Mechanical Anchorage Research Articles

An analytical model to predict bond behavior of fiber reinforced polymer bonded to concrete with an end anchorage system

The end mechanical anchorage system has been widely applied in the conventional externally bonded reinforcement (EBR) technology, to hinder the premature debonding failure of fiber reinforced polymer (FRP) laminate, especially for the reinforcement structures with prestressed FRP due to higher interfacial shear stress at the ends. Through the introduction of the hinge as the substitution of end anchorage, this paper presents a numerical model based on the bilinear bond-slip model and ordinary differential equations in elastic, elastic-softening, and elastic-softening-debonding stages. The bond behavior of the FRP-concrete interface under the end anchorage in different stages is predicted, obtaining the analytical expressions of interfacial load-slip relation, interfacial shear stress distribution, and the stress distributions of FRP. Additionally, two experimental programs from this group and previous literature were involved in this study to validate the accuracy of the numerical model. The comparison shows they are in good agreement. Moreover, it indicated that the strength increase is linear with the torque applied in the end anchorage, but bonding strength is not the case.

Evaluation of bond strength of helically ribbed CFRP bar connections as mechanical anchorage schemes

In spite of their outstanding properties, FRP reinforcing bars still face a series of drawbacks that should be addressed to widen their applications. For example, straight FRP bars must be used because those bars suffer significant strength degradation when curved. This implies that FRP bars resist the slip nearly solely through their bond strength with concrete. In addition, helically ribbed FRP bars exhibit bond strength twice higher than sand coated bars but develop weaker bond characteristics with concrete than the steel rebar. Anchorages are thus needed to improve the bond strength but may be difficult to realize in narrow spaces like joints. Therefore, this study examines the combined use of helically ribbed FRP bars with connections like lap-splice, epoxy-filled tube, coupler or expanded ribs as mechanical anchorages. A total of 36 pullout specimens considering the types of connection as parameter are tested to investigate the eventual effectiveness of the connections in enhancing the bond behavior. The use of two expanded ribs appears to be the best option. The predictions of the bond stress-slip models of current design codes are compared to the experimental data to examine whether these models can simulate accurately the connections.

Nanoscaled Titanium Oxide Layer Provokes Quick Osseointegration on 3D-Printed Dental Implants: A Domino Effect Induced by Hydrophilic Surface.

Three-dimensional printing is a revolutionary strategy to fabricate dental implants. Especially, 3D-printed dental implants modified with nanoscaled titanium oxide layer (H-SLM) have impressively shown quick osseointegration, but the accurate mechanism remains elusive. Herein, we unmask a domino effect that the hydrophilic surface of the H-SLM facilitates blood wetting, enhances the blood shear rate, promotes blood clotting, and changes clot features for quick osseointegration. Combining computational fluid dynamic simulation and biological verification, we find a blood shear rate during blood wetting of the hydrophilic H-SLM 1.2-fold higher than that of the raw 3D-printed implant, which activates blood clot formation. Blood clots formed on the hydrophilic H-SLM demonstrate anti-inflammatory and pro-osteogenesis effects, leading to a 1.5-fold higher bone-to-implant contact and a 1.8-fold higher mechanical anchorage at the early stage of osseointegration. This mechanism deepens current knowledge between osseointegration speed and implant surface characteristics, which is instructive in surface nanoscaled modification of multiple 3D-printed intrabony implants.

The effect of type of mechanical anchors on bond behavior of ribbed-surface GFRP bars embedded in concrete

The deficiency in the bond between concrete and fiber-reinforced polymer (FRP) bars is a major hindrance to their widespread use in concrete structures. One effective solution to this problem is to use mechanical anchors along the bar. This research investigates the effect of mechanical anchors on the bond behavior of glass fiber-reinforced polymer (GFRP) bars embedded in concrete. In the first phase, eight beam specimens were constructed and tested in flexure, in which the FRP bars contained no anchors or anchors made of polyethylene, aluminum, or steel. The increase in maximum tensile stress in the bar was 43 %, 17 %, and 12 % for specimens with steel, aluminum, and polyethylene anchors, respectively. Steel anchors were identified as the most effective option with the greatest maximum stress and greatest initial stiffness in the stress-slip curve. In the study's second phase, an additional set of 16 beam specimens was tested to investigate the effect of the number of steel anchors. The results showed that the tensile stress developed in the GFRP bar increases at a higher rate with a greater number of steel anchors. Compared to the specimen without anchors, the bar stresses increased by 20–25 % for one and 52–59 % for two steel anchors.

