Anchorage System Research Articles

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.

Development of a New Uplift Pile with Prestressed Semi-Bonded Composite Anchor

This paper introduces a new type of prestressed uplift pile that adopts the semi-bonded composite anchor as the main reinforcement. An in-situ experimental study was carried out to investigate the new pile’s deformation, stress, bearing capacity, and cracking characteristics, which were then compared with the conventional piles. Results show that although the reinforcement ratio of the new pile is only 0.75%, much less than that of the conventional pile (i.e., 3.84%), it achieves similar or even better mechanical properties under uplift loads. The cost of the pile’s anchorage system is reduced by 43.8%, and the total cost of a single pile is reduced by 33.6%. Compared with the conventional pile, the new pile makes better use of the lateral friction resistance of the lower pile body, and the uplift bearing capacity and the uplift resistance of the pile are improved correspondingly. In addition, the cracking resistance of the new pile is significantly improved, with the cracking load increased by 88.2% and the cracking area reduced by 48.3%. In addition, the multi-layer structure of the composite main bar provides better protection for the load-bearing steel strands against corrosion. As such, the new type of pile is expected to gain much better durability than the conventional ones.

Modelling Studies of Retrofitted Anchorage System in Exterior Beam Column Joint by Supplementary Steel

A Nonlinear finite element based ABAQUS modeling studies were conducted to evaluate the performance of exterior Beam Column Joint (BCJ) under quasi-static test loads. Six integrated BCJ models representing different configurations of beam reinforcement anchored in joint are verified by using a novel retrofitting technique called "Post Installation of Supplementary Anchorage" (PISA) by using headed bar as supplementary steel. The configuration of beam reinforcement anchored in column are described by straight bar,90 degree bend ,180 degree hook (confirming to design code IS456:2000) and single head, double head bars (confirming to ACI 318-19, ACI 352R-02 ) and 90 degree long bend of ductile detailing (as per IS 13920-2016). Two series (A&B) of integrated joint specimens representing conventional (series-A) and retrofitted anchorage (series-B) systems are modeled and tested by using ABAQUS software. The test parameters considered are configuration of anchorage system and presence of supplementary anchorage. The test variables representing nonlinear performance of retrofitted joint system are Von Mises stress conditions, Principal tensile stress, Moment-Rotation, Degraded stiffness, Crack mechanics and Damage index. The results shows good improvement of post failure conditions of exterior beam-column joint such as relocation of plastic hinge mechanism and failure mechanics of retrofitted joint system. Also the results validated with experimental program on typical specimens casted and tested. This study imparts useful information on implicit retrofitting methods applied by external means in exterior beam-column joint. It also promotes performance based design principles with viable construction practice.

Finite-Element Simulation of the Lateral Response of Posttensioned Base Rocking Steel Bridge Piers

This paper presents the results of a finite-element (FE) study on posttensioned (PT) rocking steel bridge piers, each composed of a circular tubular column, welded end plates, PT strands, and axially yielding steel energy dissipators (EDs), and corresponding chairs. The pier is configured so that it rocks at its base. Previously conducted experiments on five scaled rocking steel columns are summarized. Three-dimensional (3D) continuum FE models of the tested specimens are generated with the objective of verifying the capability of the modeling approach in the simulation of the local and global responses. Strain-controlled cyclic coupon tests were performed to quantify the kinematic and isotropic hardening material parameters. A simplified method is proposed to model the cyclic loss of prestressing because of wedge seating in a typical industry monostrand anchorage system. The FE procedure is then calibrated against the experimental data at the material, component, and global pier levels. A parametric study is conducted to examine the effects of key factors such as material model, P-Delta, base plate dimensions, column diameter-to-thickness and initial axial force ratios, ED chairs, and ED location on the lateral cyclic response. It is demonstrated that, for a given target drift, local buckling and the resulting residual lateral deformations of a rocking steel pier are a function of the diameter-to-thickness and initial axial force ratios of the column and the ED chairs. By the proper selection of these variables, a stable and robust self-centering response can be obtained with minimal damage to the bridge pier.

Effective approach for improving agummy smile : Upward movement of the maxillary occlusal plane using midpalatal miniscrews and amodified transpalatal arch.

