theA Research Articles

Uplift behavior of shallow horizontal plate anchors reinforced with geocells in cohesionless soil

Reduced scale laboratory tests were conducted to assess effects of anchor embedment ratio (), geocell width ratio (), geocell height ratio () and geometrical shapes of anchors on uplift behavior shallow horizontal plate anchors reinforced with/without geocell material in cohesionless soil. It was determined that the effects of geometrical shapes of anchors having equivalent surface area on the uplift behavior of plate anchors with/without geocell reinforcement were negligible. An increase in the and of geocell yields to an increase in both the uplift capacity and the residual capacity of anchor of shallow horizontal plate anchors while heave on the soil surface spreads to larger area. The effectiveness of geocell reinforcement was evaluated in terms of improved ratio () varying from 1.04 to 6.01 at given values of anchor displacement ratio (S/B), and Simply, optimum geocell width ratio ( of 2.4 was obtained. Additionally, failure surface and dispersion angle of anchors obtained via the help of miniature laboratory test were compared with the results of the reduced scale laboratory test. Finally, a theoretical approach was established to predict the uplift capacity of shallow horizontal plate anchors reinforced with/without geocell in cohesionless soil.

Ultimate Pullout Capacity of a Square Plate Anchor in Clay with an Interbedded Stiff Layer

Three‐dimensional nonlinear numerical analysis is carried out to determine the ultimate pullout capacity of a square plate anchor in layered clay using the large finite element analysis software ABAQUS. An empirical formula for the pullout bearing capacity coefficient of a plate anchor in layered soils is proposed based on the bearing characteristics of plate anchors in single‐layer soils. The results show that a circular flow (circulation field) is induced around the plate anchor during the uplift process and that the flow velocity and circulation field range are mainly affected by the properties of the soil around the plate anchor. The bearing characteristics of plate anchors in layered soils are influenced by factors such as the embedment depth of the plate anchor, the friction coefficient between the soil and the plate anchor, the thickness of the upper soil layer, and the thickness of the middle soil layer. The rationality of the finite element numerical calculation results and the empirical formula is verified by comparing the results from this study with results previously reported in the literature.

串联式双锚定板临界埋深及临界间距研究

串联式双锚定板临界埋深及临界间距研究

Experimental and numerical study on square anchor plate groups in geogrid reinforced sand

The paper investigates the behaviour of groups of horizontal square anchor plates in geogrid-reinforced sand using laboratory model tests. The optimum spacing for two anchor plates in unreinforced sand is 3.4 times the anchor width. The unreinforced groups of anchor plates show a clear failure at a displacement of about 5% of the anchor width, whereas this value increases to more than 45% for reinforced groups along with a two-fold increase in uplift capacity. The optimum width and length of the geogrid reinforcement for groups of two anchors is found to be 5 and 9.4 times the width of the anchor plate, respectively. The performance improvement for isolated anchor plates is found to be maximum and gradually reduces with an increase in the number of plates; however, this reduction is much less in groups of two to four. Therefore, the results obtained from the model tests for reinforced groups of two to four anchor plates can be conveniently used to extrapolate the uplift capacity of multiple anchor plate systems in a reinforced soil mass. The model test results show a reasonably good agreement with the three-dimensional (3D) numerical analysis results.

Test and Design Method for the Performance of Anchor Nodes between an Underreamed Anti-floating Anchor and the Bottom Structure

The number of applications of underreamed anchors with high bearing capacities rapidly increases with the increase in building volume. Scholars and engineers worldwide have reported their researches on the bearing mechanisms and failure modes of underreamed anchors. However, the high capacity of anchors generates new problems for building structures, including the key design point of the anchor node between the high-capacity anchor and the structure in anti-floating engineering. Currently, there is no relevant research report or technical standard. To address this issue, a series of full-scale tests on steel anchor plates are conducted in Nanjing, China. Through these tests, a regular set of test results is obtained. Based on the obtained results, a calculation method for the bearing capacity of the anchor plate is derived, and a complete design method for the anchor node is presented. Furthermore, waterproofing and anti-corrosive construction methods for the anchor node are discussed to perfect the design work of the anchor node.

Estimation of Uplift Capacity of Horizontal Plate Anchor in Sand

In this paper a detailed analysis of breakout resistance of a horizontally laid anchor plate in sandy soil is presented. To compute the distribution of soil reactive pressure on the failure surface, Kötter’s equation is employed. The failure surface is assumed to be in the form of a cone. An analytical expression for the breakout resistance is derived. Results are reported in terms of the breakout factors and net breakout resistance. A comparison is made with the available experimental data and theoretical solutions.

