Showing papers on "Embedment published in 1993"

Seismic response of steel beams coupling concrete walls

Abstract: Ductile coupled flexural walls are the primary seismic load resisting systems of many structures. The coupling beams of these structures must exhibit excellent ductility and energy‐absorption ability. To achieve better ductility and energy absorption than previously possible, the use of steel link beams with their ends embedded in the reinforced concrete walls is proposed. Preliminary experimental results are reported for two full‐scale reversed cyclic‐loading tests of portions of ductile flexural walls coupled with steel link beams. The excellent performance, together with the ease of construction, demonstrate the feasibility of this alternative form of construction. To ensure ductile response, design and detailing guidelines for both the clear span and embedded portions of the link beams and the reinforced concrete embedment region are presented. An assessment, based on comparisons with other structural systems, of this new type of construction is presented.

Behaviour of embedded model screw anchors in soft clays

Abstract: In recent years helical anchors have been used extensively in the construction of transmission tower foundations, pipelines and braced excavations. This Paper describes an experimental programme carried out to show the behaviour of multiple helical anchors at different embedment ratios in soft marine clays. The number of helical plates, their diameters and spacings are varied. Pullout tests were conducted by anchors installed in a soft marine clayey bed prepared in test tanks and at embedment ratios of 0-10. The results indicate that the anchor capacity increases with embedment ratio. The uplift capacity at any embedment ratio is explained in terms of the contribution of cohesive resistance between the top and bottom helical plates, the bearing resistance of the top helical plate alone and the shaft adhesion above. Based on embedment ratio and observations during testing, the anchors are classified as shallow, transit and deep anchors. Formulations are suggested for estimating and calculating the capaciti...

Bearing Capacity of Strip Foundation on Geogrid-Reinforced Clay

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.

The bending moment resistance of single-dowel corner joints in case construction

Abstract: This study was carried out to obtain background information concerning the bending moment resistance of single-pin dowel joints in particleboard and also to provide the background information needed to formulate expressions for predicting the bending moment resistance of single-dowel, L-type, corner joints in particleboard. Test results indicated that the bending moment resistance of the single-dowel corner joints increased significantly as dowel diameter increased from 1/4 to 3/8 inch and as the depth ofdowel embedment in the face member increased from 1 /4 to 5/8 inch. Changes in depth of embedment in the edge member from 3/4 to 1-1/2 inches, however, had no effect on bending moment resistance.

Cover and Stirrup Effects on the Shear Response of Dowel Bar Embedded in Concrete

Abstract: Twenty eight reinforced concrete specimens reinforced with a single deformed bar 14, 18, and 24 mm in diameter were tested as a part of a major research program on dowel action. Block-type specimens were loaded, and dowel displacements were detected by linear variable differential transducers. The study results consist of force-displacement curves, displacement and curvature diagrams along the axis of the bar, linear regressions of dowel ultimate capacity, and initial stiffness versus bar diameter. Comparisons with several available models predicting dowel strength are presented and design values for the subgrade stiffness of the concrete embedment are proposed.

The axial loading of a rigid circular anchor plate embedded in an elastic half-space

Abstract: The present paper examines the axisymmetric problem related to the loading of a rigid circular anchor plate which is embedded in bonded contact with an isotropic elastic half-space. A Hankel transform development of the governing equations is used to reduce the associated mixed boundary value problem to a set of coupled Fredholm integral equations of the second kind. These equatons are solved in a numerical fashion to generate results of engineering interest. In particular, the results indicate the influence of the depth of embedment on the axial stiffness of the rigid anchor plate.

