Showing papers on "Embedment published in 2002"

Pull-out behaviour of hooked steel fibres

Abstract: A programme of research is described that has investigated the fracture of steel fibre reinforced sprayed concrete under flexural load, with the aim of developing a stress-profile model to predict flexural behaviour in the form of a load-deflection response. This paper reports the work associated with establishing the pull-out characteristics of hooked end fibres. The effects of matrix strength, fibre embedment length and orientation are described, together with the interaction of these parameters. The relationships established can be used to model the tensile response of a beam at varying crack width and hence form a key part of the stress-profile for predicting residual flexural strength, which is an essential requirement of a much needed design rationale for steel fibre concrete.

Bearing capacity of strip foundation on geogrid-reinforced sand

Abstract: Results of small-scale laboratory model tests to determine the ultimate bearing capacity of a strip foundation supported by sand with multiple layers of geogrid reinforcement are presented. Tests were conducted with only one type of geogrid and a sand compacted to one relative density. The embedment ratio of the foundation was varied from zero to 0.6. It is found that, for the given reinforcement-depth ratio, the bearing capacity ratio with respect to ultimate load increases with embedment. The relationship between the bearing capacity ratio at ultimate load and at limited levels of settlement (less than or equal to 5% of foundation width) is also presented. The bearing capacity ratio at limited levels of settlement is smaller than the value at ultimate load.

Bearing properties of engineered wood products I : effects of dowel diameter and loading direction

Abstract: The embedment tests of laminated veneer lumber (LVL) with two moduli of elasticity (MOE; 7.8 GPa and 9.8GPa), parallel strand lumber (PSL), and laminated strand lumber (LSL) were conducted in accordance with ASTM-D 5764. The load-embedment relation for each of these engineered wood products (EWPs) was established. The directional characteristics of bearing strength (σe), initial stiffness (ke), and effective elastic foundation depth were obtained from the tested results. The effective elastic foundation depth (α=E/ke,E = MOE), based on the theory of a beam on elastic foundation, was obtained from theke and MOE. An α of 90° (perpendicular to the grain) was calculated by dividingE90 [MOE of 90° from the compression test, but MOE of 0° (E0), parallel to the grain, obtained from the bending test] byke90, the initial stiffness of 90°. This study aimed to obtain the bearing characteristics of each EWP, taking into consideration their anisotropic structures, for estimating the fastening strength of a dowel-type fastener. The relations between the bearing coefficients (δe,ke,α) on the loading direction and dowel diameter were established from the load-embedment curves. Based on the results of the embedment test, tested EWPs showed different tendencies in all directions from wood and glued laminated timber.

Minimising particle contamination at abrasive waterjet machined surfaces by a nozzle oscillation technique

Abstract: In this paper, the experimental study and microstructure analysis using scanning electron microscope (SEM) and advanced surface analysis techniques were performed to quantitatively evaluate particle embedment at abrasive waterjet (AWJ) generated mild steel surfaces. It is found that particle embedment depends on cutting depth, traverse speed and pump pressure. A new nozzle oscillation technique was applied to the AWJ cutting process in order to reduce contamination by embedded particles. It was found that, under identical input cutting conditions, the particle embedment at the surface could be reduced up to 200% by using the new nozzle oscillation technique compared to the traditional AWJ technique.

Seismic performance and retrofit of steel pile to concrete cap connections

Abstract: This paper looks at the seismic-performance of steel pile-to-pile cap connections representative of construction practice in the eastern U.S. Two perspectives are considered. The first is the seismic vulnerability of existing pile cap connections, where the embedment depth of the pile inside the cap beam is small. An initial experimental study, therefore, was conducted for testing 2 specimens that represented existing exterior connections under cyclic lateral loading. The second perspective is the seismic design requirements for strong cap beam-to-pile connections. Hence, a theory assuming a linear distribution of stresses along the connection embedment depth was developed, and comparisons with a finite element model were performed. A second experimental program was conducted to evaluate the performance of specimens retrofitted in accordance with the theoretical model developed in this study. Results of the second experimental study validated the proposed retrofit strategy.

