FRP-reinforced Concrete Beams Research Articles

Evaluation of Thermal Resistance of FRP Reinforced Concrete Beams in Fire

Fibre reinforced polymer (FRP) bars are made of innovative materials and establishment of the fire resistance of FRP reinforced concrete (RC) is necessary for their widespread application. Experimental behaviours of Carbon FRP (CFRP) and Glass FRP (GFRP) bar RC beams at elevated temperatures have been investigated in this paper. Data are presented from fire tests of six simply supported beams that were fabricated using normal-weight concrete. The effects of varying load levels and FRP bar type were studied. The beams were designed over-reinforced and were tested in a floor furnace. A steel bar reinforced beam was used as control specimen. A rebar temperature of 500°C was selected as failure criterion for the beam. Non-linear temperature distribution across the beam cross section was observed. Temperature rise in the compression concrete was found insignificant and its mechanical properties were nearly unaffected. All beams met the failure criterion of critical rebar temperature of 500°C. The stiffness reduction in the GFRP and steel RC beams was nearly the same at elevated temperatures and was independent of load levels and/or bar modulus. The CFRP bar reinforced beams showed better stiffness characteristics compared to other beams.

Experimental Research on Flexural Behavior of FRP-Reinforced Concrete Beams

In order to improve the durability of reinforced concrete member, fiber reinforced polymer (FRP)-reinforced concrete member is introduces. Monotonic loading was applied to a reinforced concrete beam and FRP-reinforced concrete beam, in order to investigate the failure progress and characteristics of FRP-reinforced concrete beam.. The presenting study provide a basis for improving the design method for FRP-reinforced concrete member.

Prediction of shear strength of FRP-reinforced concrete beams without stirrups based on genetic programming

The use of fibre reinforced polymer (FRP) bars to reinforce concrete structures has received a great deal of attention in recent years due to their excellent corrosion resistance, high tensile strength, and good non-magnetization properties. Due to the relatively low modulus of elasticity of FRP bars, concrete members reinforced longitudinally with FRP bars experience reduced shear strength compared to the shear strength of those reinforced with the same amounts of steel reinforcement. This paper presents a simple yet improved model to calculate the concrete shear strength of FRP-reinforced concrete slender beams (a/d>2.5) without stirrups based on the gene expression programming (GEP) approach. The model produced by GEP is constructed directly from a set of experimental results available in the literature. The results of training, testing and validation sets of the model are compared with experimental results. All of the results show that GEP is a strong technique for the prediction of the shear capacity of FRP-reinforced concrete beams without stirrups. The performance of the GEP model is also compared to that of four commonly used shear design provisions for FRP-reinforced concrete beams. The proposed model produced by GEP provides the most accurate results in calculating the concrete shear strength of FRP-reinforced concrete beams among existing shear equations provided by current provisions. A parametric study is also carried out to evaluate the ability of the proposed GEP model and current shear design guidelines to quantitatively account for the effects of basic shear design parameters on the shear strength of FRP-reinforced concrete beams.

Research on Fracture of FRP Reinforced Concrete Beams

With technology of FRP reinforcement concrete beams is applied in domain of the civil engineering, it attracts more and more scholars to study it. The paper studied of the flexural fracture performance of FRP reinforced RC beams, bringing forward how to calculate the flexural failure of FRP reinforced concrete beam, namely: bearing capacity formula about broken FRP and crushed concrete on compression zone, through comparison between calculated values and tests values, it is discovered that the numerical analysis and test result is fitting approximately, it is validated that the formula can well analyze flexural of FRP reinforced RC beams.

