• Title/Summary/Keyword: RAFT

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Ab Initio Dispersion Polymerization of Styrene in the Presence of the Poly(methacrylic acid) Macro-RAFT Agent

  • Wi, Yeon-Hwa;Lee, Kang-Seok;Lee, Byung-Hyung;Choe, Soon-Ja
    • Macromolecular Research
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    • v.17 no.10
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    • pp.750-756
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    • 2009
  • Stable, spherical, polystyrene particles were synthesized in ab initio dispersion polymerization by using the poly(methacrylic acid)[PMAA] macro-RAFT agent. The presence of the PMAA macro-RAFT agent on the polystyrene (PS) particles was confirmed by NMR and FTIR spectroscopy. The PS particle size was influenced by the concentration of the RAFT agent and monomer due to the initial nucleation. When the concentration of the PMAA macro-RAFT agent was increased from 2 to 10 wt% relative to the monomer, the average particle size decreased from 2.31 to 1.36 ${\mu}m$, the conversion decreased from 93.3 to 88.9%, the weight-average molecular weight increased from 46,300 to 150,200 g $mol^{-1}$ and the PDI decreased from 2.79 to 1.94, respectively. In particular, the incorporation of 10 wt% of PMAA macro-RAFT agent produced monodisperse PS spheres of 1.36 ${\mu}m$ with a coefficient of variation (CV) of 6.44%. Thus, the PMAA macro-RAFT agent worked as a reactive steric stabilizer providing monodisperse, micron-sized, PS particles.

Behavior of the Embankment on Normally Consolidated Clay Supported by the Piled Raft (Piled Raft 기초로 지지된 연약지반 상의 제방의 거동)

  • Kim, Sang-Kyu;Song, Sun-Ok;Han, Sung-Gil;Jeon, Jin-Kyu;Lee, Wan-Sung
    • Journal of the Korean Geotechnical Society
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    • v.27 no.4
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    • pp.33-41
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    • 2011
  • A railway embankment route extending to 2 km was laid on normally consolidated clay in the West Gimhae Plain. This embankment was first built using the stage-construction technique, but longitudinal cracks suggesting arc sliding appeared on the surface of the embankment immediately after the first stage of its construction. As an alternative, the piled raft was installed on the failed embankment and then the remaining height of the embankment was raised. The behavior of the piled raft was monitored with different instruments during construction. This paper describes the monitoring results and analyses. The results show that if the pile group essentially exhibits the behavior of friction piles, the piled raft foundation performs well even in normally consolidated soft clay.

Load Sharing Analysis of Piled Rafts Based on Non-linear Load-Settlement Characteristics (Piled Raft 기초의 비선형 하중-침하 특성을 고려한 하중분담 해석)

  • Choi, Kyu-Jin;Park, Dong-Gyu;Lee, Jun-Hwan
    • Journal of the Korean Geotechnical Society
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    • v.28 no.11
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    • pp.33-40
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    • 2012
  • The design of Piled Raft foundations considering the load sharing between raft and piles provides a more economical solution than the conventional design approach based on bearing capacity of piles only. Generally, numerical methods are used to analyze the behavior of Piled Rafts due to its complexity and load sharing ratio is also estimated by numerical methods about some limited cases under specific load level and soil conditions. In this study, a method to estimate the load sharing between the raft and piles was developed which is based on load-settlement characteristics of foundation elements. Normalized load-settlement curves of the raft and pile groups were derived individually, and the relationship between load sharing ratio and foundation settlement was proposed by using these curves. For each load-settlement curves, hyperbolic type was adopted in order to describe the non-linear behavior of foundations. Centrifuge test results were compared with the results from proposed method, and the trends of variation of load sharing ratio with settlement presented from both were similar.

Analysis of Piled Raft Interactions on Clay with Centrifuge Test (원심모형실험을 통한 점토지반에서의 말뚝지지 전면기초 상호작용)

  • Park, Dong-Gyu;Choi, Kyu-Jin;Lee, Jun-Hwan
    • Journal of the Korean Geotechnical Society
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    • v.28 no.9
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    • pp.57-67
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    • 2012
  • In the design for piled rafts, the load capacity of the raft is in general ignored and the load capacities of pile are only considered for the estimation of the total load carrying capacity of the piled raft. The axial resistance of piled raft is offered by the raft and group piles acting on the same supporting ground soils. As a consequence, pile - soil - raft and pile - soil interactions, occurring by stress and displacement duplication with pile and raft loading conditions, acts as a key element in the design for piled rafts. In this study, a series of centrifuge model tests has been performed to compare the axial behavior of group pile and raft with that of a piled raft (having 16 component piles with an array of $4{\times}4$) at the stiff and soft clays. From the test results, it is observed that the interactions of piles, soil, and raft has little influences on the load capacities of piles and raft in piled rafts compared with the load capacities of group piles and raft at the same clay soil condition.