An innovative lightweight gravity installed plate anchor and its keying properties in clay

This study puts forward an innovative lightweight gravity installed plate anchor (L-GIPLA). The L-GIPLA is dynamically installed with the aid of a booster, which is connected at the anchor tail during installation and is retrieved for re-use after installation. The L-GIPLA is designed with the aim of reducing the installed expense, increasing the anchor embedment depth and hence the anchor capacity, and expanding the usage in various seabed sediments. Moreover, the anchor can dive deeper into the soil and obtain higher capacity when the uplift load is beyond the anchor initial capacity, hence the anchor is not vulnerable to be pulled out of the seabed under extreme conditions. Compared with other anchor types, the present L-GIPLA has low fabrication cost and high efficiency in capacity. Two anchor types, triangular and peltate (shield) L-GIPLAs, were proposed in this study and the keying properties of the anchors were investigated using plasticity analysis. Parametric analyses were then carried out to study the effects of padeye offset, padeye eccentricity and loading angle on the anchor trajectory and capacity mobilization. The difference between the two anchors in anchor embedment loss, ultimate embedment depth and capacity were also systematically presented. The optimized padeye offset angles and loading angles at the mudline were also recommended.

Cyclic and post-cycling anchor response in geocell-reinforced sand

Plate anchors are commonly used to resist static, cyclic, and monotonic post-cyclic uplift loads. Under cyclic loading, progressive sudden failure may occur, characterized by accumulated displacement — even under loads significantly less than the static capacity. Despite extensive usage of geocell materials for increasing cyclic resilience, the influence of geocell reinforcements on cyclic uplift capacity is not well understood. In this study, a series of near-full-scale experimental tests, with and without geocell, are presented. Results show that the unreinforced system fails cyclically under a load that is almost 70% of its ultimate uplift capacity (Pu), but use of geocell enables stable cyclic resistance of over 100% Pu. For the given soil and configurations, a cyclic displacement rate that reaches less than 0.05 mm/cycle tends to highlight a likely stable response. Evaluation of the soil’s response to cyclic loading demonstrates that, with increasing loading cycles, the loading is increasingly transmitted through the soil close to the anchor in the unreinforced case, but that the reinforced case is less prone to this phenomenon. The monotonic post-cycling capacity of both reinforced and unreinforced anchors decreases after application of cyclic loading; however, the unreinforced scenario demonstrates larger decreases in capacity, particularly in the residual capacity.

Design equation to evaluate bursting forces at the end zone of post-tensioned members

Design equations to evaluate the bursting force in a post-tensioned anchorage zone have been introduced in many design codes, and one equation in AASHTO LRFD is widely used. However, this equation may not determine the bursting force exactly because it was designed on the basis of two-dimensional numerical analyses without considering various design parameters such as the duct hole and shape of the bearing plate. To improve the design equation, modification of the AASHTO LRFD design equation was considered. The behavior of the anchorage zone was investigated using three-dimensional linear elastic finite element analysis with design parameters such as bearing plate size and diameter of sheath hole. Upon the suggestion of a modified design equation for evaluating the bursting force in an anchorage block with a rectangular anchorage plate (Kim and Kwak 2018), additional influences of design parameters that could affect the evaluation of bursting force were investigated. An improved equation was introduced for determining the bursting force in an anchorage block with a circular anchorage plate, using the same procedure introduced in the design equation for an anchorage block with a rectangular anchorage plate. The validity of the introduced design equation was confirmed by comparison with AASHTO LRFD.

Model tests and finite element analysis for vertically loaded anchors subjected to cyclic loads in soft clays

More attention has been focused on the pull-out behaviour of plate anchors under monotonic loads. Relatively less attention has been focused on the cyclic behaviours of vertically loaded anchors (VLAs) subjected to combined average and cyclic loads in soft clays. Therefore, these anchors are investigated by conducting reduced-scale model tests under 1 g conditions, and the cyclic deformation process of VLAs in soft clays are simulated through a 3D finite element method using an advanced elastoplastic bounding surface constitutive model of soft clays proposed by the authors. The failure displacement of VLAs for the shallow-embedded and deep-embedded conditions was determined by performing monotonic loading tests. The change rules of average and cyclic displacement and the cyclic bearing capacity of anchors with the number of cycles are revealed by performing cyclic loading tests. The influence of the average and cyclic load levels and the embedded depth on the cyclic bearing capacity is clarified. The displacement time, load-displacement histories and cyclic bearing capacity of VLAs can be predicted relatively well through 3D finite element analysis. The significant plastic strain accumulation and nonlinear cyclic hysteresis responses of VLAs in soft clays and the soil flow mechanisms surrounding the plate anchors at failure can be captured.

