Showing papers on "Embedment published in 1991"

Formulas and charts for impedances of surface and embedded foundations

Abstract: A complete set of algebraic formulas and dimensionless charts is presented for readily computing the dynamic stiffnesses (\IK\N) and damping coefficients (\IC\N) of foundations harmonically oscillating on/in a homogeneous half-space. All possible modes of vibration, a realistic range of Poisson’s ratios, and a practically sufficient range of oscillation frequencies are considered. The foundations have a rigid basemat of any realistic solid geometric shape. The embedded foundations are prismatic, having a sidewall-soil contact surface of height \Id\N, which may be only a fraction of the embedment depth \ID\N. Two numerical examples illustrate the use of the formulas and charts and elucidate the role of foundation shape and degree of embedment on radiation damping for various modes of vibration. A companion paper (Gazetas and Stokoe 1991) presents supporting experimental evidence from model tests. The two papers aim at encouraging the practicing engineer to make use of results obtained with state-of-the-art formulations, when studying the dynamic response of foundations.

Characterization of Interfacial Properties in Fiber-Reinforced Cementitious Composites

Abstract: For calculating interface properties from pullout tests, a simple theoretical model is proposed. The model enables calculating of the following material parameters: the parameter of shear stiffness of the fiber–matrix boundary layer, the shear bond strength, the frictional bond strength and the specific interfacial fracture energy. These parameters can be determined from the slope of the load-slip curve, the maximum pullout load and the corresponding slip value. Slip-controlled, multiple-fiber pullout tests were conducted in a closed-loop test system. The effects of embedment length of fibers on the model-predicted material parameters were examined. The model predictions were satisfactorily compared with some previously published test data.

The analysis of offshore foundations subjected to combined loading

Abstract: Shallow offshore foundations, which achieve their stability through the foundation bearing on the seabed, can in most applications be idealised as large rigid circular footings subjected to vertical, horizontal and moment loading. A small strain linear-elastic perfectly-plastic three- dimensional finite element program was developed to analyse this combined loading problem. The selection of a suitable three-dimensional finite element for accurate and computationally efficient analysis was based on the element's ability to model incompressible soil conditions, using exact numerical integration. A new approach for evaluating element suitability is developed and is quantified in terms of the parameter free degrees-of-freedom (equal to the degrees-of-freedom minus the incompressibility constraints). The tetrahedron family of three- dimensional elements is found to be in general more suitable and computationally efficient than the Serendipity and Lagrangian cube families. The 20-node quadratic strain tetrahedron is adopted for all analyses presented in this thesis. For combined loading, most of the available elastic analytical solutions are for rigid circular footings placed at the surface. Finite element analyses reveal certain inadequacies in some of these solutions. The elastic numerical analyses also examine the effect of footing embedment for three cases of embedment geometry. This demonstrates that the increase in footing stiffness (reduction in displacement) due to embedment for horizontal and moment loading is developed at shallower depths, and has a greater magnitude, than for vertical loading. The stability of a rough rigid circular footing placed on the surface of an undrained clay is examined. Zero thickness interface elements, despite experiencing some numerical instability problems, were found to model the footing-soil interaction better than conventional continuum elements. However, application of interface elements to footings which can lose contact with the soil, under moment loading conditions, resulted in numerical instability of the solution. A simpler model was therefore used to define the shape of the three-dimensional failure envelope at high vertical load. Comparisons with the semi-empirical inclination factors of bearing capacity solutions are included.

Forced vertical vibration of rigid discs with arbitrary embedment

Abstract: This paper is concerned with the investigation of the forced time‐harmonic vertical vibration of a rigid disc embedded at an arbitrary depth in a semi‐infinite medium. By virtue of transform methods, the generalized mixed boundary‐value problem is formulated as a set of dual integral equations, which, in turn, are reduced to a Fredholm equation of the second kind. With the aid of contour integration, the governing integral equation is solved numerically. Selected results for the complex compliance are presented to illustrate the various effects of embedment on the dynamic response. In addition to furnishing a unified view of the static and dynamic solutions for zero and infinite embedments, the present analysis reveals a dynamic boundary‐layer phenomenon, which is apt to be of interest to this class of problems in general.

Method of making catheter with irregular inner and/or outer surfaces to reduce travelling friction

Abstract: Method of making a catheter having an irregular outer diameter and/or an irregular inner diameter caused by embedment of a reinforcing member, thereby reducing sliding friction compared to conventional smooth-wall catheters.

