Fiber Reinforced Polymer Anchors Research Articles

Experimental investigation and analytical prediction on bond behaviour of CFRP-to-concrete interface with FRP anchors

Hybrid bonded technology with fiber-reinforced polymer (FRP) anchors can effectively improve the load capacity of carbon fiber-reinforced polymer (CFRP)-to-concrete interface. To investigate the reinforcement effect of FRP anchors, tensile shear tests of seventeen CFRP-concrete bonded joints with additional FRP anchors were conducted in this paper. The effects of the construction sequence, anchor position, and type of FRP anchor were considered in the experimental investigation. It was found that bonding CFRP sheet before installing FRP anchor and construction simultaneously could ensure the integrity of FRP anchor and provide a better anchor effect. The ultimate load-carrying capacity was increased with the increasing of plate length after anchor, that is the effect of anchor position. From the results of specimens with different types of FRP anchors at the same location, the FRP anchor composed of multiple small anchors can take effect earlier. By fitting the test results, the exponential bond-slip model for the CFRP-to-concrete interface and the elastic constitutive model for the FRP anchor were obtained. Further, substituting the two constitutive models, analytic theoretical models for load-slip curves and strain distribution were derived to predict the bond behavior of FRP anchored CFRP-to-concrete interface in this paper. The comparison between the prediction results and experimental data shows the good predictive accuracy of these analytical models.

Evaluating the behavior and bond properties of FRP spike anchors under confined conditions and elevated temperature

The use of fiber-reinforced polymer (FRP) anchors in combination with the conventional externally bonded reinforcement (EBR) installation technique is an effective method to prevent or postpone the debonding of FRP sheets. However, their behavior under confined conditions and elevated temperatures is still unknown. In such a framework, in the first phase, the current research aims to assess pullout test results for single FRP anchors with dowels ranging from 50 to 75 mm in confined and unconfined conditions. To achieve this goal, three concrete slabs with the dimension of 1550 × 1250 × 250 mm3 were cast. Experimental results showed that the bond strength of FRP anchors in confined conditions increased by about 50% compared to the unconfined conditions. Additionally, a comparison was made between the experimental results and the literature models. In the second phase, eleven pullout tests were conducted on the cylindrical specimens with the dimension of 150 × 200 mm2 (diameter × height) under confined conditions and elevated temperatures by considering different sustained load levels.The results showed as the temperature increases and FRP anchor is constantly loaded, it fails in a shorter time before the adhesive reaches its glass transition. Finally, a bond strength vs. temperature model was developed for FRP anchors in confined conditions and high temperatures.

Shear strengthening of RC beams with NSM FRP strips: Concept and behaviour of novel FRP anchors

The high efficiency of the near-surface mounted (NSM) fibre-reinforced polymer (FRP) technique for improving the shear capacities of reinforced concrete (RC) beams has been proved by numerous studies. However, premature debonding failures including interfacial debonding and concrete cover separation, which could largely limit the utilization of FRP strength, were frequently observed in RC beams strengthened in shear with NSM FRP. Proper anchoring measures of NSM FRPs can mitigate or even prevent such debonding failures and thus enhance the FRP strengthening efficiency, but relevant research on anchoring measures for NSM FRP shear-strengthened beams is still limited. Against the above background, a novel FRP anchor for NSM FRP shear-strengthened beams is proposed in this paper. A test program consisting of eight full-scale RC beams is carried out to investigate the effectiveness of the proposed FRP anchor system. It can be seen from the test results that the proposed FRP anchor is capable of mitigating or preventing the FRP debonding failures and thus significantly enhancing the load-carrying and deformation capacities of RC beams strengthened in shear with NSM FRP strips, and the configuration of the anchor can largely influence the performance of strengthened beams.

