Fiber Reinforced Polymer Anchors Research Articles

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

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.

Pullout Strength Models for FRP Anchors in Uncracked Concrete

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 FRP anchors are proposed which can also be used in design. Finally, parametric studies are undertaken and the influence of key variables is identified.

Behaviour of Handmade FRP Anchors under Tensile Load in Uncracked Concrete

Fibre-reinforced polymer (FRP) anchors made from rolled or bundled fibres, which are known as FRP anchors amongst other names, are an emerging form of anchorage for application to externally bonded FRP strengthening systems. Little is however known of the fundamental behaviour of these anchors. This paper in turn reports the results of experiments on FRP anchors under pure tension (pullout) loading. A detailed description of the anchor construction procedure is firstly presented followed by anchor tensile strength test results. Pullout test results of FRP anchors embedded into uncracked concrete blocks are then reported with particular attention focused on the failure mechanisms, failure loads, bond strength and load-displacement and load-strain responses for varying anchor hole diameter, embedment depth and anchor fibre content. Finally, a large test data base is assembled from the results of the present study as well as two other studies found in the open literature. Relationships between the pullout load to the anchor diameter, embedment depth and concrete strength are identified while the effects of different methods of anchor construction are also discussed.

Tensile Behavior of FRP Anchors in Concrete

Strengthening of concrete structures using fiber-reinforced polymer (FRP) systems has become a widely accepted technology in the construction industry over the past decade. Externally bonded FRP sheets are proven to be a feasible alternative to traditional methods for strengthening and stiffening deficient reinforced or prestressed concrete members. However, the delamination of FRP sheets from the concrete surface poses major concerns, as it usually leads to a brittle member failure. This paper reports on the development of FRP anchors to overcome delamination problems encountered in surface bonded FRP sheets. An experimental investigation was conducted on the performance of carbon FRP anchors that were embedded in normal- and high-strength concrete test specimens. A total of 81 anchors were tested under monotonic uniaxial loading. Test parameters included the length, diameter, and angle of inclination of the anchors and the compressive strength of the concrete. The experimental results indicate that FRP ...

Flexural and Interfacial Behavior of FRP-Strengthened Reinforced Concrete Beams

Although there is a large amount of experimental data available on the fiber-reinforced polymer (FRP) strengthening of concrete structures, a full understanding of the various debonding phenomena is somewhat lacking. As a contribution to fill this need, two-dimensional and three-dimensional (3D) nonlinear displacement-controlled finite-element (FE) models are developed to investigate the flexural and FRP/concrete interfacial responses of FRP-strengthened reinforced concrete beams. Interface elements are used to simulate the FRP/concrete interfacial behavior before and after cracking. The analysis is carried out using two different relations for the interface; namely, nonlinear and bilinear bond–slip laws. The results predicted using these two laws are compared to those based on the full-bond assumption. The FE models are capable of simulating the various failure modes, including debonding of the FRP, either at the plate end or at intermediate cracks. The 3D model is created to accommodate cases of FRP-strengthened reinforced concrete beams utilizing FRP anchorage systems. In addition, the models successfully represent the actual interfacial behavior at the vicinities of cracks including the stress/slip concentrations and fluctuations. Results are presented in terms of the ultimate load carrying capacities, failure modes and deformational characteristics. Special emphasis is placed on the FRP/concrete interfacial behavior and cracking of the concrete. The numerical results are compared to available experimental data for 25 specimens categorized in six series, and they show a very good agreement.

Tests on Seismically Damaged Reinforced Concrete Walls Repaired and Strengthened Using Fiber-Reinforced Polymers

The behavior of six 1:2.5-scale reinforced concrete cantilever wall specimens having an aspect ratio of 1.5, tested to failure and subsequently repaired and strengthened using fiber-reinforced polymer (FRP) sheets is investigated. Specimens were first repaired by removing heavily cracked concrete, lap splicing the fractured steel bars by welding new short bars, placing new hoops and horizontal web reinforcement, and finally casting nonshrink high-strength repair mortar. The specimens were then strengthened using FRP sheets and strips, with a view to increasing flexural as well as shear strength and ductility. In addition to different arrangements of steel and FRP reinforcement in the walls, a key parameter was the way carbon-FRP strips added for flexural strengthening were anchored; steel plates and steel angles were used to this effect. Steel plates were anchored using U-shaped glass-FRP (GFRP) strips or bonded metal anchors. Test results have shown that by using FRP reinforcement, the flexural and shear strength of the specimens can be increased. From the anchorage systems tested, metal plates combined with FRP strips appear to be quite efficient. The effectiveness of the bonded metal anchors used was generally less than that of the combination of plates and GFRP strips. In all cases, final failure of the FRP anchorage is brittle, but only occurs after the peak strength is attained and typically follows the fracture of steel reinforcement in critical areas, hence the overall behavior of the strengthened walls is moderately ductile.

Strength and Ductility of Concrete Beams Reinforced with Carbon Fiber-Reinforced Polymer Plates and Steel

Seven concrete beams reinforced internally with varying amounts of steel and externally with precured carbon fiber-reinforced polymer (FRP) plates applied after the concrete had cracked under service loads were tested under four-point bending. Strains measured along the beam depth allowed computation of the beam curvature in the constant moment region. Results show that FRP is very effective for flexural strengthening. As the amount of steel increases, the additional strength provided by the carbon FRP plates decreases. Compared to a beam reinforced heavily with steel only, beams reinforced with both steel and carbon have adequate deformation capacity, in spite of their brittle mode of failure. Clamping or wrapping of the ends of the precured FRP plate enhances the capacity of adhesively bonded FRP anchorage. Design equations for anchorage, allowable stress, ductility, and amount of reinforcement are discussed.

Cyclic Tests on Seismically Damaged Reinforced Concrete Walls Strengthened Using Fiber-Reinforced Polymer Reinforcement

Results from tests on low-slenderness reinforced concrete walls designed to modern code provisions, initially subjected to cyclic loading to failure and subsequently conventionally repaired and then strengthened using fiber-reinforced polymer (FRP) jackets, are presented. Repair involved replacement of damaged concrete by a high-strength mortar and lap-welding of fractured reinforcement in the plastic hinge region, while strengthening involved wrapping of the walls with FRP jackets, as well as addition of FRP strips at the wall edges, to enhance both flexural and shear capacity. A key parameter was the way in which carbon FRP strips added for flexural strengthening were anchored; combinations of glass FRP (GFRP) anchors and anchoring strips, as well as anchoring steel plates, were used. Results show that the addition of steel plates to the GFRP anchors and strips lead to a more effective anchorage, with strength increases of up to 30%.