Monotonic Shear Tests Research Articles

Testing masonry blockwork panels for orthotropic shear strength

Abstract In this paper the problem of evaluation of the structural response of 1.20 m × 1.20 m blockwork masonry panels under monotonic shear and diagonal-compression tests is investigated. The digital image correlation technique was used to detect the initiation and propagation of damage. The experimental findings were analyzed and simulated also by means of accurate finite element non-linear analyses. The results revealed the non-isotropic shear response of the masonry panels, which is related to the meso-scale structure. The shear response along the two principal directions, when investigated by a test configuration which recall the Iosipescu method, proved to be quite different, being the shear strength parallel to the bed joints mainly dependent on the mortar properties, while the shear strength perpendicular to the bed joints is affected by the bond pattern. The standard diagonal compression tests, on the other hand, showed an intermediate response, even if the orthotropy of shear response could not be explicitly manifest.

Liquefaction and post-liquefaction assessment of lightly cemented sands

Post-liquefaction response of lightly cemented sands during an earthquake may change and become similar to uncemented sands due to bonding breakage. In the current study, the effect of degree of cementation on liquefaction and post-liquefaction behaviour of lightly cemented sands was studied through a series of cyclic and monotonic triaxial tests. Portland cement with high early strength and Sydney sand were used to reconstitute the lightly cemented specimens with unconfined compression strength ranging from 25 to 220 kPa. A series of multi-stage soil element tests including stress-controlled cyclic loading events with different amplitudes and post-cyclic undrained monotonic shearing tests were carried out on both uncemented and cemented specimens. Furthermore, a series of undrained monotonic shearing tests without cyclic loading history on different types of specimens was conducted to investigate the effect of cyclic loading history on the post-cyclic response of the specimens. The results show that residual excess pore-water pressure is correlated to the cyclic degradation of lightly cemented sands during cyclic loading. In addition, optical microstructure images of the cemented specimens after liquefaction showed that a major proportion of cementation bonds remained unbroken, which resulted in a superior post-liquefaction response with respect to initial stiffness and shear modulus in comparison to the uncemented sand.

Monotonic and cyclic behaviour of wood frame shear walls for mid-height timber buildings

The Chilean forestry industry has a significant presence in the economy of the country. Due to pollution problems and the high seismicity of the region, timber is a suitable material for new buildings. However, because of cultural customs and high demands of regulations, nowadays it is difficult to construct buildings higher than three stories in Chile. However, several international projects have shown that is feasible to construct mid-height timber buildings. Sturdy end studs and strong hold-downs are needed in mid-height wood buildings (up to 6 stories high) to resist large vertical and horizontal loads. However, design parameters provided by current seismic design provisions for those shear walls do not consider the effects of sturdy end studs and strong hold-downs in lateral strength and stiffness of the walls. In order to address this issue, a multidisciplinary team at the Catholic University of Chile has conducted an extensive experimental and numerical research program. This paper presents the results of seventeen in-plane monotonic and cyclic shear tests in wood frame shear walls of different lengths (1200, 2400 and 3600 mm) and 2470 mm height. The walls have five 2 × 6″ end studs, strong hold-down anchorages and standard 11.1 mm structural OSB panels (1200 × 2400 mm) on both faces of the wall and with nails in the edge of the OSB panels spaced at 50 or 100 mm. The main objectives of this research are to evaluate the seismic response of these shear walls and to assess the current code expressions applied to shear walls with sturdy end studs to be used in mid-height timber buildings. The results show that, while cyclic loads reduce the monotonic shear strength of walls, cyclic loads do not influence the ultimate displacement and stiffness. The main benefits of a smaller nail spacing are the increase of the strength and delay of stiffness degradation. The unit shear was influenced by wall length: 1200 mm walls presented a better unit shear capacity than 2400 and 3600 walls, and there were not observable differences between 2400 and 3600 mm walls. The characteristic damping of the walls varied between 7 and 10%. Finally, the current design provisions underestimate the shear strength and overestimate the stiffness of walls to be used in mid-height timber buildings.