Assessment of Post-Installed Anchor Stiffnesses in Uncracked Concrete with Different Types of Coarse Aggregates

This paper investigates the potential influence of different aggregates in the concrete mix design on the concrete cone resistance of different types of anchors as well as the anchor stiffness. In fact, bonded anchors with three different adhesives and mechanical anchors and concrete screws of two types were installed in five different concrete mixes and tested in a standard tensile configuration using pull-out tests with wide support resulting in concrete cone failure. A rigorous analysis of both the initial and secant stiffness values of the different anchor types is carried out in a comparative manner. The results of the experimental program show that the anchor stiffnesses are not influenced by the different aggregates in the concrete mixes, but rather by the type of anchor. Finally, this manuscript provides a narrow range of both initial and secant stiffness values with respect to anchor type only.

Assessment of shear capacity in NSM prestressed FRP strengthening with anchorage conditions

Efforts to achieve a defect-free flat groove in near-surface-mounted prestressed fiber-reinforced polymer (FRP) strengthening systems have proven challenging. Despite attempts, attaining an ideal groove remains formidable. In this system, anchorage device installation involves injecting epoxy resin into groove defects to achieve planarity. Structural behavior analysis and optimization of the anchorage device were conducted based on device type, anchor type, and defect depth through shear loading tests. The mechanical anchor demonstrated an ultimate load of 261 kN, with failure modes including concrete cracking, concrete compression failure, and anchor tensile failure. The chemical anchor exhibited an ultimate load of 390 kN, with its final failure attributed to anchor tensile failure. The ultimate load capacity of anchorage device surpassed that of a carbon FRP(CFRP) bar by up to 62.5%. In a parametric study, the shear strength of the anchorage device was explored concerning concrete compressive strength and anchor diameter. The ultimate load of the proposed model with low concrete compressive strength proved insufficient compared to the strength of CFRP rebar.

Development of polyamide 6‐graphene oxide nanocomposite and direct‐joining with aluminum alloy for lightweight engineering applications

AbstractLightweight polyamide composites and structures have been widely studied and employed in several industrial sectors. In this study, the development of a nanocomposite of polyamide 6 and graphene oxide (PA6‐GO) by melt‐compounding and the joining with aluminum alloy AA6061 through direct‐adhesion injection overmolding are addressed. PA6‐GO nanocomposite exhibited well‐dispersed thin (300 nm) GO platelets distributed within the PA6 matrix, which resulted in an increase of 21% in the tensile modulus and 16% in the yield stress for a filler loading of 0.5 wt%. PA6‐GO/AA6061 hybrid joints showed good mechanical anchorage through the complete filling of the polymer into micro‐scale grooves designed onto the metal surface, which ensured outstanding shear strength of 7.1 ± 1.0 MPa, comparable to other polyamide‐metal hybrid joints reported in the literature. This indicates that the processing routes and materials developed are promising for lightweight engineering applications.Highlights A PA6‐GO nanocomposite with enhanced tensile properties was developed. A joint of PA6‐GO and AA6061 with outstanding shear strength was obtained. Fast and efficient melt‐processing routes were employed. These materials are promising for lightweight engineering applications.

Experimental study on the effect of different shear reinforcement shapes and arrangement on 3D crack propagation and shear failure mechanism in RC beams

Surface crack patterns have been considered to determine the shear failure behavior of RC beams but the effect of three-dimensional crack propagation on shear crack development and shear strength of RC beams is still debatable. In this study, a three-dimensional crack evaluation was carried out to investigate the shear failure mechanism of RC beams with different shapes and arrangement of shear reinforcement (close shape shear reinforcement, rod shape reinforcement with mechanical anchorage, combination of close shape reinforcement and rod shape reinforcement, rod shape reinforcement and transverse distribution rebar) using three-point loading test by keeping the amount of shear reinforcement same in all beams. The load displacement relationships, 3D crack maps, stirrup strain and concrete strain relationships with displacement and shear resistance components were discussed in detail and these information’s are useful for designing and shear strengthening of existing beams. It was clarified that a clear difference in three-dimensional cracking pattern, shear resistance components of concrete and shear reinforcement contribution was observed in RC beams. This was due to the shear reinforcement shapes and arrangement of rod shape reinforcement, which influenced the shear strength of RC beams.