Constitutive modelling of aggregate interlock in concrete

Abstract: A model for formed cracks in concrete is presented. The model can be used in isolation for existing cracks or linked with other damage or plasticity models and applied once a crack has fully formed. It can be applied directly to interface finite elements or used to control the behaviour of crack planes in more general constitutive models that are applied to 2D and 3D continuum elements. The focus of the present development is on aggregate interlock and crack closing behaviour, which is examined from available experimental data. A contact function is derived and is used to differentiate between three contact states. These states are named open, where there is no contact, interlock, for which the stresses depend upon the nearest distance to the contact surface and closed, for which the stresses depend upon the relative displacements directly. The model is developed within an elasto-plastic framework using effective stresses, which are related to the total stresses via a contact proportion function. The relationship between the effective normal and shear yield stresses is found to be parabolic and the yield shear stress to be dependent upon the opening and embedment displacements. The performance of the model is assessed against experimental data from shear-normal tests and it is concluded that the model is able to represent the key characteristics of the behaviour of formed cracks in concrete. Copyright © 2002 John Wiley & Sons, Ltd.

Seismic horizontal pullout capacity of vertical anchors in sands

Abstract: The problem of finding the horizontal pullout capacity of vertical anchors embedded in sands with the inclusion of pseudostatic horizontal earthquake body forces, was tackled in this note. The analysis was carried out using an upper bound limit analysis, with the consideration of two different collapse mechanisms: bilinear and composite logarithmic spiral rupture surfaces. The results are presented in nondimensional form to find the pullout resistance with changes in earthquake acceleration for different combinations of embedment ratio of the anchor (lambda), friction angle of the soil (phi), and the anchor-soil interface wall friction angle (delta). The pullout resistance decreases quite substantially with increases in the magnitude of the earthquake acceleration. For values of delta up to about 0.25-0.5phi, the bilinear and composite logarithmic spiral rupture surfaces gave almost identical answers, whereas for higher values of delta, the choice of the logarithmic spiral provides significantly smaller pullout resistance. The results compare favorably with the existing theoretical data.

Increased suture embedment in tendons: an effective method to improve repair strength.

Abstract: We evaluated the effect of length of suture embedment within tendons on the tensile strength of repaired tendons. Thirty fresh pig flexor tendons were divided into three groups and subjected to repairs with the Halsted tendon sutures in which 1/3, 1/2, and 2/3 of the length of the longitudinal sutures was embedded within the tendons. The repaired tendons were pulled to complete failure by an Instron tensile testing machine. The 2 mm gap-formation force, ultimate strength, stiffness, and energy to failure were greatest when 2/3 of the suture length was embedded within the tendon. The results indicate that suture embedment is an important contributor to the tensile properties of the repair, and that increase in length of suture embedment is an effective way to strengthen tendon repairs.

Mechanical properties of self-tapping screws and nails in wood

Abstract: This paper presents results of a research programme investigating the mechanical properties of self-tapping screws and nails in wood. The programme consisted of deformation-controlled tests to determine embedment strength, withdrawal strength, pull-through strength, bending capacity of individual screws, shear strength of screwed and nailed wood–wood connections, and shear strength of screwed wood–steel connections. All test specimens showed ductile behaviour. Based on the results from the first four types of tests, a simple calculation model for the shear strength of screwed wood–wood and wood–steel connections was set up and compared with test results from the last two types of tests. The calculation model took dowel action and friction (wood–wood and wood–steel) into account and showed excellent agreement with the test results.Key words: connections, screws, nails, shear strength, embedment strength, withdrawal strength, pull-through strength.

