Shear Stiffness Properties Research Articles

A Comparison on Physical and Rheological Properties of Three Different Waste Plastic-Modified Bitumen

This study aims to investigate the effect and the possibility of using waste plastic as a sustainable cost-effective polymer to modify bitumen binders. Different types of waste plastic have been used in this modification, including polyethylene terephthalate (PET), high-density polyethylene (HDPE), and low-density polyethylene (LDPE). The modification targets the physical characteristics, rheological properties, and binders’ resistance to ageing. Both long- and short-term ageing are investigated to determine the durability and ageing resistance of the modified binder using rolling thin film oven tests (RTFOT) and pressure ageing vessels (PAVs). Penetration tests and dynamic shear rheometer (DSR) tests were conducted to investigate and evaluate the complex shear modulus, stiffness, elasticity, and viscous properties. The results show that 2% and 4% of HDPE and LDPE are recommended as ideal contents for good performance, as reflected by the penetration tests before and after ageing. However, higher contents, such as 6% and 8% HDPE and LDPE, are not significant in improving the stiffness, elasticity, and ageing resistance. Therefore, samples of 6–8% HDPE and LDPE are more vulnerable to permanent deformation. Furthermore, using waste PET exhibits obvious improvements in terms of the physical characteristics, rheological properties, stiffness, elasticity, and ageing resistance with up to 8% PET-modified bitumen. Based on the results, the ideal type and content is 6–8% PET waste plastic.

Experimental investigation and empirical model to determine the damping and shear stiffness properties of soft rock under multistage cyclic loading

The damping and shear stiffness properties of soft rock play important roles in the stability of rock masses in earthquake-prone regions. The shear modulus and damping ratio are two important dynamic rock parameters that can significantly impact the results of a seismic response analysis. Cyclic loading tests were carried out on sandstone, conglomerate and glutenite specimens at different stress levels, stress amplitudes, confining pressures and moisture contents to investigate the damping behaviour of soft rock. The effects of the stress amplitude, strain amplitude and stress level on the shear modulus and damping parameters were investigated, and the damping behaviour was comparatively analysed under different loading conditions. The dynamic shear modulus was correlated with the stress amplitude of soft rock. The results showed that as the stress amplitude decreased, the moisture content had less of an effect on the dynamic shear modulus and more of an effect on the damping parameters. The damping parameters under cyclic loading were larger for multistage stress levels than for multistage stress amplitudes. The hyperbolic model was used to describe the stress-strain relationship of soft rock under multistage cyclic loading. Finally, an empirical model was proposed to correlate the dynamic shear modulus with the damping ratio of soft rock at different stress levels and stress amplitudes and was found to effectively describe the damping behaviour of soft rock under multistage cyclic loading.

Depth-Dependent Seabed Properties: Geoacoustic Assessment

Offshore geoengineering requires reliable sediment parameters for analysis and design. This study proposes a robust framework for effective stress-dependent geotechnical and geoacoustic properties for seabed analysis based on geophysical models, new experimental data, and extensive data sets compiled from published studies that cover a wide range of marine sediments and depths. First, effective stress-dependent porosity versus depth profiles are computed using compaction models that are valid for a wide stress range. Then, P- and S-wave velocity data are analyzed in the context of effective stress-controlled density, shear stiffness, and bulk modulus within a Hertzian-Biot-Gassmann framework. Finally, this study selects six distinct “reference sediments” that range from clean sands to high-plasticity clays and assigns self-consistent compaction and shear stiffness properties using well-known correlations reported in the literature in terms of specific surface, plasticity, and grain characteristics. Results show that robust physical models for compaction and stiffness adequately predict depth-dependent geotechnical and geoacoustic properties according to sediment type. The asymptotic void ratio at low effective stress eL determines the sediment density ρo at the sediment–water boundary. New experimental studies show that the characteristic asymptotic sediment density ρo at very low effective stress σz′→0 controls the high-frequency acoustic reflection used for bathymetric imaging. The proposed analysis of geoacoustic data can be used to obtain first-order estimates of seafloor sediment properties and to produce sediment-type seafloor maps.

