Showing papers on "Embedment published in 2010"

Three-dimensional large deformation finite-element analysis of plate anchors in uniform clay

Abstract: Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to three-dimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth.

Consolidation beneath Circular Skirted Foundations

Abstract: The effect of foundation embedment on consolidation has not been considered previously in a systematic manner, although this is of particular interest for offshore foundations, where embedment is provided by skirts that enclose a compressible soil plug. For skirted foundations, critical uncertainties include what to assume in terms of the degree of drainage at skirt tip level, and the relative time scales of consolidation within the soil plug and beneath the foundation. In this paper, results from small strain finite-element analyses are used to quantify the immediate and time-dependent response of circular skirted foundations to uniaxial vertical loading. Foundations with frictionless and fully rough skirt-soil interfaces with varying ratio of embedment depth to foundation diameter are considered and the responses compared with those for surface foundations. The findings show that both skirt-soil interface roughness and embedment ratio have a significant effect on the consolidation response.

Mechanics of Drag Embedment Anchors in a Soft Seabed

Abstract: This paper presents an analysis of the load capacity and trajectory of a drag embedment anchor in a soft seabed. Anchor capacity relationships are developed for an idealized anchor comprising a rectangular fluke and a cylindrical shank. Geometric variables considered for the anchor include fluke length, fluke thickness, shank length, angle between fluke and shank, and shank thickness. Parametric studies are presented investigating the effect of these variables on anchor capacity and performance. A method of anchor trajectory prediction during drag embedment is developed by considering anchor behavior in conjunction with the mechanics of the anchor line. The anchor trajectory simulations indicate that an equilibrium condition rapidly develops during embedment in which the rate of anchor rotation is identical to the rate of change in the anchor line uplift angle at the shackle point. At the equilibrium state, the anchor load capacity normalized by soil strength remains constant and the anchor is in a state ...

Large Deformation Finite-Element Analysis of Submarine Landslide Interaction with Embedded Pipelines

Abstract: Submarine landslides represent one of the most significant geohazards on the continental slope in respect of the risk they pose to infrastructure such as deep water pipelines. A numerical approach, based on the finite-element method but using remeshing, was established in this paper to simulate large flow deformation of debris from a landslide and to quantify the loads and displacements imposed on pipelines embedded in the seabed. A simple two-dimensional elastic perfectly plastic soil model with plane strain conditions was employed in this analysis. The pipeline was restrained by a set of springs so that the load on the pipeline built up to a stable value, representing the limiting load at which the debris flowed over the pipeline. A parametric study was undertaken by varying the pipeline embedment and the relative strengths of the debris and seabed. The analysis results show that the various combinations of soil strength and embedment depth lead to different debris-pipeline movement patterns and consequ...

Three-Dimensional Finite-Element Modeling of Nailed Connections in Wood

Abstract: A three-dimensional nonlinear finite-element model of single nail connection was developed based on transversely isotropic plasticity. In order to have the connection model account for crushing behavior of wood during the nail embedment, a procedure was studied to implement the theory of a beam on a nonlinear foundation in the solid element modeling. Within a prescribed volume of wood surrounding a nail, a wood foundation was defined with the foundation material parameters, which were determined through nail-embedment tests. Introduction of the wood foundation to the connection model was justified by comparing the results of nail-embedment simulations with or without a wood foundation. Three-dimensional finite-element analyses of single nail connections incorporated with wood foundations were compared with the results of lateral resistance tests of the connections under parallel to grain loading and perpendicular to grain loading. The model predictions showed good agreement with the load-slip relations an...

Computations of uplift capacity of pile anchors in cohesionless soil

Abstract: A method of analysis for the uplift capacity of pile anchors in cohesionless soil is proposed using Kotter’s equation that facilitates computation of the distribution of soil reaction on the axis-symmetric failure surface, which is assumed to be the frustum of a cone with a characteristic angle of inclination with the pile–soil interface. A closed-form solution for the uplift capacity is obtained with no requirement of any charts or tables. Empirical relations using available literature are proposed for expressing critical embedment ratio and computation of net uplift capacity. The results are compared with a set of experimental data for 28 cases, ranging from loose to dense cohesionless soil up to maximum embedment ratio of 40, vis-a-vis available theoretical solutions. The proposed method leads to the predictions that are in good agreement with the experimental results. It further demonstrates the successful application of Kotter’s equation in the estimation of uplift capacity of pile anchors.

