Showing papers on "Embedment published in 1998"

Influence of rigidity on laterally loaded pile groups in marine clay

Abstract: Pile-supported marine structures are designed for significant amounts of lateral load. In this paper, the influence of parameters like flexural rigidity of pile material, embedment length of pile, and arrangement of piles with respect to the direction of loading on the behavior of laterally loaded pile groups has been studied through an experimental program. The results obtained from lateral load tests carried out on model pile groups arranged at different spacings and embedded in a marine clayey bed are presented and discussed. The results indicate that the lateral load capacity of the pile group depends mainly on the rigidity of pile soil system for different arrangements of piles within a group. This is further substantiated by a simplified finite element analysis bringing in the differences in passive resistance. The group efficiencies under lateral loading obtained from the present investigation are found to be in good agreement with the predictions of earlier researchers.

Fracture Width and Embedment Testing in Soft Reservoir Sandstone

Abstract: A new computer-controlled laboratory technique has been developed to measure propped fracture width and embedment in weakly consolidated cores or unconsolidated sands under simulated down-hole conditions. Previously laboratory studies on cores have determined embedment in hard rocks where embedment is normally limited to 50% of the proppant grain diameter. Several studies also indicated the importance of embedment with one monolayer or less of proppant coverage. The effects of water saturation and fracture fluid filtrate on formation softness and embedment have not been previously published. Consequently, the objectives of the current paper are to extend previous research results to include soft weakly-consolidated cores and unconsolidated sands with multiple proppant layers. The influence of water saturation and dynamic fluid leakoff on embedment are also investigated. The current investigations indicate that embedment becomes a problem when the Brinell hardness of the formation is less than about 20 kg/mm{sup 2} or when the static Young`s modulus of formations cores is less than about 2 million psi (13 GPa). Embedment has been determined for cores with static Young`s moduli between 0.1 and 1.4 million psi (0.7 to 9.6 GPa). In soft and wet sandstone, embedment can reduce fracture width up to 60% or more formore » proppant concentrations of 2 lb/ft{sup 2}. For unconsolidated sands, embedment is influenced by fracturing fluid type, water saturation and down-hole conditions. Cyclic loading conditions associated with well shut-ins also increase embedment in unconsolidated sands. Test data on formation cores from South Texas, New Mexico, the North Sea and the Gulf of Mexico arc reviewed and discussed. Current fracture design programs often neglect embedment problems in calculating fracture width and assume that most formations are hard as steel.« less

Monotonic and fatigue loading behavior of quasi-isotropic graphite/epoxy laminate embedded with piezoelectric sensor

Abstract: This study investigated the effects of embedding piezoelectric lead zirconate-titanate (PZT) sensors on the tensile strength and fatigue behavior of a quasi-isotropic graphite/epoxy laminate as well as the embedded sensor's voltage degradation under these loading conditions. For this, AS4/3501-6 laminates were fabricated with a lay-up where PZT was inserted into a cut-out area in the two middle plies. Monotonic tensile tests showed that both the average ultimate strength and Young's modulus of the tested laminate with or without PZT were within 4% of each other. The fatigue lives with and without PZT were very close to each other as well. Overall, the sequence of damage in this study agreed with previous investigations of the damage mechanisms for quasi-isotropic laminates. The ranges of modulus reduction in both cases, with and without PZT, were within 5 to 15% of each other during fatigue loading. Delamination growths in both cases during most of the fatigue life were also very comparable to each other. Further, this study showed that the embedded PZT would maintain a steady voltage output indefinitely when mechanically cycled within its operational strain limit. It thus appears that the embedment of PZTs in a cut-out area of plies of quasi-isotropic graphite/epoxy laminates would not affect their monotonic tensile and fatigue behavior.

Finite-Element Model for Nailed Wood Joints under Reversed Cyclic Load

Abstract: This paper presents a nonlinear finite-element model for predicting the load-slip response of a single-shear nailed wood joint under reversed cyclic loading. Of particular interest is the post-yielding region of the load-slip response at which the deformation of the nail is large. In the proposed theory, the nail is modeled using a finite beam element approximation that incorporates the effects of large deformation and hysteretic nature of the stress-strain behavior of the material. The embedment behavior of wood under the action of a nail is described through a hysteresis model developed by the writers. In addition the effects of shear deformation in the nail and friction between nail and wood are incorporated into the model. Results from material tests conducted to characterize the embedment behavior of wood and stress-strain curve of nail material, and from joint tests to verify the finite-element model, are presented. A comparison of test data with model predictions demonstrates the validity of the mo...