Fatigue damage of PBH shear connector of steel-concrete composite structure

Perfobond Leiste (PBL) shear connector is a widely-applied shear connector that rely on the concrete tenons and penetrating steel bars in the open hole steel ribs to resist slipping. Perfobond Hoop (PBH) shear connector uses the stirrups in the concrete structure to replace the independent penetrating straight reinforcement in the PBL shear connector, which has better spatial rigidness, and shear performance. In this paper, the static and fatigue tests of PBH shear connector are designed to analyze the static and fatigue failure characteristics and study the fatigue damage mechanism and fatigue damage evolution model of PBH shear connector. The study found that PBH shear connector has higher shear stiffness and fatigue properties than PBL shear connector. The concrete tenon in the open-hole steel rib plate is the key part of the PBH shear connector, and its failure form is different during static and fatigue failure. The fatigue shear stiffness of the PBH shear connector is shown as a jump reduction, which is different from the static shear stiffness as a smooth decline. The fatigue damage process of PBH shear connector is divided into three stages according to the failure mechanism: the bond failure stage of the steel-concrete composite interface, the crushing and migration stage of the concrete tenon, and the bending and failure stages of the penetrating steel bar. The three stages take up 10%, 80% and 10% of the fatigue life in turn. With the damage degree as the fatigue process variable, a two-line fatigue damage evolution model of the PBH shear connector is established, which can be used to predict the final interface slip value and fatigue life.

Effect of Roughness on Shear Characteristics of the Interface between Silty Clay and Concrete

In order to study the effect of roughness on the mechanical parameters of silty clay‐concrete interface, and to explore the applicability of silicon piezoresistive sensor to test the interface pressure, a large‐scale direct shear test system was used to carry out experimental research on the shear characteristics of silty clay‐concrete interface under different roughness conditions. Based on silicon piezoresistive sensor, the shear characteristics of silty clay‐concrete interface are analyzed. The results show that the silicon piezoresistive sensor has excellent performance in measuring the interface pressure and can accurately obtain the shear characteristics of the silty clay‐concrete interface. The roughness has a significant influence on the shear strength, shear stiffness, and other mechanical properties of the prefabricated pile‐soil interface. With the increase of roughness, interface shear strength, interface friction angle, shear stiffness coefficient, and interface residual shear stress all show an increasing trend, with the maximum increase of 37.0%. The interface adhesion decreased first and then increased with the increase of roughness, with an increase of 23.7%. The test results can provide reference for the engineering practice of jacked pile.

A micromechanical analysis of the effects of particle shape and contact law on the low-strain stiffness of granular soils

The effects of particle shape and contact law on the low-strain shear stiffness properties of granular soils were assessed using Discrete Element simulations. Soil grains of different shapes were obtained by clumping spheres having various levels of overlap. The conducted simulations showed that particle sphericity (or large-scale shape parameter) influences mostly the void radio term, F(e), in the expression of low-strain shear modulus as a function of void ratio, e, and mean confining stress σo. This parameter is also the main consequential factor affecting the coordination number term, FM(Mn), in the expression of low-strain shear modulus as a function of mechanical coordination number, Mn, and mean confining stress. In contrast, particle angularity affects mostly the confining stress exponent solely through the corresponding inter-particle contact law. A law reflecting an angular inter-particle contact (rather than the usual flat Hertzian one) was shown to be necessary to obtain the stress exponent n=0.5 commonly used with granular soils.

Effective Beam Stiffness Properties of n-Strut Cylindrical Tensegrity Towers

In this paper, a method to obtain effective continuum beam stiffness properties of tensegrity towers with struts in each bay is developed. Long tensegrity towers for space applications can be modeled as beam-like structures, and axial, bending, shear, and torsional stiffness properties can be used to make comparisons between alternatives to determine the optimum design for a mission. Continuum beam models and effective stiffness properties of Class-2 tensegrity towers are obtained using a modified energy equivalency approach. Self-stress levels (i.e., cable tension and strut compression) are varied to observe their influence on the effective stiffness properties. Axial and torsional rigidities are found to be highly affected by the self-stress level, while bending and shear rigidities are not affected as much. The obtained effective stiffness properties are validated with nonlinear finite element analyses. With these properties, alternative tower designs for a specific application can be readily evaluated without the need for numerous computationally expensive structural analyses.

