• Title/Summary/Keyword: loading and unloading effect

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Tensile Strength Characteristics of Steel Cord and PVA Hybrid Fiber Reinforced Cement-Based Composites (Steel Cord와 PVA 혼합섬유 보강 고인성 시멘트 복합체의 인장강도 특성)

  • Yun Hyun Do;Yang Il Seung;Han Byung Chan;Hiroshi Fukuyama;Cheon Esther;Moon Youn Joon
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.18-21
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    • 2004
  • This paper discusses how steel cord and PVA hybrid fibers enhance the performance of high performance fiber reinforced cementitious composites (HPRFCC) in terms of elastic limit, strain hardening response and post peak of the composites. The effect of microfiber(PVA) blending ratio is presented. For this purpose flexure, direct tension and split tension tests were conducted. It was found that HFRCC specimen shows multiple cracking in the area subjected to the greatest bending tensile stress. Uniaxial tensile test confirms the range of tensile strain capacity from 0.5 to $1.5\%$ when hybrid fiber is used. The cyclic loading test results identified a unique unloading and reloading response for this ductile composite. Cyclic loading in tension appears not to affect the tensile response of the material if the uniaxial compressive strength during loading is not exceeded.

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Dry friction losses in axially loaded cables

  • Huang, Xiaolun;Vinogradov, Oleg G.
    • Structural Engineering and Mechanics
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    • v.4 no.3
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    • pp.330-344
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    • 1996
  • A model of a cable comprising interacting wires with dry friction forces at the interfaces is subjected to a quasi-static cyclic loading. The first cycle of this process, comprising of axial loading, unloading and reloading is investigated analytically. Explicit load-elongation relationships are obtained for all of the above phases of the cycle. An expression for the hysteretic losses is also obtained in an explicit form. It is shown that losses are proportional to the third power of the amplitude of the oscillating axial force, and are in inverse proportion to the interwire friction forces. The results obtained are used to introduce a model of a cable as a solid rod with an equivalent stiffness and damping properties of the rod material. It is shown that the stiffness of the equivalent rod is weakly nonlinear, whereas the viscous damping coefficient is proportional to the amplitude of the oscillation. Some numerical results illustrating the effect of cable parameters on the losses are given.

Dimensional accuracy and ejecting stage in cold forging (냉간단조의 Ejecting 공정이 치수정밀도에 미치는 영향)

  • Chun S. H.;Lee Y. S.;Lee J. H.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.10a
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    • pp.338-341
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    • 2004
  • The dimension of forged part is different with the die dimension by the various effects, such as, elastic deformation and thermal effect. And, the difference amounts are not same according to the forging conditions, for example, forging mode, flow stress, etc. Therefore, the use of FEA is effective to predict and update the required die dimension. However, the variables for FE simulation are also as many as variables in the experiment. The variables give very much effect to the accuracy of FE results. At first, the material model is very deeply affected to the estimated dimension of forged part. And the considering of loading and ejecting stages is also important to increase the dimensional accuracy. The experiment and FEA are performed to investigate the dimensional changes and accuracy in cold forging. Two types of upsetting are used to survey the effects of forging mode and stages.

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Nonlinear Analysis of RC Beams under Cyclic Loading Based on Moment-Curvature Relationship. (모멘트-곡률 관계에 기초한 반복하중을 받는 철근콘크리트 보의 비선형 해석)

  • 곽효경;김선필
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2000.10a
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    • pp.190-197
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    • 2000
  • A moment-curvature relationship to simulate the behavior of reinforced concrete beam under cyclic loading is introduced. Unlike previous moment-curvature models and the layered section approach, the proposed model takes into consideration the bond-slip effect by using monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. The modification of the moment-curvature relation to reflect the fixed-end rotation and pinching effect is also introduced. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

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Experimental Test and Numerical Simulation on the SMA Characteristics and Behaviors through the Load-Training (하중 트레이닝을 통한 형상기억합금의 특성 실험과 거동 전산 모사)

  • Kim, Sang-Haun;Cho, Maeng-Hyo
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.700-705
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    • 2007
  • In this study, we observe the application of shape memory alloy(SMA) into smart structures for repeatable actuation, because SMA changes its material properties and characteristics progressively under cyclic loading conditions and finally reaches stable path(state) after a certain number of stress/temperature loading-unloading cycles, so called 'training'. In this paper, SMA wires that have been in a stable state through the training are used. Stress-strain curve of the SMA wire at different temperature levels are measured. In addition, we observe other important effects such as the rate effect according to strain rates for rapid actuation response. The current work presents the experimental test using SMA wire after training completion by mechanical cycling. Through these tests, we measure the characteristics of SMA. With the estimated SMA properties and effects, we compare the experimental results with the simulation results based on the SMA constitutive equations.

