• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.414-423
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• 1994

The planar laminar impingement jet with a confinement plate has been studied numerically. Discretzing the convection term with the QUICKER scheme, the full Navier-Stokes equations for fluid flow were solved using the well known SIMPLER algorithm. The flow characteristics with Reynolds number and jet exit velocity profile effects on it were considered for H=3, Re=200 - 2000. Results show that vortical flow forms in turn along the confinement and impingement plates as the Reynolds number increases and such a complicated flow pattern has never been reported prior. The jet exit velocity profile is shown to do an important role in determining the position of vortex flow and its size as well as in stagnation and wall jet flow region. Parabolic jet exit profile results in peak of skin friction 1.4-1.6 times greater than that of uniform profile. The channel height effects are also studied and shown to have an effect on flow pattern similar to that of Reynolds number. Also shown is that effects of the jet exit velocity profile becomes less significant over a certain channel height.

• Journal of the Korean institute of surface engineering
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• v.39 no.3
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• pp.142-146
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• 2006

A novel internal-type linear inductive antenna, which we refer to as a double comb-type antenna, was developed for a large-area plasma source with substrate size of $880\;mm{\times}660\;mm$ ($4^{th}$ generation glass size). In this study, effect of plasma confinement by applying multi-polar magnetic field was investigated. High density plasmas of the order of $3.18{\times}10^{11}\;cm^{-3}$ could be obtained with a pressure of 15 mTorr Ar at an inductive power of 5000 W with good plasma stability. This plasma density is higher than that obtained for the conventional double comb-type antenna, possibly due to the plasma confinement, low rf voltage, resulting in high power transfer efficiency. Also, due to the remarkable reduction in the antenna rf voltage and length, a plasma uniformity of less than 3% could be obtained within a substrate area of $880\;mm{\times}660\;mm$ as rf power increased.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.67-70
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• 2005

In this study, an experimental investigation of the strength of R/C columns with 300mm square sections confined by head anchorage bar is presented. This initial phase of research considers only axial loading and consists of a total of 7 column tests. The main variables are distance and anchorage type of transverse reinforcement such as standard hooks and headed bar. The purpose of this study is to investigate the confinement effect and strength increment by head and to propose the confinement model for column using the head at end of lateral tie. Also, the test results for ultimate strength and strength gain factor of columns in this study and previous study is compared with the existing analytical models. Based on the test results, the Saatcioglu's model estimates confinement effects was closed to experimental value and the developed analytical approach considered the head was capable of predicting the strength gain factor results with a resonable accuracy.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.271-279
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• 2003

The objective of this study is to evaluate the damage of the reinforced concrete bridge piers. For the purpose of this research, twelve reinforced concrete specimens were fabricated and experimented with quasi-static test method. The selected test parameters are lap splice, axial load ratio, confinement steel ratio and number of loading cycle. The method of evaluate of damage index is the model proposed by Park and Ang. In accordance with this research, the most effective test parameter is lap splice of longitudinal steel. Therefore, the retrofit scheme of reinforced concrete bridge piers with lap splice of longitudinal steel, which was constructed before 1992, must be settled without delay. Otherwise, the effect of axial force is trivial. The more confinement steel is less damage index and more loading cycle lead to raise damage. The damage statement proposed Park and Ang is the same with experimental results.

• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.151-166
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• 2004

The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.781-791
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• 2023

Lateral pressure plays a significant role in the stress-strain relationship of compressed concrete. Concrete's internal cracking resistance, ultimate strain, and axial strength are improved by confinement. This phenomenon influences the nonlinear behavior of reinforced concrete columns. Utilizing behavior factors to predict the nonlinear seismic responses of structures is prevalent in seismic codes, and this factor plays a vital role in the seismic responses of structures. This study aims to evaluate the confining action on the behavior factor of reinforced concrete moment resisting frames (RCMRFs) with shear walls (SWRCMRFs). To this end, a diverse range of mid-rise SW-RCMRFs was initially designed based on the Iranian national building code criteria. Second, the stress-strain curve of each element was modeled twice, both with and without the confinement phenomenon. Each frame was then subjected to pushover analysis. Finally, the analytical behavior factors of these frames were computed and compared to the Iranian seismic code behavior factor. The results demonstrate that confining action increased the behavior factors of SW-RCMRFs by 7-12%.

• Steel and Composite Structures
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• v.29 no.1
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• pp.125-138
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• 2018

The research on the confinement behavior of ultra high performance concrete without and with the use of steel fibers (UHPC and UHPFRC) has been extremely limited. In previous studies, authors experimentally investigated the axially compressive behavior of circular steel tube confined concrete (STCC) short and intermediate columns with the employment of UHPC and UHPFRC. Under loading on only the concrete core, the confinement effect induced by the steel tube was shown to significantly enhance the utimate stress and its corresponding strain of the concrete core. Therefore, this paper develops a simplified stress - strain model for circular STCC columns using UHPC and UHPFRC with compressive strength ranging between 150 MPa and 200 MPa. Based on the regression analysis of previous test results, formulae for predicting peak confined stress and its corresponding strain are proposed. These proposed formulae are subsequently compared against some previous empirical formulae available in the literature to assess their accuracy. Finally, the simplified stress - strain model is verified by comparison with the test results.

• Computers and Concrete
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• v.19 no.5
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• pp.477-488
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• 2017

In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core's compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.

• The Journal of Engineering Geology
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• v.9 no.2
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• pp.135-145
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• 1999

Dynamic Shear modulus (G) is one of the imfortant dynamic soil properties to estimate the response of soil to dynamic loading. Problems in engineering geo1ogy practice the require the knowledge of soil properties subjected to dynamic loadings include soil-structure interaction during earthquakes, bomb blasts, construction operations, and mining. Although the dynamic shear modulus (G) is a time-dependent property, G change with time is often neglected. In this study, the effect of duration of confinement and its affecting factors (previous stress and strain, particle size and sustained pressure, and plasticity index) on the low-amplitude shear modulus ($G_{max}$) of soils are reviewed, and some empirical correlations based on mean particle diameter and plasticity index are proposed.