• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.149-160
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• 1999

This paper is a part of a research aimed at the verification of basic design rules of high-strength concrete columns. A total of 32 column specimens were tested to investigate structural behavior and strength of eccentrically loaded reinforced concrete tied columns. Main variables included in this test program were concrete compressive strength. steel amount, eccentricity, and slenderness ratio. The concrete compressive strength varied from 356 kg/$cm^2$ to 951 kg/$cm^2$ and the longitudinal steel ratios were between 1.13 % and 5.51 %. Test results of column sectional strength are compared with the results of analyses by ACI rectangular stress block, trapezoidal stress block, and modified rectangular stress block. Axial force-moment-curvature analysis is also performed for predicting axial load-moment strength and compared with the test results. The ACI rectangular stress block provides over-estimated column strengths for the lightly reinforced high strength column specimens. The calculated strengths by moment-curvature analyses are highly affected by $k_3$ values of the concrete stress-strain curve. Observed failure mode. concrete ultimate strain, and stress block parameters are discussed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.1-10
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• 2012

This paper presents an experimental result and suggests the confinement effect of headed cross tie in reinforced concrete(RC) columns subjected to cycling horizontal loads under constant axial load. Five RC columns specimens were manufactured, taking confined type of transverse reinforcement, whether or not using cross tie, end detail of cross tie (hooked or headed), and axial stress in column as major variables, Cyclic horizontal load applied to the columns under constant axial stress and the effect of cross tie to structural capacity of column was evaluated from the test. The column without cross tie failed showing bending deformation of hoop with crack in core concrete at low horizontal load while the column with cross tie showed quite improved strength and ductility by suppressing bending deformation of hoop as well as buckling of longitudinal bar at once even after crack in core concrete. At high lateral displacement, the column with hooked cross tie showed the failure pattern loosing the confining force of cross tie since the $90^{\circ}$ hooked part of cross tie was stretched out and the cracked core concrete lumps were came off. However, the column with headed cross tie showed very stable behavior since the head of cross tie effectively confined the hoop and longitudinal bars even at high lateral displacement.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.43-53
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• 2012

In the conventional design of a piled raft, the axial resistance offered by the raft itself is typically neglected and only that of the group pile is accounted in estimating the total axial resistance of the piled raft. As a consequence, piled rafts are usually designed conservatively by neglecting the raft resistance. In this study, a series of centrifuge model tests have been performed to compare the axial behavior of a group pile with that of a piled raft (both having 16 component piles with an array of $4{\times}4$) in sands with different relative densities and in clays with different preconsolidated pressures. The test results revealed that, with respect to the allowable settlement of 25 millimeters for bridge foundations, the piled raft resistances were greater than those of the group pile by 13% for dense sand, by 22% for loose sand, by 30% for stiff clay, and by 22% for soft clay. Furthermore, the ratio of piled raft resistance to group pile resistance increased as the settlement increased.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.33-43
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• 2005

This work reports results of our study on the dynamic responses of the buried pipelines both along the axial and the transverse directions under various boundary end conditions. In order to investigate the effect of the boundary end conditions for the dynamic responses of the buried pipeline, we have devised a computer program to find the solutions of the formulae on the dynamic responses (displacements, axial strains, and bending strains) under the various boundary end conditions considered in this study, The dynamic behavior of the buried pipelines for the forced vibration is found to exhibit two different forms, a transient response and a steady state response, depending on the time before and after the transfer of a seismic wave on the end of the buried pipeline. We have observed a resonance when the mode wavelength matches the wavelength of the seismic wave, where the mode number(k) of resonance f3r the axial direction. On the other hand, we have not been able to observe a resonance in the analysis of the transverse direction, because the dynamic responses are found to vanish after the seventh mode. From the results of the dynamic responses at many points of the pipeline, we have found that the responses appeared to be dependent critically on the boundary end conditions. Such effects are found to be most prominent especially for the maximum values of the displacement, the strain and its position.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.161-168
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• 2018

This study is the analytical review on the inelastic region of CRC column strength curve. The inelastic region of CRC column strength curve is based on the Bleich theory and the maximum residual stress of $0.5{\sigma}_y$. This is somewhat conservative by considering the fact that the maximum residual stress of $0.3{\sigma}_y$ is well known. This study proposes column strength curve for nonlinear behavior of hot rolled structural steel members under axial force and tangent modulus Et, with the maximum residual stress of $0.3{\sigma}_y$ and compares them with those of CRC. The stress of the inelastic column under axial compression exceeds proportional limits and reaches yielding point before applied load render the column bent. The column strength curve that depends on gradually yielding state of section needs to be reviewed. In this study, it is derived that the critical load formular according to material yielding with the maximum residual stress of $0.5{\sigma}_y$ and compared with CRC column design curve.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.5-16
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• 2023

