• Journal of the Korean Society for Railway
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• v.3 no.2
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• pp.51-61
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• 2000

In this study, field measurements of vibration on the structures supporting railroad track were performed. The vibration data obtained were analyzed to find out any correlation between its magnitude and several factors such as type of bridges, distance from the track, type of train, frequency characteristics, etc. As a result, the magnitude of vibration turned out to be the highest in the steel bridge, the concrete bridge and steel-concrete combined bridge were the next in descending order. It was also found that the dynamic characteristics of ground were the most important factors among several affecting vibration near by the railroad track. And the empirical ground vibration estimation equation for estimating ground vibration was developed. The proposed equation with respect to distances from the railroad could be easily used for the estimation of ground vibration at the residential areas nearby the track.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.9-12
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• 2004

Coupling beams subject to cyclic loads exhibit different behavioral characteristics and energy dissipation capacity varying with re-bar layouts. In the present study, nonlinear analysis method was developed using analogous truss model. Using the numerical method, parametric studies were performed to investigate the behavioral characteristics and the energy dissipation mechanism of coupling beams with various re-bar layouts subject to cyclic loading. Based on the investigation, a simple and practical method for evaluating the energy dissipation capacity of coupling beams was developed and verified by experiments. The proposed method accurately predicted the dissipated energy during cyclic loading addressing design parameters such as re-bar layouts, re-bar ratio, and deformation. The proposed method can be easily applied to nonlinear static and dynamic methods for seismic analysis and design.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1669-1680
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• 2019

Seismic safety is considered to be one of the key design objectives of AP1000 nuclear power plant (NPP) in strong earthquakes. Dynamic behavior, damage development and aggravation effect are studied in this study for the three main components of AP1000 NPP, namely reinforced concrete shield building (RCSB), steel vessel containment (SVC) and reinforced concrete auxiliary building (RCAB). Characteristics including nonlinear concrete tension and compressive constitutions with plastic damage are employed to establish the numerical model, which is further validated by existing studies. The author investigates three earthquakes and eight input levels with the maximum magnitude of 2.4 g and the results show that the concrete material of both RCSB and RCAB have suffered serious damage in intense earthquakes. Considering RCAB in the whole NPP, significant damage aggravation effect can be detected, which is mainly concentrated at the upper intersection between RCSB and RCAB. SVC and reinforcing bar demonstrate excellent seismic performance with no obvious damage.

• Coupled systems mechanics
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• v.3 no.2
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• pp.171-193
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• 2014

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of hybrid structure with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. A numerical algorithm capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to explore the dynamic response of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified model of 2 coupled lumped masses to investigate the effects of subsystems different damping, mass ratio, frequency ratio on dynamic characteristics and equivalent modal damping; the second approach employs a detailed numerical step-by step integration procedure.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1085-1090
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• 2007

In recent railway construction, the concrete slab track is getting highlighted as main stream in track type. However, it is the fact that there are different opinions in selection of the optimized spring coefficient of elastic pad. In this study, the performance of vibration reduction in different stiffness of rail pad for ballasted track was compared, and the changes in characteristics, such as static/dynamic deflection of components, vibration acceleration, insertion loss etc., were analysed by using ISI Program for various types of rail fastening system used in concrete slab track. It was concluded that the fastening system with softer pads has shown the better performance of vibration reduction in concrete slab track and the optimized static stiffness has been calculated to 21.1kN/mm for conventional railways, 17.6kN/mm for high-speed railways and 17.8kN/mm for subways.

