• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.43-50
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• 2008

This paper presents experimental and analytical results on the long-term behavior of the reinforced recycled aggregate concrete beams under sustained loading. In this experimental program, three beams with different conditions of aggregates replacement (natural aggregate 100%, recycled coarse aggregate 100%, recycled fine aggregate 50%) were subjected to the sustained flexural loading that was a half of the nominal flexural capacity over a period of 1 year. The beam were designed with net span of 2,000 mm and rectangular cross-section of 170 mm width and 170 mm effective depth. The beams were instrumented and monitored to observe the change in the long-term behavior due to creep and shrinkage of concrete under sustained loading. The predictions of long-term deflection by ACI code, Branson, Mayer, Neville, EMM and AEMM were compared with the experimental results. From the experimental results, the reinforced concrete beams with recycled aggregates showed the same performance as that of a beam with natural aggregate. The proposed method to predict the long-term deflections of reinforced recycled aggregate concrete beams gives a good estimation for experimental results.

• Journal of the Korean GEO-environmental Society
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• v.13 no.12
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• pp.81-89
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• 2012

The existing tunnel in urban area can be enlarged because of requirement of road-widening by traffic growth. The protector with rectangular cross section can be set up in the tunnel, which will be constructed for enlargement of width, to solve traffic jam around the tunnel. It is impossible to install the rockbolt in the lower area of tunnel due to a limited space between the protector and cutting surface. The objective of this study is to suggest the method of shotcrete thickness increase instead of rockbolt installation in the side wall of tunnel for the stability of tunnel. Numerical analysis was performed to evaluate displacement at the crown of tunnel, convergence of tunnel, and stress in shotcrete lining in 3-lane and 4-lane NATM tunnels enlarged from 2-lane conventional tunnel. There were three types of analysis condition, rockbolt installation, no rockbolt installation, and increase of shotcrete thickness without rockbolt in the side wall of tunnel. There was no difference on the displacement at the crown and the convergence of upper tunnel. In the lower tunnel, the convergence in case of no rockbolt installation was larger as maximum 1.3mm than that in case of rockbolt installation. The stress in shotcrete lining in case of no rockbolt installation was larger as maximum 1.3MPa than that in case of rockbolt installation. Numerical analysis was performed to compare the behavior of shotcrete with rockbolt with that of shotcrete, which its thickness was increased, without rockbolt. The shotcrete has an increase of 20%(250mm ${\rightarrow}$ 300mm, 4-lane tunnel)~25%(200mm ${\rightarrow}$ 250mm, 3-lane tunnel) in its thickness to reduce the stress in shotcrete lining. The behavior of shotcrete lining increased the shotcrete thickness by 20%~25% was similar to that of existing shotcrete lining with rockbolt.

• Journal of IKEEE
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• v.22 no.1
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• pp.185-188
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• 2018

This paper describes the parasitic capacitance modeling according to the coil structure, section bobbin and winding method for hybrid choke coil with reduced parasitic capacitance capable of the EMI attenuation of broad bands from lower frequency to higher frequency applied in the EMI attenuation filter of LED-TV SMPS. Especially, the hybrid choke coil with reduced parasitic capacitance($C_p$) proposed in this paper can reduces the parasitic capacitance($C_p$) by adopting the winding methods of rectangular copper wire, compared to the conventional common mode choke coil with the winding method of automatic type. The first resonant frequency of the proposed hybrid choke coil has a tendency to increase as the parasitic capacitance is smaller and its impedance characteristics, especially in the high frequency bands, improves as the first resonant frequency increases. In the future, the proposed hybrid choke coil with reduced parasitic capacitance shows it can be actually utilized in not only LED-TV SMPS but also various applications such as LED Lighting, Note-PC Adapter, and so forth.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.755-759
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• 2016

The use of heat pipes in the electronic telecommunication field is increasing. Among the various types of heat pipes, the thin flat heat pipe has relatively high applicability compared with the circular heat pipe in the electronic packaging application. The thin flat heat pipe based on extrusion fabrication has a simple capillary wick structure consisting of rectangular cross sectional grooves on the inner wall of the pipe. Although the groove serves as a simple capillary wick, and many such grooves are provided on the inner wall, it is difficult for the grooves to realize a sufficiently high capillary force. In the present study, a thin flat heat pipe with a wire bundle was developed to overcome the drawback of poor capillary force in the thin flat heat pipe with grooves, and was evaluated by conducting tests. In the performance test, the thin flat heat pipe with the wire bundle showed a lower thermal resistance of approximately 3.4 times, and a higher heat transfer rate of approximately 3.8 times with respect to the thin flat heat pipe with grooves as the capillary wick respectively. The possibility of using the wire bundle as a capillary wick in the heat pipe was validated in the present study; further study for commercializing this concept will be taken up in the future.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.285-288
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• 2008

A model for the effective moment of inertia $I_{\epsilon}$ as expressed in Branson's equation, in which reduction of the flexural rigidity of RC beams due to cracking are aptly taken into accoun,t is presented. However, KCI Code isn`t considered tension stiffening as it is in debonding of reinforcing bar. Therefore, this equation need to set up suitable to our design Code. The experimental work consisted of casting and testing a total of 6 simply supported reinforced concrete beams and a total of 4 continuos reinforced concrete beams under two point concentrated loads. Main parameters are concrete strength, coverage, bond between concrete and reinforcing bars, are known as have an effect on deflection and tension stiffening. Every test beams had the same $250{\times}350$mm rectangular section, with a simply supported clear span of 4,400 mm and a continuos clear span of 6,500 mm. Comparison of the test results with values obtained using the KCI Code equation of the effective moment of inertia showed a noticeable difference.