Shear Strength of Fiber-Reinforced Polymer Reinforced Concrete Beams Subject to Unsymmetric Loading

This study is concerned with the determination of the effects of shear span-to-depth ratio (a/d) and beam depth, or size, on the concrete contribution to the shear resistance of beams longitudinally reinforced with carbon fiber-reinforced polymer (CFRP) bars. One of the distinguishing features of the study is the unsymmetrical nature of the applied load, which creates two distinct a/d ratios in the same beam and allows the effect of the a/d ratio on shear strength to be clearly seen. Six simply supported large size CFRP reinforced concrete beams without shear reinforcement were tested, each under a single concentrated load. The test variables were the a/d ratio, varying from 1.0–11.5, and the beam depth varying from 200–500 mm. All the beams failed in shear, but the failure load and location for some of these beams could not be predicted by the shear design recommendations of American Concrete Institute (ACI) Committee 440. The reason is that these recommendations do not account for the effects of a/d and beam size on shear strength. Suggestions are made for the inclusion of these parameters in the shear design equations.

Experimental study of hybrid FRP reinforced concrete beams

Fiber-reinforced polymer (FRP) has become a practical alternative construction material for replacing steel bars as reinforcement in concrete structures. However, the brittleness of FRP greatly reduces the ductility of FRP-reinforced concrete (FRPRC) beams. In order to improve its flexural ductility, and at the same time retain the high strength feature of the FRP bars, it is proposed that steel longitudinal reinforcement should be added to form a hybrid FRPRC beam. Twelve specimens consisting of plain concrete beams, steel-reinforced concrete (SRC) beams, pure FRPRC beams and hybrid FRPRC beams were fabricated and tested. The test results show the hybrid FRPRC beams behave in a more ductile manner when compared with the pure FRPRC beams. Also, it is observed that a higher degree of over-reinforcement in the beam specimen resulted in a more ductile FRPRC beams. Hence, the addition of steel reinforcement can improve the flexural ductility of FRPRC members, and over-reinforcement is a preferred approach in the design of FRPRC members.

FRP-Reinforced Concrete Beams: Unified Approach Based on IC Theory

In general, steel-reinforced concrete involves a ductile steel material and a very strong and ductile bond between the steel reinforcement and concrete, so that debonding rarely governs the design. In contrast, fiber-reinforced polymer (FRP) reinforcement is a brittle material with a weak and brittle bond, making debonding a major issue. Consequently, there has been an extensive amount of research on FRP debonding and in particular intermediate crack (IC) debonding. This paper shows that the very good research by the FRP research community on the mechanics of IC debonding can be applied to a wide range of apparently disparate reinforced concrete behaviors to produce a unified approach. Hence, a single mechanism, or unified approach, based on IC debonding is proposed in this paper for dealing with moment rotation, tension stiffening and deflections, member ductility and moment redistribution, shear capacity, confinement, and fiber concrete for FRP RC beams.

Analytical Behaviors of Steel and CFRP Reinforced Concrete Beams in Fire

Abstract The study of thermal behaviors of concrete structures has been an area of great interest to researchers over a long period of time. This paper presents the details of analytical studies, which were carried out in order to investigate high temperature performance of steel or carbon fiber reinforced polymer (CFRP) bar reinforced concrete (RC) beams. This performance is considered to be highly dependent on elevated temperature properties of employed materials (i.e., concrete, steel, and FRP), concrete cracking model, and temperature related strain components. The effects of these parameters in relation to the experimental data were studied in order to establish those that are critical for the prediction of fire resistance of steel or FRP RC beams. Constitutive models for temperature dependent thermal expansion coefficient of concrete and steel have been proposed and validated against the recorded beam behaviors. The effects of transient creep strain were found insignificant in the studies presented in this paper. Non-orthogonal and orthogonal crack formations were found to be suitable for steel and CFRP reinforced beams, respectively. A highly non-linear rebar stress distribution was observed at the mid-span of the beam. Compressive stresses were produced in the steel bars, owing to their restrained thermal dilatation during heating.

