Showing papers in "Journal of Composites for Construction in 2010"

Behavior and modeling of confined high-strength concrete

Abstract: This paper presents a study on the behavior and modeling of the stress-strain behavior of confined high-strength concrete (HSC) without silica fume. The behavior of actively confined HSC is first examined, and a unified active-confinement model applicable to both HSC and normal-strength concrete (NSC) is then proposed based on a large test database assembled from the existing literature. An experimental study on fiber-reinforced polymer (FRP)-confined HSC is next presented and interpreted to examine its behavior, forming the basis for the subsequent modeling work. It is eventually shown that a recent analysis-oriented model developed by the writers’ group for NSC also provides close predictions for FRP-confined HSC. While the work is primarily concerned with HSC without silica fume, the effect of incorporating silica fume into HSC on the behavior of confined HSC is also given appropriate attention. The presence of silica fume in HSC is shown to reduce the effectiveness of confinement in term of strain cap...

Structural Upgrade Using Basalt Fibers for Concrete Confinement

Abstract: This paper aims to appraise the opportunities provided by a new class of composites based on using basalt fibers bonded with a cement-based matrix as an innovative strengthening material for confinement of reinforced concrete members. The effectiveness of the proposed technique is assessed by comparing different confinement schemes on concrete cylinders: (1) uniaxial glass-fiber-reinforced polymer (FRP) laminates; (2) alkali-resistant fiberglass grids bonded with a cement-based mortar; (3) bidirectional basalt laminates preimpregnated with epoxy resin or latex and then bonded with a cement-based mortar; and (4) a cement-based mortar jacket. The study showed that confinement based on basalt fibers bonded with a cement-based mortar could be a promising solution to overcome some limitations of epoxy-based FRP laminates.

Unified Strength Model Based on Hoek-Brown Failure Criterion for Circular and Square Concrete Columns Confined by FRP

Abstract: Most existing models for evaluating the strength of fiber-reinforced polymer (FRP)-confined concrete columns are based in an early work. In this paper, a new model based on the Hoek-Brown failure criterion is proposed. The existing strength models for FRP-confined circular and square concrete columns are reviewed, evaluated, and compared with the proposed model. An updated database that includes a large number of test data are then used to evaluate the models. Comparisons between the models and the test results demonstrate the accuracy of the proposed model. Apart from this improved accuracy, the proposed model also has a unified form for both circular and square columns, and can be used to predict the strength of columns that have existing damage or cracks. Test data for FRP-repaired concrete columns are collected from the literature and used to evaluate and demonstrate the performance of the proposed model in predicting the strength of FRP-confined deficient columns.

Grooving as Alternative Method of Surface Preparation to Postpone Debonding of FRP Laminates in Concrete Beams

Abstract: Structural repair and strengthening have long been dynamic and challenging activities in construction work. One of the most commonly used methods for such repairs is the application of fiber-reinforced polymer (FRP) sheets to strengthen RC or even steel structure members. A major issue of concern in flexural strengthening of RC beams with FRP laminates is the debonding of the concrete substrate, which leads to premature failure of the structural member thus strengthened. One reason for this premature rupture may be the lack of proper preparation of the concrete surface in contact with the FRP sheet. Surface preparation is typically associated with such constraints as adverse environmental impacts, economic losses due to stoppage of activities, repair costs, or even inaccessibility of the member(s) to be strengthened. This study aims to investigate surface preparation for application of FRP sheets in an attempt to develop substitute methods for conventional surface preparation methods. The experimental spe...

Behavior of GFRP Reinforcing Bars Subjected to Extreme Temperatures

Abstract: Corrosion of steel reinforced concrete members has stimulated the research on fiber-reinforced polymers (FRP) to be used as an internal reinforcement for concrete structures. The behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars subjected to extreme temperatures is very critical for applications in North America, especially in Canada. There is a high demand for experimental studies to investigate the thermal stability of strength, along with the ultimate elongation, and modulus of GFRP bars. This paper evaluates the variation of mechanical properties of sand-coated GFRP reinforcing bars subjected to low temperatures (ranging from 0 to −100°C ) and elevated temperatures (ranging from 23 to 315°C ). Tensile, shear and flexural properties are investigated to get an overview of the thermal stability of mechanical properties of GFRP bars subjected to large variations of temperatures. Microstructural analyzes using scanning electronic microscopy (SEM), physical measurements by thermogravimetric...