Experimental and Analytical Study on Uplift Loading Capacity of Strip Plate Anchors Near Sand Slope

AbstractThe aim of this study is to investigate the uplift behavior of horizontal strip plate anchors constructed at a distance to the slope crest. A series of uplift load tests was conducted in la...

Research on Seismic Behavior of Double-Column Piers with Anchor Plate

In order to study the seismic performance of double-column piers with anchor plates, a model of double-column pier with anchor plates and a model of double-column pier with hooked anchorage are fabricated with a geometric similarity ratio of 1:5. Through the shaking table test, the experimental phenomena and some other data of the two double-column pier models are analyzed. Experimental results show that: (1) Their failure phenomena are similar, and no failure occurs to the anchorages. (2) The peak displacement, the strain of reinforcement and the curvature of plastic hinge in the transverse direction of the pier with anchor plates are smaller than those of the pier with bending-hook anchorage, which demonstrates that the seismic performance of the pier with anchor plates is improved in the transverse direction. However, the measurements in the longitudinal direction of the pier with anchor plates are increased, indicating that its seismic performance is slightly worse than that of the end-hook anchored pier.

Vertical uplift resistance of close-spaced shallow rectangular group anchor plates embedded in sand

This study describes an analytical solution for determining the ultimate vertical uplift resistance of a group of two and multiple number of close-spaced shallow rectangular anchor plates embedded horizontally in sand. The analysis was performed by using an upper bound theorem of limit analysis with the employment of the kinematically admissible three-dimensional (3D) rigid wedge collapse mechanisms. Results are obtained in terms of dimensionless uplift factors Fγ and Fq due to the components of soil self-weight and surcharge pressure acting on the ground surface for a wide range of parameters. It was found that the magnitude of uplift factors decreases substantially with a decrease in the clear spacing between the anchors, soil friction angle, and embedment ratio, and an increase in the aspect ratio of anchors. Further, it was noticed that when the clear spacing between the anchors is greater than or equal to the certain critical value, the interaction effect of anchors vanishes and the magnitude of uplift factors associated with a group of anchors becomes equal to that of single isolated anchors. The present solutions are found to compare reasonably well with those theoretical, numerical, and experimental results available in the literature.

Uncertainty quantification of offshore anchoring systems in spatially variable soil using sparse polynomial chaos expansions

SummaryThe trend toward deep water energy production has led to a growing use of plate anchors to moor floating production facilities. The effect on anchor uplift behaviour of the inherent spatial variability of soil deposits has so far been little considered, despite having important implications for anchor design. Spatial variability problems are commonly analysed by Monte Carlo simulation but it is difficult to establish the probabilities of failure that are of interest in practice. In this paper, sparse polynomial chaos expansions (SPCEs) are used for moment and reliability analysis of plate anchors in spatially variable undrained clay. A novel two‐stage methodology is proposed: in the first stage, an SPCE is constructed to meet a target global error, allowing statistical moments of the uplift capacity to be obtained; in the second stage, an active learning method is used to refine the SPCE for reliability analysis. Anchor uplift capacity is obtained by a finite element method, which is coupled with a random field representation of spatial variability. The effect of embedment depth and the soil‐anchor interface is investigated. The failure mechanism of the anchor is shown to have a significant effect on the statistical moments of the uplift capacity and the probability of failure in relation to current design guidelines. To inform future design, factors of safety are presented for a range of failure probabilities.

Influence of fireproof damage on structural performance of post-installed anchor joint subjected to post-earthquake fire

To study explore the influence of post-earthquake fireproof coating damage on structural behaviour of steel-concrete post-installed joint, a three-dimensional FE model has been established by ABAQUS software. Parametric analysis has been carried out and the earthquake level on fireproof coating of post-installed joint by changing thickness of fireproof coating is analyzed under the condition of thermal-force coupling. By damage degree variation of fireproof coating, the influence of fireproof coating damage of anchor plate on fire endurance and bearing capacity of post-installed joint is further analyzed.

