• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.31-34
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• 2005

An experimental investigation was conducted to examine the hysteric behavior of Ultra-High strength concrete columns for the requirement of ACI provision. Seven 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the cross section $300\times300mm$ and the shear span ratio 4. The main variables are axial load ratio, configuration and volumetric ratio of transverse reinforcement. It has been found that the behavior of columns was affected by axial load ratio rather than the amount and the configuration of transverse reinforcement. Consequently, to secure the ductile behavior of 100MPa Ultra-High strength concrete columns, ACI provision for the requirement of transverse steel may considered axial level and the detail of transverse reinforcement.

• Steel and Composite Structures
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• v.50 no.1
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• pp.25-43
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• 2024

In this article, a mathematical model is developed to predict the dynamic behavior of bio-inspired composite beam with helicoidal orientation scheme under variable axial load using a unified higher order shear deformation beam theory. The geometrical kinematic relations of displacements are portrayed with higher parabolic shear deformation beam theory. Constitutive equation of composite beam is proposed based on plane stress problem. The variable axial load is distributed through the axial direction by constant, linear, and parabolic functions. The equations of motion and associated boundary conditions are derived in detail by Hamilton's principle. Using the differential quadrature method (DQM), the governing equations, which are integro-differential equations are discretized in spatial direction, then they are transformed into linear eigenvalue problems. The proposed model is verified with previous works available in literatures. Parametric analyses are developed to present the influence of axial load type, orthotropic ratio, slenderness ratio, lamination scheme, and boundary conditions on the natural frequencies of composite beam structures. The present enhanced model can be used especially in designing spacecrafts, naval, automotive, helicopter, the wind turbine, musical instruments, and civil structures subjected to the variable axial loads.

• Steel and Composite Structures
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• v.18 no.3
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• pp.623-639
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• 2015

Self-compacting Concrete (SCC) Filled Square steel Tubes (SCFST) was used to strengthen square RC columns. To establish the efficiency of this strengthening method, 17 columns were tested under axial compression loading including 3 RC columns without any strengthening (WRC), 1 RC column strengthened with concrete jacket (CRC), 13 RC columns strengthened with self-compacting concrete filled square steel tubes (SRC). The experimental results showed that the use of SCFST is interesting since the ductility and the bearing capacity of the RC columns are greatly improved. The improvement ratio is significantly affected by the nominal wall thickness of steel tubes (t), the strength grade of strengthening concrete (C), and the length-to-width ratio (L / B) of the specimens. In order to quantitatively analyze the effect of these test parameters on axial loading behavior of the SRC columns, three performance indices, enhancement ratio (ER), ductility index (DI), and confinement ratio (CR), were used. The strength of the SRC columns obtained from the experiments was then employed to verify the proposed mode referring to the relevant codes. It was found that codes DBJ13-51 could relatively predict the strength of the SRC columns accurately, and codes AIJ and BS5400 were relatively conservative.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.04a
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• pp.371-376
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• 2010

The strength of steel material in a concrete filled steel tube (CFT) is reduced in fire, but the filled interior concrete structurally ensures the fire resistance due to its high thermal capacity. More, the contractibility of CFT is excellent since it can be constructed without form work. This research analyzed the interior concrete strength and deformation characteristics, which are the influence factors of the fire resistance of CFT, in proportion to the axial load ratio. The fire resistance performance according to changes of the axial load ratio showed great fluctuation. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the 24 MPa concrete exhibited the fire resistance time as 27, 113, and 180 minutes for the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance time were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of 40 MPa concrete showed the much lower fire resistance performance when comparing with those of 24 MPa concrete. The fire resistance performance was not increased significantly when the axial load ratio was reduced. Therefore, the deceased fire resistance performance of high strength concrete is assumed to be caused by the internal pressure increase upon the heat application.

• Journal of the Korean Geotechnical Society
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• v.35 no.1
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• pp.17-30
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• 2019

This study presents the application of the numerical and analytical technique to simulate the Load Distribution Ratio (LDR) and to define axial stiffness on reinforcing pile foundation ($K_{vr}$) in vertical extension remodeling structure. The main objective of this study was to investigate the LDR between existing piles and reinforcing piles. Therefore, to analyze the LDR, 3D FEM analysis was performed as variable for elastic modulus, pile end-bearing condition, raft contacts, and relative position of reinforcing pile in a group. Also, using the axial stiffness ($K_{ve}$) of existing piles, the axial stiffness of reinforcing pile was defined by 3D approximate computer-based method, YSPR (Yonsei Piled Raft). In addition $K_{vr}$ was defined by reducing the $K_{ve}$considering the degradation of the existing piles.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.139-145
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• 1997

Nowadays, the axial stiffness of crankshaft of long-stroke diesel engine is low compared to that of the old types of engine by increasing stroke/bore ratio and major critical speed might occur within engine operation speed. An axial damper needs to be installed in order to reduce the axial vibration of the crankshaft in the event of reduced or stopped axial damper function are discussed.