Changes in layer organization of Na- and Ca-exchanged smectite materials during solvent exchanges for embedment in resin

Abstract: The embedding process designed for impregnation i resin of hydrated clays for TEM observation comprises four steps of exchange by solvents and resin. Clay pastes of Naand Ca-exchanged Wyoming smectite were prepared at low suction pressures (3.2 and 100 kPa, respectively), and their layer organization was examined at different steps of the embedding p'rocess. X-ray diffraction was used in order to follow the evolution of layer distances and particle orientation during solvent exchanges. At 3.2 kPa as well as at 100 kPa the water-saturated clay exhibits interlayer distances of 1.9 nm. Alter methanol exchange, interlayer distrnces collapsed to 1.6-1.7 nm. With l,2-epoxypropane and resin saturation, clays behave in a similar way as with methanol. Examination of layer-stacking coherency by measurement of peak widths indicates that the fust exchange by methanol is the most critical step in the embedding process because it induces reduction of the layer distances and aggregation' especially in the case of dilute Na-exchanged clay. The final polymerization of resin inroduces further slight changes in organization of the clay.

Investigation on the bond of fiber reinforced polymer (frp) rebars in concrete

Abstract: Bond strength of fibre reinforced polymer (FRP) rebars was experimentally investigated in this study, and compared to the bond strength of steel rebars. A total of sixty four reinforced concrete beams were tested. Four nominal diameters of FRP and steel rebars, namely 12.7, 15.9, 19.1 and 25.4 mm and three embedment lengths, 6, 10 and 16 times the rebar diameter were used. The beams were reinforced with two types of FRP rebars made of glass fibres and polyester binder. Three concrete depths of 200, 600 and 1000 mm were investigated in the eighteen pull-out specimens. Results of the tests indicated that the applied tensile load approached the tensile strength of rebars as the embedment length increased. The average maximum bond strength of the FRP rebars varied from 5.1 to 12.3 MPa depending on the diameter and the embedment length. The GFRP rebars showed lower bond strength value compared to steel rebar. A modification factor of 1.29 is recommended for computing the development length, to account for the top bar effect.

The embedment of process consultation in strategy formulation

Abstract: The main goal of this research is focused on increasing the probability that strategic decisions will be implemented. The dissertation describes the strategic decision-making process followed by the top executive teams of two organisations, within a consultation framework employing the Process Consultation approach. A particular form of SWOT analysis (SWOT Positioning) was performed as a platform for interventions. It also comprised a basis for the employment of other analytical and creative tools. In constructing this research, it was hoped that the combination of Process Consultation with SWOT Positioning in this manner would prove helpful in achieving the research goal. This research found that the likelihood of implementation of decisions seemed greater following the current consultation process than in the two organisations’ previous experience with ‘expert’ and ‘doctor’ consultants. Indeed, by-product decision implementation had already begun. The preparation for general implementation of strategic decisions and the declaration of commitment on the part of team members exceeded that of the same organisations in the past. The research cannot definitively show actual implementation, as that stage was not within its scope. However, both teams indicated a sense of ownership of and responsibility for the decisions, which had been formed gradually during the process. Creativity was nurtured in the construction of strategic action alternatives, which were then organised in a Level of Innovation Matrix. The Matrix is a tool which improves the participants’ understanding of the degree of complexity and difficulty involved in the implementation of new strategies. Indeed, the quandaries which prompted this research have been somewhat diminished. This is not to claim a single conclusive solution has been discovered to all the questions asked. Rather, the statement made here is that the particular process proposed might be helpful in answering these questions in appropriate situations.

An experimental study of the behaviour of embedded lengths of cantilever walls

Abstract: Laboratory-based 1–g experiments are described which model the embedded length of cantilever walls in sand, and in which the shear and normal stresses between the soil and the wall were measured, together with wall displacements, as the load on the wall was progressively increased to failure. The results show that comparatively large earth pressures, associated with high effective angles of wall friction, are mobilized just below the soil surface in front of the wall. Earth pressures on the retained side, below the centre of rotation of the wall, were smaller than Rankine passive values, confirming Krey's original views on the downwards direction of wall friction at this location. The results fit well within the relatively small available data set for free embedded cantilever walls, and show the trend of increasing bending moment with depth of embedment, given a constant effective angle of friction.

