Shear Strain Levels Research Articles

Residual Strength of Liquefied Soil: The Effect of Induced Partial Saturation

Abstract Post-liquefaction response and residual strength play important roles in stability assessment of liquefied ground. Considering the recent advancements in the application of induced partial saturation for liquefaction mitigation, the state of knowledge in estimating the residual strength should be extended for liquefied desaturated soils. In this paper, the residual strength response of a clean sand at different saturation levels was investigated using a ring shear device. Direct air injection was used to desaturate the soil, which helped with mitigating the liquefaction under cyclic loading. However, by raising the shear strain level, both saturated and partially saturated soils were liquefied, followed by residual strength measurement. Results indicate that the residual strength increased with a reduction of the saturation level because of the change in compressibility and consequent volume reduction. In addition, the strain-rate dependency of the residual strength was confirmed because an increase of shear strain rate resulted in an increase in residual strength under both saturated and partially saturated conditions.

Horizontal capacity of base isolation rubber devices under large vertical design stress, valued through full-scale tests

An experimental campaign to investigate the effect of vertical stress on horizontal capacity of rubber bearings is argued in this paper. Results from a test program on full-scale HDRBs are discussed. They concern three different bearings (ϕ = 500–600 – 700 mm), having variable shape factors [S1 = 19,44–22,72] [ S2 2,8 ÷ 3,4]. The experimental data refer mainly to static shear tests, at varying levels of shear strain (up to γ = 250%) combined to increasing compressive stress (from 6 MPa to 20 MPa). Re-creating load conditions similar to the one occurring in situ, the experimental tests want to assess the impact of growing vertical stress on device horizontal deformability. The elaborations of data underline a progressive decrease of horizontal stiffness when even higher pressure acts. This is confirmed by visible softening effects that occur when horizontal displacement exceeds a certain percentage of device diameter, variable with the value of the applied compressive stress. This response is undoubtedly related to variations in axial load carrying capacity of bearings under large deformations: for this reason, evaluations on the critical load have been included in the discussion. Analytical formulations have been compared to experimental results to support the argumentations. The elaborations have been accompanied by the use of dimensionless parameters, in particular the ratio γ/S2, available also for design aims: this type of representation helps to evaluate deformation limits for rubber devices.

Dynamic Properties of Calcareous Sands from Urban Areas of Abu Dhabi

Abu Dhabi (ABD) has recently developed its national building code that mandates dynamic analysis of large structures to seismic loadings. Large strain dynamic properties such as shear modulus (G) and damping ratio (D) of local undisturbed calcareous sands are not available. Designers are compelled to choose degradation models from studies on calcareous sands of other regions that are usually reconstituted. This research presents for the first time large strain dynamic properties of calcareous sands of urban ABD. Undisturbed samples are collected from different areas of urban ABD and are tested in cyclic triaxial (CT) devices fitted with bender elements (BE). The dynamic properties as functions of confinement are curve fitted with power models, whereas their variation with shear strain level is curve fitted with hyperbolic models. The results are compared with findings of previous studies on calcareous and silica sands. The results indicate that dynamic properties of all samples degrade with shear strain at almost the same rate irrespective of their spatial distribution. The proposed degradation models can therefore be used in dynamic analyses. The results from this study show smaller rates of degradation in dynamic properties compared to other studies on similar sands. The change in low-strain shear wave velocity (Vs) with confinement is significant among the tested samples; therefore, a site-specific evaluation of Vs is recommended. The dynamic properties of calcareous sands of ABD and previous studies however exhibit larger degradation with shear strain and a smaller increase in confinement compared to silica sands.