Correction of agummy smile by orthodontic treatment alone has recently become feasible with the use of miniscrews. However, the optimal treatment mechanics remain unclear. Here we cephalometrically evaluated jaw and tooth displacement in cases where agummy smile was improved using alevel anchorage system (LAS). Sixteen patients underwent orthodontic treatment using anLAS consisting of amodified transpalatal arch and midpalatal miniscrews. Cephalometric pretreatment and posttreatment measurements were compared using the paired t‑test to determine significant skeletal and dental changes. The Mann-WhitneyU test was used for nonparametric data. Spearman's rank correlation coefficient was used to evaluate correlations between different variables and the vertical change in prosthion position which was used to indicate the amount of gingival exposure. The changes noted after treatment were intrusion of the maxillary first molars (P < 0.001) combined with only minor extrusion of the mandibular first molars. Suppressed extrusion of the mandibular first molars was significantly correlated with greater upward movement of the prosthion (r = 0.676, P < 0.01). Upward movement of the prosthion was also significantly correlated with intrusion of the maxillary and mandibular incisors, anterior upward movement of the maxillary occlusal plane, and an increase of the SNP angle. Treatment involving the combined use of miniscrews and amodified transpalatal arch resulted in intrusion of the maxillary first molars and maxillary incisors and consequently elevated the maxillary occlusal plane. The results of this study suggest that intruding the maxillary occlusal plane and minimizing mandibular molar extrusion were effective to induce autorotation of the mandible and to improve agummy smile.

Acute Effects of a Haptic Anchor System on Postural Sway of Individuals with Parkinson's Disease: A Preliminary Study.

Some investigators have demonstrated that an anchor system can improve postural control in elderly persons during balance tasks, but none have reported on the use of this approach in individuals with Parkinson's disease (PD). Therefore, we aimed to evaluate the effect of an anchor system on postural sway in elderly individuals with (n = 13) and without (n = 14) PD. In this cross-sectional study, we measured postural sway with a force platform based on the Clinical Test of Sensory Interaction of Balance (CTSIB). We calculated center of pressure (COP) parameters, as a function of time, based on the ellipse sway area (cm2) and evaluated self-efficacy for postural control based on the degree of difficulty in each task. With the anchor system (i.e., handheld ropes attached to weights on the floor), we observed a significant reduction in the ellipse sway area in the semi-tandem position among individuals with PD (p = .04). For participants without PD, there was no significant difference in sway with or without the anchor system in all positions. Also, for participants with PD, there was an improvement in self-efficacy for postural control associated with the anchor system in several positions while there was only a self-efficacy improvement with the anchor system in the semi-tandem position for those without PD. Acute use of a haptic anchor system reduced postural sway in the semi-tandem position in individuals with PD, and the anchor system generally improved postural control self-efficacy for body sway in individuals with PD.

Cover Picture: Geomechanics and Tunnelling 4/2022

AbstractTo increase overall safety, standardize Croatia's highway network, and adapt to the increased traffic to and from European countries, the Croatian Government decided to build a second tube for the Učka Tunnel – the third‐longest tunnel in Croatia. DSI Underground produced and supplied anchor systems and equipment to support excavation. (photo: DSI underground)

Hybrid and patch anchors for prevention of IC debonding in RC planks flexurally strengthened using FRP

One of the predominant failure modes of reinforced concrete (RC) members strengthened in flexure using fiber reinforced polymers (FRP) is intermediate crack induced (IC) debonding.This failure mode is usually brittle, premature and constitutes a significant underutilisation of the FRP material. To address this type of failure, design guidelines enforce strict limitations on the allowable FRP strain level which can be used in design. In order to suppress IC debonding failure modes, researchers have explored various anchorage systems with varying degrees of success. This paper investigates the use of patch anchors and hybrid anchors to suppress IC debonding failure. An experimental program is presented where RC planks are strengthened with FRP laminates and sheets and anchored using different arrangements. The results show that the addition of two hybrid anchors to the ends of the FRP plate results in significant load and deformation increases compared with unanchored planks.

