Showing papers on "Embedment published in 2007"

Reliability of Transfer Length Estimation from Strand End Slip

Abstract: This paper reports on an experimental program on 12 series of concrete specimens with different embedment lengths to determine the distance required to develop the effective stress in the prestressing strand (i.e., transfer length). Transfer length test results of seven-wire strands on twelve different concrete mixtures were analyzed. The study used a testing technique based on the analysis of bond behavior by means of measuring the force supported by the tendon. The specimens had been instrumented with slip measurement devices at each end of the specimen, and a sequence of slip values at each end of the specimen after release versus the embedment length has been analyzed. The expressions relating the transfer length to the tendon end slip are presented. Two criteria to determine the transfer length from the slip sequences at both ends of the specimens have been analyzed. Results verify the feasibility of applying the proposed test method to determine the transfer length of prestressing stands, even in concretes with low compressive strength. A value of Guyon’s factor for tendon stress distribution shape also has been obtained.

Analytical model for transfer length prediction of 13 mm prestressing strand

Abstract: An experimental investigation to determine the transfer length of a seven-wire prestressing strand in different concretes is presented in this paper. A testing technique based on the analysis of bond behaviour by means of measuring the force supported by the prestressing strand on a series of specimens with different embedment lengths has been used. An analytical bond model to calculate the transfer length from an inelastic bond stress distribution along the transfer length has been obtained. A relationship between the plastic bond stress for transfer length and the concrete compressive strength at the time of prestress transfer has been found. An equation to predict the average and both the lower bound and the upper bound values of transfer length is proposed. The experimental results have not only been compared with the theoretical prediction from proposed equations in the literature, but also with experimental results obtained by several researchers.

Tensile-headed anchors with large diameter and deep embedment in concrete

Abstract: This paper presents test results for large cast-in-place anchor bolts in concrete. The tests were performed to evaluate the tensile performance of large anchors, that is, anchors with a diameter greater than 2 in. (50 mm) or an embedment depth greater than 25 in. (635 mm), which are not addressed by ACI 318, Appendix D, and ACI 349, Appendix B. 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 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 tensile anchor bolts under tension load.

Three-Dimensional Response of Buried Pipes under Circular Surface Loading

Abstract: Three-dimensional response of buried pipes under circular surface loading is investigated using the finite-element method. Previous work by Poulos in 1974 is reexamined, considering the longitudinal behavior of pipes under surface loading. Analyses are performed for pipes of varying stiffnesses and embedment depths. When stiff pipes are located close to the ground surface, the burial depth has little impact on the peak deflection. However flexible pipe deflections decrease significantly as embedment depth increases. Not surprisingly, peak moments increase with pipe stiffness and decrease as the pipes become more remote from the ground surface. The comparison of the new results with those of Poulos indicates that his Mindlin solution calculations are somewhat conservative relative to the finite-element solutions for deeply buried pipes, but unconservative at shallow burial.

Structural integrity of composite laminates with embedded micro-sensors

Abstract: The study of the mechanical interaction among the host, interface, and a device embedded within a laminated composite is important. Embedding micro-sensors in composite laminates produces material discontinuity around the inclusions. This in turn produces stress concentrations at or near the inclusions. Both 2D plane strain and 3D FEM models are developed to analyze the stress/strain state surrounding the embedded micro-sensors within a unidirectional composite laminate. The objective of the present numerical effort is to take into account the observed resin-rich areas caused by embedment, and to determine their effects on the local stress field around the embedment and the corresponding potential failure modes.

Comment on "The properties of free polymer surfaces and their influence on the glass transition temperature of thin polystyrene films" by J.S. Sharp, J.H. Teichroeb and J.A. Forrest.

