• Journal of Industrial Technology
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• v.23 no.A
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• pp.69-81
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• 2003

Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.749-755
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• 2005

In this work, thermo-elastic stability behavior of laminated cross-ply elliptical cylindrical shells subjected to uniform temperature rise is studied employing the finite element approach based on higher-order theory that accounts for the transverse shear and transverse normal deformations, and nonlinear in-plane displacement approximations through the thickness with slope discontinuity at the layer interfaces. The combined influence of higher-order shear deformation, shell geometry and non-circularity on the prebuckling thermal stress distribution and critical temperature parameter of laminated elliptical cylindrical shells is examined.

• Steel and Composite Structures
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• v.28 no.1
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• pp.25-37
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• 2018

For the first time, the parametric instability characteristics of tow-steered variable stiffness composite laminated (VSCL) cylindrical panels is investigated using B-spline finite strip method (FSM). The panel is considered containing geometrical defects including cutout and delamination. The material properties are assumed to vary along the panel axial length of any lamina according to a linear fiber-orientation variation. A uniformly distributed inplane longitudinal loading varies harmoni-cally with time is considered. The instability load frequency regions corresponding to the assumed in-plane parametric load-ing is derived using the Bolotin's first order approximation through an energy approach. In order to demonstrate the capabili-ties of the developed formulation in predicting stability behavior of the thin-walled VSCL structures, some representative results are obtained and compared with those in the literature wherever available. It is shown that the B-spline FSM is a proper tool for extracting the stability boundaries of perforated delaminated VSCL panels.

• Journal of the Korean Geotechnical Society
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• v.26 no.6
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• pp.21-28
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• 2010

Decomposed granite soil is the most common type of soils. The measurement of the stress-strain-strength behavior of anisotropic decomposed granite soils is very important for the deformation and stability analysis of slopes, retaining walls, excavations. A series of unsaturated-drained triaxial compression tests were performed to know unsaturated strength properties. The sample had three different angles of the axial (major principal) direction to the sedimentation plane (compaction plane): 0, 45 and 90 degrees. The compression strain of specimens subjected to an isotropic compression was strongly influenced by the sedimentation angle. In addition, the time dependence was independent of the sedimentation angle in relation to the deformation behavior during the secondary compression process. The effect of the sedimentation angle on the triaxial compression strength and deformation was clearly shown with low confining stress. The effect of the sedimentation angle on the compressive strength and deformation was more evident in saturated specimens. A new method of predicting the shear strength of unsaturated decomposed granite soils, considering compaction angles, was proposed.

• Transactions of Materials Processing
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• v.15 no.4 s.85
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• pp.333-339
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• 2006

Hot deformation behavior of a carbon steel (A350 LF2) was characterized by compression tests in the temperature range of $800-1250^{\circ}C$ and the strain rate range of $0.001-10s^{-1}$, The microstructural evolution during hot compression was investigated and deformation mechanisms were analyzed by constructing a deformation processing map. Processing maps were generated using the combination of dynamic material model (DMM) and flow instability theories based on the flow stability criteria and Ziegler's instability criterion. In order to evaluate the reliability of the map, the mirostructural characteristics of the hot compressed specimens were correlated with test conditions in the stable and unstable regime. The combined microstructural and processing map of A350 LF2 was applied to predict an optimum condition and unstable regions for hot forming.

• Ocean Systems Engineering
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• v.4 no.4
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• pp.309-325
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• 2014

Geotextile tubes are basically a huge sack filled with sand or dredged soil. Geotextile tubes are made of permeable woven or non-woven synthetic fibers (i.e., polyester or PET and polypropylene or PP). The geotextile tubes' performances in strength, dewatering, retaining solid particles and stacked stability have been studied extensively in the past. However, only little research has been done in the observation of the deformation behavior of geotextile tubes. In this paper, a large-scale apparatus for geotextile tube experiment is introduced. The apparatus is equipped with a slurry mixing station, pumping and delivery station, an observation station and a data station. For this study the large-scale apparatus was utilized in the studies regarding the stresses on the geotextile and the deformation behavior of the geotextile tube. Model tests were conducted using a custom-made woven geotextile tubes. Load cells placed at the inner belly of the geotextile tube to monitor the total soil pressure. Strain gauges were also placed on the outer skin of the tube to measure the geotextile strain. The pressure and strain sensors are attached to a data logger that sends the collected data to a desktop computer. The experiment results showed that the maximum geotextile strain occurs at the sides of the tube and the soil pressure distribution varies at each geotextile tube section.