Novel Embedded FRP Anchor for RC Beams Strengthened in Flexure with NSM FRP Bars: Concept and Behavior

The near-surface-mounted (NSM) fiber-reinforced polymer (FRP) strengthening technique for reinforced-concrete (RC) beams has attracted worldwide research attention and application in the past two decades. In spite of improved bond strength between the NSM FRP and concrete, compared with the externally bonded (EB) FRP method, premature debonding failure still occurs, and, hence, the efficiency of the NSM FRP intervention is limited. An intuitive means to enhance efficiency is to apply anchorage devices to the RC beam; however, the availability of viable anchorage is limited for NSM applications. A novel anchorage device is therefore presented in this paper, which is referred to as an embedded FRP anchor (EFA). The concept, manufacture, and installation of the EFAs were initially presented. The effectiveness of EFAs in NSM FRP-strengthened RC beams was then ascertained through full-scale beam tests and comparison with an NSM FRP-strengthened beam anchored with a U-jacket. Moreover, the effects of EFA parameters on the behavior of anchored beam were also investigated. The test results not only prove the high anchoring efficiency of EFA but also reveal the significant effects of EFA parameters on the failure mode, load–deflection response, and NSM FRP strain of the EFA anchored beam.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

Research progress of FRP in steel and masonry bridge structures reinforcement

Fiber reinforced polymer (FRP) has been widely used in the reinforcement of concrete bridge structures, and it still has a good application prospect in the reinforcement of steel and masonry bridge structures. In order to summarize the research results of FRP in the reinforcement of steel and masonry structures, broaden the ideas of FRP strengthening bridges in China and promote its wide application in the field of bridge structure reinforcement, it is summarized from the aspects of anti-fatigue reinforcement, anti-buckling reinforcement, bearing capacity reinforcement and seismic reinforcement according to the different reinforcement mechanisms. The shortcomings of the existing studies were analyzed, some problems and ideas that can be further studied were put forward. Analysis result shows that the prestressed FRP reinforcement technology has a good application prospect because of its high material strength utilization rate. Generally, the method of prestressing FRP is used to strengthen the bridge steel members with fatigue cracks, and FRP and filler materials are used to form an external reinforcement system to improve the buckling resistance of steel members. FRP reinforcement can improve the bearing capacity and seismic performance of masonry structures. Follow-up studies should be continued to develop standardized prestressed FRP reinforcement and anchorage system with long-term reliable performance, further promote the engineering application of prestressed FRP reinforced steel structures and establish the specification system of FRP reinforced masonry bridges. The durability of FRP reinforced bridges under complex environment and coupling of various factors should be deeply studied.

Re-evaluation of shear contribution of CFRP and GFRP sheets in concrete beams post-tensioned with unbonded tendons

Contemporary design guidelines for the shear resistance of post-tensioned concrete (PC) beams retrofitted with fibre reinforced polymer (FRP) sheets are developed from the results of reinforced concrete (RC) beams. The accuracy of these guidelines for calculating the shear resistance of PC beams wrapped with FRP sheets is still questionable due to the difference in the shear behaviour of RC vs PC beams. The effects of the essential factors (e.g. tendon profile and anchorage system) on the shear resistance of PC beams have not been sufficiently studied, particularly for unbonded post-tensioned concrete (UPC) beams. This study presents an experimental investigation on the shear behaviour of UPC T-beams and the shear contribution of CFRP/GFRP sheets. The experiment consisted of 26 large-scale UPC T-beams with various factors including the tendon profile (harped or straight), concrete strength, FRP anchors, CFRP vs GFRP sheets, and various wrapping configurations. The experimental results showed that CFRP/GFRP sheets increased the shear resistance of UPC beams by 4–26%, which was much lower than that in RC beams. In comparison with the UPC beams with straight tendons, those with harped tendons exhibited a reduction in the shear contribution of CFRP/GFRP sheets (approximately 40%) and showed a more ductile failure mode with an improvement of the beam deformation (up to 2.3 times). FRP anchorage systems significantly enhanced the FRP shear contribution and energy absorption increased by 88% and 42% regarding those without anchors, respectively. Besides, it was observed from the test data that the widely-used method to determine the experimental shear contribution of FRP sheets in PC beams based on the difference between the shear resistance of strengthened and unstrengthened beams was inappropriate because it failed to consider the interactions between FPR sheets and other shear components, i.e. concrete and stirrups. Meanwhile, the experimental shear contribution of FRP sheets is recommended to be determined from the actual strain data of the FRP sheets across the main shear crack.