Lateral hysteretic behavior of a novel metal rubber bridge bearing

In this paper, a novel metal rubber bearing is proposed as an alternative to the conventional rubber bearings for small- and medium-span highway bridges to solve the aging-related issues of conventional rubber bearings such as chemical degradation and erosion. The bearing is made of porous metal wire by coiling, weaving and cold-pressing to specific shapes. A shear test program is then described on two metal rubber bearings of stainless steel wire with different densities in order to identify the characteristics of hysteretic curves. The effects of shear strain, compressive stress, loading frequency and repeated loading cycles on the hysteretic behavior were investigated. It was found that the lateral hysteretic curves are approximately in bilinear shape, which consists of an initial elastic stage and a post-yield stage. The equivalent damping ratio of the tested bearings was around 20% at 25% shear strain levels and meanwhile increased with the strain levels, indicating an appreciable energy dissipation capacity. In addition, stiffness degradation was observed for the hysteretic curves beyond a certain deformation limit due to the plastic deformation caused by wire delamination and bearing bulging. However, beyond this limit, the bearing could still work as a unit with stable hysteretic behavior. These characteristics make the metal rubber bearing a great candidate for the conventional rubber bearings. It was also found that the hysteretic behavior is related with a variety of parameters such as density, loading frequency and compressive stress. Finally, it was found that the Bouc-Wen model with appropriate input parameters representing the mechanical properties can accurately simulate the hysteretic curves of the proposed bearings.

Empirical approaches to estimate the nonlinear dynamic responses of earth-core rockfill dams subjected to earthquake ground motions

This study investigates three aspects of the dynamic response of earth-core rockfill dams (ECRDs) under earthquake loadings, including induced shear strain, increased fundamental period, and shear modulus reduction. A database of the recorded ground motions of ECRD cases in Japan is analyzed to carry out this study. The required response parameters as mentioned above are extracted by analyzing the acceleration time histories recorded at the dams’ crests and foundations. Subsequently, statistical analyses are performed to achieve the objectives of this study. A graph is developed describing the change in the dam’s fundamental period with the induced shear strain, and it is observed that the increase of the dam’s period is dependent on the increase in the shear strain levels. A relationship is established to estimate the anticipated levels of shear strain from the intensity measure (IM) of the earthquake signals. In the proposed predictive relationship, a new IM is used that can adequately characterize the severity of an earthquake. Finally, a curve and a range are suggested for the average shear modulus degradation of the ECRD’s core materials. The presented empirical graphs and relationships in this study are valuable tools to obtain an appropriate perception of dams’ nonlinear behaviour under strong earthquake excitations.

Dynamic characteristics of combined isolation systems using rubber and wire isolators

The present study aims to investigate the dynamic properties of a novel isolation system composed of separate rubber and wire isolators. The testing program comprised pure compressive, pure-shear, compressive-stress dependence, and shear-strain dependence tests that used full-scale test specimens according to ISO 22762-1. A total of 22 test specimens were fabricated and investigated. Among the tests, the pure compressive test was a destructive test that reached up to the failure stage, whereas the others were nondestructive tests before the failure stage. Similar to the pure-shear test, at each compressive-stress level in the compressive dependence test or at each shear-strain level in the shear-strain dependence test, the cyclic loading was conducted for three cycles. In the nondestructive tests, examination of the dynamic shear properties in the X-direction was independent of the Y-direction. The test results revealed that the increase in the shear strain increased the energy dissipation but decreased the damping ratio, whereas the increase in the compressive stress increased the damping ratio. In addition, a macro model was developed to simulate the load-displacement response of the isolation systems, and the prediction results were consistent with the experimental results.

Компьютерное моделирование сварки давлением образцов из гетерофазных никелевых сплавов через прослойку

Computer simulation of pressure welding of cylindrical workpieces through an interlayer was carried out using the DEFORM-2D software package in a two-dimensional formulation (axisymmetric deformation). Two combinations of materials to weld were considered: sample I — cylinders of heterophase nickel-based deformable superalloy EP975 in a coarse-grained state were welded through an interlayer of EP975 with a fine-grained microduplex structure; sample II — cylinders of dissimilar nickel-based alloys, one the deformable alloy EP975 in a coarse-grained state and the other an intermetallic alloy VKNA-25 with a single-crystal structure, were welded through an interlayer of EP975 alloy with a fine-grained microduplex structure. The welding process was carried out under isothermal conditions at a temperature of 1125°C and an initial strain rate of 10−4 s−1. The material characteristics were described by experimental curves obtained under uniaxial compression tests of alloys at the welding temperature. The Siebel friction model was used to describe the contact conditions on the surfaces to be welded. The friction coefficient was taken equal to 0.3. The distribution of equivalent, axial, radial, circumferential and shear components of stress and strain in the samples have been investigated. Analysis of the simulation results allowed one to conclude that, in comparison to welding of similar materials, during welding of dissimilar materials the values of the radial, axial and circumferential stresses increase. Radial and circumferential stresses in the material of the cylinders are tensile, while compressive stresses prevail in the material of the interlayer. Area with the maximum values of shear stresses in the region of contact between the cylinders and the interlayer also increases. In this case, axial, radial and circumferential strains decrease in a cylinder made from a material with higher strength, the overall level of shear strain does not change, and on the reciprocal contact surface of the interlayer, the region of extension of maximum shear strain extends to the entire contact zone. Such a combination of factors allows one to conclude on more favorable pressure welding conditions for welding of dissimilar alloys in comparison with similar materials.