Centrifuge model tests on embedded retaining walls supported by earth berms

Abstract: Earth berms are often used for the temporary support of embedded retaining walls, but there is a lack of information concerning the factors that influence their behaviour. In this paper, the results of a series of plane strain, 1:100 scale centrifuge model tests on berm-supported embedded retaining walls in overconsolidated clay are presented. It is shown that earth berms will probably be more effective in reducing soil and wall movements than an increase in the depth of wall embedment; that an increase in the depth of embedment of a wall of given stiffness supported by a berm of a given size will lead to an increase in wall bending moments, but only a small reduction in wall and soil movements; and that the presence of the berm in limiting wall movements and possibly preventing collapse becomes more significant as drainage occurs.

Retrievable suction embedment chamber assembly

Abstract: A method and apparatus for installing conductor casing for offshore oil wells. In the preferred embodiment of the present invention, a retrievable suction embedment chamber assembly drives a string of casing into the seafloor using hydrostatic pressure by releasably forming a seal around the casing to be driven and using a pump to lower the pressure inside the chamber. The assembly may then be flooded with seawater, released from the casing, then repositioned at a higher point on the casing, and the embedment process repeated. The assembly may also be used to embed several subsequent strings of casing in series.

The performance of pressure cells for sprayed concrete tunnel linings

Abstract: The paper examines the factors that affect the performance of tangential cells embedded in shotcrete tunnel linings. New data, derived from field monitoring, numerical modelling, and calibration tests carried out to simulate the embedment and crimping processes, are presented. These suggest that although well-designed embedded total pressure cells will have cell action factors close to unity, they cannot be assumed to provide reasonable estimates of the stresses within sprayed concrete linings, unless the influences of installation effects, temperature changes, shrinkage and subsequent crimping can be taken into account.

Shear strength of reinforced concrete deep beams with end anchorage failure

Abstract: This paper focuses on the shear strength of deep beams combined with anchorage failure, based on upper bound solutions in the theory of plasticity. The solutions showed that the shear strength combined with anchorage failure is lower than other shear strength due to web crushing in some range of design parameters. The effects of shear span ratio, ratio of embedment length of bars beyond support to beam depth, and vertical reinforcement ratio on the failure modes and strengths were also investigated. An experiment was performed to compare with the plastic solutions and displayed good agreement with those of theoretical results. Lastly, this paper proposes a range of design parameters for ductile failure mode of reinforced concrete deep beams, which ensures a safe detailing of end anchorage for the flexural failure of deep beams.

Earth retaining pile and earth retaining method using the same

Abstract: PROBLEM TO BE SOLVED: To provide an earth retaining method for effectively utilizing a site area by setting up an earth retaining piles changing a cross sectional performance in the longitudinal direction near a site boundary, and utilizing an upper pile with small cross section performance to enlarge a construction of an upper part from the depth of embedment. SOLUTION: An upper pile 12a made of H-section steel making a reference cross section or less is joined on a lower pile 12a made of H-section steel making the reference cross section of the depth D of the embedment, and the earth retaining pile 12 changing the cross section performance in the longitudinal direction is prepared. An end plate is arranged on the opposite ends of the upper and lower piles 12a and 12a, and a splice plate is fixed on flange faces of the upper and lower piles of a side receiving a side pressure. The pile 12 is set up at a position within a site area boundary B, and a horizontal lagging is fitted between the piles 12. After an underground area is excavated while an earth retaining wall is formed, an underground building frame outer layer 16 is constructed along the inner flange face of the upper pile 12b lessening the cross section performance of the lower pile. COPYRIGHT: (C)2004,JPO

Flexible tube of endoscope and method for manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To change flexibility in the curving direction of the flexible tube with simple constitution in its axial direction by changing the degree of embedment of resin layers to be laminated to a cylindrical net body into the cylindrical net body. SOLUTION: The flexible tube 10 is constituted by laminating the cylindrical net body 12 and an outer cover layer 13 to a spiral tube 11 consisting of double spirals 11a and 11b. The resins among the resin layers constituting the outer cover layer 13 are embedded to be penetrated into the meshes 12S of the cylindrical net body 12 and the amount of the resin embedment is changed toward the axial direction. The segments where the amount of the resin embedment is little are low-hardness flexible portions, and if the amount of the resin embedment is increased, high-hardness flexible portions are formed. Further, when the resins are embedded into spaces S by pitch intervals P of the spirals 11a on the outer side from the meshes 12S of the cylindrical net body 12, not only the hardness in a curving direction increases additionally but the curving angle is limited as well. COPYRIGHT: (C)2003,JPO

