Showing papers on "Direct shear test published in 1985"

Liquefaction Evaluation Procedure

Abstract: A procedure for evaluating liquefaction susceptibility of a soil mass subjected to shear stress, such as in slopes, embankments, and foundations of structures, is presented. Liquefaction analysis is a stability analysis for which the shear strength in the numerator of the factor of safety equation is the undrained steady-state strength, and the denominator is the driving shear stress. The driving shear stress is the shear stress required to maintain static equilibrium. The undrained steady-state shear strength is a function only of the void ratio. Thus, one critical step of the procedure for liquefaction evaluation is the determination of the in-situ void ratio and the correction of laboratory-measured undrained steady-state strength to account for unavoidable changes in void ratio of the soil during sampling and testing. Dilative soils are not susceptible to liquefaction. Cyclic load tests are not required to evaluate the susceptibility to liquefaction.

Plastic banding in glassy polycarbonate under plane simple shear

Abstract: Samples of amorphous polycarbonate were tested in plane simple shear at various temperatures (−100 to +150‡ C) and shear rates (3×10−5 to 3×10−2sec−1). In the glassy state, it was observed that the deformation concentrated at yield inside a single shear band whose elongation and widening phases correspond to well marked stages of the recorded stress-strain curve. Birefringence and X-ray diffraction in the growing band show that the molecular orientation follows a pseudoaffine evolution with the local plastic strain. Although the shear is inhomogeneous during the growth of the shear band, it is fairly uniform inside the band itself, down to the scale of 100 nm. After the band has completed its widening (for an overall shear of about 0.9) the overall shear in the whole specimen is homogeneous and then one can deduce the constitutive equation for steady state plasticity of the glassy material, up to shear strains as large as 2.0. It is characterized by a linear strain hardening whose value, such as the extrapolated yield stress, decreases gradually with temperature.

Observation of the stress distribution in crushed glass with applications to soil reinforcement

Abstract: The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.

Advances in the Art of Testing Soils Under Cyclic Conditions

Abstract: The session on “Advances in the Art of Testing Soils under Cyclic Loading Conditions” was organized by the Soil Dynamics committee of the American Society of Civil Engineers in an endeavor to evaluate the state of practice governing testing equipment and methodology, and behavioral analysis of materials. The topics included centrifuge modeling of soils, torsional triaxial and direct shear devices and their use with hollow cylindrical soil specimens, applications of the constant volume cyclic simple shear device, monotonic and cyclic loading behavior for triaxial stress conditions, effects of irregular and multi-directional load application, evaluation of liquefaction flow failure during earthquakes, influence of testing techniques on soil properties in a cyclic triaxial apparatus, evaluation of shear wave velocity and shear modulus using cubic soil samples or bender elements, and mathematical modeling of nonlinear behavior in a resonant column test.

Aspects of Constant Volume Cyclic Simple Shear

Abstract: Data from cyclic simple shear tests comprise the foundation on which rests most of the practical applications of theoretical soil dynamics. The importance of the test derived from two assumptions made by Seed and Idriss in their pioneering studies of liquefaction in level ground during the Niigata earthquake in Japan in 1964: (1) seismic excitation is due primarily to shear waves propagating vertically and (2) level ground conditions may be approximated by horizontal layers with uniform properties. Under these conditions the ground deforms in shear only and may be analysed by treating a vertical column of soil as a shear beam.

Pressure-shear waves in 6061-T6 aluminum and alpha-titanium

Abstract: T he pressure-shear plate impact technique is used to study material behavior at high rates of deformation. In this technique, plastic waves of combined pressure and shear stresses are produced by impact of parallel plates skewed relative to their direction of approach. Commercially pure alpha-titanium and 6061-T6 aluminum are tested under a variety of pressure and shear tractions by using different combinations of impact velocities and angles of inclination. A laser interferometer system is used to monitor simultaneously the normal and transverse components of motion of a point at the rear surface of the target plate. The experimental results are compared with numerical solutions based on an elastic/viscoplastic model of the material. Both isotropic and kinematic strain hardening models are used in the computations. The results indicate that unlike the normal velocity profiles, the transverse velocity profiles are sensitive to the dynamic plastic response and, thus, can be used to study material behavior at high strain rates. For the materials tested the results suggest that the flow stress required for plastic straining increases markedly with increasing strain rate at strain rates above 104s−1. Hydrostatic pressure of the order that exists in the tests (up to 2 GPa) does not affect the plastic flow in 6061-T6 aluminum and appears to have at most a minor effect on the deformation of the titanium.

Diffusion bonding and testing of Al-alloy lap shear test pieces

Abstract: A quantitative measure of the effect of processing variables on the shear strength of solid state diffusion bonds is often difficult to obtain because of the scatter in test data. This may be reduced by improving the bonding and testing techniques. Two jigs for bonding and testing small Al-alloy lap shear test pieces are described. These jigs enabled the precise measurement of shear stress-strain curves for lap joints and led to reproducible shear strength values. Results obtained for diffusion bonded lap joints between clad Al-Zn-Mg (7010) alloy are described.