Assessment of the loading waveform on the cyclic liquefaction resistance with Hostun 31 sand

This paper was aimed at highlighting the impact of loading waveforms on the cyclic liquefaction resistance of sand. The test specimens were reclaimed by the dry tamping method with Hostun 31 sand, and the density of sand matrix was controlled to be 0.70. Three sets of undrained cyclic triaxial tests were performed by altering the loading waveforms as follows: triangular, sine and rectangular waves. The impact of the loading waveform was experimentally observed as axial cyclic stress was applied. Under the same amplitude of loading, it was found that the rectangular wave led to the most severe liquefaction as a result of greater imposed force acting for a longer duration. The triangular wave led to the lowest liquefaction softening, and the sine wave was the case in between. Consequently, in terms of the cyclic strength curves, diverse curves related to the imposed waveform were observed, and the curve for rectangular wave was located in the lowest part of the graph, thereby reconfirming its higher liquefaction potential. An in-depth analysis of the dynamic properties suggested that the development of the damping ratio with the progression of shearing is intrinsic for a given sand fabric under a certain initial confining stress. A unique relationship between the damping ratio and the amplitude of shear strain could be roughly established. However, the number of cycles required to trigger a certain level of shear strain remained a function of the amplitude and waveform. A novel parameter was proposed in this paper on the basis of the Arias intensity in order to unify the sand liquefaction response. Compared with the conventional method, one of its advantages is its ability to express the combined influence of the amplitude and waveform through a time-integral for a given imposed loading.

Short and Long-term Behaviours of Bored Tunnels in Port-Said Clay

This study investigates the behaviour of bored tunnels in the Port-Said very soft to firm clay deposit in El-Tina Plain, north-eastern Egypt. Recent studies provided full characterization of the physical, mechanical and time-dependent properties of Port-Said Clay. This characterization enabled simulating its constitutive behaviour using the stress-dependent Modified Cam Clay model. The finite difference method is utilized to simulate the interaction between the tunnel and Port-Said Clay. The results are presented in terms of the pore water pressure regime, shear strain level, ground surface settlement and tunnel lining bending moment. The results show significant effect of the face and grouting pressures on the tunnel’s short and long-term behaviours. The term “reference hydrostatic pressure” is introduced to evaluate short-term face stability as a more practical and easy-to-quantify parameter compared to the conventional stability number. New empirical equations are developed to describe the long-term surface settlement trough (maximum settlement and trough width) in terms of the grouting pressure and tunnel diameter for tunnels in similar soft clay deposits.

Design and Optimization of Hybrid Interface Joint in a Composite Fan Blade of Aircraft Engine

Fan blades are one of the most important components of an aircraft engine. Bird strikes on fan blades have always been a cause of worry and it can cause slices of birds hitting other parts of the engine which may lead to greater damages. Bird strikes cannot be completely avoided. However, reduction of the impact of a bird on jet engines can be achieved by suitable design and manufacturing, through the simulation analysis. Although current composite blades can withstand the bird strike impact, some delamination failures are still observed on the trailing edge side of the blade, possibly due to vibration bending modes This paper talks about using two fibers in composite blade instead of the current single fiber one. For this to be feasible, two fiber joints at various locations on the blade have to be properly designed. The design criteria used here is the lowest inter-laminar shear strain level at critical joint locations. Suitable size coupon models in FEA with hybrid joints inside are used to simulate the blade bending with appropriate boundary conditions. The coupon models were developed by using the ANSYS APDL and linear static analysis was performed for different repetitive layups and varying layer by layer joint locations. The coupon joint designs with minimum inter-laminar shear strains are shortlisted to be recommended for use in sub-element and blade models.

