• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.505-511
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• 2003

Experimental investigation was conducted into the flexure/shear-critical behavior of earthquake-damaged reinforced concrete columns with lap splicing of longitudinal reinforcement in the plastic hinge region. Six test specimens in the aspect ratio of 2,5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes of which magnitude could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under a constant axial load, P=$0.1f_{ck}A_g. Residual seismic performance of damaged columns was evaluated and compared to that of the corresponding original columns. Test results show that RC bridge piers with lap-spliced longitudinal steels in the plastic hinge region appeared to fail at low ductility. This was due to the debonding of the lap splice, which resulted from insufficient development of the longitudinal steels. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region indicated significant improvement both in flexural strength and displacement ductility, and strain energy ductility.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.629-633
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• 2006

We investigated a new longitudinal acceleration wave decomposition method in time domain. The proposed method separates up- and down-stream waves with an axial strain and axial acceleration measured at a single point on the transmission path. The advantages such as low computation load and easy implementation would be possible by developing time domain under the following assumptions; low frequency range, uniform cross sectional area and elastic wave propagation. We confirmed the feasibility and performance of the method through experiment using Split Hopkinson Pressure Bar (SHPB). The method can be effective in several applications, including active vibration control with wave view point, where real time wave decomposition is necessary.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.04a
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• pp.87-94
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• 1993

The study summarized in this paper is concerned with the buckling of a longitudinal bar in reinforced concrete members by numerical analysis method. The objectives of this study are to investigate the stress transfer mechanism between concrete and reinforcment and to propose a modeling equation. The result gives an acceptable agreement between the proposed modeling equation and the computer package as follows: (1) the proposed equation is a possible prediction of the strain softening of concrete and reinforcement buckling. (2) the buckling of longitudinal bars is mainly influenced by the spacing of hoops and the location of the bar.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.199-202
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• 2009

In roll forming process, a sheet metal is continuously progressively formed into a product with required cross-section and longitudinal shape, such as a circular tube with required diameter, wall-thickness and straightness, by passing through a series of forming rolls in arranged in tandem. Tn this process, each pair of forming rolls installed in a forming machine play a particular role in making up the required cross-section and longitudinal shape of the product. In recent years, that process is often applied to the bumper rail in the automotive industries. In this study, a optimal Front Bumper Beam manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle. And also effects of the process parameters on the final shape formed by roll forming defects were evaluated.

• Advanced Composite Materials
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• v.18 no.3
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• pp.251-264
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• 2009

Nonlinear mechanical behaviors of unidirectional carbon fiber-reinforced plastic (CFRP) laminates using cup-stacked carbon nanotubes (CSCNTs) dispersed epoxy are evaluated and compared with those of CFRP laminates without CSCNTs. Off-axis compression tests are performed to obtain the stress-strain relations. One-parameter plasticity model is applied to characterize the nonlinear response of unidirectional laminates, and nonlinear behaviors of laminates with and without CSCNTs are compared. Clear improvement in stiffness of off-axis specimens by using CSCNTs is demonstrated, which is considered to contribute the enhancement of the longitudinal compressive strength of unidirectional laminates and compressive strength of multidirectional laminates. Finally, longitudinal compressive strengths are predicted based on a kink band model including the nonlinear responses in order to demonstrate the improvement in longitudinal strength of CFRP by dispersing CSCNTs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.357-360
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• 2008

In roll forming process, a sheet metal is continuously progressively formed into a product with required cross-section and longitudinal shape, such as a circular tube with required diameter, wall-thickness and straightness, by passing through a series of forming rolls in arranged in tandem. In this process, each pair of forming rolls installed in a forming machine play a particular role in making up the required cross-section and longitudinal shape of the product. In recent years, that process is often applied to the bumper rail in the automotive industries. In this study, a optimal SILL SIDE manufacturing technology, model deign and proper roll-pass sequences can be suggested by forming number of roll-pass and bending angle. And also effects of the process parameters on the final shape formed by roll forming defects were evaluated.

• Advances in concrete construction
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• v.10 no.2
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• pp.151-159
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• 2020

An experimental study on the stress-strain relation of PVC-CFRP confined reinforced concrete columns subjected to eccentric compression was carried out. Two parameters, such as the CFRP strips spacing and eccentricity of axial load, were considered. The experimental results showed that all specimens failed by compressive yield of longitudinal steel bar and rupture of CFRP strips. The bearing capacity of specimen decreases as the eccentricity or the CFRP strips spacing increases. The stress-strain relation of specimens undergoes two stages: parabolic and linear stages. In the parabolic stage, the slope of stress-strain curve decreases gradually as the eccentricity of axial loading increases while the CFRP strips spacing has little effect on the slope of stress-strain curve. For the linear stage, the slope of stress-strain curve decreases as the eccentricity of axial load or the CFRP strips spacing increases. A model for predicting the stress-strain relation of columns under eccentric compression is proposed and it agrees well with various test data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4D
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• pp.485-492
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• 2008

This study presents a viscoelastic characterization of flexible pavement subjected to moving loads. A series of field tests have been conducted on three pavement sections (A2, A5, and A8) at the Korea Expressway Corporation (KEC) test road. The effect of vehicle speed on the responses of each test section was investigated at three speeds: 25 km/hr, 50 km/hr, and 80 km/hr. During the test, both longitudinal and lateral strains were measured at the bottom of asphalt layers and in-situ measurements were compared with the results of finite element (FE) analyses. A commercial FE package, ABAQUS was used to model each test section and a step loading approximation has been adopted to simulate the effect a moving vehicle. For viscoelastic analysis, relaxation moduli of asphalt mixtures were obtained from laboratory test. Field responses reveals the strain anisotropy (i.e., discrepancy between longitudinal and lateral strains) and the amplitude of strain normally decreases as the vehicle speed increases. In most cases, lateral strain was smaller than longitudinal strain, and strain reduction was more significant in lateral direction.

• Computers and Concrete
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• v.22 no.1
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• pp.11-25
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• 2018

A numerical approach for the evaluation of the flexural response of Steel Fibrous Concrete (SFC) cross-sections with arbitrary geometry, with or without conventional steel longitudinal reinforcing bars is proposed. Resisting bending moment versus curvature curves are calculated using verified non-linear constitutive stress-strain relationships for the SFC under compression and tension which include post-peak and post-cracking softening parts. A new compressive stress-strain model for SFC is employed that has been derived from test data of 125 stress-strain curves and 257 strength values providing the overall compressive behaviour of various SFC mixtures. The proposed sectional analysis is verified using existing experimental data of 42 SFC beams, and it predicts the flexural capacity and the curvature ductility of SFC members reasonably well. The developed approach also provides rational and more accurate compressive and tensile stress-strain curves along with bending moment versus curvature curves with regards to the predictions of relevant existing models.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.612-617
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• 2014

It is generally known that the automotive road wheel involves the non-proportional multiaxial loading condition, therefore the measuring dynamic stress and strain in driving state is very important to predict an endurance characteristic of the automotive road wheel. In this study, the ultimate driving test using F1 circuit with respect to 2 kinds of velocity conditions have been carried out in order to measure dynamic stress, strain of the wheel and acceleration of a vehicle. Based on the measured results, the characteristics of dynamic stress generation have been analyzed, and factors which have effect on the dynamic stress generation have been studied.