• Title, Summary, Keyword: confinement

Search Result 1,096, Processing Time 0.037 seconds

The Confinement Problem: 40 Years Later

  • Crowell, Alex;Ng, Beng Heng;Fernandes, Earlence;Prakash, Atul
    • Journal of Information Processing Systems
    • /
    • v.9 no.2
    • /
    • pp.189-204
    • /
    • 2013
  • The confinement problem was first noted four decades ago. Since then, a huge amount of efforts have been spent on defining and mitigating the problem. The evolution of technologies from traditional operating systems to mobile and cloud computing brings about new security challenges. It is perhaps timely that we review the work that has been done. We discuss the foundational principles from classical works, as well as the efforts towards solving the confinement problem in three domains: operating systems, mobile computing, and cloud computing. While common issues exist across all three domains, unique challenges arise for each of them, which we discuss.

Effect of nitrogen doping and hydrogen confinement on the electronic properties of a single walled carbon nanotube

  • Bhat, Bashir Mohi Ud Din;Dar, Jehangir Rashid;Sen, Pratima
    • Carbon letters
    • /
    • v.17 no.1
    • /
    • pp.29-32
    • /
    • 2016
  • This paper addresses the effect of dopants on the electronic properties of zigzag (8, 0) semiconducting single walled carbon nanotubes (SWCNTs), using extended Hückel theory combined with nonequilibrium Green’s function formalism. Through appropriate dopant concentrations, the electronic properties of SWCNTs can be modified. Within this context, we present our ongoing investigation on (8, 0) SWCNTs doped with nitrogen. Quantum confinement effects on the electronic properties of the SWCNTs have also been investigated. The obtained results reveal that the electronic properties of SWCNTs are strongly dependent on the dopant concentration and modification of electronic structures by hydrogen confinement.

Behavior of circular CFT columns subject to axial force and bending moment

  • Kwak, Ji-Hyun;Kwak, Hyo-Gyoung;Kim, Jin-Kook
    • Steel and Composite Structures
    • /
    • v.14 no.2
    • /
    • pp.173-190
    • /
    • 2013
  • The major objective of this paper is to evaluate the behavior and ultimate resisting capacity of circular CFT columns. To consider the confinement effect, proper material models with respect to the confinement pressure are selected. A fiber section approach is adopted to simulate the nonlinear stress distribution along the section depth. Material nonlinearity due to the cracking of concrete and the yielding of the surrounding steel tube, as well as geometric nonlinearity due to the P-${\Delta}$ effect, are taken into account. The validity of the proposed numerical analysis model is established by comparing the analytical predictions with the results from previous experimental studies about pure bending and eccentric axial loading. Numerical predictions using an unconfined material model were also compared to investigate the confinement effects on various loading combinations. The ultimate resisting capacities predicted by the proposed numerical model and the design guidelines in Eurocode 4 are compared to evaluate the existing design recommendation.

Combined effect of CFRP-TSR confinement on circular reinforced concrete columns

  • Berradia, Mohammed;Kassoul, Amar
    • Computers and Concrete
    • /
    • v.19 no.1
    • /
    • pp.41-49
    • /
    • 2017
  • The use of external carbon-fiber-reinforced polymer (CFRP) wraps is one of the most effective techniques existing for the confinement of the circular concrete columns. Currently, several researches have been made to develop models for predicting the behavior of this type of confinement. The disadvantage of the most models, is to not take into account the contribution of the transverse steel reinforcements (TSR) effect, However, very limited models have been recently developed that considers this combined effect and gives less accurate results. This paper presents the development of a new model for the axial behavior of circular concrete columns confined by combining external CFRP warps-and-internal TSR (hoops or spirals) based on the existing experimental data. The comparison between the proposed model and the experimental results showed good agreement comparing to the several existing models. Moreover, the expressions of estimating the ultimate strength and the corresponding strain are simple and precise, which make it easy to use in the design applications.