Effect of Gradation and Non-plastic Fines on Monotonic and Cyclic Simple Shear Strength of Silica Sand

Monotonic and cyclic direct simple shear tests with shear wave velocity measurements were conducted on a series of silica sand gradations to examine the effect of both fines content and grain size distribution. Two test series were considered, one with parallel gradations with decreasing D50 and constant Cc, Cu values (N-series), and a second one where Cc was kept constant and Cu, D50 values varied (W-series). In both series, the fines content varied from 0 to 50%. The most dramatic effects were noted for the clean sands as the Cu value increased and for the silty sands as fines content increased from 1 to 50%. In general, static and dynamic behavior was observed to depend on the amount of fines, Cu and D50 values. The same was true for pre-cycling and post liquefaction shear wave velocities. Post-liquefaction shear wave velocities were on the order of 8–13% of the pre-cycling values.

Behaviour of a loose silty sand under static and cyclic loading conditions

In recent years, considerable progress have been made in the study of liquefaction and flow failures with the introduction of the notion of steady-state of deformation and “collapse” envelope. These concepts are increasingly used in seismic stability analysis of slopes or embankments. However, as most of these studies were carried out on clean sands in the triaxial apparatus, one may question the general applicability of these results to practical conditions as several factors such as anisotropy, fines content, undrained strength anisotropy, boundary deformation conditions, stress history, etc. may play an important role. In this paper, the behaviour of the same soil, a loose silty sand, is compared for different loading and testing conditions: drained and undrained triaxial compression tests, drained and constant volume monotonic and cyclic direct simple shear (DSS) tests. Results allow to identify similarities and differences, in terms of undrained initial and steady-state shear strength and modes of undrained failure between triaxial and DSS test conditions and show that liquefaction in DSS cyclic tests is an instability triggered by shear failure developing once the friction corresponding to the characteristic envelope, as identified in the monotonic test, has been mobilized.

Shear Behavior of Wheat‐Concrete Interface during Monotonic and Cyclic Loading

The interface behavior between wheat and concrete plays a decisive role in the design of silo structures. In this paper, a series of strain‐controlled monotonic direct shear (MDS) tests, cyclic direct shear (CDS) tests, and postcyclic direct shear (PCDS) tests were conducted to investigate the wheat‐concrete interface behavior under monotonic and cyclic loading. The influence of cycle numbers, shear displacement amplitude, normal stress, and preloading consolidation was discussed in detail. In particular, the preloading consolidation simulates the partly discharging state of wheat. The values of peak stress increase with increasing displacement amplitude and cycles, and they change slightly after 10 cycles. The interface exhibits an overall contraction deformation during the MDS tests without preloading, but the contraction is suppressed by an alternating dilation during the DCS tests, and an overall small dilation occurs at small normal stress during PCDS tests. It is observed that the cyclic loading and preloading normal stresses result in an increasing peak strength, internal friction angle, and apparent cohesion, whereas a decrease in interface contraction deformation.

Experimental study of shear-key equipped pile to grout connection under cyclic loading

A technical solution for tidal turbine foundation in granite seabed consists of grouted steel piles. The piles would be subjected to cyclic loading due to the severe service conditions. The mechanical behaviour at the interface between the pile and the surrounding media is one of the key points that determine the bearing capacity of the foundation system. Experimental research work has been carried out in the laboratory to study the grouted pile-to-rock connection (GPRC) and focused more precisely on the pile to grout connection when the pile is equipped with shear-keys that enhance the interface capacity. Monotonic and cyclic shear tests were performed using a specific direct shear test device (BCR3D), allowing application of sample confining conditions close to the in-situ conditions, namely constant normal stiffness conditions. Cyclic tests - either under one way or two-way shear loading application - were performed on several samples, under both constant volume and various constant stiffness boundary conditions. This study has shown that the strength of the interface is highly dependent on the combination of mean load, cyclic amplitudes and number of cycles applied to the interface. Cyclic failure was observed with less than 30 cycles for two-way and one-way cyclic loading.