Structural performance of RC beams with openings shear strengthened by hybrid techniques (EBR/EBRIG)

Creating the openings in the existing reinforced concrete (RC) beams causes sudden deterioration, especially in the shear zone. This study investigates the effectiveness of a novel strengthening technology using externally reinforced fibre-reinforced polymer (FRP) strips in groves (EBRIG) on the shear behaviour of RC beams, compares it to that of externally reinforced (EBR) strips, and uses hybridisation between them to address the weakness brought on by the presence of an opening in the shear zone. Also, an innovative anchorage mechanism is suggested and studied to postpone the beginning of the strengthening system’s debonding. The strengthening material used in this research is glass fibre-reinforced polymers (GFRPs). For this study, 11 RC beams with an opening and a control beam without an opening, each measuring 120 × 300 × 2600 mm in size, were cast and subjected to the four-point loading test. All test beams had the same geometry and reinforcement details. The effect of the following parameters was investigated in this study: the dimension of the opening (square ‘150 × 150’ or rectangle ‘100 × 300’ mm), the strengthening technique used (externally bonded reinforcement [EBR], EBRIG and hybrid technique ‘EBRIG + EBR’) and the wrapping configuration of the strengthening (fully warped strips or U-shaped sheets with anchors). All techniques used raised the efficiency of shear resistance to approximate the fading effect of the opening, especially the technique of hybridising EBRIG and EBR. All strengthened beams showed an increase in the ultimate shear capacity ranging from 74% to 142% compared with the reference beams with the opening. The EBRIG technique shows numerous advantages over the EB system and can employ the strength of FRP materials. It also deals with the problems of weather factors that were facing EBR, and this is because of the covering that protects in the EBRIG technique. The technique to hybridize EBRIG and EBR was more effective at withstanding shear.

Bond-slip response of end-hook and half-hooked steel fibers in moderately strong SIFCON matrix

In this study, an attempt was made to study the bond-slip performance of end-hook and half-hooked steel fibers embedded in moderately strength SIFCON matrix, to find out the cause of excessive mechanical anchorage and to further optimize the bond-slip equation of steel fibers. Used end-hook steel fibers with embedded depths 10 and 15 mm, pullout offset angles 0°, 30°, 45°, and 60°; Half-hooked steel fiber with embedded depths 10 and 15 mm, end-hook bending angles 30°, 45°, 60°, and 90°; Novel end-hook and novel half-hooked steel fibers with end-hook length doubled, which were subjected to a static pullout test at a rate of 0.01 mm/s. Experiments showed that the half-hooked steel fiber took the best end-hook bending angle at 60°; The novel end-hook and half-hooked steel fiber had a good bonded performance. The single steel fiber anchorage performance evaluation index K was proposed. Through experimental phenomena, data analysis, and X-ray flaw detection, the existence of “local damage” was proved. Based on the traditional bond-slip formulation, a new bond-slip formulation for moderately strength SIFCON substrates is proposed by adding a plastic hinge in the “local damage” region. By comparing the old and new equation, it was found that the calculation error of the maximum pullout load of end-hook steel fibers was reduced by 3.77 times and that the calculation error of the maximum pullout load of half-hooked steel fibers was reduced by 2.8 times, and the calculation equation for the peak load of secondary reinforcement of half-hooked steel fiber was supplemented, which is of application value for further optimization of the shape of steel fibers.

Feasibility of hybrid waste fishing net textile and fiber reinforced cementitious composites in strengthening concrete and retrofitting damaged concrete

This study investigated the feasibility of hybrid waste fishing net (W) textile and fiber reinforced cementitious composites (HWRCCs) for strengthening and/or retrofitting structural concrete. W textile and fibers (WT and WF, respectively), cut from two types of W, were used as hybrid reinforcements within HWRCCs for strengthening/retrofitting normal concrete with various types of anchorage methods. The compressive and flexural behavior of concrete strengthened by using HWRCCs were compared with those of non-strengthened normal concrete and those of strengthened concrete using commercial glass textile reinforced cementitious composites (GTRCC). The axial load carrying, and flexural load of normal concrete were significantly increased as strengthening by HWRCCs, and the flexural load of damaged concrete after retrofitting by HWRCCs was even higher than that of normal concrete, even though the mechanical properties of concrete strengthening by using HWRCCs were lower than those of concrete strengthening by using GTRCC. The use of epoxy resin was more effective than that of mechanical anchors for strengthening/retrofitting structural concrete with HWRCCs.

Cutting On Existing Bonded Post-Tensioned Slabs: Safety Precautions, Procedures and Execution

Post-formed cut-off or cutting of the post-tensioned slabs is a common practice during post-tensioning work. However, cutting on existing post-tensioned slabs must be done carefully to avoid severe damage to the building. The measurements during the design review are critical in considerations of post-cutting conditions, variations between shop drawings and site, possible grouting failure and excessive deformation. This paper presents a successfully execution of cutting operations on bonded post-tensioned slabs without compromising the structural strength and serviceability. There are procedures and requirements that need to be considered prior to cutting at the design stage, prior to cutting at the site and at slab cutting stage. The safety precautions are necessary for unintentional scenarios that require immediate action. Cutting the slab creates potential hazards. It was found that the grouting material plays an important role not only in solidifying the concrete but also in forming a secondary anchorage mechanism. Therefore, selection of suitable grouting material should be based on the dimension of the locking area. In contrast to unbonded post-tensioned slabs, bonded post-tensioned slabs do not require de-tensioning and re-tensioning.

