• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1035-1041
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• 2013

To evaluate the structural integrity and dynamic characteristic of the knuckle part of a KTX anti-roll bar, an experimental and a numerical approach were used in this study. In the experimental approach, the acceleration and strain data for the knuckle parts of the KTX and KTX-SANCHUN anti-roll bar were respectively measured to evaluate and compare its structural dynamic characteristics under the operating environments of the Honam line. In the numerical approach, the evaluation of its structural integrity was conducted using LS-DYNA 3D, and then, the reliability of the finite element model used was ensured by a comparative evaluation with the experiment. The numerical results showed that the stress and velocity field of the knuckle part composed of a layered structure of a thin steel plate and rubber were more moderate than those of the knuckle part made of only a thick steel block owing to the reduction of relative contact between the knuckle and the connecting rod. It was found that the knuckle part made of a thin steel plate and rubber was recommended as the best solution to improve its structural integrity resulting from the elastic behavior of the KTX anti-roll bar being enabled under a repeating external force.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.2
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• pp.197-206
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• 2003

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of solid and hollow hemispherical shells of revolution of arbitrary wall thickness having arbitrary constraints on their boundaries. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. Displacement components μ/sub Φ/, μ/sub z/, and μ/sub θ/ in the meridional, normal, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the Φ and z directions. Potential (strain) and kinetic energies of the hemispherical shells are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies obtained by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Novel numerical results are presented for solid and hollow hemispheres with linear thickness variation. The effect on frequencies of a small axial conical hole is also discussed. Comparisons are made for the frequencies of completely free, thick hemispherical shells with uniform thickness from the present 3-D Ritz solutions and other 3-D finite element ones.

• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.61-74
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• 2018

In this study, the pull-out behavior of tunnel type anchorage of suspension bridges was analyzed based on results from laboratory size model tests and numerical analysis. Tunnel type anchorage has found its applications occasionally in both domestic and oversea projects, therefore design method including failure mode and safety factor is yet to be clearly established. In an attempt to improve the design method, scaled model tests were conducted by employing simplified shapes and structure of the Ulsan grand bridge's anchorage which was the first case history of its like in Korea. In the model tests, the anchorage body and the surrounding rocks were made by using gypsum mixture. The pull-out behavior was investigated under plane strain conditions. The results of the model tests showed that the tunnel type anchorage underwent wedge shape failure. For the verification of the model tests, numerical analysis was carried out using ABAQUS, a finite element analysis program. The failure behavior predicted by numerical analysis was consistent with that by the model tests. The result of numerical analysis also showed that the effect of Poisson's ratio was negligible, and that a plugging type failure mode could occur only when the strength of the surrounding rocks was 10 times larger than that of anchorage body.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.5
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• pp.463-474
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• 2009

Double symmetric patch repair of existing structures always causes membrane action only, however, in many cases this technique is not practical. On the other hand, the bending stiffness of the patch and the skin increases as tensile loading is increased and affects the bending deformation significantly in the case of single-sided patch repair. In this study, the p-convergent full layerwise model has been proposed to determine the stress concentration factor in the vicinity of a circular hole as well as across the thickness of plates with single-sided patch repair. In assumed displacement field, the strain-displacement relations and 3-D constitutive equations of a layer are obtained by the combination of 2-D and 3-D hierarchical shape functions. The transfinite mapping technique has been used to represent a circular boundary and Gauss-Lobatto numerical integration is implemented in order to directly obtain stresses occurred at the nodal points of each layer without other extrapolation techniques. The accuracy and simplicity of the present model are verified with comparison of the previous results in literatures using experiment and conventional 3-D finite element. Also, the bending effect has been investigated with various patch types like square, circular and annular shape.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.53-68
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• 2015

Longitudinal strain is an important component of seismic design for buried pipelines. A design procedure which determines the wavelength from site natural period and shear wave velocity of the soil layer and closed-form solutions of pipelines under a harmonic motion is typically used in design. However, the applicability of the procedure has not yet been thoroughly investigated. In this paper, displacement-time histories extracted from 1D site response analyses are used in 3D shell-spring model to accurately predict the response of pipelines. The results are closely compared to those from the design procedure. The area of interest is East Siberia. Performing a site response analysis to determine site specific displacement time history is highlighted. The site natural period may be used to predict the predominant period of the acceleration time history, but cannot be used to estimate the predominant period of the displacement time history. If an accurate estimate of the predominant period of the displacement time history is provided, it is demonstrated that the design equation can be successfully used to predict the response of pipelines.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.196-205
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• 2017

In precast deck system, structural performance and serviceability are mostly determined by the connection methods between the precast decks. This study proposes precast deck system with asymmetric ribbed connection details using High Strength Fiber Reinforced Concrete(HSFRC) with filler. To verify the proposed method, the flexural performance experiment was carried out with variation of joint cross section type and splice rebar details. From the test results, regardless of joint details, spliced tensile rebars of specimens were deformed to yielding strain level. Also, all types of specimens resulted in sufficient flexural performance. These test results show that the minimum lap splice length specified in current Korea Highway Bridge Design Code is conservative for precast deck joint using HSFRC. Therefore, splice details can be simplified and joint width can be reduced by using HSFRC with filler between the precast decks, and the proposed precast deck systems can be applied to the connection part of precast decks effectively.