Method for detecting longitudinal tear in a conveyor belt

Abstract: At each of a plurality of points of embedment in a conveyor belt, a set of at least two detectable elements is embedded, and a control unit is arranged (a) to receive and process signals from an externally installed sensor, the signals having a varied intensity corresponding to the number of detectable elements in a given embedment point, (b) to average the intensities of a plurality of the signals for the given embedment point, and (c) to judge, on the basis of the average obtained in (b), the presence or absence of a breakage of detectable element or elements at the given embedment point. The abovementioned arrangement is able to judge whether one of the two detectable elements is broken, and the judgment is not affected by variation of the distance between detectable elements and the sensor. If breakage of a single detectable element of any set is identified, the affected element may be repaired during an outage of the conveyor. In this way, breakage of two elements of a point without any longitudinal tear will be eliminated.

Response of circular footings and anchor plates in non‐homogeneous elastic soils

Abstract: The axisymmetric elastic response of circular footings and anchor plates in a linearly non-homogeneous elastic soil is analysed. It is assumed that footings/anchors are flexible and subjected to axisymmetric vertical loads. The response of the footing/anchor is modelled by using the classical Poisson–Kirchhoff thin plate theory. A variational technique is used to analyse the interaction problem. A representation for the contact stress is established by using a fundamental solution corresponding to a unit vertical pressure acting over an annular region in the interior of the non-homogeneous soil. The fundamental solution can be derived by using rigorous analytical procedures. The influence of the footing flexibility and the degree of soil non-homogeneity on the displacements, bending moments and contact stresses of a surface footing is examined over a wide range of governing parameters. In the case of anchor plates the influence of depth of embedment, degree of soil non-homogeneity and anchor flexibility on the anchor displacement is investigated.

Modelling the load–slip behaviour of timber joints with mechanical fasteners

Abstract: An analytical model of behaviour is presented, which uses one-dimensional finite element approximations to predict the short-term load – slip response of a single fastener joint. The model treats the elastoplastic behaviour of the fastener as well as the nonlinear, nonelastic properties of the wood. It accounts for some of the distinctive behaviour of timber joints such as fastener withdrawal, rotational restraint at the fastener ends, joint interface characteristics, and combined fastener bending and axial tension. Good agreement is obtained between model predictions and test behaviour for single fastener glulam rivet, nail, and bolt joints. The model can be adapted to include the variability in wood and fastener properties, and can be incorporated into a large number of computer simulations in order to predict the fifth fractiles of the populations of joint resistances, which can be used in a limit states design approach. Key words: timber structures, glulam rivet connections, nailed connections, bolted...

Plastics fastener to attach door trim panel

Abstract: A retainer for receiving a fastener and adapted for loading into a mold for embedment in a trim article molded of molding material. The retainer has a housing having an upper portion for accepting the fastener and a lower portion for embedment in the molded trim article. A flexible lip encompasses the housing for sealingly engaging with the mold thereby preventing the molding material from making contact with the upper portion of the housing and allowing the molding material to make contact with the lower portion of the housing.

Horizontal impedance of embedded strip foundations in layered soil

Abstract: This paper presents a detailed investigation of the influence of key mechanical and geometrical parameters on the dynamic horizontal stiffness of rigid strip foundations embedded in layered soil. Geometrical parameters include the depth of embedment, the thickness of the top soil layer, and the height of contact of foundation sidewalls with surrounding backfill soil. The influence of the relative shear wave velocities of the layers for a two-layered soil profile is also investigated. The results are presented in the form of simple, versatile dimensionless graphs. The investigation was conducted using a rigorous algorithm of the boundary element method incorporating isoparametric boundary elements. Higher-order quadratic elements were used because they can model accurately the wavy nature of the dynamic problem.

A Study of Free Embedded Cantilever Walls in Granular Soil.

Abstract: A review of experimental data on free embedded cantilever walls is presented. Normalization of limit equilibrium depths of embedment and maximum bending moment was successfully carried out, but it was found that very little data were in existence. In contrast, many methods of limit equilibrium design were found to be in use. Subsequently, new experiments have been performed, using a small-scale model of a free embedded cantilever wall. Further experimental data have been obtained on maximum bending moments, depths of embedment at failure, and also normal and shear stresses mobilized between soil and wall. New comparative analyses have been performed between these data and predictions by current design methods. The adequacy of these methods has been assessed in the light of the new data. A special model wall facility was built for these experiments. It comprised a test tank, a small-scale model wall, and instrumentation for measuring normal and shear stresses between soil and wall. New types of boundary normal stress and boundary shear stress transducers were developed, using the Hall effect principle. A re-assessment of the phenomenon of cell action factor has also been carried out. Previous design criteria for diaphragm-type boundary normal stress transducers did not predict accurately values of cell action factor measured in this thesis. Accurate predictions of cell action factor were obtained only by a design criterion considering the influence of soil modulus, which was determined in the triaxial test using local strain devices.

