• Geomechanics and Engineering
• /
• v.19 no.3
• /
• pp.201-215
• /
• 2019

A new approach of analyzing the displacements and stress of the surrounding rock for shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface is investigated in this study. In the proposed approach, by using a virtual image technique, the shear stress of the vertical ground surface is revised to be zero, and elastic solutions of the surrounding rock are obtained before stress revision. To revise the vertical normal stress and shear stress of horizontal ground surface generated by the combined action of the actual and image sinks, the harmonic functions and corresponding stress function solutions were adopted. Based on the Boussinesq's solutions and integral method, the horizontal normal stress of the vertical ground surface is revised to be zero. Based on the linear superposition principle, the final solution of the displacements and stress were proposed by superimposing the solutions obtained by the virtual image technique and the stress revision on the horizontal and vertical ground surfaces. Furthermore, the ground settlements and lateral displacements of the horizontal and vertical ground surfaces are derived by the proposed approach. The proposed approach was well verified by comparing with the numerical method. The discussion based on the proposed approach in the manuscript shows that smaller horizontal ground settlements will be induced by lower tunnel buried depths and smaller limb distances. The proposed approach for the displacement and stress of the surrounding rocks can provide some practical information about the surrounding rock stability analysis of shallow tunnels excavated under non-axisymmetric displacement boundary conditions on a vertical surface.

• Geomechanics and Engineering
• /
• v.21 no.3
• /
• pp.227-236
• /
• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

• Smart Structures and Systems
• /
• v.18 no.6
• /
• pp.1125-1143
• /
• 2016

Forced vibration analysis of a simple supported viscoelastic nanobeam is studied based on modified couple stress theory (MCST). The nanobeam is excited by a transverse triangular force impulse modulated by a harmonic motion. The elastic medium is considered as Winkler-Pasternak elastic foundation.The damping effect is considered by using the Kelvin-Voigt viscoelastic model. The inclusion of an additional material parameter enables the new beam model to capture the size effect. The new non-classical beam model reduces to the classical beam model when the length scale parameter is set to zero. The considered problem is investigated within the Timoshenko beam theory by using finite element method. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The obtained system of differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. Numerical results are presented to investigate the influences the material length scale parameter, the parameter of the elastic medium and aspect ratio on the dynamic response of the nanobeam. Also, the difference between the classical beam theory (CBT) and modified couple stress theory is investigated for forced vibration responses of nanobeams.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.4
• /
• pp.109-118
• /
• 2005

A concrete shear wall system is commonly adopted in high-rise residential apartment buildings. In the construction stage, a rectangular opening is often made for the convenience of horizontal movement of workers, and construction materials and equipment. In the case of safety or stability assessment of a shear wall, the cutout part can be a critical factor. Finite element method is adopted to investigate the elastic stability behavior of the perforated unit shear wall. The key analysis parameters are the cutout location and its size. The effect of out-of-plane bending and horizontal shear are also examined in the stability analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.25 no.3
• /
• pp.502-509
• /
• 2001

In this paper, when stress waves are propagated along the reinforced direction of the composite, the characteristic equation of Rayleigh wave is derived. The relationships between velocities of stress waves and Rayleigh wave are studied for anisotropic ratios(E(sub)11/E(sub)12 or E(sub)22/E(sub)11). The increments of anisotropic ratios is made by using known material properties and being constant of basic properties. When the anisotropic ratios are increased, Rayleigh wave velocities to the shear wave velocities are almost equal to 1 with any anisotropic ratios. Rayleigh wave velocities to the longitudinal wave velocities and Shear wave velocities ratio to the longitudinal wave velocities are almost identical each other, they are between 0.12 and 0.21. When the anisotropic ration is very high, that is, E(sub)11/E(sub)22=46.88, Rayleigh wave velocities and the shear wave velocities are almost constant with Poissons ratio, longitudinal wave velocities are very slowly increased with the increments of Poissons ratios. When E(sub)11(elastic modulus of the reinforced direction)and ν(sub)12 are constant, Rayleigh wave velocities and the shear wave velocities are steeply decreased with the increments of anisotropic ratios and the velocities of longitudinal wave are almost constant with them. When E(sub)22(elastic modulus of the normal direction to the fiber) and ν(sub)12 are constant, Rayeigh wave velocities is slowly increased with the increments of anisotropic ratios, the shear wave velocities are almost constant with them, the longitudinal wave velocities are steeply increased with them.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.25-30
• /
• 2003