Evaluation on the effect of anchor embedment depth on the flexural capacity of concrete prisms

Using fiber-reinforced polymer (FRP) composites to strengthen and retrofit existing reinforced concrete (RC) structures has gained wide acceptance owing to the superior properties of FRPs such as high strength-to-weight ratios and corrosion resistance. Externally bonded FRP (EB-FRP) laminates can be applied to enhance the flexural and shear capacities of RC beams and improve the ductility of RC columns. However, the premature debonding of FRP laminates from the concrete substrate is a major concern and usually results in a brittle member failure. To tackle this issue, many studies proved that adequate anchorage systems could improve the FRP-to-concrete bond, and therefore results in delaying the FRP debonding and further developing the tensile strength of the FRP laminates. One of the most commonly used anchorage systems is FRP spike anchors. Compared to other anchorage systems (for e.g., metallic anchors), FRP anchors have high compatibility with the FRP laminates. In addition, FRP spike anchors are noncorrosive and have high tensile strengths. Although several studies addressed FRP spike anchors in flexural and shear strengthening of RC beams and slabs, the literature still lacks comprehensive information on the effect of all anchor parameters on the performance of the strengthening system. As a result, the aim of this study is to investigate the effect of anchor embedment depth on the behavior, strength, and effectiveness on the FRP spike anchorage system. Six concrete prisms were cast and strengthened with carbon FRP (CFRP) laminates and spike anchors then tested in flexure under four-point bending tests. Test results showed that installing anchored CFRP laminates increased the capacity of the plain concrete prism by 80-120%. Anchoring the laminates at different embedment depths of 50mm, 75mm, 100mm, and 125mm enhanced the capacity of the unanchored prisms by 11%, 13%, 15%, and 33% respectively. Thus, it was concluded that increasing the anchor embedment depths increased the ultimate load carrying capacity of the prisms.

Pullout behaviour of FRP anchors in clay bricks

Fiber reinforced polymer (FRP) anchors have been shown to be effective for delaying or even preventing premature FRP debonding failures in concrete and masonry structures strengthened with externally bonded FRP. A number of researchers have conducted extensive research on their anchorage behaviour in concrete, but little research is concerned with the behaviour of FRP anchors embedded in masonry. An important difference between a brick unit and common concrete specimens is that the former usually has smaller dimensions. This study investigated the performance of FRP anchors embedded in solid clay bricks. Five parameters, including anchor types, hole diameter, hole depth, anchor size and brick strength, were considered in the test programme. The experimental results showed that anchors made from folded pre-wet FRP sheet has the best anchorage performance. Four failure modes were observed from the pullout tests in this study, with the brick triangular prism failure most common. The hole depth showed a more significant effect on the pullout capacity than the hole diameter. After reviewing the existing pullout strength models for concrete cone failures, two predictive and accurate pullout strength models are proposed in this paper for the triangular prism failure in bricks.

Effect of FRP Spike Anchor Installation Quality and Concrete Repair on the Seismic Behavior of FRP-Strengthened RC Columns

The use of fiber-reinforced polymer (FRP) to repair and seismically strengthen existing deficient or damaged structural elements is now widespread. FRP anchors have become an important component of such FRP strengthening. However, while reasonable quality control and field quality assurance measures exist for FRP fabrics and plates, such attention has not yet been given to FRP anchors. It seems logical to expect that poor FRP anchor installation will adversely impact the performance of the repaired element. This experimental program was envisaged to assess the level of such an adverse impact. It consists of six RC columns subjected to axial load and quasi-static cyclic load. Of the six columns cast for the experimental work, three columns had good concrete placement, while the remaining three showed poor consolidation, with substantial honeycombing and segregation at the base. It was decided that the latter columns could be used as examples of damaged concrete and so they were repaired by a local contractor by removing the poor concrete and replacing it with a commercially available bagged concrete repair material. One column of each set of three was designated as a control column without any FRP strengthening, while the four remaining columns were strengthened using longitudinal FRP sheets for flexural strengthening, anchors to develop the FRP into the foundation, and transverse FRP sheets for confinement. It was observed that the concrete repair did not adversely affect the behavior of the columns or the interaction between the concrete and the FRP. The FRP anchors were installed to replicate poor installation in the field. Those with improperly placed fans, or splays, did not perform at all as intended and it is recommended that such anchors be removed and replaced without exception. Inadequately saturated anchors were able to achieve their design rupture capacity but failed in a more brittle manner than adequately saturated anchors. Based on the observations from the experimental program, several ideas and options are proposed to enhance the quality of FRP anchors. Accompanied with onsite testing and mockups, these suggestions will substantially contribute to the mitigation of the associated variability in the performance of the rehabilitation.