• Advances in concrete construction
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• v.2 no.3
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• pp.177-192
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• 2014

One of the main applications of FRP composites is confining concrete columns. Hence identifying the cyclic and monotonic stress-strain behavior of confined concrete columns and the parameters influencing this behavior is inevitable. Two significant parameters affecting the stress-strain behavior are aspect ratio and corner radius. The present study aims to scrutinize the effects of corner radius and aspect ratio on different aspects of stress-strain behavior of FRP confined concrete specimens (rectangular, square and circular). Hence 44 FRP confined concrete specimens were tested and the results of the tests were investigated. The findings indicated that for specimens with different aspect ratios, the relationship between the ultimate stress and the corner radius is linear and the variations of the ultimate stress versus the corner radius decreases as a result of an increase in aspect ratio. It was also observed that increase of the corner radius results in increase of the compressive strength and ultimate axial strain and increase of the aspect ratio causes an increase of the ultimate axial strain but a decrease of the compressive strength. Investigation of the ultimate condition showed that the FRP hoop rupture strain is smaller in comparison with the one obtained from the tensile coupon test and also the ultimate axial strain and confined concrete strength are smaller when a prism is under monotonic loading. Other important results of this study were, an increase in the axial strain during the early stage of unloading paths and increase of the confining effect of FRP jacket with the increase and decrease of the corner radius and aspect ratio respectively, a decrease in the slope of reloading branches with cycle repetitions and the independence of this trend from the variations of the aspect ratio and corner radius and also quadric relationship between the number of each cycle and the plastic strain of the same cycle as well as the independence of this relationship from the aspect ratio and corner radius.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.4
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• pp.393-400
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• 2002

In this paper, a novel series feeding cross-aperture coupled microstrip antenna with the effect of hybrid feeding is proposed and demonstrated experimentally to improve narrow axial ratio bandwidth of cross-aperture coupled antenna with single feeding among the various methods for generating circular polarization. The validity of a proposed series feeding cross-aperture coupled microstrip antenna is shown by comparing experimental results between the reported and the proposed microstrip antenna, and 2${\times}$2 array microstrip antenna based on the proposed single microstrip antenna used sequential rotation technique to accomplish broader axial ratio bandwidth. In the proposed single and 2${\times}$2 array microstrip antenna, the measured axial ratio bandwidths are 110 ㎒(4.6%) and 420 ㎒(17.5%), maximum gains are 8.2 ㏈i and 12.5 ㏈i, 3 dB gain bandwidths are above 400 ㎒(16.7%), and impedance bandwidths for the VSWR<1.5 are 240 ㎒(10%) and 500 ㎒(20.8%), respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.251-260
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• 2017

This paper describes the design of a slit on ground plane to improve the axial ratio of the spiral antenna for the NLJD system application. A proposed slit shape located on the ground plane is changed to compare with the archimedean spiral slit shape of the antenna in reference [7]. In order to improve the axial ratio, the slit on the ground plane is divided by the uniform angle and the conductor of position where the current has the opposite direction each other is eliminated. Measured return loss, radiation pattern and gain show a good agreement with the computer simulation results. Even though the proposed slit structure on the ground plane was changed to compare with ones of reference [7], the characteristics such as return loss, radiation pattern and gain are not almost changed and only the axial ratio was remarkably improved at 4.88 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.26-36
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• 2000

A circularly polarized $12\times12$ array with application in the satellite communications is designed at 10 GHz. The radiator is an aperture-coupled ring patch, which is suitable of large arrays. The element spacing of the array is chosen to be $0.7\lambda_0$to maintain the main beam in the broadside direction. The array is a sequential array constructed on a series-parallel feed network to obtain high gain and low axial ratio. Measurement results for the array, acquired by experiments in the compact range of POSTECH, showed a directivity of 27.88 dB, a high gain of 25.55 dB, an efficiency of 60%, an axial ratio of 1.74 dB, and a side-lobe level of -13 dB. The bandwidth of the array was 43% when the VSWR was 2, and the bandwidth of the axial ratio was 16%.