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Experimental Test and Numerical Simulation on the SMA Characteristics and Behaviors for Repeated Actuations (반복적인 작동을 위한 형상기억합금의 특성 실험과 거동 전산 모사)

  • Kim, Sang-Haun;Cho, Maeng-Hyo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.3 s.258
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    • pp.373-379
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    • 2007
  • In this study, we observe the application of shape memory alloy(SMA) into smart structures for repeatable actuation, because SMA changes its material properties and characteristics progressively under cyclic loading conditions and finally reaches stable path(state) after a certain number of stress/temperature loading-unloading cycles, so called 'training'. In this paper, SMA wires that have been in a stable state through the training are used. Stress-strain curve of the SMA wire at different temperature levels are measured. In addition, we observe other important effects such as the rate effect according to strain rates for rapid actuation response. The current work presents the experimental test using SMA wire after training completion by mechanical cycling. Through these tests, we measure the characteristics of SMA. With the estimated SMA properties and effects, we compare the experimental results with the simulation results based on the SMA constitutive equations.

CFS Strengthening Effect of Reinforced Concrete Beams under Loading States (재하상태에 따른 철근콘크리트 보의 탄소섬유쉬트 보강효과)

  • 김민수;오용복;권영웅
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.04a
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    • pp.757-762
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    • 2000
  • The target of this study is to compare and analyze the strengthening effect of damaged reinforced concrete beams under unloading and loading conditions through the simulation of strengthening condition in real structures. The conclusion of test results are as follows : For the concrete beam wrapped at the side in addition to be strengthened at the bottom, the strength and stiffness increase. although the flexural capacity depends on the strengthening method, it generally shows that the strength improve in the range of 22% to 39% in comparison with the specimen without strengthening. In case of applying th equation suggested by CangaRao & Vijay for the wraped concrete beam, it must be modified because it is likely to overestimate the flexural capacity considering the height of wrapping as the width of concrete. The strength an stiffness of reinforced concrete beams in proportion to the percentage of damage decrease. Damaged beams, which are strengthened by CFS, is structurally efficient and show reduction of strength comparing with the specimen without strengthening but stiffness is increasing.

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Experimental study of rockburst under true-triaxial gradient loading conditions

  • Liu, Xiqi;Xia, Yuanyou;Lin, Manqing;Benzerzour, Mahfoud
    • Geomechanics and Engineering
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    • v.18 no.5
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    • pp.481-492
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    • 2019
  • Due to the underground openings, the tangentially concentrated stress of the tunnel remains larger at excavation boundary and decreases toward the interior of the surrounding rock with a certain gradient. In order to study the effect of different gradient stress on rockburst, the true-triaxial gradient and hydraulic-pneumatic combined test apparatus were carried out to simulate the rockburst processes. Under the different gradient stress conditions, the rock-like specimen (gypsum) was tested independently through three principal stress directions loading--fast unloading of single surface--top gradient and hydraulic-pneumatic combined loading, which systematically analyzed the macro-mesoscopic damage phenomena, force characteristics and acoustic emission (AE) signals of the specimen during rockburst. The experimental results indicated that the rockburst test under the gradient and hydraulic-pneumatic combined loading conditions could perfectly reflect the rockburst processes and their stress characteristics; Relatively high stress loading could cause specimen failure, but could not determine its mode. The rockburst under the action of gradient stress suggested that the failure mode of specimen mainly depended on the stress gradient. When the stress gradient was lower, progressive and static spalling failure occured and the rockburst grades were relatively slight. On the other hand, shear fractures occurred in rockbursts accounted for increasingly large proportion as the stress gradient increased and the rockburst occurred more intensely and suddenly, the progressive failure process became unconspicuous, and the rockburst grades were moderate or even stronger.

Strut-and-Tie Models for RC Flexural Members under Cyclic Loading (스트럿-타이 모텔을 이용한 RC 휨부재의 주기적 거동에 관한 연구)

  • 이수곤;홍성걸
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.11a
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    • pp.453-458
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    • 2001
  • This paper presents the procedure to find the hysteresis loop of RC member using a modified strut-and-tie model. The forces and displacements at critical points, that are initial yielding point, target displacement point, unloading elastic limit, and reloading point after pinching, are investigated with the strut-and-tie models. Using bond-slip relationship, the elastic behavior of tie element is determined. The plastic flow behavior after flexural yielding is expressed by changing the location of longitudinal strut. Determination of pinching effect completes the initial hysteresis loop, assuming that the behavior of the opposite direction is symmetrical form.

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The Effect of Cross Beam on the strength and Stiffness of the Frame in Shuttle Car for LMIT (LMTT용 Suhttle Car의 Frame 강도 및 강성에 미치는 Cross Beam의 영향)

  • Lim J. H.;Han G. J.;Lee K. S.;Han D. S.;Shim J. J.;Lee S. W.;Jeon Y. H.
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2004.11a
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    • pp.323-328
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    • 2004
  • According as the quantity of goods transported by ship is increasing about $7\%$ per year, a port environment is rapidly changing. To meet this situation successfully, the development of the next generation port loading and unloading system (LMTT) is studied. A Frame of shuttle car for LMTT(Linear Motor-based Transfer Technology) consist of three parts which are outer beam inner beam and cross boom. Outer boom supports a container and inner boom is a framework and cross boom reinforces outer and inner boom. In this study, we carried out the finite element analysis for the effect of cross boom on the strength and stiffness qf the frame according to the number if cross beam leading position of container, the distance ratio if inner boom from center.

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