Pullout Load Research Articles

Modeling the role of phase boundaries on the pullout response of shape memory wire reinforced composites

Shape memory alloy (SMA) wire-reinforced composites are being widely adopted in several applications. The interactions of the SMA wires with the matrix are quite complex due to heterogeneous strain distributions arising from phase transformations in SMA wires. There have been few studies of the role of the phase boundaries and their effect on debonding of the SMA wire. In this work, a discrete particle approach is used to model the effect of microstructure on the debonding of SMA composites. The force versus displacement response is studied under pullout loading conditions and the microstructure is found to have a strong effect.

Influence of Corrosion on Anchoring Bond Behavior of Jointed Rock Mass

In order to investigate the effect of corrosion on bond behavior of anchored jointed rock masses, based on the migration law of pitting corrosion obtained by laboratory tests and the concept of strength reduction, the anchoring pull-out test of jointed rock mass was simulated by using Discrete Element Method (DEM). The results show that for uncorroded rock specimens, due to the existence of joints, there are significant differences for granular displacement and bond failure on both sides of the rock bolt during pull-out process, and phenomenon of eccentric tension also appears; for corroded rock specimens, the reduction rate of bond strength and slip ratio of single and double joint specimens decrease linearly with the increase of pitting corrosion rate. The decreasing rate gets fast with the increase of joints, but it is not a multiple relationship. Compared with the test with uncorroded specimens, when the pitting corrosion rate is 15%, the maximum pull-out load of the single-joint specimen with joint angel of 45° is reduced by 1 7.8%, and the slip value is reduced by 14.6%; the maximum pull-out load of the double-joint specimen is reduced by 31.9%, and the slip value is reduced by 24.9%. The numerical test results are in good agreement with the laboratory test results. The research results can provide reference for the selection and optimization of the design parameters of anchoring support structure of jointed rock mass under the erosion environment in the future.

Mesoscale modelling of bond performance between deformed steel bar and concrete subjected to dynamic loads

The good bond property is the base for rebar and concrete to work together, influencing the mechanical behaviour of reinforced concrete structures. To investigate the bond-slip performance between deformed steel bars and concrete under dynamic loadings, a three-dimensional meso-scale numerical model was established, considering the inherent heterogeneity of concrete and explicitly modelling the surface characteristics of the rebar. The interaction between the rebar and concrete was implemented by the surface-to-surface contact strategy. The strain rate effect of materials was also taken into account. The rationality and accuracy of the proposed model were verified by the good consistency between the simulation and available test results in terms of failure pattern and bond stress-slip curves. With the help of the meso-scale model, the bond-slip behaviour under various loading rates was simulated and analysed. Finally, a simplified model to describe the dynamic bond stress-slip relationship was developed. It has been found that due to the propagation of stress waves, the cracking process of the specimen varies with the strain rate while the final failure pattern is similar, exhibiting splitting type failure. Thus, a considerable part of pull-out loading was resisted by the inertia of the system at the initial stage. With the increase of strain rate, the shape of the dynamic bond stress-slip curves is similar with a significantly increased bond strength and reduced slip, especially at high strain rates. The ratio between the residual and peak bond stress is approximately constant, irrespective of strain rate. The proposed simplified model is able to effectively characterize the dynamic bond stress-slip relationship between the deformed rebar and concrete.

Bone density may affect primary stability of anterior cruciate ligament reconstruction when organic core bone plug fixation technique used