Pull-out Strength of Suture Anchor and Torque of Buddy Anchor for an Osteoporotic Humeral Head in Rotator Cuff Repair: Parallel Versus Divergent Insertion

Background: The buddy anchor technique is useful to reinforce loose anchors in the osteoporotic humeral head during arthroscopic rotator cuff repair. However, theoretical parallel insertion of the buddy anchor to index a loose anchor is challenging in arthroscopy and can widen the entry site and decrease structural integrity. Purpose: To investigate and compare the biomechanical stability between 2 buddy anchor insertion techniques (parallel insertion vs divergent insertion) in the osteoporotic humeral head. Study Design: Controlled laboratory study. Methods: A total of 24 paired fresh-frozen cadaveric shoulders were used, and each pair was randomly assigned to either the parallel insertion group or the divergent insertion group. In the parallel insertion group, the buddy anchor was inserted parallel to the index loose anchor. In the divergent insertion group, the buddy anchor was inserted at a 20° angle in the medial direction to the index loose anchor. The insertion torque of the buddy anchor and ultimate pull-out strength of the index anchor were measured and compared between the 2 groups. Results: The mean maximum insertion torque was significantly higher in the parallel insertion group (16.1 ± 1.8 cN·m) compared with the divergent insertion group (12.0 ± 1.5 cN·m) (P < .001). The mean ultimate pull-out strength was significantly higher with divergent insertion (192.2 ± 28.6 N) than with parallel insertion (147.7 ± 23.6 N) (P < .001). Conclusion: For application of the buddy anchor system in the cadaveric osteoporotic humeral bone model, divergent insertion showed better ultimate pull-out strength than conventional parallel insertion, despite inferior maximum insertion torque. Clinical Relevance: The results of this study widen the applicability and accessibility for the buddy anchor system.

Numerical Simulation of Ground Anchor-Soil Nail Retaining Systems for Academic-Learning Purposes

The ever-expanding urban architecture in developing areas requires more land space for construction purposes to be available. For this, utilizing the sub-surface areas through excavations in populous cities is now on the increasing trend. Two major concerns in such excavation projects are excavation-wall stability and the induced ground settlements which can be countered by a soil nailing-ground anchor system. In this regard, influential factors such as nail length and nail inclination angles can affect the overall performance of stabilized ground. Therefore, the focus of the present study is on how the aforementioned influence excavation-induced ground deformations. The numerical simulation is conducted using the software Plaxis 2D. The established numerical models help to explain how changes in the nails’ inclination angles and anchor lengths can change the observed behavior of the walls; from which helpful tips for practicing engineers are drawn accordingly. Such results could also be utilized for classroom presentations to aid students’ understanding of geotechnical engineering concepts.

Influence of Cross-Section Shape and FRP Reinforcement Layout on Shear Capacity of Strengthened RC Beams.

The evaluation of the shear capacity of an FRP-strengthened reinforced-concrete beam is challenging due to the complex interaction between different contributions provided by the concrete, steel stirrup and FRP reinforcement. The shape of the beam and the FRP inclination can have paramount importance that is not often recognized by the models that are suggested by codes. The interaction among different resisting mechanisms has a significant effect on the shear capacity of beams, since it can cause a reduction in the efficiency of some resisting mechanisms. A comparative study of the performance in the shear resistance assessment provided by three models with six different effectiveness factors (R) is performed, considering different cross-section shapes, FRP wrapping schemes, inclination and anchorage systems. The results revealed that the cross-section shape, the FRP inclination and the efficiency of the FRP anchorages have a significant effect on the shear strength of beams. The analysis results show that the three models are able to provide an accurate average estimation of shear strength (but with a coefficient of variation up to 0.35) when FRP reinforcement orthogonal to the beam axis is considered, while a significant underestimation (up to 19%) affected the results for inclined FRP reinforcement. Moreover, all the models underestimated the resistance of beams with a T section.

Seismic response distribution expressions for rocking building contents under ordinary ground motions

Analytical expressions are proposed for predicting the rocking response of rigid free-standing building contents subjected to seismic-induced floor excitations. The study considers a wide range of rigid block geometries and seismic floor acceleration histories that were recorded during actual earthquakes in instrumented Californian buildings, so as to cover, in a fully probabilistic manner, the entire spectrum of potential pure rocking responses, i.e. from the initiation of rocking up to the block overturning. Contrary to past observations on anchored building contents (prior to any failure in their anchorage system that could alter their response and mode of failure), it is shown that the response of free-standing blocks is not influenced by the predominant period of the supporting structure. The proposed set of equations can be utilised for estimating the response statistics and consequently for undertaking an analytical seismic fragility assessment on rocking building contents.