Flexural Strength and Fracture Toughness of Dicor Glass-ceramic after Embedment Modification

Abstract: Previous studies on the surface properties of Dicor castable glass-ceramic have shown the formation of a specific crystalline phase at the glass-ceramic/embedment interface. If this phase is not removed by grinding, it leads to an undesirable strength decrease. The aims of this study were: (1) to determine the nature of this surface layer, (2) to promote the formation of a different crystalline phase at the surface with the intention of improving the properties of the glass-ceramic, by modification of the composition of the Dicor ceramming embedment, and (3) to evaluate the fracture toughness and flexural strength of Dicor glass-ceramic after embedment modification. Modifications were made to the embedment by incorporation of 2.5 wt% of lithium fluoride and ceramming at various temperatures. X-ray diffraction was used to determine the crystalline nature of the surface layer. Fracture toughness was investigated by the indentation technique. The maximum bi-axial stresses were calculated after the samples were fractured in water on a ball-on-ring fixture at 0.5 mm/min. With the recommended embedment and ceramming cycle, the crystalline phase constituting the ceram layer was a calcium magnesium silicate CaMg(SiO3)2 (diopside). The crystalline composition of the ceram layer was successfully modified by addition of 2.5 wt% lithium fluoride to the embedment. This promoted the crystallization of mica in the ceram layer and increased the fracture toughness of the glass-ceramic when the ceramming temperature was 950 or 975 degrees C. The flexural strength was significantly increased when the ceramming temperature was 1000 degrees C.

Non-corrosive tie reinforcing and dowel bars for highway pavement slabs. final report

Abstract: The use of non-metallic load transfer and reinforcement devices for concrete highway pavements is a possible alternative to avoid corrosion problems related to the current practice of steel materials. Laboratory and field testing of highway pavement dowel bars, made of both steel and fiber composite materials, and fiber composite tie rods were carried out in this research investigation. Fatigue, static, and dynamic testing was performed on full-scale concrete pavement slabs which were supported by a simulated subgrade and which included a single transverse joint. The bahavior of the full-scale specimens with both steel and fiber composite dowels placed in the test joints was monitored during several million load cycles which simulated truck traffic at a transverse joint. Static bond tests were conducted on fiber composite tie rods to determine the required embedment length. These tests took the form of bending tests which included curvature and shear in the embedment zone and pullout tests which subjected the test specimen to axial tension only. Fiber composite dowel bars were placed at two transverse joints during construction of a new concrete highway pavement in order to evaluate their performance under actual field conditions. Fiber composite tie rods were also placed in the longitudinal joint between the two fiber composite doweled transverse joints.

Effect of embedded fiber optics on the mechanical properties of a composite host material

Abstract: The effects of embedded fiber optics (FO) on the mechanical properties of a graphite/epoxy composite host material were studied. Optical fibers 125 micrometers and 240 micrometers in diameter were embedded in AS4/3501-6 graphite/epoxy, and the static performance of the material was evaluated. FO were placed in the midplane of the specimens both parallel and perpendicular to the loading direction. The mechanical tests included O degree(s) compression, 90 degree(s) tension, (0, +/- 45, 90)S tension, and first ply failure of (O2, 902)S specimens. Microstructural analysis of the fracture surfaces showed little influence of the FO on crack initiation or propagation. Test results showed no distinct influence of the FO on failure strength or modulus, but did open questions on the coupled effects of processing history, FO embedment, and failure strength.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pipelines and Laterally Loaded Piles in Elastoplastic Medium

Abstract: The uplift behavior of a shallow pipeline embedded in an elastoplastic medium is examined. An analytical solution for a beam on elastoplastic foundation is developed and a characteristic nondimensional load-displacement and stress-displacement relationship are presented. An approximate three-dimensional (3D) solution is proposed that accounts for embedment and breakaway condition behind the pipeline making use of the load-displacement curves developed for rigid anchors by Rowe and Davis in 1982. A comparison of these results with those obtained by 3D finite-element analysis indicates that the simplified solution of a beam on elastoplastic foundation is a practical alternative for analyzing the uplift behavior of shallow pipelines. The approximate solution is also used to compare the behavior of a laterally loaded pile for which no separation or separation between the surrounding soil and the back of the pile is permitted as the load is monotonically increased. The results are presented in the form of nondimensional charts that permit hand calculations and rapid verification of structural design of the pipeline and piles.

