• Title, Summary, Keyword: range of confinement

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Effect of confinement on flexural ductility design of concrete beams

  • Chen, X.C.;Bai, Z.Z.;Au, F.T.K.
    • Computers and Concrete
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    • v.20 no.2
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    • pp.129-143
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    • 2017
  • Seismic design of reinforced concrete (RC) structures requires a certain minimum level of flexural ductility. For example, Eurocode EN1998-1 directly specifies a minimum flexural ductility for RC beams, while Chinese code GB50011 limits the equivalent rectangular stress block depth ratio at peak resisting moment to achieve a certain nominal minimum flexural ductility indirectly. Although confinement is effective in improving the ductility of RC beams, most design codes do not provide any guidelines due to the lack of a suitable theory. In this study, the confinement for desirable flexural ductility performance of both normal- and high-strength concrete beams is evaluated based on a rigorous full-range moment-curvature analysis. An effective strategy is proposed for flexural ductility design of RC beams taking into account confinement. The key parameters considered include the maximum difference of tension and compression reinforcement ratios, and maximum neutral axis depth ratio at peak resisting moment. Empirical formulae and tables are then developed to provide guidelines accordingly.

Confinement Range of Transverse Reinforcements for T-shaped Reinforced Concrete Walls (철근콘크리트 T형 벽체의 콘크리트 구속을 위한 횡철근의 배근범위)

  • 하상수;오영훈;최창식;이리형
    • Journal of the Korea Concrete Institute
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    • v.14 no.6
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    • pp.1001-1009
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    • 2002
  • The objective of this study is to determine the range of confinement (or the transverse reinforcement of the reinforced concrete structural walls with the T-shaped cross section subjected to cyclic lateral loads. The range of confinement for transverse reinforcement is related to the location of neutral axis and determined by the magnitude and distribution of compressive strain. The compressive strain depends on the ratio of wall cross sectional area to the floor-plan area, the aspect ratio, configuration, the axial load, and the reinforcement ratios. By affection of flange, the neutral axis appears different depending on positive and negative forces and because of this reason, when web and flange are subjected to compressive stress, the range of confinement for the transverse reinforcement of T-shaped walls would shows different result. Therefore this experimental research focused on the structural characteristics of T-shaped walls and suggested the neutral axis depth through comparing the results of this study with sectional analysis.

Compressive behavior of short fibrous reinforced concrete members with square cross-section

  • Campione, G.
    • Structural Engineering and Mechanics
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    • v.37 no.6
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    • pp.649-669
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    • 2011
  • In this paper an analytical model is presented that addresses the compressive response of short-fiber reinforced concrete members (FRC) with hooked steel fibers. This model is applicable to a wide range of concrete strengths and accounts for the interaction between the cover spalling and the concrete core confinement induced by transverse steel stirrups and also for buckling of longitudinal reinforcing bars. The load-shortening curves generated here analytically fit existing experimental data well.

Flexural ductility of RC beam sections at high strain rates

  • Pandey, Akhilesh K.
    • Computers and Concrete
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    • v.12 no.4
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    • pp.537-552
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    • 2013
  • Computation of flexural ductility of reinforced concrete beam sections has been proposed by taking into account strain rate sensitive constitutive behavior of concrete and steel, confinement of core concrete and degradation of cover concrete during load reversal under earthquake loading. The estimate of flexural ductility of reinforced concrete rectangular sections has been made for a wide range of tension and compression steel ratios for confined and unconfined concrete at a strain rate varying from $3.3{\times}10^{-5}$ to 1.0/sec encountered during normal and earthquake loading. The parametric studies indicated that flexural ductility factor decreases at increasing strain rates. Percentage decrease is more for a richer mix concrete with the similar reinforcement. The confinement effect has marked influence on flexural ductility and increase in ductility is more than twice for confined concrete (0.6 percent volumetric ratio of transverse steel) compared to unconfined concrete. The provisions in various codes for achieving ductility in moment resisting frames have been discussed.

The Channel Wall Confinement Effect on Periodic Cryogenic Cavitation from the Plano-convex Foil

  • Ito, Yutaka;Nagayama, Tsukasa;Yamauchi, Hiroshi;Nagasaki, Takao
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.383-390
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    • 2008
  • Flow pattern of cavitation around a plano-convex foil, whose shape is similar to the inducer impeller of the turbo-pumps in the liquid fuel rocket engine, was observed by using a cryogenic cavitation tunnel of blowdown type for visualization. Working fluids were liquid nitrogen and hot water. The parameter range to be varied was between 20 and 60mm for channel width, 20 and 60mm for foil chord, -1.8 and 13.2 for cavitation number, 3.7 and 19.5m/sec for averaged inlet velocity, $8.5{\times}10^4$ and $1.5{\times}10^6$ for Reynolds number, -8 and $8^{\circ}$ for angle of attack, respectively. Especially at positive angle of attack, namely, convex surface being downstream, the whole cavity or a part of the cavity on the foil surface departs periodically. Periodic cavitation occurs only in case of smaller cavitation size than twice foil chord. Cavitation thickness and length in 20mm wide channel are larger than those in 60mm due to the wall confinement effect. Therefore, periodic cavitation in 60mm wide channel easily occurs than that in 20mm. These results suggest that the periodic cavitation is controlled by not only the hydrodynamic effect of vortex shedding but also the channel wall confinement effect.