Abstract: Sharp, Teichroeb and Forrest [J.S. Sharp, J.H. Teichroeb, J.A. Forrest, Eur. Phys. J. E 15, 473 (2004)] recently published a viscoelastic contact mechanics analysis of the embedment of gold nanospheres into a polystyrene (PS) surface. In the present comment, we investigate the viscoelastic response of the surface and conclude that the embedment experiments do not support the hypothesis of a liquid surface layer of sufficiently reduced “rheological temperature” to explain reports of very large reductions in the glass temperature of freely standing ultrathin polystyrene films. We also report some errors and discrepancies in the paper under comment that resulted in an inability to reproduce the reported calculations. We present our findings of error in a spirit of clarifying the problem of embedment of spheres into surfaces and in order that others can understand why they may not reproduce the results reported by Sharp, Teichroeb and Forrest. In the comment, we also examine the effects of the magnitude of the forces that result from the polymer surface-nanosphere particle interactions on the viscoelastic properties deduced from the embedment data and we provide a comparison of apparent surface or “rheological” temperature vs. experimental temperature that indicates further work needs to be performed to fully understand the surface embedment experiments. Finally, we comment that the nanosphere embedment measurements have potential as a powerful tool to determine surface viscoelastic properties.

On mechanical behavior of traditional timber shear wall in Taiwan I: background and theory derivation

Abstract: The objectives of this study were to explore the mechanical behavior of traditional timber shear walls in Taiwan and to propose a theoretical model to predict their lateral force resistance. An extensive field investigation was conducted, and the dimensions, tectonic detail, and materials used were recorded. The data collected were used as the reference for theoretical derivation and experimental design. In the theoretical model, the moment resistance of entire shear walls was derived from the contributions of the moment-resisting capacity supplied not only by embedment and friction action between board units and beams but also the dowel action of bamboo nails. Timber shear walls with various geometric conditions and material properties are considered. The theoretical model demonstrated in this study can be used to predict the mechanical behavior of timber shear walls and will be verified by experiments in our next article.

Method for smoothing cementitious slurry in the production of structural cementitious panels

Abstract: A vibrating smoothing device or plate transverse to a direction of travel of deposited gypsum-cementitious slurry and embedded chopped fibers. The plate is used to smooth the top surface of the slurry panel as it exits a first fiber embedment station and a second slurry depositing station before passing through a second fiber embedment station of a structural cementitious panel production line to remove grooves and other non-uniform surface imperfections to have the slurry cover the embedded fibers. The plate is designed to float over the surface of the formed slurry without tearing or otherwise damaging the surface of the heavily fiber reinforced surface layers of the formed slurry before it sets. The vibrating plate is pivotally mounted on the web production line so it can float over the panel surface during use, but be raised off the line when not in use.

Embedment roll device

Abstract: An embedment device (60) includes a first integrally formed elongate shaft (62) rotatably secured to the support frame (12) and having a first plurality of axially spaced disks (64) axially fixed to the first shaft, a second integrally formed elongate shaft (66) rotatably secured to the support frame and having a second plurality of axially spaced disks (68) axially fixed to the second shaft, the first shaft being disposed relative to the second shaft to be horizontally aligned and so that the disks intermesh with each other, and wherein, when viewed from the side, peripheries of the first and second pluralities of disks overlap each other.

Wedge-Type Expansion Anchors in High-Performance Concrete

Abstract: Since the mechanical properties between ordinary and high-performance concrete (HPC) differ greatly, the performance of an anchor in each type of concrete will differ as well. This paper reports on experiments that were performed to evaluate the mechanical response of torque-controlled expansion anchors embedded in HPC, subjected to tensile loads. The variables include compressive strength of the concrete, addition of steel fibers, and embedment length of the anchors. The embedment length influences the results in terms of both strength and ductility, while fibers strongly affect only the post-peak behavior and the failure pattern. By reducing the embedment length, a reduction in the ultimate load and a more brittle behavior was observed. The specimens without fibers also exhibited a more brittle behavior. Fibers also had a strong influence on the cracking pattern and on the size of the concrete cone. A comparison between the results of HPC and normal-strength concrete and the pullout load given by the manufacturer shows that HPC leads to an increase of the strength. A comparison between standard design equations and experimental results is provided in order to suggest some proposals for the extension of the model prediction on normal-strength concrete to HPC. Future research is needed to suggest reliable relationships to be used in HPC and for different anchor types.