• Journal of Industrial Technology
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• v.17
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• pp.227-232
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• 1997

This study was conducted to evaluate durability of concrete which are increasingly demanded recently. Concrete durability properties incorporating waste foundry sand was performed with the variable of W/C ratio, Sand/Waste foundry sand ratio and Air entrainment-Non air entrainment. Cylinder specimens were made and subjected to freezing and thawing cycle at $-18^{\circ}C$ and $4^{\circ}C$. Dynamic modulus of elasticity were evaluated as F/T cycle increase. The results show that decreasing W/C ratio and AE concrete makes improved resistance of freezing and thawing improved. Especially, resistance of freezing and thawing is improved by Fine aggregate/Waste foundry sand ratio which is 50%, 25%, 0% in a row.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.601-606
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• 2002

This study explored physical properties of a hardened cement and a concrete specimen using a high performance cement type solidification consisting of a weathered granite soil and a yellow soil mainly. Also the development of high performance cement type solidification was purposed for an intensity improvement and a long-term durability. As the experimental results, a mortar used by the weathered granite soil shows positive result, however using the yellow soil as a mortar Shows less positive result at the compressive strength. Also the dynamic modulus of elasticity measurement result, the concrete specimens used by the weathered granite and the yellow soil reached above 90%, so it seems to have the durability of freezing and thawing.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.4
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• pp.77-85
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• 1999

In this study, a computer program considering initial imperfection of axisymmetric reinforced concrete shell which plastic deformation by large external loading was developed . Initial imperfection of dome was assumed as 'dimple type' which can be expressed as Wi=(Wo/h)(1-x$^2$)$^3$. The developed model applied to the analysis of dynamic response of axisymmetric reinforced concrete shell when it has initial imperfection. The initial imperfection of 0.0, -5.0, and 5cm and steel and steel layer ratio 0,3, and 5% were tested for numerical examples . The results can be summarized as follows ; 1. Dynmaic response of vertical deflection at dome crown showed slow increased if it has not inital imperfection . But the response showed relatively high amplitude when initial imperfection was inner directed (opposite direction to loading). Similar trends also appeared for different steel layer ratios. 2. Dynamic responses of radial displacement at the junction of dome and wall showed the highest amplitude when initial imperfection was inward directed (opposite direction to loading). The lowest amplitude occurred when initial imperfection was outward directed (same direction to loading). Vibration period also delayed for inward directed initial imperfection . These trends were obvious as steel layer ratio increasing. 3. The effects of imperfection for the dynamic response of radial displacement a the center of wall scarely appeared. The effects of initial imperfection of dome on the dynmaic response of the wall can be neglected. 4. Effect of steel on the dynmic response of axisymmetric shell structure was great when initial imperfection did not exist. And the effect of direction of initial imperfection (inward or outward) did not show big difference.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.653-660
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• 2017

The aim of this study is to accurately estimate seismic damage and the collapse mechanism of the historical stone masonry minaret "Hafsa Sultan", which was built in 1522. Surveying measurements and material tests were conducted to obtain a 3D solid model and the mechanical properties of the components of the minaret. The initial Finite Element (FE) model is analyzed and numerical dynamic characteristics of the minaret are obtained. The Operational Modal Analysis (OMA) method is conducted to obtain the experimental dynamic characteristics of the minaret and the initial FE model is calibrated by using the experimental results. Then, linear time history (LTH) and nonlinear time history (NLTH) analyses are carried out on the calibrated FE model by using two different ground motions. Iron clamps which used as connection element between the stones of the minaret considerably increase the tensile strength of the masonry system. The Concrete Damage Plasticity (CDP) model is selected in the nonlinear analyses in ABAQUS. The analyses conducted indicate that the results of the linear analyses are not as realistic as the nonlinear analysis results when compared with existing damage.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.31-40
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• 2008

The dynamic moduli of asphalt concrete are very important for the analysis and the design of asphalt pavement systems. The dynamic modulus master curve is usually represented by a sigmoidal function. The Ramberg-Osgood model was widely used for fitting of normalized modulus reduction curves with strain of soils in soil dynamic fields. The master curves were obtained by both sigmoidal functions and modified Ramberg-Osgood model for the same dynamic modulus data set, the fitting abilities of both methods were excellent. The coefficients in sigmoidal function are coupled. Therefore, it is not possible to separate the characteristics of the master curve with absolute value and shape. However, the each fitting coefficient in the Ramberg-Osgood model has a unique effect on the master curve, and the coefficients are not coupled with each other.