• Title/Summary/Keyword: Failure Length

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Optimization of Soil-Nailing Designs Considering Three Failure Modes (쏘일네일링의 세 가지 파괴모드를 고려한 설계 최적화에 대한 연구)

  • Seo, Hyung-Joon;Lee, Gang-Hyun;Park, Jeong-Jun;Lee, In-Mo
    • Journal of the Korean Geotechnical Society
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    • v.28 no.7
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    • pp.5-16
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    • 2012
  • Soil-nailing is the most popular method of reinforcing for slope stability. In general, two factors are considered as failure modes during the soil-nailing design stages: pullout failure mode and shear failure mode that will occur on the most probable failure plane. In many cases, however, shallow failure can also occur when the ground near the slope face is swept away by the horizontal stress release during the staged top-down excavation. In this paper, an optimized soil-nailing design methodology is proposed by considering the three failure modes mentioned above: pullout failure; shear failure; and shallow failure. The variables to be optimized include the bonded length and number of soil-nailings, and the confining pressure that should be applied at the slope face. The procedure to obtain the optimized design variables is as follows: at first, optimization of soil-nailings, i.e. bonded length and number, against pullout and shear failure modes; and then, optimization of confining pressure at each excavation stage that is needed to prevent shallow failure. Since the two processes are linked with each other, they are repeated until the optimized design variables can be obtained satisfying all the constrained design requirements in both of the two processes.

Fault Tolerance in Control of Autonomous Legged Robots (자율 보행 로봇을 위한 내고장성 제어)

  • 양정민
    • Journal of Institute of Control, Robotics and Systems
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    • v.9 no.11
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    • pp.943-951
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    • 2003
  • A strategy for fault-tolerant gaits of autonomous legged robots is proposed. A legged robot is considered to be fault tolerant with respect to a given failure if it is guaranteed to be capable of walking maintaining its static stability after the occurrence of the failure. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. If a failed joint is locked, the workspace of the resulting leg is constrained, but legged robots have fault tolerance capability to continue static walking. An algorithm for generating fault-tolerant gaits is described and, especially, periodic gaits are presented for forward walking of a hexapod robot with a locked joint failure. The leg sequence and the formula of the stride length are analytically driven based on gait study and robot kinematics. The transition procedure from a normal gait to the proposed fault-tolerant gait is shown to demonstrate the applicability of the proposed scheme.

An Experimental Study to Prevent Debdonding Failure of RC Beams Strengthened by Aramid Fiber Sheets (아라미드섬유쉬트로 휨 보강된 RC보의 부착파괴 방지 상세에 관한 실험적 연구)

  • Choi, Ki-Sun;You, Young-Chan;Kim, Keung-Hwan
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.84-87
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    • 2004
  • Nominal flexural strength of RC members strengthened with FRP sheets is generally based on the tensile strength of composite materials obtained from coupon tests. This method is based on the assumption that bond failure does not occur until the FRP sheet reaches its rupture strength. According to the previous researches, however, bond failure often occurs before the FRP sheet reaches its rupture strength. Some attempts were made to control debonding failure by increasing the bonded length of sheet or wrapping the section around their side of the member(U-wrap). In this study, the flexural failure mechanism of RC beams strengthened with AFRP sheets with different bond lengths is investigated. Their strengthening details to prevent the premature debonding failure are also suggested and its effectiveness is verified.

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Reliability Estimation of the Buried Pipelines for the Ground Subsidence (지반침하에 대한 매설배관의 건전성 평가)

  • 이억섭;김의상;김동혁
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2003.06a
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    • pp.1557-1560
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    • 2003
  • This paper presents the effect of varying boundary conditions such as ground subsidence on failure prediction of buried pipelines. The first order Taylor series expansion of the limit state function is used in order to estimate the probability of failure associated with three cases of ground subsidence. We estimate the distribution of stresses imposed on the buried pipelines by varying boundary conditions and calculate the probability of pipelines with von-Mises failure criterion. The effects of random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and thickness of pipeline on the failure probability of the buried pipelines are also systematically studied by using a failure probability model for the pipeline crossing a ground subsidence region.

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An Analytical Model on the Interface Debonding Failure of RC Beams Strengthened by GFRP (GFRP로 보강된 RC보의 계면박리파괴 해석모델)

  • 김규선;심종성
    • Journal of the Korea Concrete Institute
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    • v.11 no.3
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    • pp.69-80
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    • 1999
  • The strengthening of reinforced concrete structures by externally bonded GFRP has become increasingly common in resent years. However the analysis and design method for GFRP plate strengthening of RC beams is not well established yet. The purpose of present paper is, therefore, to define the failure mechanism and failure behavior of strengthened RC beam using GFRP and then to propose a resonable method for the calculation of interface debonding load for those beams. From the experimental results of beams strengthened by GFRP, the influence of length and thickness, width of plate on the interfacial debonding failure behavior of beam is studied and, on the basis of test results, the semi-empirical equation to predict debonding load is developed. The proposed theory based on nonlinear analysis and critical flexural crack width, predicts relatively well the debonding failure load of test beams and may be efficiently used in the analysis and design of strengthened RC beams using GFRP.