PurposeCore Bone Plug Fixation (CBPF) technique is an implant-less methodology for ACL reconstruction. This study investigates the effect of bone density on CBPF stability to identify the bone quality that is likely to benefit from this technique.MethodsArtificial blocks with 160 (Group 1), 240 (Group 2), and 320 (Group 3) kg/m3 densities were used to simulate human bone with diverse qualities. These groups are representative of the elderly, middle age and young people, respectively. A tunnel was made in each test sample using a cannulated drill bit which enabled harvesting the core bone plug intact. Fresh animal tendon grafts were prepared and passed through the tunnel, so the core bone was pushed in to secure the tendon. The fixation stability was tested by applying a cyclic load following by a pullout load until the failure occurred. The selected group was compared with interference screw fixation technique as a gold standard method in ACL reconstruction.ResultsThe Group 2 stiffness and yield strength were significantly larger than Group 1. The graft slippage of Group 1 was significantly less than Group 3. The ultimate strengths were 310 N and 363 N, in Groups 2 and 3, significantly larger than that of Group 1. The ultimate strength in fixation by interference screw was 693.18 N, significantly larger than the bone plug method.ConclusionsThe stability of CBPF was greatly affected by bone density. This technique is more suitable for young and middle-aged people. With further improvements, the CBPF might be an alternative ACL reconstruction technique for patients with good bone quality.Clinical relevanceThe CBPF technique offers an implant-less organic ACL reconstruction technique with numerous advantages and likely would speed up the healing process by using the patient’s own bones and tissues rather than any non-biologic fixations.

Bond to Bar Reinforcement of PET-Modified Concrete Containing Natural or Recycled Coarse Aggregates

The use of post-consumer plastics in concrete production is an ideal alternative to dispose of such wastes while reducing the environmental impacts in terms of pollution and consumption of natural resources and energy. This paper investigates different approaches (i.e., reducing water-to-cement ratio and incorporating steel fibers or polymeric latexes) that compensate for the detrimental effect of waste plastics on the drop in concrete mechanical properties including the bond to embedded steel bars. The polyethylene terephthalate (PET) wastes used in this study were derived from plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete properties are degraded with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The threshold PET volumetric rates are 4.5% and 3% for concrete made using natural or recycled aggregates, respectively. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the concrete performance. The incorporation of 0.8% steel fibers (by volume) or 15% polymers (by mixing water) were appropriate to enhance the bridging phenomena and reduce the propagation of cracks during the pullout loading of steel bars.

Study on the Horizontal Movement State of Suction Anchor Piles for Offshore Wind Power during Horizontal Pulling

The subsea anchor piles of offshore wind power floating platform structures are mainly subjected to uplift and horizontal loads, and this paper focuses on the case of horizontal loads. A three-dimensional numerical simulation study of the horizontal pullout characteristics of wind power suction anchor piles in clay layers was carried out to reveal the horizontal movement state of the anchor piles during horizontal pile pullout, the range of pile depth at the pullout point where the horizontal movement is achieved (referred to as the horizontal movement range), the relationship between the pullout load and the ultimate load during the horizontal movement, and the optimal location of the pullout point for the horizontal movement. The results show that at certain pull-out points, the anchor pile produces an overall horizontal movement state under suitable horizontal pull-out loads. The depth of the pile pull-out point for horizontal movement is in the middle and lower part of the pile, i.e. 14.2 m to 14.5 m. The horizontal pull-out load of 24,000 kN at a depth of 14.5 m within the pile horizontal movement range of 14.2m to 14.5 m is the maximum ultimate horizontal pull-out load; the optimum pull-out point depth is 14.5 m at 0.275 L (L is the pile length). For each pull-out point of the anchor pile in horizontal movement, the horizontal pull-out load in horizontal movement and the horizontal ultimate pull-out load existed and it was found that the two values were not exactly the same, the values were compared and it was found that at the optimum pull-out point the value of the ultimate horizontal pull-out load/horizontal pull-out load in horizontal movement tended to 1.

