theA Research Articles

Influence of Water on Anchor Plate Behavior in Sandy Soil with and Without Improvement

Plate anchors are one of the most common types of ground anchors used in foundation systems, as they transfer loads from the foundation to the soil to prevent overturning the foundation and overcome the forces that could threaten the integrity of the structure. The present work concerns the study of the combined effects among the behavior of the anchor plate in sandy soil with and without water presence as a static state at a different head level (h=15, 30, and 40 cm) above the base of the anchor plate and for two states of the soil with improvement by geogrid at various location and without improvement. The soil sample was brought from AL-Nidaa district in the city of AL-Najaf (Iraq). The highest value of the ultimate uplift capacity is observed when the geogrid layer is adjacent to the anchor plate for dry and submerged cases of the soil. The negative effect of the presence of the geogrid layer appears when the water table level rises above the ground surface level.

Effects of Heterogeneity and Nonlinearity on Uplift Characteristics of Shallow Horizontal Anchor Plates

Effects of Heterogeneity and Nonlinearity on Uplift Characteristics of Shallow Horizontal Anchor Plates

Investigation of the installation process of drag-in plate anchors from LDFE modelling

The installation of drag-in plate anchors is investigated using advanced large-deformation finite-element (LDFE) analysis. A new modelling technique that can realise the continuously evolving loading angle on the anchor line is described. The entire anchor trajectory is simulated until the anchor reaches an ultimate state after dragging for a very large distance, typically in the range of 40–70 times the anchor width. An installation in simple uniform and non-sensitive soil is first presented with agreement against well-established plasticity analysis and an analytical solution offering verification of the techniques developed. The effects of anchor padeye position, seabed soil conditions, anchor line properties and the anchor–soil interface on the installation response are then discussed. The findings highlight that plasticity and analytical approaches are not necessarily conservative when the yield surface derived from deep embedded anchors is applied in shallow conditions. The LDFE results also demonstrate the importance of accounting for soil remoulding around both the anchor and anchor installation line. The results of this study provide insights for offshore engineers to consider and incorporate when estimating a drag anchor installation trajectory and holding capacity.

Numerical and analytical investigation on inclined plate anchors in sand

The paper investigates the ultimate capacity of inclined plate anchors in sand through a series of finite element (FE) analyses. The FE simulations adopted a sophisticated bounding surface plasticity model that accounts for stress and density dependent behaviour, thus portraying a realistic estimate of the shear stresses and shear strains within the failure mechanism. The simulations considered a strip anchor with different plate widths, plate inclination angles and shallow embedment ratios in dense sand. The FE results show good agreement with previously reported experimental data. A limit equilibrium solution is subsequently proposed to predict capacity of inclined strip anchors in sand, based on mathematical expressions of the FE simulated normal and shear stresses along mobilised failure planes. The limit equilibrium solution is shown to produce satisfactory agreement with results from a large database of inclined plate anchors.

The performance of the dynamically installed plate anchor in sand and silt

Dynamically installed anchors (DIA) provide a time-efficient and cost-effective anchoring solution for offshore floating moorings. The dynamic installation and capacity mobilisation of the DIA in clayey seabed have been systematically investigated. However, the performance of the DIA in sand and silt is rarely studied. This study aims at investigating the performance of a newly proposed light-weight gravity installed plate anchor in sand and silt by conducting large deformation finite element (LDFE) analyses. Parametric studies were conducted to investigate the effects of varied factors on the final penetration depth of the anchor. By combining the present numerical results and previous experimental results, a comprehensive theoretical model was proposed for predicting the final penetration depth of the anchor in sand, silt and clay. Then the anchor-chain-soil interaction was simulated to investigate the keying behaviour of the anchor in silt, such that the motion trajectory and capacity mobilisation of the anchor could be derived. The conditions ensuring the anchor diving have been recommended.