Experimental Behavior of FRP Strengthened Masonry Arches

Abstract: This paper deals with the experimental behavior of solid clay brick masonry arches strengthened with glass fiber-reinforced polymer composites. Twelve half-scaled segmental masonry arches subjected to a load applied at the quarter span were tested under displacement control up to failure. The arches were built using handmade low strength bricks and a commercial lime-based mortar, trying to mimic ancient structures. Besides reference unreinforced arches, five different strengthening arrangements, including the use of spike anchors, were studied. The experimental results provide significant information for validation of advanced numerical models and analytical tools and for code drafting. The experimental results also show that (1) only continuous strengthening strategies are able to prevent typical local failure mechanisms of unreinforced arches; (2) strengthening at the intrados is the most effective option to increase strength; and (3) strengthening applied at the extrados provides the higher deformation...

Seismic Behavior of Posttensioned Concrete-Filled Fiber Tubes

Abstract: Precast segmental construction technique is an excellent candidate for economic rapid bridge construction in highly congested urban environments and environmentally sensitive regions. This paper presents the seismic behavior of four hybrid segmental columns consisting of precast posttensioned concrete-filled fiber tubes (PPT-CFFTs). A fifth monolithic column was also tested as a reference specimen. The columns were tested under increasing lateral loading cycles in a displacement control. The columns had circular cross section diameters of 203 mm and heights of 1,524 mm each. The parameters investigated included different construction details and energy dissipation systems. The PPT-CFFT columns developed lateral strength and deformation capacity comparable to those of the monolithic reinforced concrete column. However, the PPT-CFFT columns dissipated smaller hysteretic energy compared to that of the monolithic reinforced concrete column. Finally, a simple model was used to predict the backbone curves of se...

Experimental Study of Normal- and High-Strength Concrete Confined with Fiber-Reinforced Polymers

Abstract: The experimental program reported here was conducted to gain insight into the behavior of concrete confined with fiber-reinforced polymers (FRPs). A total of 112 cylindrical concrete specimens, each 150 mm in diameter, 300 mm in height, and concrete strength up to 112 MPa, were tested under monotonic uniaxial compression. Test variables included amount of FRP, strength and stiffness of FRP, concrete strength, and the health of concrete at the time of strengthening. Results showed that, with an increase of the unconfined concrete strength, the strength enhancement, energy absorption capacity, ductility factor, and work (energy) index at rupture of FRP jackets all decreased remarkably. A positive correlation was found between concrete ductility and FRP rupture strain. A gradual post-peak failure of the specimens, observed previously from FRP-confined concrete columns tested at the University of Toronto, was also observed in some of the current tests. This ductile failure, attributed to the gradual unzipping failure of FRP jacket, is related to specimen size and is explained in terms of various confinement parameters.

Analytical Model for FRP Confinement of Concrete Columns with and without Internal Steel Reinforcement

Abstract: The paper aims to contribute to a better understanding of the behavior of reinforced concrete columns confined with fiber-reinforced polymer (FRP) sheets. In particular, some new insights on interaction mechanisms between internal steel reinforcement and external FRP strengthening and their influence on efficiency of FRP confinement technique are given. In this context a procedure to generate the complete stress-strain response including new analytical proposals for (1) effective confinement pressure at failure; (2) peak stress; (3) ultimate stress; (4) ultimate axial strain; and (5) axial strain corresponding to peak stress for FRP confined elements with circular and rectangular cross sections, with and without internal steel reinforcement, is presented. Interaction mechanisms between internal steel reinforcement and external FRP strengthening, shown by some experimental results obtained at the University of Padova with accurate measurements, are taken into account in the analytical model. Four experimen...

Shear Strength of Large Concrete Members with FRP Reinforcement

Abstract: Increasing interest in the use of fiber-reinforced polymer (FRP) reinforcement for reinforced concrete structures has made it clear that insufficient information about the shear performance of such members is currently available to practicing engineers. This paper summarizes the results of 11 large shear tests of reinforced concrete beams with glass FRP (GFRP) longitudinal reinforcement and with or without GFRP stirrups. Test variables were the member depth, the member flexural reinforcement ratio, and the amount of shear reinforcement provided. Results showed that the equations of the Canadian CSA shear provisions provide conservative estimates of the shear strength of FRP-reinforced members. Recommendations are given along with a worked example on how to apply these provisions including to members with FRP stirrups. It was found that members with multiple layers of longitudinal bars appear to perform better than those with a single layer of longitudinal reinforcing bars. Overall, it was concluded that t...