Finite Element Analysis on Behavior of Single Battered Pile in Sandy Soil Under Pullout Loading

Batter piles are the piles driven in the soil at an inclination with the vertical to withstand oblique loads or large horizontal loads and have been widely used to support high buildings, offshore buildings, and bridges. These constructions are risky because of the exposure to moments and overturning resulting from winds, waves, and ship impact. A 3D FEA using PLAXIS 3D software was used to investigate the effect of several variables that affect the behavior of single batter piles under pull-out loads. The study is achieved on a steel pipe pile model embedded in a dry sandy soil with three relative densities (loose, medium, and dense) at different inclination angles and three embedment ratios, L/D of 25, 37.5, and 50, respectively. The numerical results showed that the ultimate pull-out resistance of the battered pile raise as the battered angle increases reaches a maximum value, then decreases. The ultimate pull-out load capacity of a single battered pile is directly proportional to the slenderness ratio and relative density; the ultimate pull-out load increases with the increase in the ratio of slenderness and relative density. The ultimate uplift load of the battered pile was less affected by the free-standing length. Vertical and battered piles at a battered angle of (10ᵒ and 20ᵒ) and free-standing lengths equal to zero have higher ultimate pull-out capacity; by increasing the free-standing length, the ultimate pull-out capacity decreased.

Microscopic Bearing Behavior of Horizontally Loaded Vertical Plate Anchors in Sandy Soil

Vertical plate anchors are an effective technique to enhance the stability of various structures, such as retaining walls and sheet piles. More research has been devoted to their bearing capacity and macroscopically affecting parameters, while less research can be found on their microscopic bearing behavior. In this paper, the microscopic bearing behavior of vertical plate anchors subjected to a horizontal pullout load in sandy soil was investigated with the particle flow code (PFC) based on the model test results. Results show that the larger‐sized anchor plates withstand greater soil pressure and affect a broader range of soil during the pullout process. The soil not behind the anchor plate is pressed, and the pressure in front of the anchor plate increases with increasing size. The soil close to the plate anchor suffers larger pressure while the soil far away from the plate anchor is less affected, and the soil is redistributed to a more stable state during the pullout process of the plate anchor. The particles with a long axis distributed in the horizontal direction are the most stable, while those with a long axis distributed in the vertical direction are the most unstable.

Behaviour of Steel Fibre Reinforced Concrete Pavements on A Single Fibre Level

Concrete is a popular construction material used all around the globe. It is strong in compression and weak in tension. To mitigate this tensile weakness, various reinforcement methods have been used over the years, of these, fibre reinforced concrete (FRC) has gained popularity. Fibres not only improve the tensile strength of the concrete matrix, but also control crack propagation through crack bridging action. The goal of this study is to investigate the long-term behaviour of FRC pavements through conduction of static and fatigue meso-scale level tests using different steel fibres. To achieve this goal, the influence of different fibre geometries and embedment angles on the pull-out behaviour of fibres in FRC was investigated first. This was carried out by examining 60mm Dramix 3D steel and 5D steel fibres at single fibre level. The embedment depth was kept constant at half the fibre length, and the fibre embedment angles were tested at 0°, 15° and 30°. The average maximum pull-out load, Amax, was determined first through static tests then fatigue tests were carried out using 85% of the Amax value on pre-damaged samples. These tests indicated that an increase in fibre embedment angle and number of hooks leads to additional anchorage of the fibre. Fibre pull-out was found to be the dominant fibre failure mechanism for the static single fibre pull-out tests (SFPTs).

Laboratory investigation of dowel bars’ misalignment using pull-out test

Joint lockup due to dowel misalignment significantly affects joint and concrete pavement performance by causing joint distresses. The current paper presents an experimental study to assess the effectiveness of standard pull-out test in the evaluation of dowel misalignment effect on joint lockup of Jointed Plain Concrete Pavement (JPCP). The tests were conducted at two different ages of concrete ; 3 and 28 days. The results showed that the standard pull-out test or individually pulling of misaligned dowels cannot reflect the realistic defect of dowel misalignment. It also showed that the vertical orientation of misaligned dowel bars during the concrete casting reduces the pull-out load due to more distance from the exposure surface. Another observation was for all specimens, the pull-out load increases with an increase in concrete age

Simplified analytical model to assess key factors influenced by fiber alignment and their effect on tensile performance of UHPC