Dynamic Nonlinear and Residual Deformation Behaviors of the Fly Ash‐Modified Loess

Metastable loess soils can deform, inducing geological and engineering disasters. Therefore, the behavior of the loess under dynamic load is gaining massive attention from researchers to improve the strength of the soils. Fly ash mixed with loess can improve strength and reduce construction costs and environmental pollution. Moreover, it has strong economic and social benefits. This paper investigates the influence of fly ash on the dynamic properties of the modified loess through a series of dynamic triaxial tests of the fly ash modified loess with different fly ash contents. The treated soil samples were prepared using a static compaction method in both ends and cured for 28 days. The dynamic shear modulus ratio, the damping ratio, and the dynamic residual strain of the modified loess were analyzed. The variation characteristics of the dynamic shear modulus ratio and damping ratio with the dynamic shear strain of the fly ash modified loess were obtained. The effect of fly ash content on the dynamic nonlinear parameters of the modified loess was also investigated. In addition, the relationship between the dynamic residual strain and the fly ash content was discussed. The results show that the dynamic shear modulus ratio of fly ash modified loess decreases nonlinearly with the increase in the dynamic shear strain. However, the attenuation rate difference of the curves is small. The damping ratio increases gradually with increasing dynamic shear strain. Under a certain dynamic shear strain level, the damping ratio decreases with the increase in the fly ash content. The dynamic residual strain increases with the increase in the dynamic stress. However, it decreases with the increase in the fly ash content. When the fly ash content is between 10% and 20%, the dynamic residual strain of fly ash modified loess is reduced rapidly. However, when the fly ash content exceeds 20%, the dynamic residual strain decreases slowly. The fly ash content of 20% could be suggested as an optimal content for seismic resistance of the loess foundation.

Granule attrition by coupled particle impact and shearing

A novel device has been developed for continuous shearing and repeated impact of granules in order to simulate granule attrition and dust formation under realistic plant conditions of mechanical stresses, shear strains and strain rates. The device subjects the granules to multiple impacts at a range of velocities prevailing in typical process plants, and to shear deformations using two rollers with an adjustable gap to simulate the level of shear stresses and strains experienced during bulk motion, e.g. discharge from silos onto conveyor belts, etc. In this paper, the device operation and tests carried out to determine the settings required for attaining a desired impact velocity and shear strain rate are described. Subsequently, the extent of breakage of the granules is determined for the specified settings and the results are compared with data obtained by more established methods, e.g. annular shear cell and single particle impact tests.

Dynamic Characterization of Tire Derived Aggregates

Despite the recent efforts in characterizing and investigating the dynamic properties of tire-derived aggregates (TDA) and its use in civil engineering applications, the size of TDA used in most of the previous work was significantly smaller than the TDA size range mentioned in ASTM D6270 standards. There are two types of TDA, Type A and Type B, in which the maximum aggregate size of Types A and B are 200 and 450 mm, respectively. Thus, the availability of experimental data and shear modulus reduction curves for the dynamic behavior of TDA of larger sizes are deemed necessary for practical engineers to assess and investigate the behavior of such material under dynamic loads. This paper provides the results of large-scale undrained cyclic triaxial tests performed on Type A TDA at large strain amplitudes. The tests were performed under confining pressures ranging from 25 to 200 kPa and shear strain levels ranging from 0.1% to 10%. Furthermore, each test consisted of successive stages in which the number of cycles and axial strain levels varied. The shear modulus of Type A TDA has a range of 245–1,796 kPa, with a decreasing trend with increasing shear strain amplitudes. Furthermore, the dampening ratios were found to range from 11% to 23.5%. Finally, the shear modulus reduction curves were obtained through curve fitting techniques and nonlinear regression.

On Cohesive Soil Damping Estimation by Free Vibration Method in Resonant Column Test

Abstract Measurement of soil properties under cyclic and dynamic loading conditions is a critical task in the solution of most geotechnical earthquake engineering problems. The main dynamic properties of soils are usually expressed in terms of shear modulus and damping ratio that are generally obtained from laboratory tests. To date, the resonant column test is considered one of the most accurate ways to determine dynamic soil properties at low to medium-strain levels. Because it allows for investigation of a wide range of strain amplitudes, it is a valuable tool for characterizing the shear soil behavior for a large number of practical geotechnical problems. One of the approaches followed in estimating the damping ratio from the resonant column test is the free vibration method (also called logarithmic decrement or amplitude decay method). It consists of analyzing the time history of the damped free vibrations of the specimen once harmonic loading is cut off after reaching the resonant conditions. The soil damping ratio is determined measuring the logarithmic ratio of the amplitude of any two successive peaks of the system damped motion (logarithmic decrement). In this article, the influence on the damping ratio of the shear strain level, the plasticity index, the confining pressure, and the time interval between the peaks selected in calculating the logarithmic decrement is evaluated from the results of resonant column tests performed on 51 undisturbed isotropically consolidated fine-grained soil specimens.