Observation of the stress distribution in crushed glass with applications to soil reinforcement

Abstract: The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.

Iosipescu shear properties of graphite fabric/epoxy composite laminates

Abstract: The Iosipescu shear test method is used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/934 epoxy composite materials. Different weave geometries tested include an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties are obtained for laminates of all four fabric types. Overall, little difference in shear properties attributable to the fabric weave pattern is observed. The auxiliary warp material is significantly weaker and less stiff in interlaminar shear parallel to its fill direction. A conventional strain gage extensometer is modified to measure shear strains for use with the Iosipescu shear test. While preliminary results are encouraging, several design iterations failed to produce a reliable shear transducer prototype. Strain gages are still the most reliable shear strain transducers for use with this test method.

Effect of Initial Shear on Cyclic Behavior of Sand

Abstract: Drained and undrained cyclic torsional simple shear tests are conducted for saturated Ottawa sand with and without initial static shear applications. It was found from the experiment that when the tests were conducted under uniform cyclic shear strains, both pore water pressure generation in undrained conditions and the volume changes in drained conditions were affected very little by the level of the initial static shear applications. The strain method, which uses shear strain parameters as determinative parameters, has been proven to be very useful for liquefaction and cyclic volume change analyses.

RC Structural Walls: Seismic Design for Shear

Abstract: Provisions of 1982 UBC, ACI 318-83, and ATC 3-06 pertaining to seismic shear design of slender walls in mid-rise construction are evaluated. In the event of major ground shaking in regions of high seismic risk, the actual shear strength demand is expected to equal that associated with the axial-flexural supply. Thus, the codes’ minimum design requirements ought to insure that flexure, and not shear, will control the seismic response during the expected rare, major seismic event in the western U.S. The codes do not implement this condition. Expressions suggested by design documents for computing the shear strength of walls were evaluated by comparing the predicted and measured strengths of 10 wall specimens tested at Berkeley. Although generally conservative, since code expressions do not incorporate the actual shear resisting mechanisms of walls under seismic effects, it is possible for the expressions to mislead the designer to poor shear design. Recommendations are formulated to improve the current shear design procedures by: (1) relating the shear strength demands to the actual axial-flexural supply; and (2) incorporating the actual shear resisting mechanisms in predicting shear strength supply of walls.

Shear strength of smooth unreinforced construction joints

Abstract: Synopsis The results of 60 tests on smooth unreinforced construction joints in concrete prisms are presented. Each specimen was subjected to loading which induced combined direct and shear stresses at the joint. It was found that shear was transmitted by a combination of ‘cohesion’ and ‘friction’. A slight dependence of the shear strength upon the age ofthe first pour of concrete at the time of the second pour was found. A relation for the shear strength of a smooth unreinforced construction joint is proposed as a function of concrete compressive strength and the associated direct stress at the joint.

Laboratory evaluation of four rapid-setting concrete patching materials

Abstract: Many proprietary patching products are available for the repair of portland cement concrete (PCC) pavement. These materials must cure rapidly to minimize delay and limit safety hazard exposure to both the traveling public and maintenance personnel. However, long-term strength and durability are equally important, although information concerning these properties and direct comparisons between patching alternatives is limited. Compressive strength, tensile strength, direct shear, and energy absorption tests were used to evaluate polymer concrete, magnesium phosphate cement, Roadpatch with steel fibers, and epoxy-bonded PCC. The split-cylinder tensile bond strengths of the patching materials were comparable to those of the base concrete. The shear bond strengths and energy absorption tests indicated that polymer concrete has good cured properties as a composite patch but may be susceptible to weathering or thermal deterioration. Roadpatch also had satisfactory cured strength properties but had better resistance to decreases in direct shear bond strength and tensile strength when exposed to simulated weathering. Roadpatch appeared to exhibit a good overall combination of characteristics that indicate satisfactory short-term and long-term durability. The epoxy-bonded PCC alternative demonstrated substantial strengths, but the slow rate of strength gain noted was a major disadvantage for potential field application. Magnesium phosphate concrete does not appear to be an attractive early cure material and it may be susceptible to damage from dynamic loading.

Cyclic Simple Shear, Torsional Shear and Triaxial—A Comparative Study

Abstract: Many different testing apparatus are used to duplicate in laboratory soil samples the stress state generated in situ by earthquakes. A wide diversity of data has been generated and this paper compares the cyclic behavior of soil predicted by cyclic triaxial, simple shear and torsional shear test apparatus. Comparisons are made for drained and undrained samples with and without initial static shear stresses and for both stress and strain controlled tests. Results show that similar volume change, pore pressure build up and stress ratios to cause liquefaction are measured by the different apparatus. In general, triaxial tests predict the largest liquefaction resistance, simple shear the lowest, and torsional shear somewhere in between.