Slip modulus of inclined screws in timber–concrete floors

Abstract: This paper presents a model for the stiffness of inclined screws used as shear connectors in timber and concrete composite floors Screws inclined in the direction of slip have been shown to provide a higher stiffness (slip modulus) than vertically placed screws An increased slip modulus per screw enhances the effective flexural stiffness of a partially composite timber and concrete beam, or, alternatively, allows the same flexural stiffness to be achieved with fewer screws The model assumes that the screw behaves as a beam on a two-dimensional elastic foundation: it takes account of the inclination of the screw and models the timber as orthogonal springs with differing stiffnesses in the grain and transverse directions The model also considers axial deformation, and hence shear lag, of the screw Optimum inclination angle and embedment length of screw can be predicted Preliminary validation of the model is provided by comparison with some experimental results

Pullout Characterizations of Various Steel Fibers E mbedded in Very High-Strength Concrete

Abstract: Problem statement: There is a real need for a fundamental understandi ng of bond and bond mechanisms in the newly developed Very-High-Strength-Concrete (VHSC) materials. The interfacial steel fiber/VHSC matrix bond tests are needed to ch aracterize VHSC and to aid in the development of analytical models that describe bond behavior of th is new material. Approach: This research investigated bond-slip characteristics of four diff erent steel fiber types embedded in Very-High- Strength-Concrete (VHSC). Parameters investigated include: Mechanical affect of the fiber geometry, fiber embedment length, medium strength and embedment method. Results were measured in terms of peak pullout load and total pullout work or dissipa ted bond energy. Results: Results indicated that the mechanical affect of fiber geometry had the most in fluence on both peak load and total work with increases over 100% for some fibers. The increase i n embedment length also increased both peak load and total pullout work but was found to have more i nfluence on smooth, undeformed fibers. Conclusion/Recommendations: Findings of this research should aid in the ration al predictions of VHSC's mechanical performance and help identify the effectiveness of different types of steel fibers on improving its tensile properties and toughness. It is recommended that an analytical model should also be developed to analyze the interfacial debond ing process of VHSC composites.

Numerical analysis of pipeline in J-lay problem

Abstract: The pipe configuration and internal loads along the pipeline during the pipeline laying process have long been the focus of engineers. Most researchers simplify the seabed to be rigid and the water to be calm, ignoring the pipe embedment into the seabed and the influence of ocean currents. In this paper, a novel numerical approach is proposed for the laying of pipelines in the so-called J-lay method, taking into account the importance of both pipe embedment and ocean currents. The pipeline is divided into two parts, one part suspended in water, and the other laid on the seabed. The continuity of the two parts at the touch down point (TDP) is guaranteed to make a whole. The feasibility of the model is proved by the comparison between the present model and an analytical model, which shows good agreement in both pipeline configuration and bending moment distribution. Finally, parametric study was performed to consider the influence of current velocity, water depth, top inclination angle, and seabed stiffness, and conclusions are drawn.

Shear Behavior of Headed Anchors with Large Diameters and Deep Embedments

Abstract: This paper presents shear test results for large cast-in-place anchor bolts in concrete. The tests were performed to evaluate the shear performance of large anchors, that is, anchors with a diameter greater than 2 in. (50.8 mm) or an embedment depth greater than 25 in. (635.0 mm), which are not addressed by ACI 318-08, Appendix D and ACI 349-06, Appendix D. The tests were also intended to investigate the safety of such anchors for use in nuclear power plants, and the effects of regular (conventional) and special reinforcement on the shear strength of such anchors. The test results are used to assess the applicability of existing design formulas valid for smaller anchors to large anchors. Suggestions are made for incorporating the effects of deep embedment or large diameter in existing design provisions for cast-in-place anchor bolts under shear load.

Centrifuge modelling of circular shallow foundations on sand

Abstract: Drum centrifuge tests on circular footings resting on medium dense silica sand subjected to combined vertical, moment and horizontal loading are reported and compared with existing data from similar studies carried out at 1g. Vertical loading tests and displacement-controlled horizontal and rotational swipe tests were carried out; the results are reported in terms of load–displacement relationships and yield surfaces in (V, M/D, H) load space. The centrifuge test results from this study are well described using the existing theoretical framework of strain-hardening plasticity applied to surface footings on sand, developed on the basis of experimental data from 1g tests. Attention is given to the embedment effect, which can be especially pointed out by centrifuge testing.