Buckling of piles in a layered elastic medium

Abstract: The stability of piles that are supported laterally along part of their length or their entire length by a layered elastic medium is investigated for the case in which each layer has the general power distribution of the coefficient of horizontal subgrade reaction. The potential energy method is used to develop the model. The deflection functions for nine different boundary condition combinations developed using the Rayleigh‐Ritz method by Gabr et al. (1997) are adopted in the study. Numerical examples for effects of pile boundary conditions, soil subgrade reaction, pile embedment, axial load transfer, and layered soil conditions on the buckling capacity of piles are also presented.

Failure Analysis of Compressor Blade of vpical Fighter-class Aero-engine-A Case Study

Abstract: Failure of second-stage compressor rotor blade of a typical Russian fighter-class aero-engine has resulted in few accidents and many incidents. Apart from this, during manufacturing stage there was high rejection rate of this rotor blade in vibrational fatigue tests. Metallurgical investigations of the failed rotor blade reveals that the mode of failure'is fatigue. The various reasons of this fatigue crack are micro-inclusion, silica embedment and hydrogen attack. This was analysed from the three different approaches, namely, theoretical stress analysis, basic design and quality control. To contain the possibility of silica embedment and hydrogen attack, sand electro-corrundum blasting and measure-replaced blasting have been taken to control hydrogen embedment.

Seismic performance and retrofit of steel pile to concrete cap connections

Abstract: This paper looks at the seismic-performance of steel pile-to-pile cap connections representative of construction practice in the eastern U.S. Two perspectives are considered. The first is the seismic vulnerability of existing pile cap connections, where the embedment depth of the pile inside the cap beam is small. An initial experimental study, therefore, was conducted for testing 2 specimens that represented existing exterior connections under cyclic lateral loading. The second perspective is the seismic design requirements for strong cap beam-to-pile connections. Hence, a theory assuming a linear distribution of stresses along the connection embedment depth was developed, and comparisons with a finite element model were performed. A second experimental program was conducted to evaluate the performance of specimens retrofitted in accordance with the theoretical model developed in this study. Results of the second experimental study validated the proposed retrofit strategy.

Anchor installed in seabed

Abstract: PROBLEM TO BE SOLVED: To improve durability of an anchor for preventing it from moving by a shock of waves and stably installing it in the seabed SOLUTION: This anchor is constructed by covering the surface of concrete C with a closed-structure metal plate A bottom plate 1 covering the concrete C is provided with a plurality of embedment projection parts 6 protruded downward Each of the embedment projection parts 6 is provided with a locking part 6A, and when the embedment projection parts 6 are buried and anchored in the seabed, the anchor is firmly fixed to the seabed

Failure assessment of anchor bolts by means of nonlinear finite element analyses

Abstract: Numerical simulations in structural engineering require the use of realistic material models. As far as simulations of concrete structures are concerned, material models have to account for different degradation processes within the cement matrix-aggregate composite. In uniaxial tension experiments, highly localized tensile cracks result in brittle failure. In the low-confined compression regime, a region of transition from brittle to ductile fracture exists, separating brittle softening behavior from ductile failure regimes characterized by little or no degradation of strength. In this paper, the Extended Leon Model (ELM) is considered for the description of failure of concrete. It accounts for the dependence of strength on the Lode angle. Moreover, the influence of confinement on the ductility of concrete is considered by means of a pressure-dependent ductility function. The fictitious crack concept which is employed for the calibration of the ELM is reformulated for application to axisymmetric problems such as failure assessment of anchor bolts. The ELM is applied to the simulation of an anchor bolt with a small embedment depth. Failure of this type of anchors is characterized by the development of a cone-shaped failure surface.