Resilient modulus prediction of soft low-plasticity Piedmont residual soil using dynamic cone penetrometer

Dynamic cone penetrometer (DCP) has been used for decades to estimate the shear strength and stiffness properties of the subgrade soils. There are several empirical correlations in the literature to predict the resilient modulus values at only a specific stress state from DCP data, corresponding to the predefined thicknesses of pavement layers (a 50 mm asphalt wearing course, a 100 mm asphalt binder course and a 200 mm aggregate base course). In this study, field-measured DCP data were utilized to estimate the resilient modulus of low-plasticity subgrade Piedmont residual soil. Piedmont residual soils are in-place weathered soils from igneous and metamorphic rocks, as opposed to transported or compacted soils. Hence the existing empirical correlations might not be applicable for these soils. An experimental program was conducted incorporating field DCP and laboratory resilient modulus tests on “undisturbed” soil specimens. The DCP tests were carried out at various locations in four test sections to evaluate subgrade stiffness variation laterally and with depth. Laboratory resilient modulus test results were analyzed in the context of the mechanistic-empirical pavement design guide (MEPDG) recommended universal constitutive model. A new approach for predicting the resilient modulus from DCP by estimating MEPDG constitutive model coefficients (k1, k2 and k3) was developed through statistical analyses. The new model is capable of not only taking into account the in situ soil condition on the basis of field measurements, but also representing the resilient modulus at any stress state which addresses a limitation with existing empirical DCP models and its applicability for a specific case. Validation of the model is demonstrated by using data that were not used for model development, as well as data reported in the literature.

Test method development and determination of three-dimensional stiffness properties of polyvinyl chloride structural foams

A study has been conducted to develop proper test methods and to utilize the tests to evaluate three-dimensional mechanical behavior of a polyvinyl chloride structural foam (Divinycell H80 with nominal density of 80 kg/m3). Transversely isotropic foam microstructure was examined and it revealed that the cell size aspect ratio in in-plane directions was near unity but greater than one in the out-of-plane (rise) direction. Foam stiffness properties, i.e. moduli and Poisson’s ratios, were obtained in different loading modes, along both in-plane and out-of-plane directions. The influence of test specimen geometry on compressive properties was studied. Foam specimens with both straight-side and reduced gage sections were designed, fabricated and tested. The effect of specimen gage-section aspect ratio was identified as a critical geometric parameter, affecting foam compressive properties. For foam tensile properties, specimens with different cross-sectional dimensions in the gage section were used. The results revealed transversely isotropic characteristics of the foam material. To evaluate foam shear properties a scaled shear test method was developed. The results indicated a significant difference in in-plane and out-of-plane foam shear stiffness properties.

Topological design optimization of lattice structures to maximize shear stiffness

To improve the poor shear performance of periodic lattice structure consisting of hexagonal unit cells, this study develops a new computational design method to apply topology optimization to search the best topological layout for lattice structures with enhanced shear stiffness. The design optimization problem of micro-cellular material is formulated based on the properties of macrostructure to maximize the shear modulus under a prescribed volume constraint using the energy-based homogenization method. The aim is to determine the optimal distribution of material phase within the periodic unit cell of lattice structure. The proposed energy-based homogenization procedure utilizes the sensitivity filter technique, especially, a modified optimal algorithm is proposed to evolve the microstructure of lattice materials with distinct topological boundaries. A high shear stiffness structure is obtained by solving the optimization model. Then, the mechanical equivalent properties are obtained and compared with those of the hexagonal honeycomb sandwich structure using a theoretical approach and the finite element method (FEM) according to the optimized structure. It demonstrates the effectiveness of the proposed method in this paper. Finally, the structure is manufactured, and then the properties are tested. Results show that the shear stiffness and bearing properties of the optimized lattice structure is better than that of the traditional honeycomb sandwich structure. In general, the proposed method can be effectively applied to the design of periodic lattice structures with high shear resistance and super bearing property.

Interaction of a pile with layered-soil under vertical excitations: field experiments versus numerical simulations

Data recorded during a field test involving an instrumented drilled shaft under vertical excitations are examined in order to (1) extract the soil–pile system’s dynamic impedance, and (2) to evaluate the small-strain shear stiffness and material damping properties of the surrounding soil. Numerical simulations of steady-state vibration tests with an axisymmetric finite element model are used for back-calculating the in-situ small-strain dynamic soil properties (i.e., shear stiffness and material damping ratio). Also, a numerically computed impedance function is compared with known analytical solutions and that obtained through direct processing of the field test data. These analyses revealed that the discrete numerical model can successfully reproduce the measured responses of the shaft-soil system, and yield its frequency-dependent impedance function as well as equivalent small-strain dynamic soil properties. The validated numerical model presented here offers a detailed view of the vertical dynamic responses of drilled shafts within the small-strain range, and can be used for design and analysis of future field tests.