Monitoring & Analysis on Excavation Failure Modes by Centrifugal Model Experiment (원심모형실험에 의한 지하굴착 붕괴양상에 관한 계측 및 해석)

  • Heo, Y.;Ahn, K.K.;Lee, C.K.
    • Journal of the Korean Society of Safety
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    • v.13 no.3
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    • pp.135-142
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    • 1998
  • This paper is to investigate the failure surface and modes in a soil mass by a excavation of the model ground. To study the failure surface for the excavated slope, centrifugal model tests were performed by changing the angle of the excavated slope(50, 75, $90^{\circ}$) and the ground condition($D_r$=60, 90%, dry and submerged ground). Excavation was simulated during the centrifuge tests by operating a valve that allowed the zinc chloride solvent to drain from the excavation. Results of model tests were compared with those obtained with theoretical solutions using limit equilibrium analysis method. The results of model tests show that, there is a failure to create a straight line in the low angle of excavated surface and a create a circle as the angle increases. Also, as the angle of excavated surface is increasing, the angle of the failure surface increases. The failure length in the submerged ground increases approximately 1.10~1.34 times more than that of the dry ground.

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Comuarative Evaluation on Strength of Several Grout-filled Splice Sleeve (각종 그라우트 충전식 철근이음의 내력에 대한 비교평가)

  • Kim Hyong-Kee
    • Journal of the Korea Concrete Institute
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    • v.16 no.5 s.83
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    • pp.635-643
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    • 2004
  • In this study, the tensile strength of 321 full-sized grout-filled splice steeve specimens were compared and analyzed in order to afford the data for a reasonable and economical design of this system. The experimental variables analyzed in this study were embedment length of reinforcing bars, compressive strength of grout, sleeve geometry, loading pattern and final failure mode of specimen. Following main conclusions are obtained : 1) The strength of grout-filled splice sleeve tends to be improved with increasing compressive strength of grout and embedment length of reinforcing bars. Specially this tendency appears apparent in specimens of bond failure rather than rebar failure. 2) The results of this study show that the sleeve geometry have influence on the bond strength of grout-filled splice sleeve. 3) The grout-filled splice sleeve of bond failure don't show the difference of tensile strength according to size of rebar. 4) It is verified that the tensile strength required in ACI and domestic code is retained either when the compressive strength of grout over 70 MPa is used with embedment length of reinforcing bars over 4.5d or when the compressive strength of grout over 80 MPa is used with embedment length of rebars over 3.9d. 5) It is verified that the tensile strength required in AIJ code is retained in case when the embedment length of reinforcing bars is 0.8 times the rebar diameter longer than in ACI code.

An Experimental Study on the Strengthening Effect of RC Beams Strengthened by CFRP (탄소섬유 보강재로 보강한 RC 보의 보강효과에 관한 실험적 연구)

  • Kim, Jae-Hun;Park, Sung-Moo;Kang, Joo-Won
    • Journal of Korean Association for Spatial Structures
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    • v.5 no.4 s.18
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    • pp.71-77
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    • 2005
  • Bonded CFRP Plate method used murk in reinforcement method is very efficient for stress increment of reinforced members. But CFRP plate dosen't display enough its capacity and have the destruction characteristic of premature failure that reach failure by debond plate, because near-surface-bond using epoxy. Such destruction character of reinforced specimens take the influence at variables as steel reinforcement ratio, concrete strength, kind of reinforcement materials, reinforced length, property of epoxy used in binder and so on. In this study, performed experiment results are compared and considered on flexural performance of Near Surface Mounted Reinforcement used CFRP-Rod, as complement about structural behavior of RC beam reinforced flexural capacity in CFRP plate and premature failure of reinforcement material. Main variables of RC beam applied CFRP Plate external bond method are experimental variables as reinforcement length, reinforcement position (tension face and side face of beam) and existence of ironware in end parts. In case of CFRP-Rod, variable is reinforcement length.

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Strength of Unidirectional and Fabric Hybrid Laminate Joints (일방향-평직 복합재 혼합 적층판의 체결부 강도 연구)

  • An,Hyeon-Su;Sin,So-Yeong;Gwon,Jin-Hui;Choe,Jin-Ho;Lee,Sang-Gwan;Yang,Seung-Un
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.1
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    • pp.25-33
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    • 2003
  • The failure load and mode of the unidirectional and fabric hybrid composite laminate joints are studied by test and finite element analysis. Test is conducted for the specimens with nine various geometries under pin loading. Finite element analysis is performed considering the contact and friction effects between the pin and laminate by MSC/NASTRAN. Failure is estimated by Tsai-Wu and Yamada-Sun criteria on the characteristic curve. While the failure of the specimens with the small width and edge length are much affected by the joint geometry, the geometry effects are negligible in the specimens with large width and edge length. Finite element analysis based on the characteristic length method reasonably predicts the failure load and mode of the joints.

Experimental Study on Bond Behavior of 1/12.5 Scale Model of the Steel Tubular Joint Connection Subjected to Compressive Loads (압축하중을 받는 1/12.5 축소모형 강관 연결부의 부착전단 거동에 대한 실험적 연구)

  • Hongseob Oh
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.28 no.3
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    • pp.19-26
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    • 2024
  • In this study, the compressive behavior of a 1/12.5 scale model of a wind tower support structure connection was experimentally analyzed. A high-performance cementitious grout with a compressive strength of 140 MPa was used to fill the connection, and experiments were conducted with shear key spacing, the shape, and connection length as variables. When the number of shear keys in the connection is the same, the smaller the spacing of the shear keys than the length of the connection, the higher the shear strength, and for the same spacing and connection length, the higher the height of the shear keys, the higher the strength. In addition, it was found that the strength showed a linear behaviour until the connection slip reached 1.0 mm, and it reached the maximum strength at 7.0 mm connection slip showing a non-linear behaviour as the load increased. It was found that the failure mode changed from interfacial shear failure to grout failure as the strength increased according to the shape and spacing of the shear key, and brittle failure did not occur due to steel fibers.