Innovative prestressing method for externally bonded CFRP laminates without mechanical anchorage

Strengthening of reinforced concrete (RC) structures by externally bonded carbon fiber reinforced polymer (CFRP) laminates has been widely accepted as an effective and cost-efficient method. It is well known that advantages offered by the bonded CFRP laminates can be further increased by prestressing the laminates prior to bonding. Mechanical anchors are essential, in this case, to prevent debonding since interfacial stress at areas close to the ends of the strengthening laminate is several times higher than the strength of the concrete substrate. Common anchorage solutions often consist of bolted metallic plates to clamp the prestressed CFRP laminate. Besides labor-intensive installation operation, the anchor plates are vulnerable to galvanic corrosion, which further complicates the inspection and increases the maintenance costs. There are also doubts about the long-term performance of such anchorage systems as it highly depends on the quality of the adhesive layer between the plate and laminate, and the level of pre-tension in clamping bolts.This paper presents the work conducted at Chalmers University of Technology on the development of an innovative prestressing method and a tool which allow for the application of prestressed CFRP laminates without mechanical anchors. The principles of the novel method and the prestressing system are explained. Experimental and numerical work carried out on an RC beam strengthened with this method is presented. Results indicate that CFRP laminates with high prestressing forces (approximately 30% of CFRP tensile strength) can be safely anchored without the need for mechanical anchors. Numerical results based on finite element analyses show that the proposed prestressing method can reduce the interfacial shear stresses in the CFRP-concrete adhesive joint below the bond strength with a reasonable safety margin.

Rebar Anchor Plate Research and Application

Recently, rebar anchor plate has been widely used in the project, which solve the rebar anchor problem and improve the construction quality. This paper introduced the rebar mechanical anchorage technology background, research content and progress, and rebar anchor plate application, which would offer the guidance and reference for the designers and constructors.

Numerical Investigation of Uplift Behavior of Circular Plate Anchors in Uniform Sand

AbstractEmbedded plates provide an attractive anchorage alternative for mooring floating structures owing to their light weight and high efficiency. They can be installed through a variety of means...

Research on Anchorage Performance of New CFRP Plate Anchorage Based on Displacement Control

The anchorage characteristics of CFRP plate anchors are controlled by anchorage deformation. The anchoring efficiency of anchors under tension and the force mechanism of CFRP plates are studied. The preliminary design of splint anchors is carried out by ANSYS general software. The deformation and stress of the CFRP plate under the displacement control of the different splint edges are analyzed, and the corresponding splint displacement is 0.55mm when the anchoring efficiency is 100%. At the same time, the finite element analysis results were compared by the anchor static test, and the stress loss and relative slip of the CFRP plate were analyzed. The research shows that: from the test results, when the total displacement of the splint reaches 0.55mm, the CFRP plate undergoes longitudinal splitting failure; when the total displacement of the splint reaches 0.50mm, the test anchoring performance is the best, the anchoring efficiency is 82%; the total displacement of the splint is 0.30∼0.55. When mm is used, the slip amount of CFRP plate is 0.69∼3.31mm. The better the anchoring performance is, the smaller the slip amount is. The loss of stress caused by CFRP plate retraction and anchorage deformation is recommended to be 7.5% of the total tensile stress.

Spectrum of UGT1A1 variants in Pakistani children affected with inherited unconjugated hyperbilirubinemias

Inherited unconjugated hyperbilirubinemias are a group of disorders characterized by increased levels of serum unconjugated bilirubin and arise because of the imbalance between its production and elimination from the body. It includes Crigler-Najjar syndrome and Gilbert syndrome. Crigler-Najjar syndrome type 1 represents the extreme severe end of the spectrum with complete absence of hepatic bilirubin uridine diphosphoglucuronate glucuronosyltransferase (UGT1A1). Crigler-Najjar syndrome type 2 patients have intermediate levels of bilirubin owing to incomplete deficiency of UGT1A1, and Gilbert syndrome lies at the extreme mild end of the spectrum with only slightly raised bilirubin level. Here, we present spectrum of UGT1A1 genetic variants in 25 Pakistani children from 23 unrelated families affected with persistent unconjugated hyperbilirubinemias. The promoter region, coding exons and splice junctions of the UGT1A1 were PCR amplified and subjected to Sanger sequencing. Eleven sequence variants were identified underlying disease phenotype including a novel c.582delC variant. Overall, c.622_625dupCAGC was the most frequent variant followed by c.1021C>T found in Crigler-Najjar syndrome type 1 patients. The evaluation of promoter polymorphism A(TA)nTAA in the affected children and their families further supported the body of evidence that the A(TA)7TAA allele could enhance the effect of other structural variants in Crigler-Najjar syndrome patients. To our knowledge, this is the first comprehensive study on molecular genetics of persistent unconjugated hyperbilirubinemias from Pakistan. This study expands the spectrum of UGT1A1 variants and should help in improved clinical diagnosis, genetic counseling and prenatal diagnosis of the affected families.