Experimental and analytical investigation of the influence of compressive load on rate-dependent high-damping rubber bearings

High-damping rubber bearings (HDRBs) have been widely accepted as a relatively novel type of seismic isolation devices in civil infrastructures construction, they are known to possess significant rate-dependent behavior and accommodate the gravitational load of the superstructure in typical applications. Hence, it necessitates better understanding of the mechanical behavior of HDRBs under coupling effect of compression and shear. The objective of the paper was to conduct experimental and analytical investigation to characterize the influence of compressive load on rate-dependent HDRBs. Firstly, a series of material tests including multi-step relaxation and monotonic shear tests were carried out on high-damping rubber, the strain rates and compressive stresses applied on specimens were varied and analyzed. Then, on the basis of experimental investigation, the classical Zener model was extended and a rate-dependent analytical model of HDRBs allowing for the consideration of compressive load was proposed. Finally, comparing the numerical simulations and experimental data obtained from both material tests and full-scale bearing tests, a reasonably good agreement was observed and the validity of the proposed model was demonstrated.

A fabric-based sand plasticity model with reversal surfaces within anisotropic critical state theory

The paper describes the formulation and capabilities of a new constitutive model that accounts for the effects of fabric anisotropy on the response of granular materials under monotonic loading. It is developed within the framework of bounding surface plasticity in conjunction with the concept of (stress) reversal surfaces, i.e., the use of the last stress reversal point as projection center for defining the image stress on the bounding surface. A key constitutive ingredient is the fabric anisotropy variable A, relating the fabric tensor to the plastic strain rate direction, that acquires the value A = 1 as the third requirement for critical state according to the anisotropic critical state theory. This A is used in the definition of dilatancy, the plastic modulus and the evolution equation of the fabric tensor, thus simulating experimental results that show more dilative and stiff response when the loading is applied along the direction of the fabric. Model performance is verified against a large database of monotonic shearing tests on samples of Toyoura sand prepared with three different methods, as well as similar tests on samples whose (initially horizontal) deposition plane was rotated by up to 90 degrees. All simulations are performed with a single set of constants, thus validating the efficiency of the model to account for density, stress level and, most importantly, fabric anisotropy effects on the monotonic shearing response. The paper shows that considering dependence of strength and dilatancy on Lode angle θ and state parameter ψ does not suffice for simulating fabric anisotropy effects on sand response. It ends with a discussion of how fabric effects on sand response are more pronounced under undrained, versus drained conditions.

Effect of Sample Reconstitution Methods on the Behaviors of Granular Materials under Shearing

Abstract The effect of sample reconstitution methods on the behavior of sand under shearing is investigated by using the first commercially available Variable Direction Dynamic Cyclic Simple Shear System. Three sample reconstitution methods are used in this study, which are as follows: the dry funnel method, air pluviation, and dried wet tamping. Because only dry specimens can be tested in many simple shear apparatuses, in this study, a new method called dried wet tamping is used to model the soil fabric generated by the wet tamping method, wherein the soil sample prepared by wet tamping is dried before being tested. Leighton Buzzard sand at various relative densities is tested in monotonic, one-directional cyclic, and two-dimensional circular cyclic simple shear tests. Experimental results show that different sample reconstitution methods have limited effects on the shear behavior in monotonic loading tests. On the contrary, the sample reconstitution methods greatly influence the dynamic responses of sand, including the undrained one-dimensional cyclic and two-dimensional circular cyclic loading. The liquefaction resistance is the greatest using the dried wet tamping method, followed by the dry funnel method and air pluviation method. These test results are also compared with previous studies on sample reconstitution methods, and their similarities and differences are analyzed.