Fatigue analysis of notched laminates: A time-efficient macro-mechanical approach

A coupled, transversely isotropic, deformation and damage fatigue model has been implemented within the finite element method and utilized, along with a static progressive damage model, to predict the fatigue life, stiffness degradation as a function of number of cycles, and post-fatigue tension and compression response of notched, multidirectional laminates. The material parameters for the fatigue model were obtained utilizing ply-level classical lamination theory simulations and the provided [0], [90] and [±45] experimental composite laminate S–N data. Within the fatigue damage model, the transverse and shear stiffness properties of the plies were degraded with an isotropic scalar damage variable. The stiffness damage in the longitudinal (fiber) ply direction was suppressed, and instead the strength of the fiber was degraded as a function of fatigue cycles. A maximum strain criterion was used to capture the failure in each element, and once this criterion was satisfied, the longitudinal stiffness of the element was eliminated. The resulting, degraded properties were then used to calculate the new stress state. This procedure was repeated until final failure of the composite laminate was achieved or a specified number of cycles was reached. For post-fatigue tension and compression behavior, four internal state variables were used to control the damage and failure. The predictive capability of the above-mentioned approach was assessed by performing blind predictions of notched multidirectional IM7/977-3 composite laminate response under fatigue and post-fatigue tensile and compressive loading, followed by a recalibration phase. Tabulated data along with detailed results (i.e. stress–strain curves as well as damage evolution states at given number of cycles compared to experimental data) for all laminates are presented.

Stiffness and shear strength of unsaturated soils in relation to soil-water characteristic curve

This paper introduces a methodology to predict the non-linear stiffness–suction and shear strength–suction relationships for unsaturated soils within the lower suction range from the non-linearity of the soil-water characteristic curve (SWCC), using a normalised function formulated with ‘suction times exponential degree of saturation’. The information required in this methodology includes (a) measurements of the shear strength or stiffness properties at saturation condition and one unsaturated condition and (b) the SWCC. Published experimental data on the stiffness and shear strength properties and the SWCC obtained from 25 different soils varying from coarse-grained sands to expansive clays are used to validate the proposed normalised function and to calibrate the exponent value. It is found that the normalised function, using exponent values of 1·0 and 2·0, respectively, for cohesionless and cohesive soils, provides reasonable predictions of the stiffness–suction and shear strength–suction relationships for all the soils used in this study, taking account of various influencing factors including external stress, soil structure, anisotropy, hydraulic hysteresis and testing technique.

Experimental investigations of a rolling-based seismic isolation system

This paper presents the results of an extensive series of experimental tests to identify the mechanical characteristics of a recently-proposed seismic isolation device known as the Roll- In-Cage (RNC) isolator. Several 1/10 reduced-scale experimental prototypes are examined considering different configurations, characteristics and construction materials. Cyclic horizontal displacement tests, varying the test parameters of shear displacement amplitude, axial load, and loading frequency are performed. The RNC isolator’s force-displacement relationship, shear stiffness and damping properties are investigated in terms of different test parameters. In addition, vertical cyclic displacement is applied to examine the RNC isolator’s capability to withstand vertical axial tension. Furthermore, tests at the ultimate-level consisting of an increasing monotonic shear loading beyond the bearing’s design displacement are also carried out to investigate its behavior after activating its self-stopping or buffer mechanism. Some experimentally obtained results are verified using numerical simulation models. A comparative analysis of the results is then performed to allow for highlighting the main features of the RNC isolator.

Shear stiffness and its relation to the microstructure of 10 European and tropical hardwood species

In this study, shear stiffness properties of 10 different hardwood species and their relation to the corresponding species-specific microstructure are investigated. For this purpose, shear stiffness of 10 different hardwood species is experimentally measured by means of ultrasonic testing. In addition, a micromechanical model for hardwood is applied in order to illustrate the influence of certain microstructural characteristics such as mass density and volume fractions of vessels and ray cells on the shear stiffness. Comprehensive microstructural and mechanical data from previous investigations of the same hardwood material support the interpretation of the microstructure–shear stiffness relationships. Mass density was confirmed to be the dominant microstructural characteristic for shear stiffness. Also, ultrasound shear wave propagation velocity increases with density, particularly in the radial-tangential (RT) plane. In addition to density, comparably higher shear stiffness GLR can be explained by comparably higher ray content and lower vessel content. As for GLT, a ring porous structure seems to lead to higher shear stiffness as compared to a diffuse porous structure. For this shear stiffness, vessel and ray content were found to have a less impact. Also, the rolling shear stiffness GRT was found to be higher for a diffuse porous structure than for a ring porous one. Moreover, the data supports that ray cells act as reinforcements in the RT plane and lead to higher GRT.