The increase in single-fiber pullout strength usually improves tensile strength and toughness of UHPC. An increase in fiber orientation angle (θ) up to 45° to the direction of pullout load was found to enhance the single-fiber pullout strength. However, such increase in predominant θ value along tensile strength specimens led to a reduction in tensile strength of UHPC. In order to elucidate this controversial observation, analytical models combined with experiments were carried out to assess the key factors influencing the tensile properties of UHPC due to variations of fiber orientation. The test parameters involved the evaluation of the effect of θ (0°–60°) and fiber embedment length (le) of 5 and 10 mm on the single-fiber pullout performance. The influence of fiber orientation on UHPC tensile performance was also investigated by casting tensile strength samples having predominant θ values of 25°, 30°, 40°, and 50° along the tensile loading direction. Test results indicate that the key factors influencing the tensile properties of UHPC included the fiber-matrix bond strength (τθ), le, and fiber number in a given cross section (Nf). The highest τθ was obtained at a θ value of 45°. The increase in θ from 0° to 90° led to a consistent reduction in le and Nf. A simplified model that considers these factors was proposed to assess the effect of each factor on UHPC tensile strength. The model indicates that le had the greatest influence on tensile strength, followed by Nf and τθ. The decrease of predominant θ in tensile strength specimen from 45° to 25° enhanced le by 65% and Nf by 60%, compared to a 7% reduction in τθ, thus leading to a net increase in tensile strength of UHPC by 60%.

Numerical evaluation of the combined effect of dowel misalignment and wheel load on dowel bars performance in JPCP

The paper presents a comprehensive experimental and analytical (3D finite element modelling-FEM) investigation into the combined effect of dowel misalignment and wheel load on dowel bars response in Jointed Plain Concrete Pavement (JPCP). The study also investigated the suitability of Glass Fibre Reinforced Polymer (GFRP) dowels as an alternative material to epoxy-coated steel dowels. The experimental tests focused on the pull-out load joint-opening behaviour and relative deflection (RD) of the joint. A 3D FEM was developed to investigate the most frequent cases of dowel misalignment for steel and GFRP dowels and estimate the damaged volume in the surrounding concrete pavement due to dowel misalignment. The results showed that using GFRP dowels significantly reduces the pull-out load required to open the joint and also reduces joint lockup possibilities even when dowel misalignment exists. Consequently, the surrounding pavement deteriorates much less.

Cyclic Behavior of Bucket Anchor Foundation in Silty Sand under Sustained Pull-Out Loads via Centrifuge Model Tests

In recent, suction anchor foundations have been encouraged as an alternative for supporting offshore wind turbines in the deep sea. The foundation for offshore wind turbine foundation should be designed considering the cyclic forces, which cause an accumulated displacement of the structure and degradation of the stiffness of the ground-foundation system. However, previous researches for suction anchor behaviors have mostly focused on static loads, although the forces applying on the offshore structure are cyclic in the sea. Moreover, since the suction anchors are always subjected to sustained pullout loads combined with cyclic loading due to the buoyancy forces of the structure, evaluating the in-service performance of suction anchor foundations considering cyclic loadings with sustained pullout loads is also required. In this study, the responses of a suction anchor foundation under cyclic loading along with sustained pull-out loads were investigated via centrifuge model tests. Consequently, it was observed that the behavior of the suction anchor are dependent on the sustained pullout loads, as well as the cyclic loading. This study highlights that the ratio of sustained pull-out loads as well as the cyclic load effect must be considered when analyzing design loads to accurately evaluate the bearing resistance of the suction anchor foundation.