3-hinge embedment tunnel

Abstract: PROBLEM TO BE SOLVED: To provide a 3-hinge embedment tunnel, which can be applied to a comparatively soft ground and can be executed efficiently and economically. SOLUTION: The 3-hinge embedment tunnel has a tunnel wall assembled by connecting the upper ends of a pair of slab materials 2 by a hinge 21 and independent footings 3 bearing the lower ends of the tunnel wall by the hinges, and the independent footing 3 is constituted by unifying a base slab 5 extended to the inside and the outside of the tunnel wall and a wall slab 4 extended in the tunnel axial direction crossing the base slab 5 at a proper position containing a base slab end on the outside.

Fracture Analysis of Beam-Column Joints due to Bond-Slip Mechanism

Abstract: In order to predict a bond-slip behavior of the reinforcement bar in inner joint in a ‘seismic’ reinforced concrete frame structure, experiments and numerical analyses were conducted. A reinforced cylinder with a centrally embedded deformed rebar served as a simple joint model. The bar was fully loaded on a protruding end. Cyclic loading was applied neither in the experiments nor in the numerical analysis since the first inten-tion was to numerically simulate the experiments. Bond-slip mechanism was studied as an axi-symmetrical 2-D problem using DIANA Finite Element Analysis. The input data for the numerical analysis were used from the previously conducted experiments. The influence of the variations in the bar embedment length (full/local) as well as the addition of a different percentage of polypropylene fibers in fiber reinforced concrete on bond-slip, bond stress, deformation and cracking patterns was examined. The results from the numerical analysis are presented.

Experimental analysis on the bond-slip properties of steel reinforced concrete structures

Abstract: In this paper, according to the bond-slip behaviors of steel reinforced concrete, a new type of steel concrete slip transfer were designed, and two type of push-out test were conducted for studying the bond-slip properties of SRC (steel reinforced concrete) structures. In the push-out tests, the strains of steel flanges and webs, and the local slip were both measured by experimental method, and the P-S curves of the experimental results, the distributions of the strain of the steel flanges and webs, the distributions of the local slip along the embedment length were obtained. The failure mechanism and the distribution of cracks were also analyzed. All these will be helpful to the further experiments, researches and theoretic studies on the bond-slip behaviors of SRC structures.

Performance test of Chemical Anchor Bolts for Concrete Repair

Abstract: A research on the performance of retrofit anchors was conducted using adhesives for rehabilitation From the pull-out tests of the chemical anchors, the effect of the hole diameter, spacer, temperature, moisture, embedment depth, and aging time were investigated The spacer did not directly increased the pull-out load hilt increased post-yielding resistance therefore the ductility of the retrofit anchors When the hole was cleaned and dried after the immersion, the pull-out load was greatly increased compared to the wet hole A design equation was unposed depending on the embedment depth of the anchor bolt

Comportement sous charge des ancrages avec vis d'ancrage

Abstract: SUMMARY Concrete screws are a relatively new fastening system. Their main advantage compared to traditional post-installed fastening systems is a quick and easy installation. A hole is drilled into the concrete and threads are cut in the concrete by the screw as it is installed. Concrete screws transfer tensile loads into the base material by mechanical interlock of the threads. Due to their load-bearing mechanism, concrete screws with a technical approval of the DIBt can be used for fastenings in cracked and non-cracked concrete. The typical failure mechanism for concrete screws is concrete-cone failure. With increasing embedment depth the ratio of the depth of the concrete failure cone to the embedment depth decreases. The failure load of concrete screws with continuous threads along the entire embedment depth increases proportionally to hef 1,5 (hef = effective embedment depth), but it is about 20 % smaller than the failure load of expansion and undercut anchors with the same embedment depth. In order for concrete screws to function properly, the threads cut into the wall of the drilled hole must not be damaged during the installation. This requirement is achieved by using the embedment depth defined in the Technical Approvals.