A novel variable curvature clamping anchor for the multilayer CFRP plate cable: Concept, numerical investigation, and design proposals

This paper proposed a novel variable curvature clamping anchor (VCCA) for the multilayer carbon fiber-reinforced polymer (CFRP) plate cable and systematically evaluated the anchor performance using the finite element (FE) method. The design concept of the anchor, function of variable curvature waveform, anchor configuration and components design were first presented, then the stress distribution of the CFRP plate with different layers and failure mode of the anchor system were investigated. The six parameters affecting the anchor performance were also studied, including the number of waveforms, bolt preload, anchor length, thickness of ear plate, thickness of clamping plate, and thickness of clip. Finally, the design proposals of the anchor were given. The results indicate that the peak compressive stress has been successfully transferred from the loading end to the back of the anchor, and the interfacial shear stress of the CFRP plate was small and less than one-sixth of the shear strength. In addition, the failure of the anchor system occurred in the cable body part and not inside the anchor. The number of waveforms and the thickness of the clip slightly affected the peak transverse compressive stress, whereas the bolt preload, anchor length, ear plate thickness, and clamping plate thickness had an important influence on the axial stress distribution and peak transverse compressive stress. The novel VCCA proposed in this paper has essential engineering value and significance, filling the gap of the anchor for the multilayer CFRP plate cable, contributing to promoting the application of large-tonnage CFRP plate cable in bridges and space structures, and landing a solid foundation for subsequent experiments.

Behavior of bond-slip relationship of lightweight and normal weight geopolymer with various FRP sheets using end-groove anchorage

In this study, the effect of using an end-groove anchorage system (EGA) on the bond-slip behavior between fiber-reinforced polymer (FRP) sheets and both normal weight geopolymer (NWG) and lightweight geopolymer (LWG) concrete was investigated by considering the effects of different types of FRP sheets (CFRP, BFRP, and GFRP), FRP bonding lengths of 50 and 100 mm, FRP bonding widths of 50 and 75 mm, and with and without an EGA system. A total of 96 specimens of NWG and LWG concrete were cast, bonded with FRP sheetsand tested under double-shear tension. The results of employing EGA revealed that the bond-slip behavior of NWG specimens differed from that of LWG specimens. Using the EGA system significantly enhanced the bond force by an average of 16 % and 18 % for NWG and LWG, respectively. However, the ultimate slippage of NWG specimens was reduced by as high as 60 % as a result of using the EGA system, but it contributed to increasing the ultimate slippage remarkably by as high as 73 % for LWG concrete specimens. It's worth noting that the bond-slip behavior of CFRP sheet outperformed all other types of FRP sheets for both NWG and LWG concrete. The type of geopolymer concrete, the kind of FRP sheets, and the EGA process all influence specimen failure modes. The EGA system was more favorable for the bond failure of CFRP sheet and NWG concrete specimens, resulting in the avoidance of sudden debonding of CFRP composite and block contacts. A bond-slip model was proposed in this study to predict specimen bond force and slippage. The model was well fitted to the experimental data and appeared to have potential as a practical application which is the first and only model in the literature in this field.

Performance of a U-shaped anchoring system for cable-stayed bridges

An innovative U-shaped anchoring system was previously proposed to prevent the cracking of cable-pylon anchorage zones of concrete pylons in long-span cable-stayed bridges. The anchoring system transfers the cable force to the concrete pylon in the form of radial pressure, which fundamentally prevents the tension cracking of the concrete pylon column. In this study, the mechanical performance of the U-shaped anchorage system was investigated using finite element analysis. Subsequently, the fatigue performance of the steel strand in the U-shaped saddle, the anti-sliding performance of the U-shaped saddle, and the corrosion resistance of the steel strand were experimentally studied. The results of finite element analyses indicate that the U-shaped anchorage system significantly avoids concrete cracking in the cable anchorage zones provided that the strength grade of concrete filler is no less than C30. The experimental results show that the steel strand with polyurea coating has sufficient fatigue resistance as well as adequate anti-corrosion performance, and the anti-sliding performance of the anchoring system is sufficiently good. These critical studies validate the superiority of the U-shaped anchoring system with polyurea-coated steel strands, which should observe wide engineering applications in long-span cable-stayed bridges.