Tensile behavior of FRP anchors made from CFRP ropes epoxy-bonded to uncracked concrete for flexural strengthening of RC columns

One of the major problems with using fiber reinforced polymer (FRP) in strengthening reinforced concrete (RC) structures is FRP premature debonding. Anchoring FRP materials to concrete has become associated with most of the strengthening techniques. One of the anchoring techniques is using handmade anchors made from FRP materials. In previous studies, most FRP anchors were made from rolling pre-cut FRP sheets and had short embedment (<100 mm) as they were used for flexural or shear strengthening of RC beams. In the present study, FRP anchors were made from carbon fiber reinforced polymer (CFRP) ropes and had long embedment to be used for flexural strengthening of RC columns. A total of twenty-one pullout tests were conducted on CFRP rope anchors bonded to concrete using chemical epoxy. The test parameters were embedment length (45, 90, 135, 180, 270, and 315 mm), anchor hole diameter (12.7, 19.1, and 25.4 mm), and epoxy type (Hilti 500 vs. MasterBrace SAT 4500). Test results showed that the pullout strength of CFRP anchors increased with the increase of embedment length, and no significant effect of the hole diameter on the pullout strength was observed. However, the bond strength increased with decreasing embedment length and hole diameter. The observed pullout results and failure modes were compared to the predictions of the available models. Finally, a modified model was proposed to be used to predict the pullout strength of CFRP rope anchors until more tests become available to develop a more realistic model.

Flexural performance of Reinforced Concrete One-way Slabs Strengthened by FRP Grid

Fiber reinforced polymer (FRP) grid is a kind of two-way fiber material. Its transverse reinforcement and longitudinal reinforcement have the same physical characteristics. Experiments on the reinforced concrete one-way slabs strengthened by FRP grid were conducted to study the influences of bonding area and FRP anchors on its flexural performance. The results showed that the flexural capacity of reinforced concrete one-way slabs strengthened by FRP grid is increased by 7% - 21%. FRP grid can effectively slow down the crack expanding, increases the stiffness and improve the flexural behavior of the slab.

Evaluation of a new bond-type anchorage system with expansive grout for a single FRP rod

Prestressed concrete applications require a high strength prestressing material that could apply and maintain effective compressive force to concrete members. Although fiber reinforced polymer (FRP) materials, especially carbon FRP (CFRP), have the desired strength, no efficient system for its anchorage to concrete has been devised yet. This paper presents an experimental evaluation on a new bond-type anchorage system using an expansive grout as a filling material to anchor CFRP rods. A total of twelve specimens were fabricated and tested. Short-term and long-term pullout tests were performed. The CFRP rods were 0.375 in. (10 mm) and 0.50 in. (13 mm) in diameter. The parameters investigated were the bond length, rod diameter, and curing time of the expansive grout. The experimental results showed that 12 in. (305 mm) and 15 in. (381 mm) were adequate bond lengths to effectively anchor the 0.375 in. (10 mm) and 0.50 in. (13 mm) CFRP rods, respectively. The results also indicated that the anchor strength and stiffness were directly proportional to the bond length, and cross-sectional area ratio of CFRP rods to anchor borehole affected the stiffness and bonding capacity of the proposed anchor. Finally, a numerical analysis was carried out to predict the tensile behavior of FRP anchors. The numerical results had good agreement with the experimental results.