Method for making sheet materials such as security paper

Abstract: In a method of making sheet materials such as security paper having partially embedded therein an elongate security element (20) which is partially disposed within the thickness of the sheet and exposed at spaced locations, fibres (24) are deposited onto a moving support surface (11) and the security element (20) is introduced into the fibres by rotating embedment means (14) having a plurality of spaced-apart raised portions (16) with recesses (17) therebetween, so that some fibres move into said recesses between the security element and the embedment means so that said security element is covered by fibres while fibres are substantially prevented from penetrating under the raised portions. The security element (20) may be laid in an oscillating path. The embedment means (14) may additionally impress a watermark.

A new design approach for direct embedment foundations (for power line supports)

Abstract: An improved model has been developed for the analysis and design of directly embedded, single-pole transmission structures subject to high overturning moments. The model uses a multispring, nonlinear subgrade modulus approach to predict the load deflection response and ultimate capacity of direct embedment foundations placed in a multilayered soil subsurface profile, and with uniform or multilayered annulus backfill. To verify the predictive capabilities of the model, ten full-scale lateral load tests were conducted on directly embedded transmission poles. The model is described, and a comparison is made between the results of full-scale load tests and model predictions of the ultimate overturning moment capacity and load deflection behavior. The semiempirical model has been implemented in the computer program MFAD (Moment Foundation Analysis and Design) contained in EPRIs TLWorkstation. The results of 10 full-scale load tests demonstrate that the model, on the average, conservatively underpredicts ultimate moment capacity by approximately 20% and has a coefficient of variation of 12%. The model is also a good predictor of moment-deflection and moment-rotation response for well-compacted backfill materials, conservatively overpredicting deflection by approximately 16% and rotation by approximately 8%. >

Consideration of the effect of embedment depth and lateral backfilling of machine foundations on the dynamic properties of their beds

Abstract: 1. Recommendations are given for consideration of the effect of embedment and lateral backfilling in determining the stiffness and damping coefficients of the beds of foundations concreted under pressure against the soil, or in forms with the condition that backfilling be carefully performed. 2. A method is proposed for the calculation of the horizontal-rotary oscillations of embedded machine foundations; this method makes it possible to use computational equations familiar for nonembedded foundations with varied initial data. 3. The developed computational methods are confirmed experimentally, indicating their applicability. The proposed method is most reliable for a set of predicted parameters of the horizontal-rotary and vertical oscillations of embedded foundations. 4. The developed computational methods are being incorporated in a reference manual on the design of machine foundations with dynamic loads, which is being prepared for publication.

Results and analysis of soil‐structure interaction experiments performed in the centrifuge

Abstract: In this paper a centrifuge model that is capable of realistically representing soil-structure systems subjected to earthquake-like excitation is used to create a data pool which demonstrates the influence of (i) the frequencies of the structure, (ii) the foundation embedment and (iii) the foundation shape on radiation damping and soil-structure interaction effects for a structure on a semi-infinite soil layer over bedrock. The centrifuge model used in this study was developed and validated by the authors in an earlier publication,1 and employs an internal method of earthquake simulation, and the clay-like material, Duxseal, to absorb wave reflections at the boundary of the soil sample. The results of the experimental study are used to compute damping and stiffness values of a two-degree-of-freedom piecewise-linear numerical model of the soil-structure systems. The experimental parameter values are then compared to the values computed using classical text book formulae. The analysis demonstrates the value of the experimental data in validating and developing soil-structure interaction theory, and confirms the accuracy of classical text book formulae in the linear range.

Seismic response analyses of base isolated structures with high damping elastomeric bearings

Abstract: Seismic response analysis of base-isolated structures with high damping elastomeric bearings is described. Emphasis is placed on the adaptation of a nonlinear constitutive model for the isolation bearing together with the treatment of foundation embedment for the soil-structure-interaction analysis. The constitutive model requires six input parameters derived from bearing experimental data under sinusoidal loading. The characteristic behavior of bearing, such as the variation of shear modulus and material damping with the change of maximum shear deformation, can be captured closely by the formulation. In the treatment of soil embedment a spring method is utilized to evaluate the foundation input motion as well as soil stiffness and damping. The above features have been incorporated into a three-dimensional system response program, SISEC, developed at Argonne National Laboratory. Sample problems are presented to illustrate the relative response of isolated and unisolated structures. 11 refs., 12 figs.

Analytical Model of Fibre Pull-Out Mechanism

Abstract: The main assumption for the proposed model is that the interfacial stress τ is related to the fibre-matrix slip and can be treated as one combined stress field regardless of the nature of that stress: bond or friction. To determine this relation a series of tests was performed in which fibre–matrix slips were measured and interfacial stress distributions were derived. The searched bond–slip relation has been found out as a function of two variables: slip s and distance x along the embedment zone. Agreement of test and model simulation results confirms the assumptions of the model.