• Title/Summary/Keyword: Critical Plane

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Stability of rectangular tunnel in improved soil surrounded by soft clay

  • Siddharth Pandey;Akanksha Tyagi
    • Geomechanics and Engineering
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    • v.34 no.5
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    • pp.491-505
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    • 2023
  • The practical usage of underground space and demand for vehicular tunnels necessitate the construction of non-circular wide rectangular tunnels. However, constructing large tunnels in soft clayey soil conditions with no ground improvement can lead to excessive ground deformations and collapse. In recent years, in situ ground improvement techniques such as jet grouting and deep cement mixing are often utilized to perform cement-stabilisation around the tunnel boundary to prevent large deformations and failure. This paper discusses the stability characteristics and failure behaviour of a wide rectangular tunnel in cement-treated soft clays. First, the plane strain finite element model is developed and validated with the results of centrifuge model tests available in the past literature. The critical tunnel support pressures computed from the numerical study are found to be in good agreement with those of centrifuge model tests. The influence of varying strength and thickness of improved soil surround, and cover depth are studied on the stability and failure modes of a rectangular tunnel. It is observed that the failure behaviour of the tunnel in improved soil surround depends on the ratio of the strength of improved soil surround to the strength of surrounding soil, i.e., qui/qus, rather than just qui. For low qui/qus ratios,the stability increases with the cover; however, for the high strength improved soil surrounds with qui >> qus, the stability decreases with the cover. The failure chart, modified stability equation, and stability chart are also proposed as preliminary design guidelines for constructing rectangular tunnels in the improved soil surrounded by soft clays.

Lateral-Torsional Buckling Strength of Parabolic Arches (포물선 아치의 횡-비틂 좌굴 강도)

  • Moon, Jiho;Yoon, Ki-Yong;Lee, Tae-Hyung;Lee, Hak-Eun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.2A
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    • pp.145-153
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    • 2009
  • The lateral-torsional buckling strengths of the parabolic arches are investigated in this study. The curvatures of a parabolic arch vary along the center line of the arch. Thus, the problem is much more complicated comparing that of arches with constant curvature such as circular arches. Moreover, most of previous studies are limited to the circular arches. In this study, lateral-torsional buckling equations are derived for the arches with varying curvatures considering the warping effects. To obtain the buckling strength of parabolic arches, numerical solutions based on the finite difference technique are provided. The numerical solutions are compared with the those of previous researchers and finite element analyses. Then, the lateral-torsional strengths of parabolic arches are successfully verified. Finally, comparison study of critical buckling loads of parabolic arches with those of circular arches for the various rise to span ratios are discussed.

A refined quasi-3D theory for stability and dynamic investigation of cross-ply laminated composite plates on Winkler-Pasternak foundation

  • Nasrine Belbachir;Fouad Bourada;Abdelmoumen Anis Bousahla;Abdelouahed Tounsi;Mohamed A. Al-Osta;Mofareh Hassan Ghazwani;Ali Alnujaie;Abdeldjebbar Tounsi
    • Structural Engineering and Mechanics
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    • v.85 no.4
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    • pp.433-443
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    • 2023
  • The current paper discusses the dynamic and stability responses of cross-ply composite laminated plates by employing a refined quasi-3D trigonometric shear deformation theory. The proposed theory takes into consideration shear deformation and thickness stretching by a trigonometric variation of in-plane and transverse displacements through the plate thickness and assures the vanished shear stresses conditions on the upper and lower surfaces of the plate. The strong point of the new formulation is that the displacements field contains only 4 unknowns, which is less than the other shear deformation theories. In addition, the present model considers the thickness extension effects (εz≠0). The presence of the Winkler-Pasternak elastic base is included in the mathematical formulation. The Hamilton's principle is utilized in order to derive the four differentials' equations of motion, which are solved via Navier's technique of simply supported structures. The accuracy of the present 3-D theory is demonstrated by comparing fundamental frequencies and critical buckling loads numerical results with those provided using other models available in the open literature.