Cyclic degradation and pore pressure dynamics of EICP treated hydrocarbon contaminated sands

Enzyme-induced carbonate precipitation (EICP) is an innovative bio-inspired approach that has emerged in recent years, offering a more environmentally sustainable option for soil improvement. The present article aims at extensively examining the effect of EICP treatment on the cyclic response of silty sands containing petroleum hydrocarbon compounds. Strain-controlled cyclic triaxial tests have been carried out on hydrocarbon contaminated sand with and without EICP treatment. Several independent variables such as hydrocarbon content (2, 4, 6, 8, and 10%), shear strain amplitudes (0.5% and 1%), and curing period (7 days and 14 days) were considered in the study. Prior to this, a baseline analysis was conducted to determine the effect of EICP treatment solution composition on the efficiency of carbonate precipitation. The effectiveness of the treatment was systematically investigated based on cyclic pore pressure response and degradation of cyclic shear modulus. The results revealed that petroleum contamination moderately increases the cyclic resistance up to a transition point beyond which it falls off sharply. The coupled effect of increasing oil content and curing time of EICP treatment has also been assessed. The variation of cyclic strength with crude oil content results in a single-peaked profile for both untreated and treated specimens. EICP treatment increases the cyclic resistance of oil-contaminated sand up to 1.5 times by suppressing the excess pore pressure build-up. A signification recovery in the degradation parameter, as high as 80%, was also observed. However, with increasing oil content and shear strain levels, the efficacy of EICP treatment exhibited a remarkable decline. The microstructural mechanism believed to be responsible for such a behavior has also been discussed.

Simulation of the Strain Amplification in Sulci Due to Blunt Impact to the Head

Traumatic brain injury (TBI) has become a concern in sports, automobile accidents and combat operations. A better understanding of the mechanics leading to a TBI is required to cope with both the short-term life-threatening effects and long-term effects of TBIs, such as the development chronic traumatic encephalopathy (CTE). Kornguth et al. (1) proposed that an inflammatory and autoimmune process initiated by a water hammer effect at the bases of the sulci of the brain is a mechanism of TBI leading to CTE. A major objective of this study is to investigate whether the water hammer effect is present due to blunt impacts through the use of computational models. Frontal blunt impacts were simulated with 2D finite element models developed to capture the biofidelic geometry of a human head. The models utilized the Arbitrary Lagrangian Eulerian (ALE) method to model a layer of cerebrospinal fluid (CSF) as a deforming fluid allowing for CSF to move in and out of sulci. During the simulated impacts, CSF was not observed to be driven into the sulci during the transient response. However, elevated shear strain levels near the base of the sulci were exhibited. Further, increased shear strain was present when differentiation between white and gray matter was taken into account. Both of the results support clinical observations of (1).

Mechanobiological model for simulation of injured cartilage degradation via pro-inflammatory cytokines and mechanical stimulus

Post-traumatic osteoarthritis (PTOA) is associated with cartilage degradation, ultimately leading to disability and decrease of quality of life. Two key mechanisms have been suggested to occur in PTOA: tissue inflammation and abnormal biomechanical loading. Both mechanisms have been suggested to result in loss of cartilage proteoglycans, the source of tissue fixed charge density (FCD). In order to predict the simultaneous effect of these degrading mechanisms on FCD content, a computational model has been developed. We simulated spatial and temporal changes of FCD content in injured cartilage using a novel finite element model that incorporates (1) diffusion of the pro-inflammatory cytokine interleukin-1 into tissue, and (2) the effect of excessive levels of shear strain near chondral defects during physiologically relevant loading. Cytokine-induced biochemical cartilage explant degradation occurs near the sides, top, and lesion, consistent with the literature. In turn, biomechanically-driven FCD loss is predicted near the lesion, in accordance with experimental findings: regions near lesions showed significantly more FCD depletion compared to regions away from lesions (p<0.01). Combined biochemical and biomechanical degradation is found near the free surfaces and especially near the lesion, and the corresponding bulk FCD loss agrees with experiments. We suggest that the presence of lesions plays a role in cytokine diffusion-driven degradation, and also predisposes cartilage for further biomechanical degradation. Models considering both these cartilage degradation pathways concomitantly are promising in silico tools for predicting disease progression, recognizing lesions at high risk, simulating treatments, and ultimately optimizing treatments to postpone the development of PTOA.