Bond properties of high-strength fiber reinforced concrete

Abstract: Compact Reinforced Composite (CRC) is a special concept for high performance concretes, where ductility is achieved through incorporation of a large content of short, stiff and strong steel fibers (6 vol.%). This ductility combined with high strength (150-400 MPa) and the ability of the small fibers to provide an effective reinforcement against even small cracks, makes it possible to obtain exceptional bond properties for deformed reinforcing bars. Results show that full anchorage is achieved with an embedment length of only 5-10 diameters for ribbed bars, which has led to applications in buildings, where CRC is used for in-situ cast joints between pre-cast decks - joints which can transfer full moments with a width of 100 mm. This type of joint, which was used for a university building, has been extensively tested for different loading situations and for behavior in a standard fire. As the fiber reinforced matrix provides a strong, ductile joint which responds well to dynamic loads it is expected to perform well under seismic loads.

The influence of a stabilizing platform on the performance of an embedded retaining wall: a finite element study

Abstract: This note reports a study based on an embedded bored pile retaining wall on the A406 North Circular Road at South Woodford, Essex, England. In the study's finite element analysis, the wall was modelled as having an 880mm thick equivalent uniform cross-section, made of reinforced concrete having Young's modulus 28 x 10power6 kPa. The clay soil was represented by a finite element formulation of the model proposed by AN Schofield in 1980. The numerical analyses presented here show that the addition of a stabilising platform to a cantilever retaining wall reduces both wall movements and long-term bending moments. Support is obtained mainly by applying to the wall a moment, which results from the contact pressure between the stabilising base and the underlying ground. For the wall geometry and ground conditions considered here, wall movements are reduced more effectively by providing a stabilising platform than by increasing the wall's embedment depth, at least if the wall's bending stiffness remains unchanged. For the specific problem investigated, the optimal stabilising platform length was about 50% of the embedment depth. The use of temporary props near the crest, to support the wall during excavation before placing the platform, increases the maximum bending moment to which the wall is subjected.

Centrifuge model tests on doubly propped embedded retaining walls in overconsolidated kaolin clay

Abstract: A series of tests on model diaphragm walls embedded in an overconsolidated clay was carried out at the London Geotechnical Centrifuge Centre. The walls were propped at the crest at the start of excavation and, following the simulation of excavation, were immediately propped at formation level. A retained height of 10 m was modelled in all tests, and the depth of embedment below dredge level varied between 5 m, 10 m and 15 m. A 'softer' construction sequence was also investigated, with excavation to 5 m below the retained surface taking place prior to the installation of the crest-level prop. The effect of pre-excavation lateral earth pressure was also investigated. The test results show that an in- crease in embedment depth will lead to an increase in wall bending moment and a reduction in bottom prop load. There is no real advantage in terms of limiting ground movements in increasing the embedment depth without also increasing the wall stiffness. Nous avons effectue une serie d'essais sur une maquette de...

A comparison of pull-out and tensile behaviors of frp reinforcement for concrete

Abstract: Commercially available FRP reinforcement rods with well-controlled variations in depth and pitch of indented helical wrappings were investigated experimentally and analytically to determine the effect of rod geometry on (1) concrete bond strength and (2) stand-alone tensile strength and modulus. Maximum bond stress increased with increasing indent depth, but did not display any particular dependence on indent pitch. Loaded-end slip at the onset of free-end slip increased with increasing embedment length and decreasing rod diameter and was relatively constant for rods with similar embedment length to diameter ratios. In tension tests, deeper indents weakened the rods while smaller indent pitches strengthened the rods. Parameters for a general analytical model of local slip within the embedment length were determined.

Cooling device for turbine moving blade

Abstract: PROBLEM TO BE SOLVED: To prevent cooling steam from bypassing a moving blade and leaking to the outside. SOLUTION: An embedment part 3 of a moving blade 1 is embedded in an embedment groove 8 of a rotor disc 4a. Cooling steam is fed to the moving blade 1 foor cooling through a supply passage 6 formed between the rotor discs 4a and 4b. After cooling, the steam is discharged outside through a recovery passage 7. A groove 10 is formed on the bottom of the embedment part 3, while a seal spring 11a is arranged inside the groove 10. The seal spring 10a prevents the cooling steam inside the supply passage 6 from directly flowing into the recovery passage 7 through the embedment groove 8. A transverse groove 12 is formed on an upper end of the rotor disc 4b, while a seal spring 11b is arranged inside the transverse groove 12. The seal spring 11b prevents the cooling steam inside the supply passage 6 from leaking to the outside.