Playing with Rauschenberg: Re-reading Rebus (라우센버그와 게임하기-<리버스> 다시읽기)

  • Rhee, Ji-Eun
    • The Journal of Art Theory & Practice
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    • no.2
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    • pp.27-48
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    • 2004
  • Robert Rauschenberg's artistic career has often been regarded as having reached its culmination when the artist won the first prize at the 1964 Venice Biennale. With this victory, Rauschenberg triumphantly entered the pantheon of all-American artists and firmly secured his position in the history of American art. On the other hand, despite the artist's ongoing new experiments in his art, the seemingly precocious ripeness in his career has led the critical discourses on Rauschenberg's art to the artist's early works, most of which were done in the mid-1950s and the 1960s. The crux of Rauschenberg criticism lies not only in focusing on the artist's 50's and 60's works, but also in its large dismissal of the significance of the imagery that the artist employed in his works. As art historians Roger Cranshaw and Adrian Lewis point out, the critical discourse of Rauschenberg either focuses on the formalist concerns on the picture plane, or relies on the "culturalist" interpretation of Rauschenberg's imagery which emphasizes the artist's "Americanness." Recently, a group of art historians centered around October has applied Charles Sanders Peirce's semiotics as art historical methodology and illuminated the indexical aspects of Rauschenberg's work. The semantic inquiry into Rauschenberg's imagery has also been launched by some art historians who seek the clues in the artist's personal context. The first half of this essay will examine the previous criticism on Rauschenberg's art and the other half will discuss the artist's 1955 work Rebus, which I think intersects various critical concerns of Rauschenberg's work, and yet defies the closure of discourses in one direction. The categories of signs in the semiotics of Charles Sanders Peirce and the discourse of Jean-Francois Lyotard will be used in discussing the meanings of Rebus, not to search for the semantic readings of the work, hut to make an analogy in terms of the paradoxical structures of both the work and the theory. The definitions of rebus is as follows: Rebus 1. a representation or words or syllables by pictures of object or by symbols whose names resemble the intended words or syllables in sound; also: a riddle made up wholly or in part of such pictures or symbols. 2. a badge that suggests the name of the person to whom it belongs. Webster's Third New International Dictionary of the English Language Unabridged. Since its creation in 1955, Robert Rauschenberg's Rebus has been one of the most intriguing works in the artist's oeuvre. This monumental 'combine' painting($6feet{\times}10feet$ 10.5 inches) consists of three panels covered with fabric, paper, newspaper, and printed reproductions. On top of these, oil paints, pencil and crayon drawings connect each section into a whole. The layout of the images is overall horizontal. Starting from a torn election poster, which is partially read as "THAT REPRE," on the far left side of the painting. Rebus leads us to proceed from the left to the right, the typical direction of reading in a Western context. Along with its seemingly proper title. Rebus, the painting has triggered many art historians to seek some semantic readings of it. These art historians painstakingly reconstruct the iconography based on the artist's interviews, (auto)biography, and artistic context of his works. The interpretation of Rebus varies from a 'image-by-image' collation with a word to a more general commentary on Rauschenberg's work overall, such as a work that "bridges between art and life." Despite the title's allusion to the legitimate purpose of the painting as a decoding of the imagery into sound, Rebus, I argue, actually hinders a reading of it. By reading through Peirce to Rauschenberg, I will delve into the subtle anxiety between words and images in their works. And on this basis, I suggest Rauschenberg's strategy in playing Rebus is to hide the meaning of the imagery rather than to disclose it.