Performance-based optimal design of compression-yielding FRP-reinforced concrete beams

Abstract The application of fiber-reinforced polymer (FRP) composite in concrete structures has drawn worldwide interest recently. However, a critical drawback of the resulting structures is their poor ductility performance, due to FRP’s linear-elastic mechanical properties. “Unless ductility requirements are satisfied, FRP materials cannot be used reliably in structural engineering applications” [1] . To resolve this problem, the authors recently developed a new technology to improve the ductility of flexural members through compression yielding (CY). In the experimental and theoretical investigations that have been undertaken so far, the CY concept has proved to be not only theoretically interesting and attractive, but also practically feasible. As CY beams make use of a different avenue to deliver ductility, their design is different from that in conventional reinforced concrete theory. This paper investigates the mechanical behavior of CY structures and proposes a criterion-based optimal design methodology that directly and quantitatively addresses ductility and strength demands.

Flexural Behavior of Continuous FRP-Reinforced Concrete Beams

Continuous concrete beams are commonly used elements in structures such as parking garages and overpasses, which might be exposed to extreme weather conditions and the application of deicing salts. The use of the fiber-reinforced polymers (FRP) bars having no expansive corrosion product in these types of structures has become a viable alternative to steel bars to overcome the steel-corrosion problems. However, the ability of FRP materials to redistribute loads and moments in continuous beams is questionable due to the linear-elastic behavior of such materials up to failure. This paper presents the experimental results of four reinforced concrete beams with rectangular cross section of 200×300 mm continuous over two spans of 2,800 mm each. The material and the amount of longitudinal reinforcement were the main investigated parameters in this study. Two beams were reinforced with glass FRP (GFRP) bars in to different configurations while one beam was reinforced with carbon FRP bars. A steel-reinforced conti...

Ductility analysis of compression-yielding FRP-reinforced composite beams

Ductility is one of the major issues of concern in achieving the widespread acceptance of FRP-reinforced concrete structures in practice. A new technique for improving the ductility of FRP-reinforced concrete beams through compression yielding (CY) instead of tensile yielding in the plastic hinge zone has recently been developed. A CY beam is a relatively complicated composite member that incorporates an additional composite material into the plastic hinge of a FRP-reinforced concrete beam. This paper presents the results of an investigation into the ductility behavior of CY beams. Results from a numerical study are first presented to illustrate the effects of key variables on the ductility performance of CY beams. These effects are then comprehensively examined through an analytical study. Finally, general conclusions on the ductility design of CY beams are provided.

Parametric space for the optimal design of compression-yielding FRP-reinforced concrete beams

Ductility of flexural members reinforced with fiber reinforced polymer (FRP) has been a serious concern for the application of FRP in structural engineering. A new and effective structural design concept of achieving ductility for FRP-reinforced concrete beams through compression yielding (CY) instead of tensile yielding has recently been developed. The ductility of CY beams depends very much on the details of the CY zone. A previous theoretical investigation into beams with an elastic-perfectly plastic CY block has shown that an optimal level of ductility exists in certain regions of the parametric space. However, experimental investigations have found that elastic-perfectly plastic CY blocks are difficult to construct, and often the post-yield behavior features some strain hardening or softening. For this reason, the present study aims to clarify the ductility behavior of CY beams with a more general CY block model, focusing on the effects of the post-yield modulus of the CY block. The key variables of the CY beam system are first identified. Subsequently, the ductility performance of CY beams is investigated using a combination of analytical study and numerical simulation. Finally, the parametric space that produces an optimal level of ductility is further identified which could form the basis for the optimal design of CY beams. The results demonstrate that a small post-yield modulus of the CY block can be beneficial for ductility performance. However, a large post-yield modulus will significantly reduce the ductility.