3D FE Analysis of Anchor Bolts with Large Embedment Depths

Abstract: In engineering practice, headed anchors are often used to transfer loads into reinforced concrete members. Experience, a large number of experiments as well as numerical studies of anchors of different sizes confirm that fastenings are capable to transfer a tension force into a concrete member without using reinforcement. Provided the steel strength of the stud as well as the load bearing area of the head are large enough, a headed stud subjected to a tensile load normally fails by cone shaped concrete breakout. To better understand the crack growth and to predict the concrete cone pull-out failure load of headed studs for different embedment depths a number of experimental and theoretical studies have been carried out. Due to the fact that the tests with large embedment depths are rather demanding, most of the experiments were carried out for embedment depths that range from hef = 100 to 500 mm. For anchorages with larger embedment depths, which are relatively often used in the engineering practice, there are almost no experiments available. Consequently, for these fastenings the influence of the geometry (edge influence, influence of the anchor spacing, influence of the thickness of the concrete member, etc.) and type of loading (tensile, shear or combined) on the failure load and failure mode is not confirmed by experiments. In last two decades significant work has been done in the development and further improvement of numerical tools. These tools can be employed in the analysis of non-standard anchorages. Unfortunately, the objectivity of the numerical simulation depends very much on the choice of the material model. Therefore, the numerical results should be confirmed by experiments. In the present paper the results of a finite element study of fastenings which were designed for the application in nuclear power plants in Korea are presented. In the three-dimensional finite element analysis the code MASA, which is based on the microplane model for concrete, is performed. The numerical investigations were actually a part of an extensive test program. The results of the study were used to support a test program that had to be carried out for a non-standard fastening systems in which the anchor bolts with embedment depths that varied from 0.5 m to over 1.0 m were employed. Furthermore, the head sizes of the anchor bolts were much larger than that used in the standard pull-out experiments. The analysis was carried out for tensile and shear loads. For both cases the edge influence and the influence of the reinforcement was investigated. The numerical results are compared with test results, which were obtained afterwards. Therefore, the numerical study was a real benchmark test for the finite element code used in the numerical investigations. The calculated failure modes and failure loads shows very good agreement with measured data. It is interesting to observe that for some cases the measured and calculated data shows disagreement with the data obtained using current design code recommendations.

Behavior of Rigid Footings on Gravel under Axial Load and Moment

Abstract: A laboratory testing program was conducted to study the settlement and rotation response of rigid square footings under combined axial load and moment. A total of 17 tests were performed in which the size of the footing, footing embedment, axial load, and load eccentricity were changed. The test soil consisted of a fine and well-graded gravel contained in a box with dimensions: 1.52 x 1.52 m (5 x 5 ft) cross section and 0.91 m (3 ft) deep. The soil was compacted in layers 150 mm (6 in.) thick to an approximate relative density of 84%. In each test, the axial load, moment, settlement at the center of the footing, and footing rotation were measured. Concentrically loaded footings with different sizes exhibited a similar behavior in terms of the applied stress-normalized settlement (settlement divided by size of footing) response. The analytical model proposed was based on such normalized response as an input, and it was calibrated to account for the change in soil stiffness with confinement. The formulation captures the inherent nonlinear deformations of the soil with load and the coupled nature of settlements and rotations of footings under axial load and moment. The model was tested by comparing calculated values with laboratory measurements from tests not included in its calibration. The comparisons showed a satisfactory agreement between calculations and measurements, bringing confidence in the analytical formulation proposed and the methodology used.