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Effect of Flushing on Nutrient Utilization and Reproductive Performance of Ewes Grazing on Community Rangeland

  • Chaturvedi, O.H.;Bhatta, Raghavendra;Verma, D.L.;Singh, N.P.
    • Asian-Australasian Journal of Animal Sciences
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    • v.19 no.4
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    • pp.521-525
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    • 2006
  • The present study was undertaken to evaluate the effect of flushing of ewes with concentrate pellets just before the mating season on their nutrient utilization and reproductive performance on farms. Forty-eight Malpura ewes, 1-5 years old were randomly divided into 2 groups of 24 each (G1and G2). Ewes in both the groups were grazed on natural rangeland from 07.00 to 18.00 hr followed by night shelter in animal shed. G1 ewes were maintained on sole grazing while G2 ewes, in addition to grazing, received concentrate pellets at the rate of 1.5% of their body weight. The mean biomass yield of the community rangeland was 0.46 ton DM/hectare. The intakes of DM (g/kg $W^{0.75}$), DCP (g/kg $W^{0.75}$) and ME (MJ/kg $W^{0.75}$) were higher (p<0.01) in G2 as compared to that of G1 being 86.5, 10.2 and 1.15 and 57.5, 4.7 and 0.75, respectively. The digestibility of DM, OM, CP, NDF and hemicellulose were also higher (p<0.01) in G2 as compared to that of G1 being 57.2, 76.7, 78.9, 51.9 and 81.6 and 50.8, 68.7, 68.4, 45.4 and 74.4, respectively. The conception rate was higher (79.2%) in flushed ewes as compared to that of non-flushed (66.7%). Five of the pregnant ewes died and another 5 aborted in G1 while in G2, 5 ewes aborted with no mortality. The lambing was higher (73.7%) in G2 than that in G1 (37.5%). The birth weight of lambs was higher (p<0.05) in G2 (3.47 kg) than that in G1 (2.95 kg). Further, the birth weight of male lambs was higher (3.28) than that of female lambs (3.14). It is concluded that the biomass yield of the community rangeland in semi-arid region of India is low and insufficient to meet the nutrient requirement of ewes prior to mating season. However, concentrate supplementation at the rate of 1.5% of body weight to ewes during this critical stage enhanced their plane of nutrition, reproductive performance, body condition and birth weights of lambs.

Life Prediction of Composite Pressure Vessels Using Multi-Scale Approach (멀티 스케일 접근법을 이용한 복합재 압력용기의 수명 예측)

  • Jin, Kyo-Kook;Ha, Sung-Kyu;Kim, Jae-Hyuk;Han, Hoon-Hee;Kim, Seong-Jong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.11 no.9
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    • pp.3176-3183
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    • 2010
  • A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.

Prediction of Rock Fragmentation and Design of Blasting Pattern based on 3-D Spatial Distribution of Rock Factor (발파암 계수의 3차원 공간 분포에 기초한 암석 파쇄도 예측 및 발파 패턴 설계)

  • Shim Hyun-Jin;Seo Jong-Seok;Ryu Dong-Woo
    • Tunnel and Underground Space
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    • v.15 no.4 s.57
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    • pp.264-274
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    • 2005
  • The optimum blasting pattern to excavate a quarry efficiently and economically can be determined based on the minimum production cost which is generally estimated according to rock fragmentation. Therefore it is a critical problem to predict fragment size distribution of blasted rocks over an entire quarry. By comparing various prediction models, it can be ascertained that the result obtained from Kuz-Ram model relatively coincides with that of field measurements. Kuz-Ram model uses the concept of rock factor to signify conditions of rock mass such as block size, rock jointing, strength and others. For the evaluation of total production cost, it is imperative to estimate 3-D spatial distribution of rock factor for the entire quarry. In this study, a sequential indicator simulation technique is adopted for estimation of spatial distribution of rock factor due to its higher reproducibility of spatial variability and distribution models than Kriging methods. Further, this can reduce the uncertainty of predictor using distribution information of sample data The entire quarry is classified into three types of rock mass and optimum blasting pattern is proposed for each type based on 3-D spatial distribution of rock factor. In addition, plane maps of rock factor distribution for each ground levels is provided to estimate production costs for each process and to make a plan for an optimum blasting pattern.