The preliminary design of free embedded cantilever walls in granular soil

Abstract: This paper describes new model wall experiments which were undertaken at the University of Surrey. Their aim was to provide further data on the performance of free embedded cantilever walls in granular soil. These experiments used a simplified technique which consisted of modelling only the segment of wall which was situated below the excavation level. These results fit well with a previously normalized data set. The trend of increasing bending moment with depth of embedment, for a constant plane strain angle of internal friction, which was postulated on the basis of the previously available experimental results, is confirmed. These data have been re- interpreted in the form of charts, which the authors suggest may be used for preliminary design purposes. For the covering abstract see IRRD 860485.

Fastening elements in concrete structures - numerical simulations

Abstract: Anchoring elements such as headed and expansion studs and grouted or undercut anchors, are often used for local transfer of loads inlo concrete members. In order to better understand the failure mechanism, a large number of experiments have been carried out in the past. Ho,\·cver. due to the complicated three-dimensional load transfer a. very few or no numerical studies have been performed for a. number of different fastening situations i.c. influence of the embedment depth, crack-width in­ ftuence (fastening in cracked concrete), influence of the edge distance etc. Therefore, in the present study some results of the axisymmetric and three-dimensional nume­ rical analysis of the headed studs embedded in plane concrete block are presented. Influence of different geometrical and material parameters have been studied em­ ploying finite element method and nonlocal microplane model. Comparison between experimental and numerical results indicate reasonable good agreement. Generally it has been observed that the failure mechanism is governed by fr acture energy ral­ her than by tensile strength of concrete. As a consequence, the size effect is strong

Negative skin friction on single piles in a layered half-space

Abstract: Settlement of the surrounding soil due to surcharge placement may give rise to negative skin friction developed in piles. In this paper, a simple discrete element approach using subgrade reaction method is proposed to analyse negative skin friction on single piles. The pile is embedded in a two-layer soil where the upper soil layer undergoes consolidation while the lower soil layer acts as a stiffer bearing stratum. Two different and uncoupled deformation modes, one at the pile shaft and the other at the pile toe have been assumed in the determination of the soil stiffness. The effects of a compressible bearing stratum and embedment length of the pile in the bearing stratum are considered in the analysis. This simple approach is verified by comparison with rigorous methods of modelling the soil as an elastic continuum. Three reported case histories are analysed and the computed results are shown to be in reasonable agreement with the field measurements.

Analysis of the behaviour of propped diaphragm walls in a deep clay deposit

Abstract: Modern techniques of excavation, including the use of structural diaphragm walls and top-down construction, provide effective methods to minimize deformations in the surrounding soil. However, for deep excavations and walls embedded in deep layers of soft clays, it is difficult to control soil movements. In these situations, reliable predictions of deformations are an important consideration in the design of the earth support system. This paper describes results of numerical experiments, based on non-linear finite element analyses and incorporating an effective stress soil model which describes observed aspects of soft clay behaviour including small strain non-linearity and anisotropic stress-strain-strength. The analyses consider the undrained deformations around a braced diaphragm wall in a soft clay deposit. Principal parameters considered in the study are the wall embedment depth and support spacing. A simplified framework is developed to interpret wall deflections and ground movements with excavation depth. (A) For the covering abstract see IRRD 860485.

Centrifuge model studies of a cantilever retaining wall in sand

Abstract: In this paper centrifuge model studies on a flexible wall, with different surface roughnesses, in both loose and dense sands are described. The cantilever retaining wall model was a flat stainless steel sheet. The results are presented in terms of the behaviour of an 11 m high, Frodingham No. 5 section, sheet pile wall. The magnitudes of displacements are reported and the observed bending moments and critical embedment depths compared to those predicted by limit state analyses. Limit state predictions of critical heights was very close to the observed results. However, observed maximum displacements, and the rates of change of displacements with heights of excavation corresponding to design with a factor of 1.5 on passive pressure were high. Design bending moments were also significantly higher than those observed for all but very rough piling. For the covering abstract see IRRD 860485.