Experimental investigation on sing fiber pullout behaviour on steel fiber-matrix of reactive powder concrete (RPC)

A new single fiber pullout testing method was applied to characterize the interfacial bond performance, which includes the pullout load-slip relationship, pullout energy, bond strength, and fiber utilization ratio, of the steel fiber-matrix in reactive powder concrete (RPC). The bond properties and bond strengthening mechanism were investigated from the perspective of certain parameters, including the fiber type, fiber embedment angle, silica fume content, magnetic nanoparticles content, and curing time. The microstructure of the steel fiber and longitudinal morphology of the tunnel after the pullout test were determined by scanning electron microscope (SEM). In terms of the results, the bond strength of the end-hooked steel fiber is much stronger than that of the straight steel fiber. With the increasing of embedment angle, the ultimate pullout load and pullout energy of straight steel fibers increase, and the interfacial bond strength increases. It is found that the incorporation of silica fume can effectively enhance the matrix strength. In addition, RPC containing 20%∼30% silica fume shows significant improvement in pullout behavior. The appropriate curing age contributes greatly to the hydration reaction and the matrix strength of RPC. Steaming curing for 2 d can effectively improve the interfacial bond performance. A content of 1% magnetic nanoparticles enhances the pullout behavior of straight steel fibers with no brass coating, because the maximum pullout load and pullout energy increase by 33.6% and 79.0%, respectively. The microstructural observations confirm the conclusions regarding the bond mechanism drawn from the pullout tests. In conclusion, the performance of the matrix, the characteristics of the fiber-matrix interface area and the friction of the steel fiber in the tunnel can influence the bond performance of the fiber-matrix interface of RPC.

Local bond strength prediction of deformed reinforcing bars in concrete considering heterogeneity at interface regions

An analytical model is proposed to predict local bond strength (τf) by incorporating heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on the bar surface is introduced as an interfacial characteristic parameter G in the proposed model; this accounts for the heterogeneity. Both τf and the local interfacial fracture energy (GIIf) of each specimen were found to be linked to G and can be determined analytically from the maximum pull-out loads (Fmax) from tests. It was found that the predicted τf was larger than the maximum average bond stress (τavg-max); the discrepancy between the two values reduced with an increase in L/G. Moreover, with an increase in L/G, the predicted τf showed a certain decrease, with the reduction decreasing with stronger interfacial homogeneity. The predicted GIIf was found to be significantly increased because of the weaker boundary effect. The validity of the proposed model was verified using comparisons of predicted Fmax (using the determined values of τf and GIIf) and the experimental Fmax, with the only failure mode being bar pull-out. Moreover, the model can be applied to steel or fibre-reinforced polymer bars and the concrete refers to all types of cementitious materials.

The effect of cement augmentation on pedicle screw fixation under various load cases

AimsAnchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques.MethodsMicro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S4). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads.ResultsExperimental pull-out strengths were excellently correlated to the µFE pull-out stiffness of the ROI (R2 > 0.87) and FV (R2 > 0.84) models. No significant difference due to screw design was observed. Cement augmentation increased pull-out stiffness by up to 94% and 48% for L and R screws, respectively, but only increased bending stiffness by up to 6.9% and 1.5%, respectively. Cementing involving only one screw tip resulted in lower stiffness increases in all tested screw designs and loading cases. The stiffening effect of cement augmentation on pull-out and bending stiffness was strongly and negatively correlated to local bone density around the screw (correlation coefficient (R) = -0.95).ConclusionThis combined experimental, µCT and µFE study showed that regional analyses may be sufficient to predict fixation strength in pull-out and that full analyses could show that cement augmentation around pedicle screws increased fixation stiffness in both pull-out and bending, especially for low-density bone.Cite this article: Bone Joint Res 2021;10(12):797–806.