Strut-and-tie model for development of headed bars in exterior beam-column joint

Abstract: Headed bars have been proposed as an alternative to hooked bars in anchoring longitudinal reinforcement terminated within exterior or corner beam-column joints. This paper proposes a strut-and-tie model (STM) for the development of headed bars in an exterior beam-column joint that investigates realistic force transfer by headed bars within the joint. The tensile force in a headed bar is considered to be developed by head bearing together with bond along a partial embedment length. The model consists of struts with nodal zones for head bearing and fan-shaped stress fields for bond resistance along the bonded length. The model shows how to decompose the tensile force developed in headed bars into direct strut action and fan action and their effects on joint shear strength. Tests on exterior beam-column joints without transverse reinforcement, and that neglect axial forces due to self-weight and live load, are intended to focus on the effect of anchorage capacity of headed bars on joint shear strength. Findings show that the STM explains two different load transfers from the headed bar to the exterior beam-column joint. The proposed model is also capable of considering not only the head size and material strengths, but also the structural configurations of the system under consideration. Finally, it is applicable to anchorage zones of headed bars with various geometries and boundary conditions.

On mechanical behavior of traditional timber shear wall in Taiwan II: simplified calculation and experimental verification

Abstract: In the previous report of this ongoing study, results of an extensive field survey were collated and a theoretical model was proposed to predict the mechanical behavior of timber shear walls of traditional design in Taiwan. The initial objective of the present report was to propose a simplified calculation method for estimating the initial stiffness and yield strength of traditional timber shear walls. Based on the results of the field survey, a total of 15 full-scale specimens were tested to verify the theoretical model and simplified calculation proposed previously. Good agreement was found from comparison of analytical and experimental results. The results of this study show that the friction behavior between board units and beams plays the major role in resisting the lateral force applied on the timber shear wall, followed by the resistance supplied by embedment. The resistance provided by bamboo nails is minor due to the small section. Another trend found was that for set dimensions of a timber shear wall, the board width can be increased to obtain higher stiffness and strength of the shear wall.

Embedment device for fiber reinforced structural cementitious panel production

Abstract: An embedment device for use in a cementitious panel production line such as a structural cementitious panel (SCP) production line wherein hydraulic cement slurry is transported on a moving web on a support frame, and chopped fibers are deposited upon the slurry. The device includes as one embodiment, a wire grid structure mounted on a reciprocating shaft driven by a piston which moves the grid down into the slurry and then up out of the slurry transverse of the travel of the slurry layer on the web. An alternative embodiment device includes a grid cell structure with thin walls extending upward from the grid surface in contact with the slurry that is moved up and down in a reciprocating motion transverse of the travel of the slurry layer on the web. The intermeshing relationship of the grid cell with the fiber and slurry enhances embedment of the fibers into the slurry and also prevents clogging of the device by fibers and prematurely set slurry particles.

Mechanical Performance of Curved FRP Rebars: Part I - Experimental Study

Abstract: This paper summarised an experimental programme undertaken at the University of Sheffield to examine the performance of curved FRP composites as structural reinforcing materials. Direct pullout tests were conducted on thermoplastic composite strips embedded in concrete cubes. A total of 47 specimens and 19 different configurations were tested. The parameters that were investigated included geometry of the bend, surface treatment, embedment length and concrete strength. Results on the pullout tests on curved FRP composites indicated that the capacity of the composite could be as low as 25% of the ultimate tensile strength of the material parallel to the fibres. Based on the test results, it is recommended that the bending radius of 4 times the bar thickness could be used to guarantee the strength of composite to 40% of the strength parallel to the fibres.

Stability of plate anchors in NC clay

Abstract: Soil anchors are commonly used as foundation systems for structures requiring uplift or lateral resistances,such as transmission towers,sheet pile walls and foundations of floating offshore platforms.This paper applies displacement finite element analysis to estimate the ultimate pullout capacity of pre-embedded inclined strip anchors in normally consolidated(NC) clay.Results are presented in the familiar form of break-out factors,which are based on various soil strength profiles,anchor embedment ratios and pullout inclined angles.The influences of the soil self weight,soil strength gradient and anchor base type on the pullout capacity are discussed.The continuous pullout analysis,in which Remeshing and Interpolation Technique with Small Strain model(RITSS) is applied,shows that the ratio of the vertical stress to the soil shear strength plays an important role in the separation underneath the plate when vented base is assumed.