Rate of Shear Effects on Vane Shear Strength

Abstract: A series of laboratory vane shear tests was performed on sedimented samples of kaolinite and slaked Pierre shale to determine the effects of shear rate and vane dimensions on measured strength. Results of the tests were expressed in terms of shear strength on a vertical plane and were plotted versus average shear rate. For kaolinite samples vane shear strength decreased as shear rate increased because of partial drainage occurring at slower shear rates. However, for the highly plastic Pierre shale vane, shear strength increased as shear rate increased because of undrained creep occurring at slower rates of shear. Test results for kaolinite and Pierre shale are compared to published information from other studies.

Impulsive Direct Shear Failure in RC Slabs

Abstract: Direct shear failure in reinforced concrete slabs under impulsive loads is relatively undocumented because of the paucity of data showing failure characteristics. The combined effects of beam action and wave action are likely to be important in developing models to understand the dynamic direct shear phenomenon. The research summarized in this paper makes an initial attempt to understand this phenomenon by considering elastic beam action to describe incipient direct shear failure conditions. The effects of load rate and beam‐end restraint are investigated. Failure curves developed from elastic Timoshenko beam models are compared with experimental data on one‐way slabs which failed in direct shear.

Shear transfer across a single crack in reinforced concrete under sustained loading. Part I: Experiments

Abstract: The experimental investigation relates to the behaviour of concrete specimens with a single crack under sustained shear loading. The crack plane is crossed perpendicularly by embedded reinforcing bars, each of 8mm diameter. The variables of the tests were the concrete grade, the initial crack width, the shear stress level and the reinforcement ratio. The constant shear stress level was 45%-90% of the static shear strength. The experimental program comprised 34 specimens. The duration of load application was at least 90 days. Periodically the crack width and the shear slip of the opposing crack faces were measured. Experiments started at a concrete age of 28 days at 20°C and 50% RH. On the one hand, the test results refer to measured material characteristics such as development of concrete compressive strength, shrinkage and loss of weight by the drying process. On the other, the measured instantaneous and the time-dependent displacements under sustained shear loading are given for each specimen. Moreover the crack-opening path and the displacements after release of the shear force are presented. The measured displacement-paths are described by non-linear regression analysis. Detailed information is also presented in report 5-85-6 [39]. In an additional test series similar specimens were used. Now the normal restraint stiffness of the crack was governed by four steel bars having no bond with the concrete. As an advantage the axial steel stresses could be measured by strain gauges. Moreover, pull-out tests were performed to study the bond behaviour of 8 mm diameter reinforcing bars. See reporc 5-85-11 [40].

Electron irradiation effects on interlaminar shear strength of glass or carbon cloth reinforced epoxy composites

Abstract: Interlaminar tensile shear tests are conducted to study the degradation mechanisms of electron irradiated glass or carbon cloth reinforced epoxy laminates. Interlaminar shear strength decreases significantly after the dose exceeds 3000 Mrad for glass/epoxy, but remains constant up to 12 000 Mrad for carbon/epoxy. SEM photos reveal that debonding of glass fibres and epoxy matrix (or degradation of silane coupling agents) plays an important role in the dose-dependent strength reduction of glass/epoxy laminates. The decrease in the interlaminar shear strength corresponds to that in the three-point bending strength. On the other hand, the SEM fracture appearance is almost dose-independent for carbon/epoxy laminates. In addition, some preliminary irradiation tests are conducted at −120° C to observe the effects of irradiation temperatures.

Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties

Abstract: Geotechnical engineers have recognized in the past decade that shear wave velocity is a basic soil property and have begun to use it to characterize sites for many uses. Most notable has been the realization that the so called “dynamic modulus” is simply the low strain value of elastic modulus and this can be used in many “static” as well as “dynamic” applications. Because of its basic nature, it has also been recognized that shear wave velocity is an excellent diagnostic tool which can be used to evaluate the results of soil modification techniques. Three of the papers included in this publication deal with the measurement of shear wave velocity; one through its relationship with Rayleigh Waves, another by coupling with cone penetration sounding, and the third by combined field and lab measurements. All represent significant advances in the art of shear wave velocity measurements but for different reasons. Other papers take advantage of the long known connection between time and frequency domains and the powerful relationships provided by Fourier Duals. Geotechnical engineers are finally beginning to recognize and take advantage of some of the tools which the geophysicist has been using for several decades. The relationships between well known in-situ exploration techniques, cone penetration tests and down-hole seismic tests are presented. The combining of these two should result in data which is greater than the sum of the two methods separately. An application of shear wave velocity in the identification of the potential for liquefaction and in the evaluation of the stability of an earth embankment subject to earthquake shaking is described. An empirical correlation between shear wave velocity and depth of overburden is presented.

Aramid/Epoxy vs. Graphite/Epoxy: Origin of the Difference in Strength at the Interface

Abstract: In single filament pull-out tests, the graphite/epoxy inter-facial bond strength was found to be twice as large as the aramid/epoxy interfacial bond strength. This difference carried over to unidirectional filamentary composites made with the same resin system. Short beam shear test results for graphite/epoxy were nearly twice as high as those for aramid/epoxy. Graphite/-epoxy similarly exceeded aramid/epoxy in the Iosipescu shear tests used as a cross check to the short beam shear test.