Estimating normal effective stress degradation in sand under undrained simple shear condition

The degradation of the effective normal stress in soil surrounding the pile caused by undrained cyclic loading affects the shaft capacity of the pile and can lead to structural instability. In order to investigate this phenomenon, a series of constant volume monotonic and cyclic simple shear tests on Fontainebleau sand has been conducted. Based on the experimental results, the shear stress at phase transformation state is first determined for different initial void ratios and initial normal effective stresses. Then, the number of cycles to liquefaction is estimated as a function of both the cyclic and the average shear stresses normalised by the shear stress at phase transformation. An empirical equation to evaluate the normal stress degradation is formulated and the procedure of parameter identification is presented. The performance of the suggested formulation has been analysed, based on simple shear test results on Fraser River sand and Quiou sand, and triaxial tests on Karlsruhe sand, and it has been validated by a series of additional tests on Fontainebleau sand. All the results indicate that the proposed formulation is able to estimate with good accuracy the effective normal stress degradation in sand subjected to undrained cyclic shearing.

A 3D crystal plasticity model of monotonic and cyclic simple shear deformation for commercial-purity polycrystalline Ti with a harmonic structure

A micromechanical model was developed to describe the monotonic and cyclic simple shear deformation behavior of commercial-purity polycrystalline titanium (CP-Ti) with a harmonic structure (HS) design. The crystalline plasticity theory was implemented to model the constitutive behavior of the hexagonal close-packed (HCP) polycrystals. The grain size effect on the plastic yielding and hardening properties was considered by means of the classic Hall-Petch relation. Multiscale analyses were carried out for a representative volume element (RVE), including an fine-grained (FG) phase and a coarse-grained (CG) phase. This model was implemented into a finite element code (Cast3M) by means of a user subroutine. Monotonic simple shear tests and cyclic shear tests with imposed increasing strain amplitudes were carried out for CG and HS samples. Comparisons between the numerical results and the experimental data revealed the model's ability to describe the overall response correctly for both the HS CP-Ti and the homogenous CG CP-Ti under monotonic and cyclic shear loading.

Monotonic and cyclic simple shear response of gravel-sand mixtures

Understanding the factors that affect the monotonic and cyclic response of gravelly soils during earthquake events is critical to infrastructure design. In this study a large-size Cyclic Simple Shear (CSS) device was utilized to perform monotonic and cyclic shear tests on mixtures of either subrounded 9 mm Pea Gravel or angular 8 mm Crushed Limestone (CLS8) with subrounded Ottawa C109 sand. Tests were performed in constant volume conditions and shear wave velocity was measured for each specimen. Monotonic and cyclic test results at Dr = 47% show that there is an optimum mixture percentage that results in the greatest shear strength and resistance to liquefaction (40% Sand for Pea Gravel Mixtures and 60% Sand for CLS8 Mixtures). The effects of particle angularity, cyclic stress ratio, and initial vertical stress on monotonic and cyclic response of loose and dense gravel mixtures were investigated and are presented. Comparison of the results from the cyclic simple shear tests with existing liquefaction triggering charts suggests the need for improved charts for gravelly soil liquefaction evaluation.

A micromechanical experimental study of highly/completely decomposed tuff granules

In this paper, an experimental micromechanical study is presented investigating the contact mechanics and tribological behaviour of highly/completely decomposed tuff granules. The parent material was taken from two locations—named the top and bottom—from a recent landslide in Hong Kong, and in this study the tested granules were obtained from the parent material after drying and sieving processes. Basic material characterisation was conducted quantifying the particle shape, the surface roughness and the strength of a set of grains. A set of twenty-nine monotonic inter-particle shearing tests were conducted on pairs of granules taken from the top and bottom of the landslide. It was found that the granules had very high friction angles at their contacts, in general greater in comparison with other materials reported in the literature. The slightly greater inter-particle friction for the granules taken from the top of the landslide might be because of their higher roughness in comparison with the ones from the bottom. Additional experiments were conducted to investigate the normal and tangential load–displacement response of the granules subjected to cyclic loading. A good curve fitting for the normal load–displacement response could be obtained by using very low apparent Young’s moduli in the Hertzian model. In general, the decomposed tuff granules showed significant plastic response during the first normal load cycle, and this plastic behaviour continued for the subsequent third and fourth cycles. In the cyclic inter-particle shearing tests, the nonlinearity and hysteresis increased for larger cyclic displacements, but the effect of the number of shearing cycles on the energy loss was generally small. Finally, a limited discussion is presented on the applicability of a theoretical model on the tangential load–displacement behaviour of the granules.