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Evaluation of Structural Performance of RC T-shaped Walls with Different ratios of axial load and vertical reinforcement (압축력비와 수직철근비에 따른 RC T형 벽체의 구조성능 평가에 관한 해석적 연구)

  • 하상수;최창식;이리형
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.403-408
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    • 2003
  • The objective of this study is to understand the variables affected the confinement for the transverse reinforcement of the reinforced concrete structural walls with the T-shaped cross section subjected to cyclic lateral loads. The structural performance of T-shaped walls was advanced by the transverse reinforcement which restrained the concrete subjected to compressive stress. If the arrangement of transverse reinforcement was not suitable for the confinement, T-shaped walls happened the brittle failure by web crushing or bucking of vertical reinforcement at the compression zone. It is necessary to confine transverse reinforcement in order to prevent the these failure. But the location of neutral axis and the magnitude of ultimate strain vary according to the section shape, a ratio of axial load, a ratio of wall cross sectional area to the floor-plan area, an aspect ratio and the reinforcement ratio. Therefore, the objective of this research is to grasp the location of neutral axis and the range which needs for the confinement of transverse reinforcement through the results of the sectional analysis which varies the ratio of axial load and the ratio of vertical reinforcement.

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FE modeling of Partially Steel-Jacketed (PSJ) RC columns using CDP model

  • Ferrotto, Marco F.;Cavaleri, Liborio;Trapani, Fabio Di
    • Computers and Concrete
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    • v.22 no.2
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    • pp.143-152
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    • 2018
  • This paper deepens the finite element modeling (FEM) method to reproduce the compressive behavior of partially steel-jacketed (PSJ) RC columns by means of the Concrete Damaged Plasticity (CDP) Model available in ABAQUS software. Although the efficiency of the CDP model is widely proven for reinforced concrete columns at low confining pressure, when the confinement level becomes high the standard plasticity parameters may not be suitable to obtain reliable results. This paper deals with these limitations and presents an analytically based strategy to fix the parameters of the Concrete Damaged Plasticity (CDP) model. Focusing on a realistic prediction of load-bearing capacity of PSJ RC columns subjected to monotonic compressive loads, a new strain hardening/softening function is developed for confined concrete coupled with the evaluation of the dilation angle including effects of confinement. Moreover, a simplified efficient modeling approach is proposed to take into account also the response of the steel angle in compression. The prediction accuracy from the current model is compared with that of existing experimental data obtained from a wide range of mechanical confinement ratio.

Wall charge effects on structural properties of a coarse-grained FENE polyelectrolyte confined in slit nanochannels by Brownian dynamics simulation

  • Jeon, Jong-Gu;Chun, Myung-Suk
    • Korea-Australia Rheology Journal
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    • v.19 no.2
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    • pp.51-59
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    • 2007
  • A polyelectrolyte chain confined in a slit nanochannel exhibits a structural transition from the one in free space. In this paper, the effect of the long-range electrostatic interactions between the xanthan polyelectrolyte and the slit wall on the confined xanthan conformation is investigated via the Brownian dynamics simulation. A neutral and two negatively charged surfaces of polydimethylsiloxane (PDMS) and glass are combined to make four kinds of slit channels with different charge characteristics: i) neutral-neutral, ii) glass-glass, iii) neutral-PDMS and iv) neutral-glass walls. Their walls are characterized by uniform surface charge densities determined from experimental data of zeta potential. Both the nonmonotonic chain size variation and the loss of long-range bond vector correlation, previously observed under confinement in the PDMS-PDMS slit, are also found in the neutral slit, demonstrating the nonelectrostatic origin of such crossover behaviors. As expected, the effect of wall charges is negligible at sufficiently high medium ionic strength of 100mM but it becomes significant in the opposite limit of 0.01mM. In the latter case, the high charge density of glass walls strengthens the effective confinement of a negatively charged polyelectrolyte and produces a xanthan structure comparable to that confined in a much narrower neutral slit. The obtained structural data suggest the possibility of controlling the structure of confined polyelectrolytes by the modification of surface charge characteristics of micro/nanofluidic devices in combination with the adjustment of the medium ionic strength.

EFFECTS OF GEOMETRIC PARAMETERS ON NUCLEATE POOL BOILING OF SATURATED WATER IN VERTICAL ANNULI

  • Kang, Myeong-Gie
    • Nuclear Engineering and Technology
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    • v.41 no.3
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    • pp.271-278
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    • 2009
  • Nucleate pool boiling of water in vertical annuli at atmospheric pressure has been studied experimentally and two empirical correlations have been suggested to obtain effects of geometric parameters on heat transfer. Data of the present and the previous tests range over a tube length of 0.50-0.57 m, a diameter of 16.5-34.0 mm, and an annular gap size of 3.7-44.3 mm. Through the analysis, tube bottom confinement (open or closed) has been investigated, as well. The developed correlations predict experimental data within a ${\pm}25%$ error bound. It has been identified that effects of the diameter and the length of heated tubes as well as the annular gap size should be counted into the analyses to estimate heat transfer coefficients accurately.

An Experimental Study on the Inelastic Rotation Capacity of Reinforced Concrete Beams with Lateral Reinforcement (횡방향보강근을 갖는 철근콘크리트보의 비탄성 회정능력에 관한 실험적 연구)

  • 연규원;이주나;강민철;윤정민;박찬수
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.433-439
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    • 2000
  • Reinforced concrete beams show increased ductile behavior when the compressive concrete is confined with transverse steel. In the inelastic range, the most variations of ductile behaviour are defined the equivalent length of the plastic hinge and the plastic hinge rotation. In an investigation to study the influence of such confinement, sixteen reinforced concrete beams were tested in flexure and the deflections noted at all stages of loading. For all the beams tested, the plastic hinge rotation have been computed and the effect of confinement on the same examined. The conclusions are summarized as follows: The equivalent lengths of the plastic hinge are ranged within the effective depth comparatively. The ability of the plastic hinge rotation of the reinforced concrete beams confined with transverse steel are enlarged when transverse reinforcement content are increased, but the spaces are more important as the shear force are largely increased.

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