• Journal of the Korean Society for Railway
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• v.19 no.2
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• pp.224-233
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• 2016

Embedded Railway Systems (ERS) will be adapted for wireless trams and will be constructed along city roadways. An asphalt layer should be overlaid on top of the concrete slab used as the trackbed structure in order to ensure smoothness and surface levels equal to those of existing road pavement in downtown city areas. However, the characteristics of an asphalt layer when used as overlay pavement for an ERS are complicated and the behavior of this material is not yet well defined and understood. Therefore, in this study, laboratory shear and tensile bond strength tests were conducted to investigate the bonding behavior of an asphalt layer in a multilayered trackbed section of an ERS. For the laboratory tests, a waterproof coating material was selected as a bonding material between the asphalt overlay and a concrete specimen. Valuable design parameters could be obtained based on the tensile and shear bond strength test results, providing information about the serviceability and durability of the overlaid pavements to be constructed alongside the ERS for wireless trams. In addition, a deformation analysis to assess the tensile strain generated due to truck axle loads at the interface between the asphalt layer and the concrete slab was conducted to verify the stability and performance of the asphalt layer.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.67-75
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• 2019

The diaphragm used for CFT columns has a small amount of steel to be used, but has a disadvantage that welding is difficult and openings are required because the steel tube and four sides must be welded. The improved diaphragm to be examined in this study was cut into four corners by cutting the center hole for concrete filling. In the improved diaphragm, the width of the center hole is the same as that of the previous diaphragm, but the width of the diaphragm contacting the steel tube is reduced, thereby reducing the welding length by about 70% compared to the previous diaphragm. The in-plane strain of each specimen was analyzed when the same load was applied to the interior diaphragm through a simple tensile test. Using the general FEM program(ANSYS 19.2), the analysis was performed under the same conditions as the actual simple tensile test, and the load transfer between the improved diaphragm and the previous diaphragm was compared. When the width of the diaphragm is equal to or smaller than the flange width, stress is concentrated from the end of the diaphragm, and when the flange width is larger, stress is concentrated at the center.

• Journal of the Korean Geotechnical Society
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• v.35 no.4
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• pp.15-26
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• 2019

The stability of the gravity quay wall against earthquakes is evaluated on the basis of the allowable displacement of the wall. To estimate the displacement caused by external forces, empirical equations based on the Newmark sliding block method or numerical analysis are widely used. In numerical analysis, it is possible to analyze precisely a complicated site and structure, but difficult to set the appropriate parameters and environments; there are limitations in obtaining reliable results, depending on one's level of expertise. The Newmark method, with only seismic motions, is widely used because it is simpler than numerical simulations when estimating permanent displacement. However, the empirical equations do not have any parameters for the response characteristics and sliding block of the structure, and sliding blocks being assumed as rigid bodies does not consider the nonlinear behavior of the soil and interaction with the structure. Therefore, in order to evaluate the seismic stability of the gravity quay wall, a newly-developed empirical equation is needed to overcome the above-mentioned limitations. In this study, numerical simulations are performed to analyze the response characteristics of the backfill of the structure, and to propose an optimal method of calculating the active area. For this purpose, finite element analyses were performed to analyze the response characteristics, and stress-strain relationships for various seismic motions. As a result, the response characteristics, sliding block, and failure surface of the backfill vary depending on the input seismic motions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.2
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• pp.73-82
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• 2022

The study presents a three-dimensional approach to simulate the nonlinear behavior of a 72 m long Ultra High Performance Fiber Reinforced Concrete (UHPFRC) pre-stressed box girder for a pedestrian bridge in Busan, South Korea. The concrete damage plasticity (CDP) model is adopted to model the non-linear behavior of the UHPFRC material, in which the material properties are obtained from uniaxial compressive and tensile tests. The simulation model based on the proposed stress-strain curve is validated by the results of four-point bending model tests of a 50 m UHPFRC pre-stressed box girder. The results from the simulation models agree with the experimental observations and predict the flexural behavior of the 50 m UHPFRC pre-stressed box girder accurately. Afterward, the validated model is utilized to investigate the flexural behavior of the 72 m UHPFRC pre-stressed box girder. Here, the load-deflection curve, stress status of the girder at various load levels, and connection details is analyzed. The load-deflection curve is also compared with design load to demonstrate the great benefit of the slender UHPFRC box girder. The obtained results demonstrate the applicability of the nonlinear finite element method as an appropriate option to analyze the flexural behavior of pre-stressed long-span girders.