastic branch is missing in the σ-ε diagrams, what leads to a sudden failure of the reinforced concrete element, either by tensile rupture of the reinforcement or by crushing the concrete. The most used FRP reinforcement is made of glass fibres - GFRP reinforcement. The paper deals with the possible replacement of steel reinforcement by GFRP reinforcement for slab and beam elements. The text describes a parametric study for different reinforcement ratio with GFRP reinforcement and steel reinforcement. The study is performed for a cross-section of 500x500 mm for a column element and a cross-section of 1000x250 mm for a slab element. The effect of longitudinal GFRP reinforcement in elements under compression was investigated. The study contains a comparison of interaction P-M diagrams of concrete elements with steel and GFRP reinforcement. For design of GFRP reinforced concrete elements, it is necessary to consider different material characteristics such as tensile strength and modulus of elasticity. The contribution of the GFRP reinforcement in compression was neglected due to the anisotropic nature of the GFRP reinforcement and the low modulus of elasticity. The main reference basis for the elaboration of a parametric study is the fib Bulletin No. 40.

Designing GFRP-Reinforced Tilt-up Wall Panels

Tilt-up construction was effectively enabled on a wide scale in 1979, when the ACI committee 551 report on Tilt-up construction was published, the Recommended Tilt-Up Wall Design, aka, the Yellow Book and the subsequent ACI-SEASC Task, aka the Green Book, and another Tilt-up design and construction manual developed by the ACI in 1988. The Tilt-up Concrete Association was created in 1986 by a group of industry professionals who had the need of an organization dedicated to the industry. ACI 551 maintains a document outlining the standard practice for contemporary Tilt-up design and construction. The ACI 551 document does not consider walls reinforced with non-ferrous reinforcement. However, recent events have made glass fiber-reinforced polymer rebar a more economical option when compared to traditional steel reinforcement. This white paper is intended to provide the unfamiliar engineer a bridge between the ACI 318, ACI 551 and ACI 440 documents to engineer a tilt-up wall including differences between GFRP reinforcement and steel reinforcement with respect to design. Steel, is an isotropic ductile metal extensively used in construction, mechanical, and electronic devices. Steel is often designed as elastic-perfectly plastic where it has an elastic modulus of 29,000ksi and yield stress of 60ksi. GFRP reinforcement is considered brittle-elastic with an elastic modulus often between 6,000ksi – 8750ksi and guaranteed ultimate tensile strength between 90-150ksi. Figure 1 presents an example of the design-assumed uniaxial stress versus strain comparing traditional steel and GFRP. While GFRP reinforcement has different physical and mechanical properties the differences and behaviors are well understood by the engineering community. There are ASTM material standards for GFRP bars, namely ASTM D7957 and a complete suite of ASTM test method by which the basic properties are verified. The following sections will illustrate the differences between steel and GFRP reinforced concrete members with a focus on slender tilt-up wall panels.

Flexural Behavior of Simply Supported Beams Consisting of Gradient Concrete and GFRP Bars

In order to study the flexural behavior of simply supported beams consisting of gradient concrete and GFRP bars, 28 simply supported beams were designed. The main parameters included the strength grades of high-strength concrete (HSC), GFRP reinforcement ratio, and sectional height of HSC. Based on nonlinear constitutive models of materials, meanwhile, considering the bond slip between concrete and GFRP bars, five simply supported beams with gradient concrete and five simply supported beams with GFRP bars were simulated, respectively. Then the mid-span load–displacement curves of beams were obtained. By comparing with the experimental data, the rationality of material constitutive models and finite element modeling was verified. Based on this, the parameter analysis of the beams with GFRP bars and gradient concrete was carried out, and the failure modes of the beams were obtained through investigation. The results show that the failure process of the beams can be divided into two stages: elastic stage and working stage with cracks. With the increase of GFRP reinforcement ratio, the flexural bearing capacity of the beams does not change significantly, while their stiffness increases gradually. The flexural bearing capacity of the beams can be significantly improved by appropriately increasing the strength and sectional height of HSC. The ultimate bearing capacity of the beams is 40% higher than that of the GFRP concrete beams. Finally, based on the plane-section assumption, the calculation formula of normal-section flexural bearing capacity of this kind of beams is proposed through statistical regression method.

Neural Networks—Deflection Prediction of Continuous Beams with GFRP Reinforcement

Deflections on continuous beams with glass fiber-reinforced polymer (GFRP) reinforcement are calculated in accordance with the appropriate standards (ACI 440.1R-15, CSA S806-12). However, experimental research provides results which differ from the values calculated pursuant to the standards, particularly when it comes to continuous beams. Machine learning methods can be applied for predicting a deflection level on continuous beams with GFRP (glass fiber-reinforced polymer) reinforcement and loaded with a concentrated load. This paper presents research on using artificial neural networks for deflection estimation and an optimal prediction model choice. It was necessary to first develop a database, in order to train the neural network. The database was formed based on the results of the experimental research on continuous beams with GFRP reinforcement. Using the best trained neural network model, high accuracy was obtained in estimating deflection, expressed over the mean absolute percentage error, 9.0%. This result indicates a high level of reliability in the prediction of deflection with the help of artificial neural networks.

Deflection of GFRP-reinforced concrete beams

This paper presents an investigation of the performance of concrete beams reinforced with glass fiber-reinforced polymers (GFRP) under short-term loading. A total of six specimens with rectangular cross-sections (75 mm in height and 150 mm in width) were tested under a four-point bending test to failure. Each specimen was reinforced with two GFRP bars with diameters of 8 mm. The results of this study demonstrated the behavior of GFRP-reinforced concrete members and a validation of the available calculation methods for the deflection of these members and assumed possibilities of the use of a GFRP reinforcement over the long term. The results of the study presented show a very good agreement of an experimentally measured and theoretically calculated instantaneous deflection when using the approaches in the European and American standards. In calculations of long-term deflections, the results are highly inconsistent and seem to be quite overestimated in some cases. The study shows the necessity of real-time long-term measurements to demonstrate the real deformations to be assumed during design of structures reinforced with GFRP reinforcement.