Experimental Evaluation of Back-to-Back Anchored Walls by Single Plate Anchors

Experimental Evaluation of Back-to-Back Anchored Walls by Single Plate Anchors

Three-dimensional analysis of inclined anchors in reinforced sand

Inclined anchors are used in civil engineering structures where the foundations are expected to resist pullout forces during their operational period. This paper presents a three-dimensional numerical analysis of inclined anchors placed in unreinforced and reinforced sand. The influence of several parameters on the response of inclined anchor plates has been investigated in this study. Results indicate that geogrid reinforcement placed on top of the anchor plate significantly influences the anchor plate's performance. The ultimate pullout capacity is found to increase with the inclination angle (varied from 30° to 60°) of the anchor plate both in unreinforced and reinforced sand. The anchor capacity is also affected by other parameters such as friction angle of sand (varied from 35° to 45°), embedment depth of the anchor plate (varied from 2 to 10) and tensile stiffness of the geogrid. Besides, the comparison between piles and anchors has been presented with the help of an illustrative example of a transmission tower foundation. The design calculations indicate that inclined anchors placed in reinforced sand can lead to economical design at shallow depth as compared to piles.

Numerical investigation of pullout capacity for inclined strip plate anchors in sand

Plate anchors have been widely regarded as one of the most efficiency solutions for offshore structures in deep sea. Most of previous studies focus on the vertical or horizontal plate anchors embedded in sand. However, after the caisson foundation is withdrawn, the vertical plate anchor rotates to a certain angle from the horizontal plane in the process of resisting tension, which makes the analysis of pullout capacity of inclined plate anchors in sand relatively complex. This study, by using two dimensional finite element (2D-FE) method, takes a deep insight on the behaviour of strip plate anchors with different inclinations in loose to dense sand. A modified soil model is adopted to explore the hardening and softening behaviour of medium dense and dense sand. The FE results show a good agreement with previous numerical results and centrifuge test data. A series of FE cases are conducted to explore the effect of embedment ratios, plate inclinations and sand relative densities on the pullout capacity of inclined strip plate anchors. A new equation is proposed to estimate the ultimate pullout capacity of strip plate anchors with different inclinations in different relative densities of sand, which serves as a guidance for engineering design of inclined strip plate anchors in sand.

Evaluation of the Cable Force by Frequency Method for the Hybrid Boundary between the Ear Plate and the Anchor Plate

For the quick and accurate determination of the cable force under the hybrid boundary between the ear plate and the anchor plate, this paper proposes a method for identifying the boundary conditions and bending stiffness of the cables based on the frequency method. First, the influence of the parameters, namely, cable boundary conditions, bending stiffness, inclination angle, and linear density, on the cable force was analyzed. Next, the actual bending stiffness of the cable under the boundary conditions of the upper hinged support and the lower solid support and the solid support at both ends were determined, and the cable force in the two states was calculated. Finally, the hydraulic jack tension and the cable force in the two states were compared and analyzed to define the actual boundary conditions and bending stiffness of the cable. The results show that the boundary conditions, bending stiffness, and linear density of the cable considerably influence the cable force, whereas the inclination angle has a negligible effect on the cable force. The bending stiffness under the two boundary conditions of the cable were both 0.12Eimax, and the calculated value of the cable force under the solid support boundary condition at both ends was consistent with the value of the hydraulic jack tension.

Six-Degree-of-Freedom Measurement of Plate Anchors in Centrifuge by Magnetometers

Six-Degree-of-Freedom Measurement of Plate Anchors in Centrifuge by Magnetometers

Anchor plate bearing capacity in flexible mesh facings

This work addresses the problem of the loading capacity of an anchor plate coupled with a steel wire mesh in soil retaining applications. The interaction mechanism between the flexible mesh facing, the underlying soil layer and the plate is studied starting from the results of several laboratory punch tests involving both the plate and the mesh only, and the whole soil-mesh-plate system. The experimental tests have been reproduced by adopting a 3D discrete element model where also the wire mesh is discretized as an assembly of interconnected nodal particles. The interaction between these particles is ruled by elasto-plastic tensile force–displacement laws in which a distortion is introduced in a stochastic manner to account for the wires’ geometrical irregularities. The mesh model is then validated with reference to a set of punch tests in which the shape and size of the punching element as well as the nominal wire diameter were varied. Subsequently, the model is extended to a punch against soil test configuration permitting an insight into the nontrivial local mechanism between the mesh facing and the underlying granular layer. The good agreement between the numerical predictions and the experimental observations at the laboratory scale allowed us to extend the model towards more realistic field conditions for which the role of the mesh panel boundary conditions, the mesh mechanical properties, the soil mechanical properties and the anchor plate geometry is investigated.