Safety performance monitoring of smart FBG-based FRP anchors

Fibre Reinforced Polymer (FRP) bar is a versatile element applied to the civil engineering industry. Considering its low shear strength, the anchoring performance is of concern. For FRP anchoring system, the safety monitoring is a new approach to investigate the performance in anchoring and long-term safety use. Based on the material properties and the requirements of anchorage and safety monitoring, this paper proposes an innovative smart Fibre Bragg Grating (FBG)-based FRP anchor by introducing FBG into FPR bonding anchor. The debonding damage process and the failure sensitivity of the smart anchor were investigated during the pull-out tests. Additionally, the strain distribution inside the anchor under pull out load and the law of strain varying with load were analysed. Based on the experimental results, the theoretical analysis and numerical simulation of the smart anchor were carried out. Further, the debonding damage mechanism and failure mode, the distribution model and simplified calculation model of the interfacial shear stress between FRP bar and epoxy were put forward. Moreover, the FRP bonding anchor theory, the safety monitoring and failure evaluation method of FBG-based FRP anchor were developed.

Axial stress–strain model developed for rectangular RC columns confined with FRP wraps and anchors

It is widely reported that using fiber-reinforced polymer (FRP) as confinement jackets for concrete can significantly enhance its strength and ductility. The confinement effectiveness for rectangular columns has revealed significant enhancements in their strengths, in particular for well-confined columns with a cross-sectional depth of <300 mm. However, for larger-sized columns with a section depth of larger than 300 mm and an aspect ratio of larger than 2.0, the confinement effectiveness is most limited. One of the key solutions to significantly increase the confinement effectiveness is by using a combination of FRP anchors and wraps. For good analysis and design of FRP confinement for rectangular RC columns, a model for the stress–strain behavior of rectangular reinforced concrete (RC) columns confined with FRP wraps and FRP anchors is provided in this paper. The model is mainly based on results from tests reported in recent studies, in which a series of axial compressive tests on a total of 80 FRP-confined rectangular RC columns of large size were conducted. The database included columns with aspect ratios ranging from 1.5 to 4.0. Furthermore, the depth of the section is up to 600 mm. key parameters such as the aspect ratio and size of cross section, number of layers of FRP wraps, volumetric ratio of internal hoop steel reinforcement, and cross-sectional area and configuration of anchors were all considered. All predicting expressions were validated against the test database used in the model calibration. In terms of average absolute error and mean square error, comparisons with other existing expressions were conducted, showing that the expressions of the present model reveal more accuracy. Finally, comparisons revealed the model can estimate the confinement effectiveness and predict the stress–strain relationships of FRP-confined rectangular RC columns with additional FRP anchorage.

Innovative warp and woof strap (WWS) method to anchor the FRP sheets in strengthened concrete beams

U-shaped straps are an effective means to postpone premature debonding failure when fiber-reinforced polymer (FRP) composites are applied in structures. However, the U-wrap anchors are not cost-effective and in many cases cannot completely prevent the debonding phenomenon. In the current study, an innovative technique named “warp and woof strap” (WWS) is introduced for anchoring longitudinal FRP sheets, in which some parts of FRP fibers are manually made bi-directionally. Unlike the conventional U-shaped anchors, the anchorage system in this method is in direct contact with the tension side of the beam. Totally, 20 reinforced concrete (RC) beams, 120 × 160 × 1400 mm in size, were subjected to the four-point loading to evaluate the efficiency of the introduced anchorage system in comparison to the U-shaped anchorage. The effect of different parameters including the method employed for anchoring the longitudinal carbon fiber reinforced polymer (CFRP) sheet, anchorage height and width, location of FRP anchorage application, use of the corner strip and rounding corner method, and configuration of WWS anchorage were investigated. The experimental results indicated that the efficiency of the WWS method in preventing undesired debonding mode of failure is much better than that of conventional U-shaped anchor. It was also observed that using WWS method can improve the load carrying capacity and ductility up to 32% and 80%, respectively, compared to U-shaped anchors.