Three-dimensional FE analysis of headed stud anchors exposed to fire

Abstract: In the present paper a transient three-dimensional thermo-mechanical model for concrete is presented. For given boundary conditions, temperature distribution is calculated by employing a three-dimensional transient thermal finite element analysis. Thermal properties of concrete are assumed to be constant and independent of the stress-strain distribution. In the thermo-mechanical model for concrete the total strain tensor is decomposed into pure mechanical strain, free thermal strain and load induced thermal strain. The mechanical strain is calculated by using temperature dependent microplane model for concrete (Ožbolt et al., 2001). The dependency of the macroscopic concrete properties (Young’ s modulus, tensile and compressive strengths and fracture energy) on temperature is based on the available experimental database. The stress independent free thermal strain is calculated according to the proposal of Nielsen et al. (2001). The load induced thermal strain is obtained by employing the bi-parabolic model, which was recently proposed by Nielsen et al. (2004). It is assumed that the total load induced thermal strain is irrecoverable, i.e. creep component is neglected. The model is implemented into a three-dimensional FE code. The performance of headed stud anchors exposed to fire was studied. Three-dimensional transient thermal FE analysis was carried out for three embedment depths and for four thermal loading histories. The results of the analysis show that the resistance of anchors can be significantly reduced if they are exposed to fire. The largest reduction of the load capacity was obtained for anchors with relatively small embedment depths. The numerical results agree well with the available experimental evidence.

Structural Research on Embedment of a Bare Deflated Spiral Case

Abstract: Complete bearing spiral case has not been applied to large power stations in China so far. The proposal of applying complete bearing spiral case necessitates an analysis of the reliability of the spiral case structure and the security of units under various working conditions. In combination with practice of a project, this paper presents a three-dimensional nonlinear finite element static analysis of the concrete using a concrete smeared crack model by means of the well-known finite element method (FEM) software ABAQUS. The stress distribution of the spiral case and reinforcing bars, the range of damages in surrounding concrete, and the displacement of structure are quantified. The computational results indicate that the embedment method ensures the structure’s safety in strength. At the same time, the result shows that this embedment is a kind of preponderant method for embedment in aspects of economy and technique of construction, and the application of this embedment method to the hydropower station is feasible provided that some proper engineering measures are taken to constrain the width of the concrete in accord with the code’s requirements. The paper proves the security and reliability of the structural design of spiral case in hydropower station accordingly.

Embedment structure of optical fiber and embedment method for enhancing cohesive force between optical fiber and packaging material

Abstract: A method for burying optical fiber and its packaging material includes coating adhesive uniformly on surface of optical fiber to be buried and optical fiber sensing element, soaking it in silane coupler after said adhesive is cured, drying up coupler on optical fiber in the air then positioning it in mould, setting portion to be buried on central axle of mould and adding silane coupler in packaging material to make curing-forming. The burying structure for realizing said method is also disclosed.

Wire fabric laths

Abstract: Furred woven wire fabric lathing is provided which incorporates a plurality of wires twisted together forming a wire mesh with a major portion of the wire in a plane with a portion of the mesh comprising furr portions extending out of the plane of the mesh and configured for embedment in plaster upon application of plaster to the wire mesh.

Study of dynamic characteristics of a giant spiral case with different embedment manners

Abstract: With the increase of unit capacity of hydro-generators,the spiral case becomes a giant hydraulic structure with very high HD value,but its dynamic characteristics which should be paid particular attention to in the design stage have rarely been touched both in theory and practice.Three typical manners of steel spiral casing(SC) embedded in concrete,i.e.,manner of SC embedded in concrete with soft cushion layer(MSCL),manner of SC embedded in concrete while holding a certain water head inside SC(MHWH) and manner of SC embedded directly in concrete(MD),were researched on the performances of a giant spiral case performed by 3-D finite element methods.To optimize the design of the giant spiral case,free-vibration and stiffness behaviors,dynamic responses under water pressure pulsation and anti-fatigue performance were analyzed and compared respectively.Results show that the influence of different embedment manners on the static and dynamic performances of the powerhouse is minor and should not be the control factor while selecting embedment manners.