Development and preliminarily tests of superelastic Ni-Ti SMA ribbed bars for reinforced concrete applications

The research on superelastic shape memory alloy (SMA) bars reinforced concrete members and structures has received a great deal of attention recent years. In this study, novel superelastic Ni-Ti SMA ribbed bars were developed and investigated to improve the bonding performance and to avoid the problem that the threaded or mechanical anchorage parts of the SMA plain round bars (used in many previous studies) were easy to break in advance. A comprehensive experimental program was conducted to characterize the cold-rolled superelastic Ni-Ti SMA ribbed bars, including scanning electron microscopy to observe the micromorphology, differential scanning calorimeter tests to analyze the phase transformation temperatures, and cyclic tensile tests to examine their mechanical properties. Moreover, five reduced-scale concrete beams were prepared and tested to verify the advantages of the superelastic SMA ribbed bars as bottom longitudinal reinforcements. Results shown that the cyclic tensile response of the cold-rolled SMA ribbed bar subjected to some degree of annealing can be similar with that of the annealed SMA plain round bar. Compared with the beam specimen incorporating ECC and superelastic SMA plain round bars and the beam specimen incorporating normal concrete and superelastic SMA ribbed bars, the specimen incorporating ECC and superelastic SMA ribbed bars exhibited a significantly improved deformation ductility, ultimate bearing capacity, energy dissipation ability, self-centering capability, and cracking performance under the cyclic flexural loads. Besides, no reinforcement slippage or fracture were observed during the entire loading process in all beams, suggesting satisfactory bonding effect and uniformity.

Experimental study on anchorage and activation performance of Fe-SMA strips for structural reinforcements

Iron-based shape memory alloy (Fe-SMA), taking advantage of its unique shape memory effect, is increasingly used to strengthen and rehabilitate deficient or deteriorated structures. The connection and activation methods are considered as the key techniques for the application of Fe-SMA. In this work, the China-made Fe-SMA strips were used and the material characteristics at room and elevated temperatures were examined. Two types of mechanical anchorages were designed to connect Fe-SMA strips with steel beam. A simple setup was designed to evaluate the performance of anchorages. Fe-SMA strips were heated by a low-cost activation method with hot gun. The temperature transfer law and recovery stress of Fe-SMA strips during activation were monitored during experiment. The test results indicated the mechanical anchorages showed good performance and the strength of Fe-SMA strips at failure was over 85% of its ultimate strength. The influence of activation decreases rapidly with the increase of distance from heating area, and the elevated temperature did not cause thermal damage on the reinforced structure. A theoretical equation was proposed based on the temperature transfer law to predict temperature of each point on Fe-SMA strips, which could be employed in determining the bonding length of adhesive bonding joint for Fe-SMA reinforcement in practice.

Shear strength of the anchor embedded into masonry

This paper focuses on any straight bar, herein called “anchor”, inserted within a hole drilled into a masonry structure, installed orthogonally to the masonry surface, and bonded to the masonry either with an anchoring material or without (adhesive or mechanical anchors). The anchor is subjected to a transverse force applied at the end that protrudes from the masonry (i.e., a shear force having direction parallel to the masonry surface), while no appreciable axial force is applied to the anchor (shear anchor). In brief, the paper is devoted to the post-installed horizontal anchor that transfers vertical loads from a horizontal structure to a vertical masonry structure.On site experiments on real anchors allowed the author to establish the mechanical assumptions that govern the behavior of the shear anchor. Based on those assumptions, an analytical (closed form) model was created. The model is comprised of a function that gives the ultimate contact pressures, and a two-equation system whose solution is the maximum shear force that the anchor can bear, therefore called “shear strength”. The model also provides the elastic limit shear strength. The data to be entered into the model is composed of the geometry of the anchor and the strength of the masonry.The paper presents the experimental campaigns, the model, the application of the model to case studies, and a comprehensive discussion. The results put forward the optimal technical solutions for the masonry shear anchor, which are described.