Experimental Testing and Analytical Prediction of the Behaviour of Timber Bolted Connections Subjected to Fire

Abstract: The ultimate strength of bolted and dowelled connections in timber members at ambient temperatures have been assessed using Johansen’s yield equations in Europe and USA. More recently, several researchers have begun to investigate the strength of bolted and dowelled connections at elevated temperatures. Research has been carried out at the University of Canterbury to investigate the application of Johansen’s yield equations to the prediction of the failure strength of bolted connections in fire conditions. A series of single bolted connections using steel side plates was heated at constant temperature for several hours, then loaded to failure and used to determine the embedment strength of the wood over a range of temperatures from ambient to 300°C. The temperature-dependent embedment strengths are employed in Johansen’s equations for connections using a central steel plate as well as connections using steel and wood side members. Comparisons are also being made with the results of several similar connections tested in fire conditions and show considerable promise for predicting failure of such joints. A proposal for implementation of an easy-to-use approach for the prediction of the fire resistance of bolted joints is discussed in the paper, based on an extension of the Johansen’s yield equations to fire conditions, including a model for the variation of the embedment strength with temperature.

Development Length of Straight FRP Composite Bars Embedded in Concrete

Abstract: This article presents an analytical study performed on concrete girders reinforced with FRP bars with the goal of evaluating current design guidelines for FRP rebar development lengths. The analytical model is based on finite element formulation of embedded bar problems with inelastic constitutive laws for the constituent materials. The bond stress—slip behavior between FRP bars and concrete was calibrated from experimental data obtained from a large database set of 48 test specimens, most of which were collected from the open literature. The collected data was modified to emulate a specific bar size and embedment length for various scenarios. A large number of analytical simulations were conducted in order to investigate the effect of different parameters on the development length. These parameters include: bar type (GFRP, CFRP), bar strength, bar modulus of elasticity, bar diameter, bar surface coatings, concrete strength, and confinement. For each specimen, the analytical model was conducted for a set ...

Bond-Slip Analytical Formulation toward Optimal Embedment of Concrete-Filled Circular FRP Tubes into Concrete Footings

Abstract: This paper presents a robust analytical model for a moment connection of concrete-filled fiber reinforced-polymer (FRP) tubes (CFFTs) to concrete footings. The CFFT connection is based on a simple approach of direct embedment into the footing, thereby eliminating the need for connection rebar or mechanical devices. The CFFT is externally subjected to lateral and axial loads, resembling practical applications such as piles affixed to pile caps, bridge columns, or utility poles. The model adopts the concepts of equilibrium, deformations compatibility, and nonlinear concrete stress-strain behavior. It also employs a “bond stress-slip” relation that can be obtained from simple push-through tests on some of the commercially used tubes. The model can predict the critical embedment length Xcr , which is the minimum length required to achieve material failure of the CFFT outside the footing, and bond failure inside the footing, simultaneously. If the actual embedment length is less than Xcr , bond failure occurs ...

Analyzing Drivability of Open Ended Piles in Very Dense Sands

Abstract: The successful installation of long piles driven into very dense sands relies on the occurrence of the reduction in local friction with increased pile embedment, a phenomenon known as ‘friction fatigue’. The underlying mechanisms controlling friction fatigue are poorly understood, with some design methods including an adjustment for the influence of pile diameter while others do not. This paper back calculates the installation resistance of 0.356m to 2m (14in to 78in) diameter open ended piles driven into very dense sands using wave equation analyses. Cone penetration test data are used to link soil properties to installation resistance. The study illustrates consistent interpretation of a variety of case histories of open ended piles driven in very dense sands using newly developed analysis techniques and normalized parameters. Results provide information on methods for incorporating friction fatigue into drivability studies as well as a discussion of mechanisms related to pipe pile installation ...

Evaluation and modelling of perpendicular to grain embedment strength

Abstract: Different test setups for determining perpendicular to grain embedment strength of timber have been reported in literature. In addition, different definitions of strength have been used associated with the deformation level underneath the fastener. It is shown that all reported experimental results can be related, which enables comparison on a common basis. Furthermore, several models for embedment strength perpendicular to the grain which primarily depend on timber density (specific gravity) and fastener diameter are evaluated. It is shown that the model currently prescribed by the European structural timber design code [Comite Europeen de Normalisation (CEN) EN 1995-1-1: 2004: Eurocode 5—design of timber structures. Part 1.1: general rules and rules for buildings. CEN, Brussels, 2004] is unable to accurately predict the strength and an alternative is proposed. This may result in more reliable timber connections in applying the European Yield Model to determine the connection strength.

Laterally loaded pile cap connections.