Confinement Steel Amount for Ductility Demand of RC Bridge Columns under Seismic Loading (지진하중을 받는 철근콘크리트 교각의 소요연성도에 따른 심부구속철근량)

  • Son, Hyeok-Soo;Lee, Jae-Hoon
    • Journal of the Korea Concrete Institute
    • /
    • v.15 no.5
    • /
    • pp.715-725
    • /
    • 2003
  • This paper is a part of a research program to develop a new design method for reinforced concrete bridge columns under seismic loading. The objectives of this paper are to investigate the relationship between ductility and confinement steel amount and to propose a design equation for reinforced concrete bridge columns. Computer program NARCC was used for parametric study, which was proved to provide good and conservative analytical result especially for deformation capacity and ductility factor compared with test result. A total of 7,200 reinforced concrete columns confined with spirals or perfect circular hoops were selected by combination of variables such as section diameter, aspect ratio, concrete compressive strength, yielding strength of longitudinal and confinement steel, longitudinal steel ratio, axial load ratio, and confinement steel ratio. Based on the parametric study a new design equation for confinement steel amount considering ductility demand was proposed, which can be used in the new seismic design method, i.e. ductility-based seismic design, for RC bridge columns.

Nonlinear Analysis considered Confinement Effect of Precast Concrete Segment (프리캐스트 콘크리트 세그먼트의 구속효과를 고려한 비선형 해석)

  • Lee, Heon-Min;Kim, Tae-Hoon;Park, Jae-Keun;Kim, Young-Jin;Shin, Hyun-Mock
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.305-308
    • /
    • 2008
  • The purpose of this study is to propose the confinement effectiveness of precast segmental concrete that binding by lateral confining steel in the method of precast segmental concrete pridge piers construction. Generally, the confinement effect of concrete that binding by lateral confining steel is defined by the confinement effectiveness coefficient and the confinement effectiveness coefficient is defined as the ratio of area of effectively confined concrete core to area of confined concrete core. The area of effectively confined concrete core is defined by Arching action occurred on a space of lateral confinement steel and The area of confined concrete core is defined by the ratio of area of longitudinal reinforcement to area of core of section. But in case of precast segmental concrete, concrete cover that exist on top and bottom of concrete segment should be considered.

  • PDF

Failure Behavior of Octagonal Flared RC Columns Using Oblong Hoops (장방형 띠철근을 이용한 팔각형 플레어 RC 기둥의 파괴거동)

  • Ko, Seong-Hyun
    • Journal of the Korea institute for structural maintenance and inspection
    • /
    • v.18 no.3
    • /
    • pp.58-68
    • /
    • 2014
  • Transverse steel bars are used in the plastic hinge zone of columns to insure adequate confinement, prevention of longitudinal bar buckling and ductile behavior. Fabrication and placement of rectangular hoops and cross-ties in columns are difficult to construct and require larger amount of transverse steels. In this paper, to solve these problems, the new lateral confinement method using oblong hoop is proposed for the transverse confinement of columns of the oblong cross-section and flared column. The experimental study for octagonal oblong cross-section was carried out by the flared columns test in strong axis. The lateral confinement method using proposed oblong hoop detail showed satisfactory performance of lateral confinement. Therefore it can be the alternative for oblong cross-section and flared column with improved workability and cost-efficiency.

Effects of Confinement and Transport Stress on Physiological Condition in Olive Flounder (Paralichthys olivaceus)