Measuring parameters that control acoustic propagation in granular sediments near the seafloor

Abstract: Propagation of acoustic waves in granular sediments near the water‐sediment interface is controlled by a number of parameters such as fluid and grain compressibility, permeability, and the compressibility and shear stiffness of the skeletal frame in a water environment. A new experimental technique for evaluating several of these properties is described wherein a cylindrical, water‐saturated sample is subjected to vertical, steady‐state fluid flow. By controlling the hydraulic gradient, any desired vertical, effective stress may be generated and acoustic measurements then made across the diameter. When the effective stress is reduced to zero, acoustic measurements yield the compressibility of the grains, whereas at nonzero effective stress levels, it is possible to assess the effects of depth of embedment which causes changes in the compressibility and stiffness of the frame. Finally, by measuring the flow rate at each gradient, a direct evaluation of permeability is made. Preliminary measurements agree with most historical evaluations of these parameters suggesting that some recent work which challenges the traditional values is in error. [Work supported by ONR, code 321OA.]

Structural body having diamond thin film and its production

Abstract: PROBLEM TO BE SOLVED: To provide a structural body having diamond thin films enhanced in the adhesion property to a substrate and a method for producing the same. SOLUTION: An embedment region 3 consisting of a material having the adhesiveness higher than the adhesiveness of diamond to the front surface of the supporting substrate 1 is formed atop the supporting substrate 1. Diamond particles 2 are embedded in the embendment region 3. These diamond particles 2 are distributed like islands within the front surface of the supporting substrate 1 and their surfaces are partly exposed on the surface of the embedment region 3. The diamond thin film 4 is directly formed on the embedment region and the diamond particles.

Strain measurement in concrete using modulus-matched embedded composite sensing bars

Abstract: A composite strain sensing system was developed for measuring uniaxial strain in concrete. The most crucial piece of the system was a modulus-matched composite sensing bar whose axial rigidity was designed to match the rigidity of the embedment concrete. This was achieved using a combination of axially oriented fiberglass tows and vinyl ester resin. Laboratory verification tests consisted of a 6.1 m (20 ft) pile instrumented with a pair of diametrically opposed sensors embedded at depts of 0.61, 1.2, 1.8, 2.7, 3.7, and 4.6 m (2, 4, 6, 9, 12 and 15 ft). Lateral load was applied over the length of the pile to approximate the moment distribution observed in the field. Strain gages mounted on the surface of the pile confirmed the strain distribution measured by the embedded sensing bars. The laboratory test results demonstrate the accuracy of embedded composite sensing bars in field tests of laterally loaded concrete filled steel piles.

A Study on the Behavior of Vertical Plat Anchor under Horizontal Forces in Sands

Abstract: To study the behavior of a vertical plate anchor under horizontal forces in sands widely used in retaining walls and sheet piling walls, load tests on model ground made of carbon rods were carried out. The model may be considered to simulate the plane strain condition. The pressure distribution near a plate anchor. the failure mechanism of the ground around a plate anchor the ultimate holding capacity, and the load-horizontal displacement relationship were studied. As a result of this study, the critical embedment ratio (H/h)cr, differentiating a shallow anchor from a deep anchor was about 8, and the breakout factor at (H/h)cr. was about 8.5. The failure mechanism was coincided with that of the Terzaghi's theory and was similar to that of the Biarez et at.'s theory. The failure surface was gradually changed from a straight shape to a curved shape as the embedment depth was increased, and the shape was relatively similar to that of the Biarez et at.'s theory. The holding capacity of a deep anchor was slowly increased to reach the maximum value compared to that of a shallow anchor. The passive pressure was developed in front of the plate anchor and the active pressure at the back of the plate. And assuming the failure of the ground was reached at the maximum passive resistance, the pressure on the active side was already reached to the minimum. The load-displacement relationship approximated as a hyperbolic curve was coincided with the result by Das and Seely at relatively shallow anchors. From the results of this research, the fact that the behavior of a deep anchor is remarkably different from that of a shallow anchor was confirmed. And this results can be used as basic data for the design criteria of anchors.

Nondestructive determination of pile tip elevation using modal analysis

Abstract: Pile tip elevations are unknown for nearly half of Georgia's 14,500 bridges. Since the length of a pile is directly related to its capacity, and ultimately, to a bridge's load capacity, the need for a straightforward, effective, and inexpensive method to determine pile embedment lengths is apparent. If the top of the pile is exposed and free to be impacted and instrumented, the task is relatively simple. The exposed pile top is impacted axially, and the resulting longitudinal wave motion is monitored and used to calculate the pile lengths. However, such piles rarely exist in bridge structures, and the more common case is that the tops of the piles are cast into the bent cap. This lack of access poses a challenging problem when trying to nondestructively ascertain the length of pile that is embedded in the surrounding soil. Although soil borings and other intrusive tests are capable of determining pile tip elevations, the time and cost of performing these tests on a large number of bridges is prohibitive. The research project described here uses flexural waves, induced by exciting piles laterally, to determine the unknown embedment lengths. Modal analysis techniques are employed to quantify the difference in modal characteristics (natural frequencies, damping, and mode shapes) of piles with differing lengths, to create a modal model of the system, and finally to back-calculate the unknown pile embedment lengths.