Ultimate Uplift Capacity Relation of Plate Anchor Using Model Testing

Friction anchors are gaining popularity in civil structures. However, the bond length can be increased to use the friction between the ground and friction anchor body. They are often bonded deep in the ground and fixed to the bedrock; this causes problems, including the anchor overlapping the underground structure or invading the lower part of another structure when anchors are installed in downtown sites. Herefore, combination anchors that combine the advantages of plate anchors that resist uplift because of the ground's bearing capacity with a friction-type anchor have gained attention. However, the ground failure mechanism of plate anchors applied to combination-type anchors has not been accurately analyzed; therefore, various theoretical anchor uplift capacity formulas have been proposed. A model test was performed in this study by forming a sandy ground in a state of plane strain to verify the uplift capacity of the plate anchor installed at a shallow depth and ground failure mechanismPhotos obtained from experiment were evaluated to analyze the shape of the ground failure of the plate anchor. Furthermore, by classifying the depth of the installed anchor, an equation for calculating the ultimate uplift capacity of the plate anchor was proposed according to the classified depth. A model test was performed in this study based on the formation of a sandy ground in a state of plane strain to verify the uplift capacity of the plate anchor installed at a shallow depth and ground failure mechanism. Photos obtained from experimental tests were evaluated to analyze the shape of the ground failure of the plate anchor. Furthermore, by classifying the depth of the installed anchor, an equation for calculating the ultimate uplift capacity of the plate anchor was also proposed according to the classified depth.

Erratum for “Accounting for Soil Spatial Variability in Plate Anchor Design” by Yongmin Cai, Mark Fraser Bransby, Christophe Gaudin, and Yinghui Tian

Erratum for “Accounting for Soil Spatial Variability in Plate Anchor Design” by Yongmin Cai, Mark Fraser Bransby, Christophe Gaudin, and Yinghui Tian

Flexural Test and Numerical Simulation of a New Combination Splice for Prestressed, Precast Concrete Piles Using High-Strength Steel Strands

Prestressed, precast concrete piles using High-Strength Steel Strands (PPCPs using HSSS) are a new type of precast pile. Compared with prestressed high-strength concrete (PHC) piles, the adoption of ultra-high-strength concrete and HSSS not only improves the load-bearing capacity, but also enhances the ductility of precast piles. The engineering application of PPCPs using HSSS requires not only a high bearing capacity of the pile segments, but also reliable splicing to ensure cooperation between pile segments. Based on the characteristics of strand anchorage plates, this paper proposes a new combination splice using the clamp ring and welding (Combination Splice). The theoretical analysis and design method of this Combination Splice is introduced. This research gives a thorough investigation into the flexural performance of PPCPs using HSSS with the Combination Splice. The flexural tests of PPCPs using HSSS with the Combination Splice were firstly conducted on eight full-scale pile specimens with three different pile diameters and four different steel reinforcement ratios. The flexural performances are evaluated in terms of crack resistance, flexural capacities, crack distribution, as well as strain development. The results indicate that the Combination Splice remain safe and intact when the piles reach the ultimate bending capacity. The ultimate bending moment of tested specimens with the Combination Splice is, on average, 10% larger than that of specimens using a theoretical formula. In light of the experimental data, a finite element analysis (FEA) model has been created to simulate the flexural performance of the piles with the Combination Splice. The FEA results show that the load–displacement curves and crack distribution regions are in good agreement with the experimental findings, which verifies the reliability and accuracy of the FEA model. The parameter analysis investigates the effects of the assembly gap and clamp ring corrosion on the flexural performance of PPCPs using HSSS. The results show that assembly gaps have a greater influence on the flexural capacity and deformation, while the influence of the clamp ring corrosion is negligible, indicating that the Combination Splice has certain advantages in terms of durability.

Rationale and design for efficacy and safety evaluation of Bone-Anchored Maxillary Protraction (BAMP) for patients with unilateral cleft lip and palate with skeletal anterior crossbite: a single-arm, open-label, non-randomised prospective study protocol

IntroductionBone-anchored maxillary protraction (BAMP) was devised recently as a method of direct maxillary protraction using anchor plates implanted in the maxilla and mandible without involving the teeth. Although several reports...