Performance Assessment of Interlayers with Different Tack Coats by Considering Loading Types and Failure Modes

A monotonic direct shear test (DST) is the most commonly used method to evaluate bond strength of interlayers; however, it does not consider the actual repetitive traffic loading that pavement undergoes during its service life. This study aims to examine the link between various parameters obtained from a monotonic DST and the results of a cyclic loading test that more realistically assesses the interlayer performance with tack coats. Furthermore, to investigate the possible effect of the interface failure mode (shear vs. tensile) on the performance assessment of the tack coat interlayers, a simple indirect tensile test was conducted to determine the tensile strength of the interlayers. Field core samples extracted from a test section constructed in Nebraska were used for various laboratory tests. The field test section included 14 subsections containing various types of tack coat materials with different application methods. Permanent shear deformation and interface stiffness were selected as the failure criteria to characterize the interface resistance associated with cyclic load repetition. Shear strength, shear stiffness, and interlayer bond energy were chosen as the failure criteria for the monotonic DST. Results show that the interlayer shear strength from the monotonic DST had an acceptable correlation with the cyclic test results, and interlayer bond energy is a good predictor of the shear resistance of the tack coats with a high correlation with the cyclic test. The simple indirect tensile test was capable of differentiating interlayer performance with different types of tack coating.

Automatic Static and Cyclic Shear Testing Machine under Constant Normal Stiffness Boundary Conditions

Abstract Dynamic loads, including earthquake, blasting, and vibration loads, induce cyclic shear loads along the joints in rock masses; hence, the risk of failure increases on the joints due to changing shear resistance. On the other hand, joints are under different boundary conditions: constant normal load (CNL) and constant normal stiffness (CNS). Normal stiffness increases on the joints with increasing depth, and it can affect shear resistance. For an accurate assessment of joint shear resistance under varying normal stiffness and number of cycles, advanced laboratory shear apparatus is essential for the shear test. Conventional direct shear apparatuses have limitations such as boundary conditions, working under monotonic (static) shear loads only, or cyclic shear loads with no change of frequency and amplitude of shear loads. Therefore, a new large-scale servo-controlled direct shear testing machine was developed to conduct cyclic shear test (as well as monotonic shear test) under CNL and CNS boundary conditions with varying normal stiffness at different frequencies and amplitudes of shear loads. In the present study, the cyclic shear tests were conducted on nonplanar joints under varying normal stiffness. Moreover, the effects of different frequencies and amplitudes of shear loads were investigated. The test results indicate that peak shear stress increases with increasing normal stiffness at the first cycle, but the influence of normal stiffness decreases with an increase in the number of shear cycles. The frequency of shear load influences peak shear stress, i.e., peak shear stress increases with increasing frequency. The number of cycles does not affect peak shear stress on the joints at low shear amplitude, but peak shear stress decreases with higher amplitude.

Identification of the anisotropic behavior of an aluminum alloy subjected to simple and cyclic shear tests

The main purpose of this paper is to study the behavior of the 2000 aluminum alloy series used particularly in the design of Airbus fuselage. The characterization of the mechanical behavior of sheet metal on 2024 aluminum alloy and its response to various loading directions under monotonic and cyclic tests are extremely considered. To solve this problem, first, an experimental platform which essentially revolves around mechanical tests and then a series of optical and transmission electronic visualizations have been carried out. These mechanical tests are monotonic and cyclic shear tests applied under the same conditions on the test specimens of 2024 aluminum alloy. Cyclic shear tests have been carried out in order to show the Bauschinger effect and then the kinematic hardening phenomenon. The hardening curves of the simple shear test showed the Portevin-Le Chatelier effect for all loading directions. Next, the experimental results obtained (Portevin-Le Chatelier and Bauschinger effects) are discussed and analyzed in relation to the microstructure of the studied alloy using an optical microscope and a transmission electron microscope. Thereafter, the plastic anisotropy is modeled using an identification strategy that depends on a plastic criterion, an isotropic hardening law, a kinematic hardening (linear and nonlinear) law, and an evolution law. More precisely, particular attention is paid to the isotropic power Hollomon law, the saturation Voce law, and the saturation Bron law. In the case of the cyclic tests, linear kinematic hardening described by the Prager law and nonlinear kinematic hardening expressed by the Armstrong–Frederick law are introduced. Finally, by smoothing the experimental hardening curves for the various simple and cyclic shear tests, a selection is made in order to choose the most appropriate law for the identification of the material behavior.