Axial Load Capacity of Concrete-Filled FRP Tube Columns: Experimental versus Theoretical Predictions

Abstract: This paper presents the experimental and theoretical results of small and medium-scale concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) columns. A total of 23 CFFT specimens were tested under axial compression load. Five different types of new FRP tubes were used as stay-in-place formwork for the columns. The effects of the following parameters were examined: the FRP-confinement ratio, the unconfined concrete compressive strength, the presence of longitudinal steel reinforcement, and the height-to-diameter ratio. Comparisons between the experimental test results and the theoretical prediction values by the three North American codes and design guidelines (ACI 440.2R-08, CSA-S6-06, and CSA-S806-02) are performed in terms of confined concrete strength and ultimate load carrying capacity. The results of this investigation indicate that the design equations of the ACI 440.2R-08, CAN/CSA-S6-06, and CAN/CSA-S806-02 overestimate the factored axial load capacity of the short CFFT columns as compared to ...

Behavior and Effectiveness of FRP Wrap in the Confinement of Large Concrete Cylinders

Abstract: This paper presents the results of an experimental investigation on the strength and behavior of large 250 mm diameter concentrically loaded unreinforced fiber-reinforced polymer (FRP) confined concrete cylinders. In this study, the effect of the number of layers of the FRP and different overlap locations on the effectiveness of the FRP wrap is determined. Discontinuous versus continuous wrapping configurations to confine the cylinder are also investigated. To quantify the level of strain in the wrap and to aid in developing a deeper understanding of the behavior of these larger sized test specimens, an extensive array of electrical resistance strain gauges is used in addition to electronic speckle pattern interferometry (ESPI) optical measurement at selected locations. The ESPI results prove especially powerful in confirming the existence of strain concentrations at the ends of the overlap region, which may contribute to rupture failure of the wrap. The strain gauges in turn enable the effectiveness of t...

Strengthening RC T-Beams Subjected to Combined Torsion and Shear Using FRP Fabrics: Experimental Study

Abstract: In several cases of loading and geometrical configurations, flexure beams, and girders are subjected to combined shear and torsion. Failure of a structural element under combined shear and torsion is brittle in nature. Externally bonded fiber-reinforced polymer FRP fabrics are currently being studied and used for the rehabilitation, repair, and retrofit of concrete structure. The objective of this study is to investigate the strengthening techniques for T-beams subjected to combined shear and torsion. Six half-scale beams—two control specimen and four strengthened beams—were constructed and tested using a specially designed test setup that subjects the beam to combined shear and torsion with different ratios. Four strengthening techniques using carbon FRPs were tested. The experimental results were reported and analyzed to assess the effectiveness of the proposed strengthening techniques. An innovative strengthening technique namely the extended U-jacket showed promising results in terms of strength and ductility while being quite feasible for strengthening. Future areas of research are being outlined.

Behavior of Large-Scale Rectangular Columns Confined with FRP Composites

Abstract: This paper focuses on axially loaded, large-scale rectangular RC columns confined with fiber-reinforced polymer (FRP) wrapping. Experimental tests are conducted to obtain the stress-strain response and ultimate load for three field-size columns having different aspect ratios and/or corner radii. Effective transverse FRP failure strain and the effect of increasing confining action on the stress-strain behavior are examined. Existing strength models, the majority of which were developed for small-scale specimens, are applied to predict the structural response. Since some of them fail to adequately characterize the test data and others are complex and require significant calculation, a simple design-oriented model is developed. The new model is based on the confinement effectiveness coefficient, an aspect ratio coefficient, and a corner radius coefficient. It accurately predicts the axial ultimate strength of the large-scale columns at hand and, when applied to the small-scale columns studied by other investigators, produces reasonable results.

Slenderness Effects on Circular CFRP Confined Reinforced Concrete Columns

Abstract: External bonding of circumferential fiber-reinforced polymer (FRP) wraps is a widely accepted technique to strengthen circular RC columns. To date, most of the tests performed on FRP strengthened columns have considered short, unreinforced, small-scale concrete cylinders, with height-to-diameter ratios of less than three, tested under concentric, monotonic, and axial load. In practice, most RC columns have height-to-diameter ratios considerably larger than three and are subjected to loads with at least minimal eccentricity. Results of an experimental program performed to study the effects of slenderness on carbon FRP (CFRP) wrapped circular RC columns under eccentric axial loads are presented. It is shown that CFRP wraps increase the strength and deformation capacity of slender columns, although the beneficial confining effects are proportionally greater for short columns, and that theoretical axial-flexural interaction diagrams developed using conventional sectional analysis (but incorporating a simple F...