• Journal of Animal Environmental Science
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• v.14 no.1
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• pp.61-68
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• 2008

The roof structural model of liquid manure storage tank was designed to improve a structural safety and an ability of resistance to corrosion by the bad environmental condition with high humidity and high gas concentration. Due to corrosion of a general steel, the 5 years used materials were reduced to one-third of a new material in the result of a bending strength test. Some structural materials were tested to evaluate a strength and an anti-corrosion, and stainless steel pipe (STS439), steel angle with zinc hot dipping, rectangular steel pipe covered with FRP (Fiberglass Reinforced Plastics) resin were selected finally. A stainless steel is more expansive about $3{\sim}5$ times than general structural steel. But its durability under heavy corrosive environment is expected twice as long as general steel. The roof models were designed as closed cone type for each of the three structural materials. In the result of a FEM (Finite Element Method) structural analysis for the developed models, the safe snow depth was higher 2.3 times than a general roof structure, when elements of equal section modulus were used.

• Tunnel and Underground Space
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• v.27 no.1
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• pp.50-57
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• 2017

In this study, the experiment for determining shock loss at the branch is conducted for the design of network double-deck road tunnel ventilation. The shock loss coefficient that determines the quantity of shock loss has been considered only regarding the constant aspect ratio of circular or rectangular section. However the suggestion of shock loss coefficient is needed since the aspect ratio of double-deck road tunnel for small vehicle is considered around 1:3 with the low height in Korea. The experiment model was made with the scale of around 1:23 applying Reynolds similarity law, so that the shock loss coefficient on the branch of the large aspect ratio was measured. The result of the study showed that shock loss coefficients of both split branch and straight branch were measured two to three times higher than those calculated from the theoretical equation or design values of previous studies. Therefore the study resulted the effect of large aspect ratio on shock loss coefficient was huge, and it is expected that precise design value can be suggested for the design of network double-deck tunnel ventilation.

• Journal of Korea Water Resources Association
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• v.46 no.9
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• pp.947-956
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• 2013

Most of flood protection walls built on the impingement in mountain rivers have been made of concrete. It may cause flood disasters because the smooth wall surface could increase flow velocity. In this study the hydraulic experiments was carried out to evaluate the effect of one side wall with rectangular vertical ribs on flow resistance in open channel. The ratio of the pitch between vertical ribs to its depth, ${\lambda}_{nv}$, was designed so that it include the so-called d type and k type roughness. The range of Froude number, $F_r$, based on hydraulic radius is 0.81~1.12. Flow resistance in the open channel with a rib sidewall depends on the interval length of each ribs and the flow discharge. Maximum flow resistance occurred when ${\lambda}_{nv}$ is 9. In the d type roughness which ${\lambda}_{nv}$ is less than 3, the flow resistance decreases with increase of flow discharge. In the k type roughness which ${\lambda}_{nv}$ is greater than 3, the flow resistance increases with increase of flow discharge. The increments of flow resistance are especially great when ${\lambda}_{nv}$ are 9 and 12. The resistance due to vertical rib is mostly by the shape resistance and the vertical rib on one sidewall of open channel affects on the flow resistance so that the equivalent roughness heights of vertical rib may occur in scale of flow depth. Therefore the vertical ribs may be used to reduce the flow velocity and to move the location of maximum flow velocity from the rib sidewall to the centerward in a cross section of channels.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.6
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• pp.1006-1014
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• 2000

Hemisphere type Luneberg lens antenna with a reflector(frequency : 9.375 GHz, -3 dB beam width 6$^{\circ}$, diameter 30.3 cm(about 10 A), which is miniaturized and lightweightized by attaching a reflector on a section of half the Luneberg lens antenna, is designed and fabricated on the basis of Luneberg lens antenna from which easy beam pointing is acquired only by movement of 1st radiator. Measurement shows -3dB beamwidth is 6.1$^{\circ}$ in case of E-plane and 5.5$^{\circ}$ in case of H-plane. These are good agreements with expected value. Gain of this antenna is 26dBi(Aperture efficiency for uniform distribution : $\pi$ = 44.97%) which is greater than that of 1st radiator(Rectangular microstrip antenna) by 20.4 dB. And, after calculating the approximated pattern of the 1st radiator, far-field pattern, whose source is the second aperture source farmed from the approximated pattern of the 1st radiator is computed. Comparing this far-field pattern with the expected pattern, a (relatively) good agreement is observed. Circular polarization Luneberg lens antenna is also manufactured by making 1st radiator so that it has the characteristics of LHCP and RHCP radiation. The results are as followings : -3 dB beamwidth 5.8$^{\circ}$ , side lobe level -15.3 dB, isolation between LHCP and RHCP radiation 2543, axial ratio 2 dB bandwidth about 1.4 GHz(14.9%).