Model Test of the Pull-up Capacity of Folding Type Ground Anchors in Cohesive Soil

The purpose of this research is to develop a folding anchor model, which is a modification of the star-shaped plate anchor, and to investigate the pull-up capability operating in cohesive soils. Physical testing is performed in the laboratory and on a full scale in the field, with the findings of the pull-up capacity achieved compared. The anchor model is made up of four leaves with varying widths and depths. It is flexible and may be closed and opened like an inverted umbrella. The effective area of each anchor was determined in laboratory experiments to be A1=30.00, A2=57.60, and A3=147.20 cm2, evaluated in a test column bath and filled with statically compressed, cohesive soil in four layers to a height of 30 cm. Each model was evaluated at three different depths: 30, 60, and 90 cm. The effective area of each anchor in field testing is B1=57.60, B2=147.20, and B3=600 cm2. The qualities of the soils chosen in the laboratory and in the field are identical. Each model was tested at three different depths: 100, 200, and 300 cm. The most resemblance to pull-up test results was found in laboratory and outdoor testing. The findings indicated that the area of each anchor model increased at each depth, resulting in a considerable rise in pull-up load. The change in depth of each anchor variation, however, did not result in a substantial increase in pull-up load. This implies that the folding type model anchors do not need extensive design. Each area change has a fundamental constraint in that adding depth will no longer result in a higher maximum pull-up capability. It also shows that these anchors are relatively simple to install in the field using basic tools without excavating or drilling the soil. Doi: 10.28991/CEJ-2022-08-09-07 Full Text: PDF

Failure mechanism of geocell-reinforced vertical plate anchors subjected to lateral loading

This paper reports the failure mechanism of geocell-reinforced vertical anchors in sand through a series of tests and numerical analyses. It is observed that the anchor load-carrying capacity significantly increases with the application of geocell reinforcement, which is primarily associated with the rupture behaviour of reinforced anchor beds. The rupture surfaces are found to have originated from the bottom edge of the geocell mattress and propagated to the soil surface in a curvilinear shape. The size of rupture surface tends to increase with an increase in length, width and height of the geocell mattress leading to an increased load-carrying capacity of the system. However, beyond a certain length, width and height of the geocell mattress, further increase in size of the rupture surfaces was marginal. Geocells of relatively smaller pocket size (i.e. close to anchor size) can effectively confine the soil leading to a coherent structure that inhibits potential rupture close to the anchors. However, geocells with wider pocket openings enable rupture to occur within the geocell mattress. Hence, it is concluded that the load-carrying capacity of reinforced anchors that is dependent on the size of the rupture surface is influenced by the geometry of the geocell mattress.

P23. Inline axial forces associated with implantation of ALIF interbody devices with integrated supplemental fixation

<h3>BACKGROUND CONTEXT</h3> Anterior lumbar interbody fusion (ALIF) allows for an optimal sized interboy device while providing correction for lumbar lordosis, restoration of disc height and indirect decompression. Spinal interbody devices with integrated fixation through blades, screws or other supplemental anchoring components mitigate the need for supplemental instrumentation, thus reducing OR time and preserving the stability of the functional spinal unit. Unfortunately, interbody devices have failed at the bone implant interface resulting in complications including implant migration and expulsion. Gaining a better understanding of the biomechanics associated with interbody placement may help to prevent these complications in the future. The aim of present study is to determine the magnitude and effect of axial forces during the deployment of an interbody device with supplemental integrated fixation. <h3>PURPOSE</h3> To understand the axial loading imparted to the functional spinal unit during lumbar interbody fusion surgery. <h3>STUDY DESIGN/SETTING</h3> Biomechanical axial load mesaurement in cadaveric functional spinal units during lumbar disc preparation and spinal interbody device implant procedures. <h3>METHODS</h3> Cadaveric functional spinal units, levels L2-L3, L3-L4, L4-L5, and L5-S1, were decorticated to the osteoligamentous structures. Posterior elements were removed to allow for MicroCT imaging of each specimen at a voxel size of 27 micron before and after instrumentation. A custom test fixture was used to apply 50N compressive force to stabilize the specimen and also record inline axial forces associated with the deployment of anchor plates during instrumentation procedures. A Chatillon DFS II force gauge was used to record axial forces during implantation of ENZA 1.0 and ENZA 2.0 interbody devices. Axial forces resulting from implant trialing, device insertion and anchor deployment were recorded. MicroCT scans were repeated to allow for quantification of damage to bony structures as a result of implantation procedures. <h3>RESULTS</h3> L2-L3 and L3-L4 force outputs are similar for both insertion, 218.82 N, 219.89 N, and deployment forces, 34.58 N, 44.88 N respectively. Insertion forces throughout all spinal levels were larger than both deployment and removal forces. Insertion forces were larger in the proximal levels, 218.82 N, 219.89 N, when compared to the distal levels, 178.96 N, 113.76 N. However, deployment force was larger in the distal levels, 99.03 N, 77.76 N, when compared to proximal 34.58 N, 44.88 N. <h3>CONCLUSIONS</h3> As evidence mounts for the cost-effectiveness of standalone cages with integrated supplemental fixation, it is imperative that design requirements of these devices continue to improve. Previous studies have shown that the vertebral endplate is susceptible to fracture under compressive loading, with the weakest area of the vertebrae being the center region. In 2001, Hasegawa et al showed a cylindrical-shaped implant caused endplate fracture between 510N and 1335N and that implant size is inversely related to the force required to cause fracture. Endplate fracture is difficult to detect with standard imaging modalities and leaves the patient vulnerable to implant subsidence and reduces segmental stability as a result of changes in load transfer. Furthermore, endplate failure may be a contributor to low back pain, further reducing the chance of a successful outcome. Our study showed interbody devices with integrated fixation plates could safely be inserted and deployed in the disc space without causing endplate fracture. The implant-endplate interface should be investigated in greater detail to allow for design of standalone interbody devices which do not cause unintended distraction or worse, damage to the vertebrae. <h3>FDA DEVICE/DRUG STATUS</h3> ENZA Lumbar Interbody Fusion Device (Approved for this indication).