Experimental Investigation of the Influence of Moisture on the Bond Behavior of FRP to Concrete Interfaces

Abstract: The effects of moisture on the initial and long-term bonding behavior of fiber reinforced polymer (FRP) sheets to concrete interfaces have been investigated by means of a two-year experimental exposure program. The research is focused on the effects of (1) moisture at the time of FRP installation, in this paper termed “construction moisture,” consisting of concrete substratum surface moisture and external air moisture; and (2) moisture, in this paper termed “service moisture,” which normally varies throughout the service life of concrete. Concrete beams with FRP bonded to their soffits were prepared. Before bonding, concrete substrates were preconditioned with different moisture contents and treated with different primers. The FRP bonded concrete beams were then cured under different humidity conditions before being subjected to combined wet/dry (WD) and thermal cycling regimes to accelerate the exposure effects. Adhesives with different elastic moduli were used to investigate the long-term durability of ...

Interaction between Steel Stirrups and Shear-Strengthening FRP Strips in RC Beams

Abstract: RC beams shear strengthened with either fiber-reinforced polymer (FRP) U-jackets/U-strips or side strips commonly fail due to debonding of the bonded FRP shear reinforcement. As such debonding occurs in a brittle manner at relatively small shear crack widths, some of the internal steel stirrups may not have reached yielding. Consequently, the yield strength of internal steel stirrups in such a strengthened RC beam cannot be fully used. In this paper, a computational model for shear interaction between FRP strips and steel stirrups is first presented, in which a general parabolic crack shape function is employed to represent the widening process of a single major shear crack in an RC beam. In addition, appropriate bond-slip relationships are adopted to accurately depict the bond behavior of FRP strips and steel stirrups. Numerical results obtained using this computational model show that a substantial adverse effect of shear interaction generally exists between steel stirrups and FRP strips for RC beams shear strengthened with FRP side strips. For RC beams shear strengthened with FRP U-strips, shear interaction can still have a significant adverse effect when FRP strips with a high axial stiffness are used. Therefore, for accurate evaluation of the shear resistance of RC beams shear strengthened with FRP strips, this adverse effect of shear interaction should be properly considered in design.

FRP Confinement of Tuff and Clay Brick Columns: Experimental Study and Assessment of Analytical Models

Abstract: In recent years, fiber-reinforced polymer (FRP) wrapping effectiveness has been clearly confirmed especially with reference to concrete structures. Despite evident advantages of FRP based confinement on members subjected to compressive overloads due to static or seismic actions, the use of such technique in the field of masonry has not been fully explored. Thus, to assess the potential of confinement of masonry columns, the present paper shows the results of an experimental program dealing with 18 square cross sections (listed faced tuff or clay brick) masonry scaled columns subjected to uniaxial compression load. In particular, three different confinement solutions have been experimentally analyzed in order to evaluate and compare the effectiveness of uniaxial glass FRP, carbon FRP, and basalt FRP laminates wrapping. The main experimental outcomes are presented and discussed in the paper considering mechanical behavior of specimens, axial stress-axial strain relationships, and effective strains at failur...

Pullout strength models for FRP anchors in uncracked concrete

Abstract: Mechanical anchorage can delay or even prevent premature debonding failure in externally bonded fiber-reinforced polymer (FRP) composite strengthening systems. A promising type of anchor made from FRP, which is known as a FRP spike anchor or FRP anchor among other names, is noncorrosive and can be applied to a wide range of structural elements and externally bonded FRP strengthening schemes. Experimental investigations have shown FRP anchors to be effective under tension (pullout) and shear loading, however, few analytical models exist to date. This paper in turn presents analytical models to quantify the pullout strength of FRP anchors. As existing research on the pullout behavior of metallic anchors is partially relevant to FRP anchors, this paper first presents a review of current pullout strength models for metallic anchors. These models are then assessed with experimental data of FRP anchors and modified and recalibrated where appropriate. As a result, simple and rational pullout strength models for ...