Digital image correlation (DIC) for measurement of strains and displacements in coarse, low volume-fraction FRP composites used in civil infrastructure

Accurately measured strains are critical when investigating the application of Fiber Reinforced Polymer (FRP) materials, but traditional mechanical strain measurement methods have several critical drawbacks related to the installation process and the recording capabilities of the devices. FRP materials typically used in the civil engineering field feature large asymmetries and heterogeneity originated from the manual installation procedures, as opposed to the highly controlled FRP fabrication methods used in other fields that result in more homogeneous materials. The feasibility of using an optical full-field Digital Image Correlation (DIC) technique for measurement of strain fields on FRP materials used in the civil engineering industry has been investigated and the level of error in the DIC method when using more traditional methods was determined. The main advantage of using DIC over more traditional methods, which is the capacity of DIC to measure full field strains instead of strains at isolated points, has been demonstrated by providing exemplar measurements of various specimens of FRP materials. The reported strain fields are examples of what was obtained during an experimental campaign to understand the behavior of FRP anchors and other materials. The main conclusions drawn from the observation of those strain fields are discussed.

FRP-to-FRP bond characterization and force-based bond length model

Fiber Reinforced Polymer (FRP) anchors are an effective method to increase the bond strength and/or ensure load path continuity between FRP materials and the concrete substrate when FRP materials are used as Externally Bonded Reinforcement (EBR) to strengthen and/or repair existing structures. While advances in developing a design methodology have been made on the fiber rupture and concrete cone failure modes for FRP anchors, the FRP-to-FRP bond behavior has received limited research attention. In an effort to develop design equations to calculate FRP-to-FRP bond capacity to be used by engineers, an extensive experimental program was undertaken to characterize the behavior of adhesively bonded FRP-to-FRP lap joints. Two force-based models to calculate the FRP-to-FRP bond capacity were proposed considering the influence of the critical bond length on lap joint behavior. A study to characterize the statistical properties of the experimental data was undertaken, and 95 and 99.87 percentile models were developed based on the statistical distribution of the experimental data set. Main conclusions inferred from the study and ideas for future work are also presented.

Experimental testing and design model for bent FRP anchors exhibiting fiber rupture failure mode

The implementation of Fiber Reinforced Polymer (FRP) anchors in Externally Bonded Fiber Reinforced Polymer (EBR-FRP) systems is an effective method to increase the bond strength and/or ensure the continuity of the load path between FRP materials and the concrete substrate when EBR-FRP systems are used to strengthen and/or repair existing structures. Multiple design examples of EBR-FRP systems exist in the literature, and design guidelines have been compiled in several countries. However, currently these design guidelines do not specifically include guidance on the design of FRP anchors. This lack of design guidance is one of the main impediments to widespread implementation of FRP anchors in the civil engineering industry. The present study reports an experimental program consisting of 32 bent FRP anchor specimens of different sizes and widths that was undertaken to characterize the behavior of bent FRP anchors when the fiber rupture failure mode is exhibited. A design methodology for the mean value and for the lower bound characteristic values (95 and 99.87 percentile equations) is proposed and the reliability of the methodology is assessed.

Strengthening RC structures using FRP spike anchors in combination with EBR systems

The use of Fiber-Reinforced Polymer (FRP) materials as Externally Bonded Reinforcement (EBR) to strengthen and/or repair existing Reinforced Concrete (RC) structures is widely documented, and various methods exist to increase the bond strength and/or ensure load-path continuity between FRP composites and the concrete substrate. The use of FRP anchors to increase the capacity of EBR systems offers a number of critical advantages compared to other existing methods. However, despite the significant amount of research previously undertaken on the topic a concise summary of the experimental performance of FRP anchors has not yet been reported. Consequently, a database consisting of five tables comprising the results from studies focused on testing isolated FRP anchors and four additional tables with results related to the use of FRP anchors in combination with FRP-EBR systems to strengthen and/or repair RC structures is presented. A number of tentative design models previously published for various failure modes are reported and reanalyzed in a critical way, and behavioral trends were identified as an effort to discern what models are ready to be used and what new further research is needed in the development of design guidelines for FRP anchors.