Bond of Ribbed Bars Modeled through Concrete Confinement

Abstract: Bond properties are usually described by empirical relations that are based on pull-out tests of bars with short embedment lengths cast in low to medium strength concrete. The limited validity of these formulations is recognized and their applicability in structural analysis is reconsidered. Results of two test series with various confining conditions and concrete strengths provide the basis for the derivation of a new bond model for ribbed bars. Pull-out bond failure in confined concrete and splitting bond failure in unconfined concrete have been studied. Steel yielding is found to have a considerable influence on bond strength. Significant differences in bond of NSC and HSC are confirmed. An analytical bond model for ribbed bars is developed. It is based on the confining capacity of the concrete surrounding the bar. This is evaluated with a thick-walled cylinder model, from which the relation between the radial displacement and the radial compressive stress at the steel-to-concrete interface is derived. The radial displacement at the interface is linked to the slip of the ribbed bar, distinguishing between the two modes of bond failure: pull-out and cover splitting. The model takes into account concrete toughness and bar contraction, also after yielding. Verification of the model against selected experimental results reflects the potential of the model to be used in a broad range of applications. In its present form the model is used for analysis of isolated bond problems using a one-dimensional finite difference approach, but its application is also considered to count for three-dimensional deformations if FE codes that treat the bar as a one-dimensional element.

Dynamic embedment of metal plate connections

Abstract: Metal plate connectors (MPCs) are a critical component of prefabricated wood trusses in that they provide an effective and efficient means of transferring chord and web forces across thejoint. Key to this process is the proper embedment ofthe connector plate into the wood. Improper embedment is generally manifested in either the compressive strength of the wood being exceeded, or in plate rejection, where the plate springs partially back out of the wood after pressing. Keyed, in part, off the findings of several independent researchers, a technique was investigated in which the MPCs were pressed into dense southern pine 2 by 4's under a low amplitude vibratory load at frequencies of 30, 50, and 70 Hz. Data for these so-called dynamic connections were collected on both the mean force necessary for pressing and on the degree of plate embedment. Comparisons were then made to similar static connections fabricated in a traditional manner using equivalent lumber. Both the static and dynamic connections were tested in tension to determine their comparative strengths and stiffnesses. Results showed some indications ofreduced press load at the 30-Hz frequency. At the 50-Hz level, an increase in plate embedment was observed, although this was attributed to an accompanying increase in mean press loads. The 70-Hz and control groups behaved quite similarly and showed only small variations between static and dynamic connections due to material variability. Tension test results were consistent throughout all MPC configurations and showed no marked differences in either capacity of stiffness as a result of the dynamic embedment.

Concrete box for underground embedment

Abstract: PROBLEM TO BE SOLVED: To prevent the occurrence of displacement of a joint even when a reaction force for thrust of a shield machine is exerted, and besides to perform effective cut-off between concrete boxes, and to prevent the occurrence of a crack and breakage of a concrete box due to floating of an end face. SOLUTION: A concrete box for underground embedment is formed such that front and rear end faces are released as an opening surface, a concrete box 4 comprises left and right side plate 4a and 4b, an upper floor plate 4c, and a lower floor plate 4d. The concrete boxes are embedded in a longitudinal train state, in order, in a ground, and a reaction force to thrust of an excavator arranged at a head is exerted. A cushioning material 11 made of a strip cushioning material 11 is widely mounted on the rear end face of the concrete box 4 and cut-off materials 7 are further disposed in an aligned state thereon.

Overlooked Assumption in Nonconstrained Post Embedment

Abstract: In the traditional formula for determining the required embedment depth for nonconstrained posts it is assumed that shear and moment at grade have the same algebraic sign, as is the case for determinant structures that are free to translate laterally (flag poles or billboard signs). This article demonstrates that in an indeterminant lateral force resistive system, which consists of a combination of embedded posts and structural diaphragms (many buildings), the shear and moment at grade most often have opposite algebraic signs. In this case the traditional formula should not be applied. This article presents an alternate method for checking embedment depth based upon the calculated lateral soil bearing pressure.