The effect of raft flexibility on piled raft foundations in sandy soil was investigated using a numerical analysis and an analytical study. The investigation's emphasis was the load sharing between piles and raft following the raft rigidity (K_R), end-bearing conditions. The case of individual piles and subsequently the response of groups of piles was analyzed using a 3D FEM. This study shows that the α_pr, load-sharing ratio of piled raft foundations, decreases as the vertical loading increases and as the K_R decreases. This tendency is more obvious when using friction piles compared to using end-bearing piles. The effect of raft rigidity is found to be more significant for the axial force distribution - each pile within the foundations has almost similar axial forces of the pile head with a flexible raft; however, each pile has different values with rigid rafts, especially with the end-bearing piles. The axial force of the pile base with floating piles shows similar point-bearing resistance for all the piles; however, it shows different values with end-bearing piles. The differential settlement ratio of rafts showed a larger value with lower K_R.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.22-29
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• 2023

In the evaluation of seismic performance for structural materials and components, the loading rate and axial force can have a significant impact. Due to time-delay effects between input and output displacements, It is difficult to apply high-rate displacement in cyclic tests and hybrid simulations. Additionally, the difficulty of maintaining a consistent vertical load in the presence of lateral displacement has limited fast and real-time tests performed while maintaining a constant vertical load. In this study, slow, fast cyclic tests and real-time hybrid simulations were conducted to investigate the rate dependency and the influence of vertical loads of Isolation Bearing. In the experiment, the FLB System including an Adaptive Time Series (ATS) compensation and a state estimator was constructed for real-time control of displacement and vertical load. It was found that the vertical load from the superstructure and loading rate can have a significant impact on the strength of the seismic isolation bearing and its behavior during an earthquake. When conducting experiments for seismic performance evaluation, they must be implemented to be similar to reality. This study demonstrates the excellent performance of the system built and used for seismic performance evaluation and enables accurate and efficient seismic performance evaluation.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.213-220
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• 2015

CFT column has a lot of structural advantages due to the composite behavior between in-filled concrete and steel tube. This paper deals with the development of an effective numerical model which can consider the bond-slip behavior between both components of concrete matrix and steel tube without taking double nodes. Since the applied axial load to in-filled concrete matrix is delivered to steel tube by the confinement effect and the friction, the governing equation related to the slip behavior can be constructed on the basis of the force equilibrium and the compatability conditions. In advance, the force and displacement relations between adjacent two nodes make it possible to express the slip behavior with the concrete nodes only. This model results in significant savings in the numerical modeling of CFT columns to take into account the effect of bond-slip. Finally, correlation studies between numerical results and experimental data are conducted to verifying the efficiency of the introduced numerical model.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.281-290
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• 2005

This paper presents experimental and analytical studies on long-term behavior of square CFT columns under central axial loading. Two loading cases are considered; (1) the load applied only at the inner concrete of the column and (2) the load applied simultaneously on both the concrete and the steel tube. Four specimens of square CFT columns were tested under the two loading cases, and basic creep test for two concrete specimens was performed to find out the creep properties of the inner concrete. Three-dimensional finite element analysis models were established and verified with the experimental results. The verification shows that the prediction for the long-term behavior of actual square CFT columns is possible from the three dimensional finite element modeling considering the bond behavior between steel tube and inner concrete. Also, experimental results and numerical calculations revealed that the bond stress Induced by the confinement pressure as well as the slip between inner concrete and steel tube were increased with time In the first loading case. However, the confinement by the loading Plate was decreased with time while increasing confinement effect by the steel tube was observed over time. In contrast no confinement effects occur in the second loading case.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.1-13
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• 2010

This paper presents an investigation on the geometric nonlinear behavior of cable-stayed bridges using geometric nonlinear finite element analysis method. The girder and mast in cable-stayed bridges show the combined axial load and bending moment interaction due to horizontal and vertical forces of inclined cable. So these members are considered as beam-column member. In this study, the nonlinear finite element analysis method is used to resolve the geometric nonlinear behavior of cable-stayed bridges in consideration of beam-column effect, large displacement effect (known as P-${\delta}$ effect) and cable sag effect. To analyze a cable-stayed bridge model, nonlinear 6-degree of freedom frame element and nonlinear 3-degree of freedom equivalent truss element is used. To resolve the geometric nonlinear behavior for various live load cases, the initial shape analysis is performed for considering dead load before live load analysis. Then the geometric nonlinear analysis for each live load case is performed. The deformed shapes of each model, load-displacement curves of each point and load-tensile force curves for each cable are presented for quantitative study of geometric nonlinear behavior of cable-stayed bridges.