A micromechanical analysis of the effect of fabric on low-strain stiffness of granular soils

The effect of fabric on low-strain shear stiffness properties of granular soils was assessed using Discrete Element simulations. These soils were idealized as a collection of non-spherical particles that interact according to Hertz׳s contact law. Different fabrics of the same soil were obtained by extracting particles from the weak or strong interparticle force networks. The associated stiffness properties were evaluated for various levels of isotropic triaxial confining stress conditions. The conducted analyses showed that a soil with a given void ratio and level of confining stress may have various fabrics associated with noticeably different low-strain shear moduli. The mechanical coordination number and particle shape were found to be the main factors that dictate the low-strain stiffness properties of a certain granular soil (with a specific contact law). For a defined level of confining stress, the shear stiffness of a particular soil is shown to be linked to the mechanical coordination number by a unique relation.

The Research of the Relative Rigid Effect in the Numerical Simulation of the Steel Plate Reinforced Concrete Coupling Beams

The coupling beam work as an important component in coupled shear walls, the strength,stiffness and deformation properties of which have great influence on the seismic performance of shear walls, the steel plate reinforced concrete coupling beams have the advantages as follows: simplify the constructional details, make the construction convenient and reliable performance [1][2]. The numerical simulation model in this paper is a coupled shear wall connected by steel plate reinforced concrete coupling beams in reference [3], and the loading mode is the same as the reference [4] . The relative stiffness effect was explored by study the internal force and displacement of the model with changing the stiffness of the coupling beams and the shear walls while the span-depth ratio is stable .The study will provide a reference for the numerical simulation of the finite element simulation analysis of the coupling beams and the steel reinforced concrete structures.

Torsional ultrasonic transducer computational design optimization

A torsional piezoelectric ultrasonic sensor design is proposed in this paper and computationally tested and optimized to measure shear stiffness properties of soft tissue. These are correlated with a number of pathologies like tumors, hepatic lesions and others. The reason is that, whereas compressibility is predominantly governed by the fluid phase of the tissue, the shear stiffness is dependent on the stroma micro-architecture, which is directly affected by those pathologies. However, diagnostic tools to quantify them are currently not well developed. The first contribution is a new typology of design adapted to quasifluids. A second contribution is the procedure for design optimization, for which an analytical estimate of the Robust Probability Of Detection, called RPOD, is presented for use as optimality criteria. The RPOD is formulated probabilistically to maximize the probability of detecting the least possible pathology while minimizing the effect of noise. The resulting optimal transducer has a resonance frequency of 28[kHz].

Strain rate and temperature effects of polymer foam core material

The objective of this research is to characterize the effect of high strain rates on polymer foam shear properties at different temperatures through direct shear tests. Three strain rates were considered ranging from quasi-static to simulated wave slamming conditions. The foam core experiments, on polyvinyl chloride and styrene acrylonitrile foam, utilized a modified version of the ASTM C273 standard test procedure. The foam core material shear strength and stiffness increased by as much as 45% and 16%, respectively, over the range of strain rates. The shear strength and stiffness properties of the foam core material showed an inverse relationship with temperature.

A homogenization approach for evaluating the longitudinal shear stiffness of reinforced soils: column versus cross trench configuration

SUMMARYThe macroscopic linear elastic behaviour of inclusion‐reinforced soils, regarded as periodic composite media, is investigated by means of the homogenization theory. Special attention is given here to the determination of their longitudinal shear stiffness properties, which strongly govern the reinforced ground response under lateral loading. Combining the use of analytical, variational and numerical methods, we thoroughly examined three particular engineering‐relevant configurations: single trench, column and cross trench reinforcements. Fairly accurate closed‐form expressions are thus obtained, giving the value of the reinforced soil longitudinal shear stiffness as a function of the individual components shear moduli and reinforcement volume fraction. It is shown in particular that adopting a cross trench reinforcement layout instead of the classical column configuration results in a much higher improvement of the longitudinal shear stiffness. The results are then applied to assessing the reduction of soil liquefaction risk, which can be attributed to the presence of the reinforcing inclusions. Again, they clearly demonstrate the excellent performance of the cross trench configuration as compared with the complete inefficiency of the column reinforcement technique. Copyright © 2013 John Wiley & Sons, Ltd.