Abstract: This study investigated the moment capacity and load-displacement response of the pile-to-cap connection details. Lateral load tests were conducted on four pile caps (3 ft. H x 3 ft. W x 6.5 ft. L) with two 40 foot-long steel pipe piles (12.75 inch OD) with different connection details. Two caps included a reinforced connection detail with six or 12 inch pile embedment while the other two relied exclusively on their respective embedment lengths of 12 and 24 inches. A hydraulic ram was used to apply a cyclic lateral force to each of these pile caps until failure occurred. Load-displacement curves were developed for each cap and bending moments were computed from strain measurements in the piles. The pile cap with piles embedded two diameters (24 inches) into the cap performed successfully. In contrast, a cap with piles embedded only one diameter failed after developing a large crack through the entire cap. The two pile caps with shallow embedment (0.5 to 1.0 diameter) and a reinforcing cage connection still developed at least 40% to 60% of the moment capacity of the pile which was much greater than predicted by PCI design equations based only on embedment. The load-displacement curves and bending moments computed using the computer program GROUP were in very good agreement with measured values when the pile connections were considered to be "fixed-head". However, assuming a "free-head" or pinned connection significantly overestimated displacement even for the connection with only 6 inches of embedment. These results suggest that it is relatively difficult to create a truly pinned connection detail and that some connections which are assumed to be pinned may actually behave more like fixed connections.

Optimum Design Of Retaining Structures Under Static And Seismic Loading : A Reliability Based Approach

Abstract: Design of retaining structures depends upon the load which is transferred from backfill soil as well as external loads and also the resisting capacity of the structure. The traditional safety factor approach of the design of retaining structures does not address the variability of soils and loads. The properties of backfill soil are inherently variable and influence the design decisions considerably. A rational procedure for the design of retaining structures needs to explicitly consider variability, as they may cause significant changes in the performance and stability assessment. Reliability based design enables identification and separation of different variabilities in loading and resistance and recommends reliability indices to ensure the margin of safety based on probability theory. Detailed studies in this area are limited and the work presented in the dissertation on the Optimum design of retaining structures under static and seismic conditions: A reliability based approach is an attempt in this direction. This thesis contains ten chapters including Chapter 1 which provides a general introduction regarding the contents of the thesis and Chapter 2 presents a detailed review of literature regarding static and seismic design of retaining structures and highlights the importance of consideration of variability in the optimum design and leads to scope of the investigation. Targeted stability is formulated as optimization problem in the framework of target reliability based design optimization (TRBDO) and presented in Chapter 3. In Chapter 4, TRBDO approach for cantilever sheet pile walls and anchored cantilever sheet pile walls penetrating sandy and clayey soils is developed. Design penetration depth and section modulus for the various anchor pulls are obtained considering the failure criteria (rotational, sliding, and flexural failure modes) as well as variability in the back fill soil properties, soil-steel pile interface friction angle, depth of the water table, total depth of embedment, yield strength of steel, section modulus of sheet pile and anchor pull. The stability of reinforced concrete gravity, cantilever and L-shaped retaining walls in static conditions is examined in the context of reliability based design optimization and results are presented in Chapter 5 considering failure modes viz. overturning, sliding, eccentricity, bearing, shear and moment failures in the base slab and stem of wall. Optimum wall proportions are proposed for different coefficients of variation of friction angle of the backfill soil and cohesion of the foundation soil corresponding to different values of component as well as lower bounds of system reliability indices. Chapter 6 presents an approach to obtain seismic passive resistance behind gravity walls using composite curved rupture surface considering limit equilibrium method of analysis with the pseudo-dynamic approach. The study is extended to obtain the rotational and sliding displacements of gravity retaining walls under passive condition when subjected to sinusoidal…

Embedment of HA/Ti composite on superplastic titanium alloy (Ti–6Al–4V)

Abstract: In this research, embedment of HA-2 wt.% Ti composite powder on superplastic Ti–6Al–4V was conducted through continuous pressing technique to improve the low strength of the conventional pure HA coatings. The embedment process was carried out at temperature below the allographic temperature. The bond strength evaluation of HA-2 wt.% Ti composite layer was performed using wear test method under different applied pressure. The experimental results indicated that the HA-2 wt.% Ti composite layer had uniform thickness and well bonded to the substrate. EDX and line scanning analysis revealed that HA elements were detected at the substrate indicating embedment process was successful. The wear test results proved that the strength of the embedded layer on the superplastic Ti–6Al–4V was much better than the as-received Ti–6Al–4V.