Evaluation of ACI 440 Deflection Model for Fiber-Reinforced Polymer Reinforced Concrete Beams and Suggested Modification

The results of a theoretical analysis of fiber-reinforced polymer (FRP) reinforced concrete (RC) flexural elements are reported in this paper. A large database of RC specimens (beams and slabs) was analyzed including beams tested by the authors. The experimental load-deflection curves of these specimens were compared with the theoretical predictions based on the deflection model as suggested by ACI Committee 440. An appropriate modification in the ACI 440.1 R method of calculating effective moment of inertia is proposed to predict deflection of concrete beams reinforced by any type of FRP bar. The modified expression provided consistent results and the predictions agreed well with the curvature and deflection data measured experimentally The investigation also considered other available methods of deflection calculation. A comparison of the results showed the effectiveness of the suggested equation over these methods.

New Approach for Estimating the Deflection of Beams Reinforced with FRP Reinforcement

Due to concerns with corrosion, the use of fiber-reinforced polymer (FRP) as a replacement to conventional steel reinforcement has greatly increased over the last decade. Researchers have identified the distinctive mechanical and bond properties of FRP reinforcement that prevent the use of existing relationships to establish serviceability of concrete structures reinforced with such products. Although studies have modified these empirical relationships to describe the behavior of structures reinforced with FRP reinforcement, this paper will provide a new approach to estimate deflection of concrete beams by considering material properties of the reinforcement and incorporating the effects of tension stiffening. Accuracy and precision of the approach was established by performing a statistical analysis on a database containing 171 FRP-reinforced concrete beams. Results were compared to those from existing proposed relationships and indicate the potential of the method to estimate deflection at various service conditions.

Experimental Behaviour of Carbon FRP Reinforced Concrete Beams at Ambient and Elevated Temperatures

The applications of fibre reinforced polymer (FRP) bars in buildings can provide a potential market for their use. Since buildings may be exposed to elevated temperatures, the behaviour of carbon FRP (CFRP) reinforced concrete (RC) beams was studied at high temperatures and compared with normal temperature behaviour. Steel RC beams were used as control specimens. The failure modes of beams at normal and elevated temperatures were found to be the same. The stiffness of cracked FRP RC was less than steel reinforced concrete at normal temperature whereas FRP reinforced beams were stiffer than steel RC beams at elevated temperatures.

Evaluation of the new Canadian highway bridge design code shear provisions for concrete beams with fiber-reinforced polymer reinforcement

The Canadian highway bridge design code (CHBDC) contains provisions for designing concrete members with fiber-reinforced polymer (FRP) reinforcement. In the second edition of the code, new shear design procedures for FRP-reinforced sections are provided. These procedures are consistent with those for steel-reinforced members in the code, in consideration of some modifications that account for the substantial differences between FRP and steel reinforcement. The shear approach adopted in the CHBDC follows the traditional approach of Vc + Vs for shear design. This paper presents an evaluation of this approach by comparing it with experimental shear strengths of available test data on beams longitudinally reinforced with FRP bars and with or without FRP stirrups. In addition, the CHBDC approach was compared with the FRP shear design provisions currently in effect in North America using the available test results. The comparison shows that the CHBDC method significantly underestimates the shear strength of FRP-reinforced concrete beams. A proposed modification to this method is presented and verified against available test results.

Optimal efficiency factor in strut-and-tie model for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5)

A new model for the efficiency factor of the concrete strut in the strut-and-tie model is proposed in this study for FRP-reinforced concrete short beams with (1.5 < a/d < 2.5). The ultimate load capacity of tested FRP-reinforced short beams was evaluated using the proposed model along with other models for the efficiency factor used in strut-and-tie models of design codes such as the ACI, CSA, and AS3600. It was found that efficiency factor models used in existing reinforced concrete design codes do not predict the ultimate load capacity of FRP-reinforced short beams as accurately as they do for steel-reinforced short beams. This can be attributed to not accounting for the effect of the shear span to effective depth ratio, a/d and the axial stiffness of the flexural reinforcement on the efficiency factor of the concrete strut in reinforced concrete short beams. Ultimate shear load capacity predictions by the proposed model were in agreement with experimental data obtained on 15 GFRP and CFRP-reinforced concrete short beams tested in the laboratory. The proposed model for the efficiency factor was shown to be statistically more accurate yielding the lowest standard deviation and coefficient of variation compared to those of the ACI, AS3600, and CSA A23.3 models. It was also found that shear equations recommended for FRP-RC beams by design guidelines such as the CSA S806-02, ISIS, JSCE, and ISE render very conservative predictions of the ultimate load capacity of FRP-reinforced short beams.