An experimental investigation for pullout response of a single granular pile anchor in clayey soil

The granular pile anchor foundation is an effective and economical foundation system to counter the pullout forces exerted in case of transmission towers or foundations in expansive soil. The pullout tests were performed to study the behaviour of a single granular pile anchor in the clayey soil bed. Tests were conducted in a steel tank of 1 × 1 × 1 m size with the help of loading frame arrangement. The pullout load required for upward movement equal to 10% diameter was considered as the pullout capacity of the granular pile anchor. In the parametric study, length and diameter of the granular pile anchor were varied to examine their effect. Number of anchor plates was also varied in few tests. The pullout capacity enhanced with an increase in the diameter and length to diameter ratio. The effect of the length to diameter ratio was appreciable up to the value of 10. However, no significant effect was found in the cases of multiple anchor plates. A relationship is proposed to predict normalized pullout capacity.

Experimental and analytical study of bond between basalt FRP bars and geopolymer concrete

This paper presents an experimental and analytical study of the bond behaviour of basalt fibre reinforced polymer (BFRP) bars in geopolymer concrete (GPC). Pull-out tests were conducted on ribbed BFRP bars embedded in GPC cubes considering different bar diameters (6, 8 and 10 mm) and embedment lengths (5db, 10db and 15db) to investigate their effects on bond behaviour in terms of bond-slip response, bond strength and failure mechanisms. Results indicate that the chemical adhesion is low, and the bond is mainly dependent on mechanical interlocking which stopped when pullout occurred by local crushing of the GPC with the BFRP ribs remaining undamaged, suggesting high rib shear strength. A theoretical bilinear model was used to describe the local bond-slip relationship and the bond interface properties. There exists nonlinear bond stress distribution, especially for longer embedment lengths and lower load levels with a bond stress concentration factor of 3.9. A parametric study was performed to estimate the influences of bar diameter, embedment length and elastic modulus on maximum pull-out load, based on which the load transfer mechanisms between BFRP bars and GPC were explored, and a formula for predicting the bond strength was proposed in comparison with experimental data.

Bond strength of GFRP bars to high strength and ultra-high strength fiber reinforced seawater sea-sand concrete (SSC)

Fiber reinforced polymer (FRP)-reinforced seawater sea-sand concrete (SSC) structures are prospective substitutions for traditional steel-reinforced concrete structures, especially in maritime environment. To demonstrate the feasibility of the FRP-reinforced SSC structures, an in-depth understanding on the bond strength of glass FRP (GFRP) bars to SSC under pull-out loading is essential. In this regard, pullout tests on 45 specimens with a 10 mm diameter GFRP bar embedded in ultra-high strength concrete (including normal concrete with river-sand and fresh water and SSC) are conducted in this study. Particularly, the experimental tests focus on some key factors that governing the GFRP bars in concrete, such as the bar embedment length, the polyethylene (PE) fiber volume fraction, and the concrete strength (i.e., 80 MPa and 120 MPa). Three major failure mechanisms and two types of average bond stress-slip curves are obtained from the tests. The results show that substitution of seawater and sea sand for normal concrete has no distinct effect on short-term change in bond strength (less than 9%). In addition, it indicates that the increase in concrete strength and PE fiber content could improve the bond strength, whereas increasing the embedment length (from 2.5 times to 10 times of bar diameter) could result in a decrease in bond strength (by 20–30%). Furthermore, it demonstrates that the CMR model has better performance than the mBPE model in capturing the experimentally observed ascending part of the bond-slip curve.

Pull-out behavior evaluation of torque-controlled expansion anchors under various installation conditions of concrete

Torque-controlled expansion anchors are widely used as anchoring elements in heavy nonstructural elements. Although the installed torque is not considered a design parameter for determination of anchor strength, it can affect the contact condition between the concrete and anchor as well as the failure mode under tensile load. This study performed pull-out experiments (total 85 specimens) for torque-controlled expansion anchors to evaluate the pull-out behavior under various installation conditions. Experimental results indicated that obtained inflection load and maximum displacement were affected by the installation torque. Concrete splitting failure was affected by pull-out behavior on concrete below critical edge distance. While maximum pull-out loads of M12 and M16 anchor was similar under the same embedment depth, pull-out behavior of the both types of anchors provide different characteristic. Accordingly, these results were analyzed to investigate the influence on anchor strength.