Fatigue Performance of Tension Steel Plates Strengthened with Prestressed CFRP Laminates

Abstract: An experimental and analytical study was conducted to investigate the fatigue behavior of tension steel plates strengthened with prestressed carbon-fiber-reinforced polymer (CFRP) laminates. A simple fracture mechanics model was proposed to predict the fatigue life of reinforced specimens. Double-edge-notched specimens were precracked by fatigue loading and then strengthened by CFRP laminates at different prestressing levels. The effects of the applied stress range, CFRP stiffness, and prestressing level on the crack growth were investigated. Experimental results show that the increase of the prestressing level extends the fatigue life of a damaged steel plate to a large amount. The CFRP with the highest prestressing level performed best, prolonging fatigue life by as much as four times under 25% higher fatigue loading. Theoretically, predicted results were in a reasonable agreement with the experimental results. A parametric analysis was also performed to investigate the effects of the applied stress ran...

Temperature as an Accelerating Factor for Long-Term Durability Testing of FRPs: Should There Be Any Limitations?

Abstract: Fiber-reinforced polymer (FRP) composites are increasingly being used in civil engineering applications due to their numerous advantages. Moreover, some environmental conditions can potentially enhance their long-term durability. Therefore, the study of their long-term behavior is crucial to ensure their durability. To perform durability study in a reasonable time limit, accelerating factor, such as high temperature, is generally used. However, the use of very high temperature of conditioning could amplify the reduction of the properties leading to conservative prediction of long-term properties. The present paper attempts to clarify the effects of high temperatures on the mechanical and barrier properties (moisture absorption) of GFRP’s internal reinforcement, by presenting some experimental results and conclusions of laboratory accelerated studies.

State of Research on Seismic Retrofit of RC Beam-Column Joints with Externally Bonded FRP

Abstract: A considerable amount of research has been directed recently toward understanding and promoting the use of externally applied fiber-reinforced polymer (FRP) for the seismic retrofit of reinforced concrete (RC) structures. In this paper, a comprehensive review and synthesis of published experimental studies on the seismic rehabilitation of RC frame beam-column joints with FRP is presented, and the issues that need to be addressed for further research are discussed. In addition, the paper presents a simple design model for predicting the contribution of the FRP to the shear strength of retrofitted joints. The key element in the model is the derivation of an expression for the effective FRP strain, based on the calibration of test data reported in the literature. A total of 54 tests carried out worldwide were considered in the review, and a database of the published studies, encompassing all relevant design parameters, was assembled. The reported test results confirm the structural effectiveness of the FRP s...

Analytical Model of Circular CFRP Confined Concrete-Filled Steel Tubular Columns under Axial Compression

Abstract: This study intends to provide a simplified analytical model of the laterally confined concrete filled steel tube (CCFT) column system which adopts carbon-fiber-reinforced polymer (CFRP) jackets in order to make up for major defects of the traditional concrete filled steel tube (CFT) column system. This CCFT analytical model, by adding one additional parameter for CFRP confinement to the CFT column analytical solution, is greatly simplified and expedites the analytical processes to explain the stress-strain relationship of the CCFT column system. In the study, several types of the CCFT column systems with different parameters are analyzed by the proposed simplified analytical model and its associated numerical program (USC-CFT). To verify the accuracy of the analytical model, this study compares the load-strain relationship calculated by USC-CFT both to the experimental results conducted by the traditional method and to the results calculated by the computer-aided finite element method (FEM) analysis metho...

Experimental Study of Rectangular RC Columns Strengthened with CFRP Composites under Eccentric Loading

Abstract: This paper presents the results of experimental studies on reinforced concrete columns strengthened with carbon fiber-reinforced polymer (CFRP) composites under the combination of axial load and bending moment A total of seven large-scale specimens with rectangular cross section ( 200 mm×300 mm ) were prepared and tested under eccentric compressive loading up to failure The overall length of specimens with two haunched heads was 2,700 mm Different FRP thicknesses of two, three, and five layers; fiber orientations of 0°, 45°, and 90°; and two eccentricities of 200 and 300 mm were investigated The effects of these parameters on load-displacement and moment-curvature behaviors of the columns as well as the variation of longitudinal and transverse strains on different faces of the columns were studied The results of the study demonstrated a significant enhancement on the performance of strengthened columns compared to unstrengthened columns

Front and Side View Image Correlation Measurements on FRP to Concrete Pull-Off Bond Tests

Abstract: Understanding the transfer of force by bond between externally bonded fiber-reinforced polymer (FRP) reinforcement and concrete is an important step in formulating good models for predicting debonding failures observed in externally bonded reinforcement strengthened systems. In this paper, a 3D optical displacement measurement system was used to capture the full-field displacements from the front and side view in pull-off bond specimens. The experiments were carried using six specimens with carbon FRP (CFRP) strips having different axial stiffnesses but a constant bond length to the concrete substrate. Using the optical measurements, it was possible to obtain the in-plane displacement or slip and the out-of-plane displacement or separation between the CFRP strip and the concrete. It was demonstrated, that the usual assumption of pure shear stresses in such pull-off tests is not true and that the bond behavior is a two-dimensional problem involving shear and peeling stresses. The bond behavior in CFRP stri...