Effect of Wave-Induced Seepage on the Stability of the Rubble Mound Breakwater (동적 파랑에 의한 침투류가 사석경사식 방파구조물의 안정성에 미치는 영향)

  • Hwang, Woong-Ki;Kim, Tae-Hyung;Kim, Do-Sam;Oh, Myounghak;Park, Jun-Young
    • Journal of the Korean Geotechnical Society
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    • v.34 no.3
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    • pp.13-27
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    • 2018
  • To study how stable the rubble mound breakwaters are, one can look to the research of wave induced seepage flow through the pores of the rubble mound. Seepage flow is generally generated by the difference between the water level around the breakwater during a typhoon. The existing stability analysis method of the rubble mound is the static analysis which simply considers the force equilibrium taking into account the horizontal force acting on the concrete block induced by a wave (calculated by Goda equation) and the vertical force induced by the weight inclusive of the concrete block, quarry run, filter, and armor layer above the slipping plane. However, this static method does not consider the wave-induced seepage flow in the rubble mound. Such seepage may decrease the stability of the rubble mound. The stability of a rubble mound breakwater under the action of seepage was studied based on the results of CFD software (OpenFOAM) and Limit Equilibrium Method (GeoStudio). The numerical analysis result showed that the seepage flow decreased the stability of the rubble mound breakwaters. The results of the numerical analyses also revealed the stability of the rubble mound was varied with time. Especially, the most critical state happened at the condition of overtopping the concrete block, acting strong uplift pressure raising along side and underneath the concrete block, and generating high pore pressure inside rubble mound due to seepage flow. Therefore, it may be necessary to conduct a dynamic analysis considering the effect of wave-induce seepage flow together with the static analysis.

Decomposition of Shear Resistance Components in Reinforced Concrete Beams (철근콘크리트 보의 전단저항 성분 분해)

  • Rhee, Chang-Shin;Shin, Geun-Ok;Kim, Woo
    • Journal of the Korea Concrete Institute
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    • v.18 no.6 s.96
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    • pp.819-825
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    • 2006
  • The objective of the present study is to verify the validity of a new truss model for evaluating the contribution by arch action to shear resistance in shear-critical reinforced concrete beams. The new truss model is based on the relationship between shear and bending moment in a beam subjected to combined shear and bending. The compatibility condition of the shear deformation that deviates from Bernoulli bending plane is formulated utilizing the smeared truss idealization with an inclined compression chord. The Modified Compression Filed Theory is employed to calculate the shear deformation of the web, and the relative axial displacements of the compression and the tension chord by the shear flow are also calculated. From this shear compatibility condition in a beam, the shear contribution by the arch action is numerically decoupled. Then the validity of the model is examined by applying the model to some selected test beams in literatures. On the basis of the analytical results, the contribution by the web to shear resistance can be constant and have an excellent linear correlation with the web reinforcement ratio. The present decoupling approach may provide a simple way for the assessment of the role of each parameter or mechanism that affects the ultimate shear behavior of reinforced concrete beams.

Prediction of Fatigue life of Composite Laminates using Micromechanics of Failure (미시역학적 파손이론을 이용한 복합재 적층판의 피로수명 예측)

  • Jin, Kyo-Kook;Ha, Sung-Kyu;Kim, Jae-Hyuk;Han, Hoon-Hee
    • Composites Research
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    • v.24 no.1
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    • pp.10-16
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    • 2011
  • Many tests are required to predict the fatigue life of composite laminates made of various materials and having different layup sequences. Aiming at reducing the number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life prediction of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure. For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. The critical plane model was introduced for the interface of the fiber and matrix, but fatigue life prediction was ignored for the interface since the interface fatigue strength was presumed high enough. The modified Goodman equation was utilized to take into account the mean stress effect. To check the validity of the theory, the fatigue life of three different GFRP laminates, UDT[$90^{\circ}2$], BX[${\pm}45^{\circ}$]S and TX[$0^{\circ}/{\pm}45^{\circ}$]S was examined experimentally. The comparison between predictions and test measurements showed good agreement.