Effect of Sand Fouling on the Dynamic Properties and Volume Change of Gravel During Cyclic Loadings

Understanding the factors that influence the dynamic behavior of granular soils during cyclic loading is critical to infrastructure design. Previous research has lacked quantitative study of the effects of fouling index (FI), mean effective confining pressure, relative density, shear strain level and anisotropic consolidation, especially when the effective vertical stress is lower than the effective horizontal stress on the dynamic behavior of gravelly soils. The objective of the present study was to evaluate the dynamic behavior and volume change of both clean and fouled specimens for practical applications. To this end, cyclic triaxial tests with local strain measurements under both isotropic and anisotropic confining conditions were conducted. It is found that the fouled specimen with 50 % sand (i.e. the specimen which contains 50 % gravel and 50 % sand) has the highest shear modulus at low shear strain levels and the largest volume reduction and damping ratio at large shear strain levels. The results of tests indicate that the effect of fouling index on the shear modulus is reduced at large shear strain levels. Volumetric contraction due to the increase in mean effective confining pressure is more significant at large shear strain levels. The results also indicate that the stiffness of the specimens under anisotropic compression mode are larger than those in extension or isotropic mode.

Effective skeleton stress and void ratio for constitutive modeling of fiber-reinforced sand

Inclusion of flexible fibers such as polypropylene and polyester is an effective method for soil improvement, as it significantly enhances the soil strength and ductility. A proper constitutive model is essential for assessing the stability and serviceability of fiber-reinforced slopes/foundations. A new method for constitutive modeling of fiber-reinforced sand (FRS) is proposed. It assumes that the strain of FRS is dependent on the deformation of the sand skeleton only, while the effective skeleton stress and effective skeleton void ratio, which should be used in describing the dilatancy, plastic hardening and elastic stiffness of FRS, are affected by fiber inclusion. The effective skeleton stress is dependent on the shear strain level, and the effective skeleton void ratio is affected by the fiber content and sample preparation method. A critical state FRS model in the triaxial stress space is proposed using the concept of effective skeleton stress and void ratio. Four parameters are introduced to characterize the effect of fiber inclusion on the mechanical behavior of sand, all of which can be easily determined based on triaxial test data on FRS, without measuring the stress–strain relationship of individual fibers. The model is validated by triaxial compression test results on four fiber-reinforced sands under loading conditions with various confining pressures, densities and stress paths. Potential improvement in the model for incorporating fiber orientation anisotropy is discussed.

Experiments on cyclic performance of external diaphragm joints between CFDST columns and steel beams

External diaphragm joint has been widely used in concrete-filled steel tubular (CFST) structure because of its large stiffness, good plasticity, and high bearing capacity. This paper studied new external diaphragm joints designed to connect concrete-filled double steel tubular (CFDST) columns and steel beams. Experiments were conducted to investigate the cyclic performance of nine joint specimens subject to cyclic horizontal load and fixed axial load at the top of the column. The variable parameters considered in the test were axial load of the CFDST column, width of external diaphragm, configuration of anchorage web and beam to column bending stiffness ratio. The load–displacement hysteresis behaviors were discussed. Failure mode of the joints was mainly dependent on beam to column bending stiffness ratio (k) and axial compression ratio (n), so the limit of these two factors should be considered to avoid the column failure in engineering design applications. The shear strain level in panel zone was high especially for weak-column joints. Results also showed that initial stiffness of external diaphragm joint significantly increased with the improvement of axial compression ratio, but the stiffness suffered a sharp degradation; the ductility and energy absorption ability improved with the width improvement of the external diaphragm; ribbed anchorage webs effectively improved initial stiffness and bearing capacity of external diaphragm joints.