Asphalt mixture layers’ interface bonding properties under monotonic and cyclic loading

This paper focuses on investigating the interface shear bonding properties of asphalt pavement structures using both monotonic and cyclic direct shear tests. Several pavement structures were considered, differing in the asphalt mixture type and tack coat type, and laboratory preparation of the double-layered asphalt specimens. Based on the results on bond materials used in this research, it was found that the resulting shear strength from monotonic shear test can be used only as a rough indicator for long term interface bonding performance, because not all research and field experience could be reflected in the test results. The cyclic shear test employed in this study can be used for evaluating the interface fatigue performance. Additionally, differentiation between particular bond materials with respect to interface shear bonding properties is assured.

Effect of glass fibre grids on the bonding strength between two asphalt layers and its Contact Dynamics method modelling

This study evaluates the effect of glass fibre grids, used to reinforce asphalt structures, on the bonding strength between a wearing and a binder layer. For this purpose, a test surface consisting of a 6-cm thick binder (0/16 mm) and a 6-cm thick wearing layer (0/11 mm) was built. Four different grids coated with various quantities of bitumen emulsions C60B4-S and C40B5-S were used. Comparison sections were made without grid but also coated with different quantities of emulsions. Extracted cores with 150 mm diameter were tested at ambient laboratory temperature with a monotonic shear test (Leutner). Displacement, shear force and shear stress were measured. The influence of grid characteristics, the existence of a non-woven and the size of the strands as well as the effect of different emulsions on the shear bonding strength were observed, and a numerical model based on DEM simulations was developed. Also, the effect of temperatures on the shear strength with different reinforced and unreinforced specimens was studied. The numerical samples were created with the particles size distribution of the material, where a spherical shape was analysed. A viscoelastic model was implemented for the contact law. We show that the numerical model is able to reproduce the mechanical behaviour of asphalt mixture and reinforced asphalt mixture under the shear loading test. We find that the tests without a reinforcement grid reach more important values of stress at failure and that the decrease in shear stress levels at failure is more important for larger sections of the strands of the grid.

Cyclic and Post-Cyclic Shear Behaviour of Interface between Geogrid and EPS Beads-Sand Backfill

Lightweight sand–EPS beads composite is a new artificial geo-material, which has been recently found applications in geotechnical engineering projects. A series of laboratory tests were carried out using a large-scale cyclic direct shear test apparatus to evaluate the monotonic, cyclic and post-cyclic behaviour of an interface between EPS-sand mixtures and a Polyfelt geogrid. EPS were added to sand at 0%, 0.5%, 1%, and 2% by weight. Tests were conducted under three different vertical stresses (30 kPa, 60 kPa and 90 kPa). The influences of cyclic shear semi-amplitude, number of cycles and normal stress on interface properties are investigated. The test results revealed that for a given strain level, interface shear stiffness decreases and damping ratio was shown to increase with increasing EPS content. Hardening behaviour was observed with the number of cycles under different normal stress levels and EPS contents. The EPS-sand-geogrid specimens did not develop clear peak shear stress at monotonic and post-cyclic direct shear tests. The EPS-sand-geogrid mixtures represent an overall contraction behaviour in monotonic, cyclic and post-cyclic stages. The apparent adhesion of interface was shown to increase and the friction angle of interface to decrease with EPS content.