Retrofitting of Rectangular Columns with Deficient Lap Splices

Abstract: The cyclic behavior of eight 0.4-scale reinforced concrete column specimens is investigated. The columns incorporated deficient design details to simulate bridge columns built in Washington State prior to 1971. Two columns were tested as reference specimens, five were tested after retrofitting using carbon fiber-reinforced polymer CFRP, and one was tested after retrofitting using a conventional steel jacket. All the specimens were tested under constant gravity load and incrementally increasing lateral loading cycles. The specimens had rectangular cross sections with aspect ratios of 1.5 and 2.0. The parameters investigated included the amount of CFRP reinforcement, different retrofitting jacket configurations, and different retrofitting materials. For the as-built specimens, two modes of failure occurred, namely low cyclic fatigue of longitudinal reinforcement and lap splice failure. For the retrofitted specimens, no lap splice failure was observed. All the retrofitted specimens failed due to low cyclic fatigue failure of the longitudinal bars. The retrofitting measures improved the displacement ductility, energy dissipation, and equivalent viscous damping. In addition, increasing the amount of CFRP reinforcement improved the performance of the test specimens.

Flexural Behavior of Continuous FRP-Reinforced Concrete Beams

Abstract: 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...

Bend Strength of FRP Stirrups: Comparison and Evaluation of Testing Methods

Abstract: This paper provides a comparison and evaluation of the current test methods used to determine the strength of fiber-reinforced polymer FRP bent bars/stirrups at the bend location bend strength. The available methods depend on applying tensile forces through the straight portion of the bent bar/stirrup and keeping the bend zone restrained to generate a stress perpendicular to the bend direction in addition to the stress in the longitudinal direction. This could be achieved through the ACI 440.3R-04 B.12 test method for U-shaped bare FRP bars. Another possible method is the ACI 440.3R-04 B.5 which evaluates the bend strength of FRP stirrups by embedding them in two concrete blocks, which are pushed apart until the rupture of the FRP bent bars. Both methods were employed in testing FRP stirrups and bent bars and the bend strength was compared. The test results showed that the ACI 440.3R-04 B.12 test method consistently underestimates the bend strength of FRP stirrups. On the other hand, B.5 test method is more reliable and representative to the actual state of stresses in real concrete structural elements.

Confinement Effectiveness of FRP in Retrofitting Circular Concrete Columns under Simulated Seismic Load

Abstract: The results of a research program that evaluated the confinement effectiveness of the type and the amount of fiber-reinforced polymer (FRP) used to retrofit circular concrete columns are presented. A total of 17 circular concrete columns were tested under combined lateral cyclic displacement excursions and constant axial load. It is demonstrated that a high axial load level has a detrimental effect and that a large aspect ratio has a positive effect on drift capacity. Compared with the performance of columns that are monotonically loaded until failure, three cycles of every displacement excursion significantly affect drift capacity. The energy dissipation capacity is controlled by FRP jacket confinement stiffness, especially under a high axial load level. The fracture strain of FRP material has no significant impact on the drift capacity of retrofitted circular concrete columns as long as the same confining pressure is provided, which differs from the common opinion that a larger FRP fracture strain is ad...

Experimental Behavior of Carbon Fiber-Reinforced Polymer (CFRP) Sheets Attached to Concrete Surfaces Using CFRP Anchors

Abstract: Fiber-reinforced polymer (FRP) composite sheets have gained popularity as a viable strengthening technique for existing reinforced concrete structures. The efficiency of the strengthening system largely depends on adequate bond between FRP sheets and the concrete substrate. In recent years, techniques to anchor FRP sheets have been proposed in applications that have limited distance to develop FRP sheet strength. One promising technique consists of fabricating and bonding FRP anchors during the FRP sheet saturation and embedding them into predrilled holes in the concrete substrate. This paper presents experimental results highlighting the complex behavior between FRP sheets and anchors. The primary failure modes that the sheet-anchor system can experience are identified. The experiments identify the main variables that influence the FRP anchor-sheet system behavior. This research contributes to the needed experimental database that will aid in future development of design recommendations of this anchorage system.