Reverse action corner embedment for stretched canvas

Abstract: A canvas tensioning frame corner having adjoining stretcher bar ends; each stretcher bar end having a tapered expanding groove from the inside of the corner to the tip of the corner; a corner embedment nested in the grooves; the corner embedment having tapered edges matching the grooves; wherein a movement of the corner embedment inward away from the tip of the corner urges the stretcher bars apart to stretch the canvas affixed to each stretcher bar, side and corner; a corner embedment brace attached across the corner to support a bolt attached to the corner embedment; and wherein a wing nut attached to the bolt urges the corner embedment toward the brace.

Power embedment anchor with high-frequency small amplitude vibration

Abstract: The invention relates to a power embedment anchor with high-frequency micro-amplitude vibration in the ship and ocean engineering technical field. The embedment anchor comprises an anchor cover, an anchor shank, an anchor hammer, a lifting lug, a high-frequency micro-amplitude vibration device, a main fin, an anchor chain, a power source and a cable, wherein the anchor cover is arranged on the upper part of the anchor shank; the anchor hammer is arranged on the lower part of the anchor shank; the lifting lug is arranged on the surface of the outer wall of the anchor shank; the anchor chain isconnected with the lifting lug; the high-frequency micro-amplitude vibration device is arranged inside the anchor shank; the main fin consists of two to four sheets which are uniformly and symmetrically arranged on the surface of the outer wall of the anchor shank; the power source supplies power to the high-frequency micro-amplitude vibration device through the cable; and the cable is connected with the power source and the high-frequency micro-amplitude vibration device through an outer cover. The embedment anchor has good holding power and underwater anchor weight ratio under different submarine sediment, can rapidly hold seabed, and is little in windlass tension needed in the process of raising anchors.

Structure of motor stator iron core punching plate

Abstract: The utility model relates to a structure of a motor stator iron core punching plate which comprises a yoke, a teeth, a plurality of wire embedment slots and a central hole. The wire embedment slot is communicated with the central hole; the wire embedment slots are in U shapes and trapezoid shapes, wherein each wire embedment slot in the U shape is formed by an arc-shaped bottom, two straight line on two sides and a gradually-narrowed open top, and each wire embedment slot in the trapezoid shape is formed by a flat bottom, two straight lines on two sides and a gradually-narrowed open top; the wire embedment slots in the U shapes and the wire embedment slot in the trapezoid shapes are symmetrically distributed on a circumference with the internal diameter ranging from Phi 56m to Phi 62m; and the teeth have different width. The utility model makes the full use of materials to a higher degree, has more reasonable layout and optimally-designed shape and size, reduces the product cost and effectively improves the efficiency of the whole motor under the condition of meeting the requirement.

Open-slip coupled model for simulating three-dimensional bond behavior of reinforcing bars in concrete

Abstract: The bond mechanism for reinforcing bars in concrete is equivalent to the normal contact and friction between the inclined ribs and the surrounding concrete. Based on the contact density model for the computation of shear transfer across cracks, an open-slip coupled model was developed for simulating three-dimensional bond behavior for reinforcing bars in concrete. A parameter study was performed and verified by simulating pull-out experiments of extremely different boundary conditions: short bar embedment with a huge concrete cover, extremely long bar embedment with a huge concrete cover, embedded aluminum bar and short bar embedded length with an insufficient concrete cover. The bar strain effect and splitting of the concrete cover on a local bond can be explained by finite element (FE) analysis. The analysis shows that the strain effect results from a large local slip and the splitting effect of a large opening of the interface. Finally, the sensitivity of rebar geometry was also checked by FE analysis and implies that the open-slip coupled model can be extended to the case of plain bar.

Numerical investigation of the response of expansion anchors used to attach helical pile connectors to concrete foundations

Abstract: This paper evaluates the performance of expansion anchors used to attach helical pile connectors to foundations. The anchors' response to pullout loads was evaluated using nonlinear finite element analysis with the aid of the commer- cial software, Abaqus. The connector capacity under horizontal movement of the foundation for different anchor diameters, embedment depths, and anchors' spacing is reported. It was found that the pre-tension load had no influence on the anchor ultimate capacity, but affected the anchor response at service load levels and the displacement at failure. Under pullout loading, increasing the anchor diameter resulted in a more brittle response, but did not affect the ultimate capacity when the concrete tensile strength dominated the response. No interaction between anchors was observed for spacing ‡ 1.67 times the anchor's embedment depth. A modification to the helical pile connector configuration is proposed.