Tensile behavior and design of adhesive-bonded anchors and dowels

Abstract: Adhesive-bonded anchors and reinforcing dowels are frequently used in highway applications. Currently, designers rely on either manufacturers' recommendations or job-by-job testing to determine the capacity of these anchors. The purpose of the research was to develop a rational design procedure for adhesive-bonded anchors. The design recommendations presented are based on a combination of a uniform bond stress model for typical embedment lengths and an elastic bond stress model for deep embedments. The use of the easily applied uniform bond stress model for typical embedment lengths is justified by comparison with an elastic bond stress model that considers compatibility of displacements for the adhesive anchor system. A total of 167 tests were performed using three anchor diameters and 16 adhesive products. Load-displacement data were collected for each test. A series of 144 baseline tests of confined, fully bonded anchors was used to determine the basic bond and stiffness properties of the adhesive-bonded anchors. The results of the baseline test series were used to compare the uniform bond stress model with the rationally based but more complicated elastic bond stress model. Another 23 tests were performed for comparison with the results of the baseline tests. These consisted of unconfined tests with both fully and partially bonded anchors and confined tests with partially bonded anchors.

Minimum-Weight Design of Machine Foundation Under Vertical Load

Abstract: In this paper a numerical model for the minimum‐weight design of a rectangular machine foundation under a harmonic vertical load is presented The analysis of the dynamics of foundation‐soil interaction is based on frequency‐dependent dynamic properties of a semi‐infinite supporting medium and includes the shape of the foundation plan, the embedment of the foundation into the soil, and hysteretic material damping of the soil Dimensions of the concrete block are assumed as design variables Constraints are placed on resonant frequency, vertical displacement amplitude, stresses in the soil and dimensions of the foundation concrete block A sequential programming method with variable move limits is used to obtain the optimal solution, which is affected by inertia properties of the machine‐foundation‐soil system, damping from dynamic soil‐foundation interaction and local soil conditions Numerical examples are given to demonstrate the applications of the proposed approach

Tests and analysis of mixed wood-concrete beams (preliminary report)

Abstract: As concrete and wood are low cost materials and require low skill levels in construction, their combined use as bridge materials is attractive to rural settings. Concrete is strong in compression and weak in tension. Wood is strong in tension parallel to grain but subject to buckling in compression. Thus, composite T-beams constructed to stress concrete in compression and wood in tension may have performance advantages for bridges. Basic research on the composite behavior of mixed concrete-wood beam construction is a first step toward understanding their potential use in bridge constructions. This project included two laboratory studies and analytical work dealing with T-beams comprised of a concrete flange connected to wood beam plus plywood sheathing. Based on the experimental results of tests of 72 slip specimens and 4 full-scale layered T-beams, the mechanical behavior of different materials in layered structure was studied. In the slip tests, concrete-wood members were tested for two different ages of concrete, 4 types of nails and two different embedment lengths. The slip modulus and ultimate load of each specimen were determined after testing. In T-beam bending tests, the deflection and the interlayer slip were measured at varying load level. The experimental results of the T-beam tests are compared favorably to theoretical values that were obtained by use of an existing computer program, FEABEA, originally configured for composite wood to wood construction. The report is organized in eight chapters as follows: (1) Introduction; (2) Literature Review; (3) The Mathematical Model for a T-Beam; (4) Testing Equipment and Procedure; (5) Properties of Materials; (6) Experimental Results; (7) Verification of the Mathematical Model; and (8) Summary and Conclusions. There are three appendices as follows: (A) The Load-Slip Curves of Slip Tests; (B) The Load-Deflection Curves of T-Beam Bending Tests; and (C) Comparison of the Theoretical and Experimental Results of T-Beam Specimens.

Evaluation of electrical material properties: Embedment stress testing on electrical encapsulation resins

Abstract: The embedment stress of a variety of encapsulation resins including HTPB (hydroxyl terminated polybutadiene) based polyurethanes, epoxies, and silicone is addressed. The embedment stress method followed is ASTM F135-76. The test determines the embedment stress of a rigid system with a peak cure exotherm under 200/spl deg/ F. The data reflect the stress exerted on a glass encased encapsulated component by measuring the stress exerted on a glass encased encapsulated component by measuring the stress exerted on a thermometer bulb below the peak exotherm of the system. In this test, a thermometer and a thermocouple are embedded in the various encapsulation systems. The test samples are subjected to a range of temperatures. Temperature readings are taken from both the thermometer and thermocouple. The relative embedment stress is calculated from the differences between the two temperature readings.