  • Hur, Jun-Wook;Park, Cheol-Young;Chang, Young-Jin;William H. Neill
    • Proceedings of the Korean Aquaculture Society Conference
    • /
    • /
    • pp.105-106
    • /
    • 2003
  • Physiological responses (cortisol, glucose, lactic acid, osmolality and hematology) of olive flounder (Paralichthys olivaceus) to stressors associated with confinement and subsequent transport were investigated. Specimens were subjected to confinement stress for 3 h, prior to transport for 15 h. Two different size cohorts of the fish, large (839.6$\pm$162.7 g) and small (98.2$\pm$14.8 g), were used. Experimental cohorts of the fish were divided into 3 groups for blood sampling: group A, sampled at the beginning of confinement and 3 h before transport (BT, -3 h), after confinement and at the beginning of transport (BT, 0 h), 3 h after transport had begun (AT, 3 h), and after 15 h transport (AT, 15 h); group B, sampled at BT, 0 h, at AT, 3 h, and at AT, 15 h; and, group C, sampled at AT, 3 h, and at AT, 15 h. In the cohort of large fish, plasma cortisol levels of the A group were increased over time, from 4.2 ng/ml (BT, -3 h), to 92.0 ng/ml (BT, 0 h), 118.5 ng/ml (AT, 3 h) and 105.5 ng/ml (AT, 15 h). A similar pattern was evident in the B group, in which cortisol increased from 47.5 ng/ml (BT, 0 h) to 53.5 ng/ml (AT, 15 h); and, for the C group, in which cortisol increased from 43.5 ng/ml (AT, 3 h) to 71.5 ng/ml (AT, 15 h). Glucose levels of the A group also were significantly increased, from 39.5 mg/dl (BT, -3 h), to 121.0 mg/dl (BT, 0 h), 298.0 mg/dl (AT, 3 h) and 260.5 mg/dl (AT, 15 h). Lactic acid levels increased markedly during transport, from less than 1 mmol/L (BT, 0 h) to 12.0 mmol/L (AT, 15 h). Plasma osmolality increased from 405.5 mOsm/kg (BT, -3 h, for group A) to values near 500 mOsm/kg subsequent to confinement and transport. In the small-size cohort, plasma cortisol, glucose, lactic acid and osmolality levels showed similar but less pronounced trends than those observed for the large-size cohort. This research provides baseline data on cortisol, glucose, lactic acid, osmolality and hematological responses to confinement and transport, which should be useful to aquaculturists working with olive flounder and to scientists studying other flatfish species.

  • PDF

Confinement Effect by Plate Type Lateral Reinforcement and Investigation of the Possibility for Use of High Strength Steel Bars in Reinforced Concrete Columns (횡방향 판재에 의한 횡구속 효과 및 철근콘크리트 기둥에서 고강도 철근의 사용성 검토)

  • Cho, Young-Jae;Kim, Jin-Keun
    • Journal of the Korea Concrete Institute
    • /
    • v.24 no.6
    • /
    • pp.643-650
    • /
    • 2012
  • The limitation of the yield strength in reinforced concrete columns is given for the effective use of high-strength steel bar, because very high-strength steel bar does not yield while concrete fails in compression. In order to overcome this limitation, it is required to increase peak strain of the concrete. The objective of this study is to examine the confinement effect of plate type lateral reinforcement in reinforced concrete columns. From this experimental study, the reinforced concrete columns confined by plate type carbon fiber sheets showed higher compressive strength and peak concrete strain comparing to the unconfined columns. The confinement effect is higher when cross-sectional type is a circular one than a square one. Moreover, the confinement effect was also higher for circular type confinement. Based on this study, high-strength steel bars with strength exceeding 800 MPa can be effectively used for reinforced concrete columns confined by plate type lateral reinforcements.

A Fundamental Study on the Performance of Spalling Resistance of High Performance Concrete with Material of Lateral Confinement Subjected to Fire (화재시 횡구속재 변화에 따른 고성능 콘크리트의 폭열방지성능에 관한 기초적 연구)

  • 배정렬;황인성;홍상희;한민철;한천구
    • Proceedings of the Korean Institute of Building Construction Conference
    • /
    • /
    • pp.47-50
    • /
    • 2002
  • This paper presents the results of fire resistance properties of high performance concrete varying with fiber kinds and the size of metal lath in order to verify the validities of fiber on the spatting resistance by fire. Metal lath, glass fiber and carbon fiber are used to confine the concrete. According to test results, plain concrete without lateral confinement and confined concrete with glass fiber and carbon fiber show entire failure after exposed to fire, while confined concrete with metal lath take place in the form of slight surface spatting by fire, which has favorable spatting resistance of concrete. As for the effect of the size of metal lath, when the size of metal lath is more than 1.2mm of thickness, the residual strength of concrete exposed to fire maintains more than 80% of its original strength. However, glass fiber and carbon fiber does not perform desirable spatting resistance by fire due to loss of lateral confinement of fiber exposed to fire caused by melting of fiber and reducing bond strength between concrete and fiber.

  • PDF