Proposed Shear Design Equations for FRP-Reinforced Concrete Beams Based on Genetic Algorithms Approach

To calculate the shear capacity of structural members reinforced with fiber-reinforced polymer (FRP), current shear design provisions generally use slightly modified versions of existing semiempirical shear design equations initially developed for steel reinforced concrete beams. Such methods generally assume that the traditional approach of superimposing concrete contribution to shear, Vc to that of stirrups, Vs can also be used to calculate the nominal shear capacity, Vn of FRP-reinforced concrete beams provided that the axial rigidity of FRP longitudinal bars and the capacity of FRP stirrups at the bent portions are accounted for. These methods also noticeably vary in the manner they account for the effect of basic shear design parameters on shear strength. This paper presents simple yet improved equations to calculate the shear capacity of FRP-reinforced concrete beams based on the genetic algorithms approach. The performance of the proposed equations is compared to that of four commonly used shear de...

New Canadian Highway Bridge Design Code design provisions for fibre-reinforced structures

This paper presents a synthesis of the design provisions of the second edition of the Canadian Highway Bridge Design Code (CHBDC) for fibre-reinforced structures. New design provisions for applications not covered by the first edition of the CHBDC and the rationale for those that remain unchanged from the first edition are given. Among the new design provisions are those for glass-fibre-reinforced polymer as both primary reinforcement and tendons in concrete; and for the rehabilitation of concrete and timber structures with externally bonded fibre-reinforced-polymer (FRP) systems or near-surface-mounted reinforcement. The provisions for fibre-reinforced concrete deck slabs in the first edition have been reorganized in the second edition to explicitly include deck slabs of both cast-in-place and precast construction and are now referred to as externally restrained deck slabs, whereas deck slabs containing internal FRP reinforcement are referred to as internally restrained deck slabs. Resistance factors in the second edition have been recast from those in the first edition and depend on the condition of use, with a further distinction made between factory- and field-produced FRP. In the second edition, the deformability requirements for FRP-reinforced and FRP-prestressed concrete beams and slabs of the first edition have been split into three subclauses covering the design for deformability, minimum flexural resistance, and crack-control reinforcement. The effect of sustained loads on the strength of FRPs is accounted for in the second edition by limits on stresses in FRP at the serviceability limit state.Key words: beams, bridges, concrete, decks, fibre-reinforced-polymer reinforcement, fibre-reinforced-polymer sheets, prestressing, repair, strengthening, wood.

Shear Strength of FRP-Reinforced Concrete Beams without Transverse Reinforcement

This paper studied the behavior and shear strength of concrete slender beams reinforced with fiber-reinforced polymer (FRP) bars. Nine large-scale reinforced concrete beams without stirrups were constructed and tested to failure. The beams measured 3250 mm long, 250 mm wide, and 400 mm deep and were tested in 4-point bending. Test variables were the reinforcement ratio and modulus of elasticity of the longitudinal reinforcing bars. The test beams included 3 reinforced with glass FRP bars, 3 reinforced with carbon FRP bars, and 3 control beams reinforced with conventional steel bars. Test results were compared with predictions provided by the different available codes, manuals, and design guidelines, indicating that the relatively low modulus of elasticity of FRP bars results in reduced shear strength compared to that of control beams reinforced with steel. The current ACI 440.1R design method offered very conservative predictions, particularly for beams reinforced with glass FRP bars. Based on obtained experimental results, a proposed modification to the current ACI 440.1R design equation is given and verified against test results from other research.