• Steel and Composite Structures
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• v.43 no.1
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• pp.31-54
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• 2022

This paper is concerned with the buckling behavior of functionally graded graphene reinforced porous nanocomposite beams based on the finite element method (FEM) using two variables trigonometric shear deformation theory. Both Young's modulus and material density of the FGP beam element are simultaneously considered as grading through the thickness of the beam. The finite element approach is developed using a nonlocal strain gradient theory. The governing equations derived here are solved introducing a 3-nodes beam element, and then the critical buckling load is calculated with different porosity distributions and GPL dispersion patterns. After a convergence and validation study to verify the accuracy of the present model, a comprehensive parametric study is carried out, with a particular focus on the effects of weight fraction, distribution pattern of GPL reinforcements on the Buckling behavior of the nanocomposite beam. The effects of various structural parameters such as the dispersion patterns for the graphene and porosity, thickness ratio, boundary conditions, and nonlocal and strain gradient parameters are brought out. The results indicate that porosity distribution and GPL pattern have significant effects on the response of the nanocomposite beams, and the results allows to identify the most effective way to achieve improved buckling behavior of the porous nanocomposite beam.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.22-31
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• 2012

In this study, scaled model tests were performed to investigate the stability of an asymmetrical twin tunnels constructed in rock mass comprising alternating layers of sandstone and shale. Each of tunnels had a differently shaped section, where the one was already constructed tunnel including lining structure but the other was planned to be under construction. Four types of test models which had respectively different pillar widths and loading conditions were experimented, where both crack initiating pressures and deformation behaviors around tunnels were investigated. The cracks of pillar mainly began to appear at the interfaces of alternating layers, following additional shear displacement between layers was confirmed as one of the most important factors of pillar failure in case of the model of pillar width 0.5D. The models with shallower pillar widths proved to be unstable because of lower crack initiating pressures and more tunnel convergences than the models with thicker pillar widths. The failure and deformation behaviors of tunnels were also dependent on the loading conditions, where the model of coefficient of lateral pressure 1.0 was more stable than the other model. Futhermore, the results of FLAC analysis were qualitatively coincident with the experimental results.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.245-259
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• 2003

Refering to the articles "Squeezing rocks in tunnels(Barla, 1995)" and "Tunnelling under squeezing rock conditions(Barla 2002)" this article deals with technologies for design, stability analysis and construction of the tunnel being driven in the squeezing rock mass. The definition of this type of behavior was proposed by ISRM(1994). The identification and quantification of squeezing is given according to both the empirical and semi-empirical methods available to anticipate the potential of squeezing problems in tunnelling. Based on the experiences and lessons learned in recent years, the state of the art in modem construction methods was reported, when dealing with squeezing rock masses by either conventional or mechanical excavation methods. The closed-form solutions available for the analysis of the rock mass response during tunnel excavation are described in terms of the ground characteristic line and with reference to some elasto-plastic models for the given rock mass. Finally numerical methods were used for the simulation of different models and for design analysis of complex excavation and support systems, including three-dimensional conditions in order to quantify the influence of the advancing tunnel face to the deformation behavior of the tunnel.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4295-4306
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• 2023

The vibration of fuel rods in axial flow is a universally recognized issue within both engineering and academic communities due to its significant importance in ensuring structural safety. This paper aims to thoroughly investigate the stability and nonlinear vibration of a fuel rod subjected to axial flow in a newly designed high temperature gas cooled reactor. Considering the possible presence of thermal expansion and large deformation in practical scenarios, the thermal effect and geometric nonlinearity are modeled using the von Karman equation. By applying Hamilton's principle, we derive the comprehensive governing equation for this fluid-structure interaction system, which incorporates the quadratic nonlinear stiffness. To establish a connection between the fluid and structure aspects, we utilize the Galerkin method to solve the perturbation potential function, while employing mode expansion techniques associated with the structural analysis. Following convergence and validation analyses, we examine the stability of the structure under various conditions in detail, and also investigate the bifurcation behavior concerning the buckling amplitude and flow velocity. The findings from this research enhance the understanding of the underlying physics governing fuel rod behavior in axial flow under severe yet practical conditions, while providing valuable guidance for reactor design.