Ultrasonic-based tensile force estimation for cylindrical rod at various temperature conditions

This study presents the development of a tensile force estimation technique based on the ultrasonic bulk wave for cylindrical rod in a suspension bridge anchor system. Three piezoelectric macro fiber composites (MFC) transducers are installed on the surface of a cylindrical rod specimen for the generation and sensing of ultrasonic bulk waves. Ultrasonic responses are obtained at various tensile force levels and temperature conditions, and the relationship between the time lag of the ultrasonic response and the tensile force is established. In particular, the temperature effect on the tensile force estimation is theoretically derived and compensated for field applications. The originality of this study includes (1) theoretical derivation and investigation of the relationship between an applied tensile force level and the time lag of an ultrasonic response considering the variations of temperature, density, and elastic modulus, (2) development of a tensile force estimation and temperature compensation technique without temperature measurement, and (3) application to the tensile force estimation of the rod structure commonly used in a suspension bridge anchor system. The performance of the developed tensile force estimation technique was examined based on mock-up experiments of the rod structure of a real suspension bridge anchor system.

Expanding the concept of orthodontic camouflage for a skeletal Class II camouflage case through the use of skeletal anchorage system

This study aimed to report the treatment steps in a 26-year male patient, presented with a class II div 1 incisor relationship on a class II skeletal base with increased vertical proportions. The case was complicated by missing lower second premolars and retained lower second deciduous molars. Severe crowding was evident in the lower arch with mild crowding in the upper arch. The overbite and the overjet were increased. Scissor bite was evident in the left buccal segment. Treatment involved extraction of upper first premolars and lower second deciduous molars, utilizing moderate anchorage using a preadjusted edgewise fixed appliance (0.022’’ X 0.028”) with Roth prescription. Treatment duration was 20 months in total. The envelope of discrepancy specifies strict rules when camouflaging class II cases. The ability to retract incisors and the use of class II mechanics are within limited range to avoid damage to the periodontium. The current case report showed that the ability of the clinician to retract incisors using TADs could be carried out with high rate of success and safety.

In-field dynamic response of instrumented wine tanks subjected to aftershock earthquakes

An experimental investigation of the dynamic behaviour of anchored flat-based wine storage tanks in a winery located in Marlborough, New Zealand is presented herein. Six wine storage tanks with different dimensions, capacities, and anchorage systems were instrumented with accelerometers for approximately six weeks following the 2016 Kaikōura earthquake, providing an opportunity to conduct a parametric study of their dynamic response when subjected to 37 aftershock earthquakes. The largest accelerations measured in the horizontal (X and Y) and vertical (Z) axes directions at the top of the six tanks occurred in conjunction with a Mw5.48 aftershock earthquake, with analysis indicating that the peak acceleration at the tank top occurred along the horizontal (Y) axis with a value of 0.545 g.Analysis of accelerations recorded at the top of the six tanks revealed that for low-intensity earthquake shaking the largest accelerations were measured at the top of the 40kL tank. A comparison of the tank instrumentation data indicated that the 175kL tank with a shear bolt anchorage system performed better than the nominally identical 175kL tank with a necked tension anchorage system, with the maximum lateral accelerations attained in the horizontal X and Y axes directions for the tank with the necked tension anchorage system being on average 1.59 times and 1.39 times the acceleration attained for the tank with the shear bolt anchorage system. Analysis of the results for the highest intensity earthquake shaking (Mw5.48) also indicated that the two tanks with installed energy dissipation systems sustained less acceleration when compared to tanks with a traditional anchorage system. Also, good agreement was observed between the values of the impulsive period attained from the analysis of the tank instrumentation data and from finite element (FE) modal analysis.

The Behavior of RC Beams Retrofitted with Carbon Fiber Reinforced Polymers (CFRP)

The need for the introduction of economical and quicker retrofitting techniques is increasing due to the ever-aging infrastructure and damages produced by major catastrophic events around the world. The application of Carbon Fiber Reinforced Polymers (CFRP) for strengthening and retrofitting of reinforced concrete structures is gaining popularity due to its higher strength, lightweight, durability, corrosion resistance, and aesthetic value. This study presents the results of two strengthened and two retrofitted beams in comparison to control specimens. Two specimens were strengthened and two were retrofitted by attaching CFRP (Sika Carbo-Dur S812 or Sika-Wrap 230C) to the tension side of the beams using high strength epoxy. The results show that one CFRP strip/wrap simply attached at the tension side can help the damaged beam regain/pass the original strength. All specimens fail due to debonding of CFRP from the concrete surface emphasizing the need for efficient anchorage systems. Among the four patterns adopted, CFRP strips along with u-shaped anchorages at the ends provided the highest strength enhancement of 17.36%.