Anchorage behavior of large shear reinforcements with anchor heads and 180-degree hooks

The use of headed bars in place of conventional hooked bars and closed stirrups can provide sufficient anchorage strength while solving the problems of rebar congestion and difficulties in construction, especially in seismic structures with large shear reinforcements. This paper conducted experimental and numerical studies to investigate the anchorage behaviors of shear reinforcements with anchor heads and 180-degree hooks. A total of 28 pull-out specimens were designed and tested. The specimens were classified into two groups based on the anchor types (180-degree hooks and friction welded anchor plates), and each group had seven nominal bar diameters. The test results show that compared with 180-degree hooked bars, the growth of the pull-out displacements of headed bars are effectively restrained, and the yielding pull-out displacements are reduced by 33%–75%. To gain a deeper understanding of anchorage mechanisms, finite element (FE) models of the specimens were established and validated. For shear reinforcements with anchored heads, the anchorage is mainly based on bearing effect. The tensile fracture of rebars is prior to the overall yielding of anchor heads and local crushing of concrete. For shear reinforcements with 180-degree hooks, to simulate the interaction condition between hooks and concrete, a highly refined rib-scale modeling method was proposed and compared with the existing bar-scale modeling method. The proposed rib-scale model can eliminate the reliance on the assumption of interfacial contact relationship and predict the anchorage behavior of hooks with discrepancies of less than 10%. The anchorage mechanism of the 180-degree hook is mainly based on bonding effect, supplemented by local bearing. When the stress of bar reached the yield strength and tensile strength, the local bearing stress accounted for 6.8% and 11.6% of the total stress, respectively.

Deformation Characteristics of Sandy Soil around a Plate Anchor under Lateral Loading

The lateral loading of a plate anchor is a complicated process that involves complex anchor-soil interactions. The deformation characteristics of the soil around an anchor have an important effect on its lateral bearing capacity. In this paper, the noncontact digital image correlation (DIC) technique is used to study the distribution and variation of the soil deformation field under a laterally loaded anchor in sandy soil. The results show that the sand density and embedment ratio significantly affect the distribution and influence range of the active and passive zones around the anchor. The active zone behind the rod gradually decreases with increasing sand density until ultimately disappearing, and the passive zone increases. The maximum influence height occurs in the passive zone behind the rod in dense sand, and the influence range of the passive zone in front of the rod expands with an increasing embedment ratio. Shear bands form during the lateral loading process, which are accompanied by dilatancy in the shear process. The motion path of the rotation center in loose and medium sand is initially rigid translational and then becomes rigid rotational, while the opposite trend occurs in compact dense sand. The results provide important guidance for the development of predictive models for anchor lateral loading and design.