The total relaxed stress in annealing and the thermal strain/stress were obtained from the identification of the residual stress-free state using electronic speckle pattern interferometry (ESPI). The residual stress fields in case of both single and film/substrate systems were modeled using the thermo-elastic theory and the relationship between relaxed stresses and displacements. We mapped the surface residual stress fields on the indented bulk Cu and the 0.5 ${\mu}m$ Au film by ESPI. In indented Cu, the normal and shear residual stress are distributed over -1.7 GPa to 700 MPa and -800 GPa to 600 MPa respectively around the indented point and in deposited Au film on Si wafer, the tensile residual stress is uniformly distributed on the Au film from 500 MPa to 800 MPa. Also we measured the residual stress by the x-ray diffractometer (XRD) for the verification of above residual stress results by ESPI.

• The Journal of Advanced Prosthodontics
• /
• v.11 no.6
• /
• pp.313-323
• /
• 2019

PURPOSE. Shear bond strength (SBS) test is the most commonly used method for evaluating resin bond strength of zirconia, but SBS results vary among different studies even when evaluating the same bonding strategy. The purpose of this study was to promote standardization of the SBS test in evaluating zirconia ceramic bonding and to investigate factors that may affect the SBS value of a zirconia/resin cement/composite resin bonding specimen. MATERIALS AND METHODS. The zirconia/resin cement/composite resin bonding specimens were used to simulate loading with a shear force by the three-dimensional finite element (3D FE) modeling, in which stress distribution under uniform/non-uniform load, and different resin cement thickness and different elastic modulus of resin composite were analyzed. In vitro SBS test was also performed to validate the results of 3D FE analysis. RESULTS. The loading flat width was an important affecting factor. 3D FE analysis also showed that differences in resin cement layer thickness and resin composite would lead to the variations of stress accumulation area. The SBS test result showed that the load for preparing a SBS specimen is negatively correlated with the resin cement thickness and positively correlated with SBS values. CONCLUSION. When preparing a SBS specimen for evaluating bond performance, the load flat width, the load applied during cementation, and the different composite resins used affect the SBS results and therefore should be standardized.

• Korea-Australia Rheology Journal
• /
• v.21 no.4
• /
• pp.269-280
• /
• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

• Earthquakes and Structures
• /
• v.14 no.2
• /
• pp.117-128
• /
• 2018

In this research work, free vibrations of simply supported functionally graded plate resting on a Winkler-Pasternak elastic foundation are investigated by a new shear deformation theory. The influence of alternative micromechanical models on the macroscopic behavior of a functionally graded plate based on shear-deformation plate theories is examined. Several micromechanical models are tested to obtain the effective material properties of a two-phase particle composite as a function of the volume fraction of particles which continuously varies through the thickness of a functionally graded plate. Present theory exactly satisfies stress boundary conditions on the top and the bottom of the plate. The energy functional of the system is obtained using Hamilton's principle. The closed form solutions are obtained by using Navier technique, and then fundamental frequencies are found by solving the results of eigenvalue problems. Finally, the numerical results are provided to reveal the effect of explicit micromechanical models on natural fundamental frequencies.

• Structural Engineering and Mechanics
• /
• v.59 no.1
• /
• pp.83-100
• /
• 2016

In this paper, the problem of interfacial stresses in steel beams strengthened with a fiber reinforced polymer plates is analyzed using linear elastic theory. The analysis is based on the deformation compatibility approach developed by Tounsi (2006) where both the shear and normal stresses are assumed to be invariant across the adhesive layer thickness. The analysis provides efficient calculations for both shear and normal interfacial stresses in steel beams strengthened with composite plates, and accounts for various effects of Poisson's ratio and Young's modulus of adhesive. Such interfacial stresses play a fundamental role in the mechanics of plated beams, because they can produce a sudden and premature failure. The analysis is based on equilibrium and deformations compatibility approach developed by Tounsi (2006). In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both the steel beam and bonded plate. The paper is concluded with a summary and recommendations for the design of the strengthened beam.