PERFORMANCE EVALUATION OF BEAMS STRENGTHENED WITH MECHANICALLY ANCHORED CARBON FIBER-REINFORCED CEMENTITIOUS MATRIX (FRCM)

Textile reinforced mortar (TRM), more popularly known as fiber-reinforced cementitious mortar (FRCM), has unique characteristics such as an excellent bond with the concrete substrate, applicability in a wet environment, and resistance to high temperatures. It is now considered a substitute for the fiber-reinforced polymer (FRP) due to the vast progress in FRCM and the increasing complexity of FRP-concrete or FRP-masonry debonding. Strengthening beams with FRCM can be implemented using direct wet layup, Near-surface mounted (NSM), etc. Observed failure modes in the literature show fiber-fiber slip and fiber-matrix debonding as dominant modes. Some authors also studied mechanical anchorages to improve these interfacial limitations. Anchorage in FRCM includes adding transverse layers at the end and intermediate locations, winding the fabric around the bar, and embedding it into the substrate or fan-type anchorage as used in FRP. The present study, 12 beams were strengthened using an indigenously developed unidirectional carbon FRCM system with anchorage. The study parameters include the number of layers and strengthening strategies such as mechanical anchoring and pressure impregnation. For the study, a novel yarn-based mechanical anchorage is developed suitable for Indian site conditions. It is found that the developed mechanical anchorage strategy improves the ultimate load-carrying capacity of the beam by about 16% compared to conventional cement-matrix impregnation. Fiber-rupture failure was observed for anchored specimens, whereas fiber-fiber slip was observed for impregnated specimens.

Nonlinear Semianalytical Prediction of Debonding at the FRP–Generic Material Interface with Mechanical End Anchorages

The full-range debonding process of a fiber-reinforced polymer (FRP)–generic material substrate interface with mechanical end anchorages requires a better understanding. In this study, we developed a nonlinear semianalytical model based on a cohesive crack model to predict the full-range debonding process of such an interface in a single-shear mode, considering the relatively deformed region in the interface as a cohesive zone. Specifically, we produced a double exponential bond–slip constitutive model with residual bonding shear stress and boundary conditions of slip constraints at both anchoring ends. Implicit solutions for the relative slips, bonding shear stresses, and axial forces in the FRP along the bond length, as well as the load–slip responses at the loading end and effective bond length, were obtained using the Chebyshev polynomial approximation strategy. The accuracy of the proposed model was verified using experimental results available in the literature. Then, the evolution of full-range interfacial bonding behavior and load–slip responses for different bond lengths was discussed. Finally, a parametric study highlighting the effect of geometry and material properties on the load–slip response at the loading end was presented.

Radiographic lead migration in percutaneous spinal cord stimulator trials

IntroductionLead migration during spinal cord stimulator (SCS) trials is relatively neglected in the literature and presents a different set of challenges compared with fully implanted leads. There is no consensus...

Fire endurance tests of CFRP-strengthened RC beams with different insulation schemes

The fire performance of externally bonded (EB) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams is an important issue in practical strengthening design. The cable mechanism of CFRP sheets in a fire can improve the fire endurance of the strengthened beams. This paper presents a feasible method to activate the cable mechanism of EB CFRP sheets in the strengthened beams by using appropriate insulation schemes and a mechanical anchorage system. Seven beams were constructed: three were tested at room temperature, while the remaining four were subjected to the ISO 834 standard fire. The experimental results showed that the three insulation schemes could provide reasonably good protection for the specimens, and thus all of them achieved a fire endurance of 2.5 h. The combined use of fire insulation and a mechanical anchorage system could reduce the deflection responses, mainly due to the active cable mechanism of the EB CFRP sheets during fire exposure. A finite element (FE) model was then proposed to predict the thermal and structural responses of insulated CFRP-strengthened RC beams. The FE parametric results further indicated that different insulation schemes with various thicknesses and thermal conductivities had significant effects on the fire performance of the strengthened beams.

Investigation of the asteroid triple-drill anchoring force under complicated working conditions

The microgravity environment on asteroids necessitates the inclusion of anchoring devices on asteroid probes to facilitate in-situ landing detection. Complicated working conditions faced by asteroid probes significantly increase the difficulty of the anchoring device’s task. In this paper, based on the discrete element method (DEM), the anchorage performance of a triple-drill anchoring device under different external forces and drilling depth combinations is investigated. The forces on the probe and landing legs and the damaged area of the particle domains are analyzed to obtain the influence of the external force direction on the anchorage performance. Five drilling depth combinations are selected to represent the complicated working conditions asteroid probes face. Then the ultimate anchoring forces of the five drilling depth combinations under the different external force directions are calculated and analyzed. This work reveals the anchorage mechanism under complex working conditions and provides a reference for asteroid exploration missions.