A Possible Significance in Vertebrate Phototransduction of Multi-Protein Signaling Complexes on Raft-Like Membranes

  • Hayashi, Fumio;Liu, Han;Seno, Keiji
    • Journal of Photoscience
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    • v.9 no.2
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    • pp.47-50
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    • 2002
  • Raft is a distinctive membrane domain enriched in a certain class of lipids, cholesterol, and proteins observed on the plasma membrane. Growing evidence has revealed that such membrane domains play key roles in signal transduction, fertilization, development, transmitter release, and so on. Recently, we have isolated raft-like detergent-resistant membrane (DRM) fraction from bovine photoreceptor rod outer segments. Transducin and its effecter, cGMP-phosphodiesterase, elicited stimulus-dependent translocation between detergent-soluble membrane and DRM. This suggested potential importance of such distinct membrane domains in vertebrate phototransduction. Here, we will discuss physiological meaning of the translocation of major components of cGMP cascade to raft-like membrane in phototransduction. We would like to propose a hypothesis that raft-like membrane domains on the disk membrane are the place where cGMP cascade system could be quenched.

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Parametric study of piled raft for three load-patterns

  • Sawant, V.A.;Pawar, S.V.;Ladhane, K.B.
    • Coupled systems mechanics
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    • v.1 no.2
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    • pp.115-131
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    • 2012
  • Paper presents an improved solution algorithm based on Finite Element Method to analyse piled raft foundation. Piles are modelled as beam elements with soil springs. Finite element analysis of raft is based on the classical theory of thick plates resting on Winkler foundation that accounts for the transverse shear deformation of the plate. Four node, isoparametric rectangular elements with three degrees of freedom per node are considered in the development of finite element formulation. Independent bilinear shape functions are assumed for displacement and rotational degrees of freedom. Effect of raft thickness, soil modulus and load pattern on the response is considered. Significant improvement in the settlements and moments in the raft is observed.

Bearing capacity of micropiled-raft system

  • Hwang, Tae-Hyun;Kim, Kang-Hyun;Shin, Jong-Ho
    • Structural Engineering and Mechanics
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    • v.63 no.3
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    • pp.417-428
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    • 2017
  • The micropile has been mainly used under the concept of supplementing structural support or reinforcing soft ground. For the micropiled-raft system which uses a micropile and a raft in combination in particular, it is generally considered as ground reinforcement rather than foundation components considering the bearing capacity of the micropile in many cases. In this study, the bearing capacity mechanism of the micropiled-raft system is investigated through a physical model test and numerical method. The numerical results have shown that not only the slender-pile-effect of the micropile, but also the ground reinforcement effect, increase the bearing capacity considerably. The bearing capacity formula of the micropiled-raft system is derived based on the failure mechanism obtained through model tests. The formula is verified and proposed as a design chart.

Optimum Design of Piled Raft Foundations using Genetic Algorithm (유전자 알고리즘을 이용한 Piled Raft 기초의 최적설계)

  • 김홍택;강인규;황정순;전응진;고용일
    • Proceedings of the Korean Geotechical Society Conference
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    • 1999.10a
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    • pp.415-422
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    • 1999
  • This paper describes a new optimum design approach for piled raft foundations using the genetic algorithm. The objective function considered is the cost-based total weight of raft and piles. The genetic algorithm is a search or optimization technique based on nature selection. Successive generation evolves more fit individuals on the basis of the Darwinism survival of the fittest. In formulating the genetic algorithm-based optimum design procedure, the analysis of piled raft foundations is peformed based on the 'hybrid'approach developed by Clancy(1993), and also the simple genetic algorithm proposed by the Goldberg(1989) is used. To evaluate a validity of the optimum design procedure proposed based on the genetic algorithm, comparisons regarding optimal pile placement for minimizing differential settlements by Kim et at.(1999) are made. In addition using proposed design procedure, design examples are presented.

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Numerical Analysis of Piled-Raft Foundations Considering the Effects of Sand Cushion (샌드쿠션을 고려한 말뚝지지 전면기초의 수치해석)

  • Kim, Nam-Ick;Seo, Young-Kyo
    • Journal of Ocean Engineering and Technology
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    • v.21 no.5
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    • pp.25-32
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    • 2007
  • The piled-raft foundation, a new design concept, is one of the most effective kinds of foundation for reducing settlement of structures. An alternative piled-raft system with disconnection cap and a sand cushion between the pile and raft was also investigated to compare the influence of ultimate bearing capacity and settlement. Load-settlement relation curves were used to evaluate the ultimate bearing capacity. In the numerical analyses, a plane strain elasto-plastic finite element model (Mohr-Coulomb model) was used to present the response of the piled-raft foundation.

Piled-Raft Foundation on Soft Clay in Gimhae Area (연약점토지반 Piled-Raft 기초의 김해지역에서의 적용성)

  • 서영교
    • Journal of Ocean Engineering and Technology
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    • v.18 no.3
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    • pp.20-25
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    • 2004
  • For the structural foundation above the soft clay layer conditions, the design charts are first presented for the evaluation of both bearing capacity and total settlement in the basic raft foundation system. wad settlement relationship curves are used to evaluate the ultimate soil bearing capacity. The total settlement is evaluated by applying various traditional factors into the ultimate bearing capacity. Then, the parametric studies are carried out for the piled-raft foundation system. In the numerical analysis, the elasto-pastic finite element model(Mohr-Coulomb model) is used to present the foundation response and design charts, which enable the determination of the raft size and pile length and spacing.