• 한국지반공학회논문집
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• 제37권11호
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• pp.51-60
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• 2021

하천의 세굴은 교각 주변의 흙을 침식시켜 교각의 횡방향 지지력을 저감시키고 구조물의 건전도를 저하시키게 된다. 본 연구에서는 세굴이 구조물의 건전도에 미치는 영향을 살펴보고자 주변지반의 굴착에 따른 교각의 고유진동수 측정실험을 수행하였다. 폐교예정인 만경강교의 우물통기초 교각에서 충격진동시험을 수행하였다. 교각의 상단, 중앙, 하단에 가속도계를 부착하고 세 지점을 타격하여 가속도를 계측하였다. 실험 결과, 타격위치에 따른 가속도 측정값 중 상단타격이 일관되고 합리적인 가속도 결과를 보여주었다. 계측된 가속도는 고속 푸리에 변환(FFT)을 통하여 주파수 영역으로 변환되었고, 이를 이용하여 고유진동수를 측정하였다. 또한, 세굴이 교각의 고유진동수 변화에 미치는 영향을 분석하기 위하여 교각 주변 지반을 굴착하면서 고유진동수의 변화를 측정하였다. 그 결과, 굴착 깊이에 따라 고유 진동수가 감소하는 경향을 보여주었지만, 우물통 기초형식이 큰 강성을 가지고 있어 그 감소폭은 작은 것으로 나타났다.

• The International Journal of Costume Culture
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• 제7권2호
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• pp.151-157
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• 2004

This research is to conservate the old hat and restore its shape and place it on a supportive form in a stable protective container. The hat is a homemade construction, utilizing three different machine made laces, and two cotton net fabrics. The exterior, particularly the top crown piece, as well as the lace along the brim's edge has been generally soiled and discolored. Inside the crown, the cotton net has broken threads, and thread loss in several areas. The paper covering the two wires is very weak, and has discolored the lace in the areas of contact. The plastic buckles of the velvet ribbon have also discolored the areas where there is contact. The wash/bleach bath procedure was very effective. Virtually all of the light brown surface discoloration stains were removed. The darker brown spots, particularly concentrated around the two paper covered wires and assumed to be rust, were $90\%$ removed by the treatment. The brown spots apparently were due to the degradation of the paper covering, and not caused by the wire itself. The buckram foundation lost about $50\%$ of its stiffness, but this was not a major concern due to the fact that this hat should remain it its mount, which has been designed to serve for both storage and exhibition purposes.

• 한국지진공학회논문집
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• 제17권6호
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• pp.257-269
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• 2013

In this study, the capability of an existing analysis method for the fluid-structure-soil interaction of an offshore wind turbine is expanded to account for the geometric nonlinearity and sea water drag force. The geometric stiffness is derived to take care of the large displacement due to the deformation of the tower structure and the rotation of the footing foundation utilizing linearized stability analysis theory. Linearizing the term in Morison's equation concerning the drag force, its effects are considered. The developed analysis method is applied to the earthquake response analysis of a 5 MW offshore wind turbine. Parameters which can influence dynamic behaviors of the system are identified and their significance are examined.

• Structural Engineering and Mechanics
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• 제63권3호
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• pp.303-315
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• 2017

This paper presents a review on getting a Weighted Multi-Objective Optimization (WMO) of Tuned Mass Damper (TMD) parameters based on Response Surface Methodology (RSM) coupled central composite design and Weighted Desirability Function (WDF) to attenuate the earthquake vibration of a jacket supported Offshore Wind Turbine (OWT). To optimize the parameters (stiffness and damping coefficient) of damper, the frequency ratio and damping ratio were considered as a design variable and the top displacement and frequency response were considered as objective functions. The optimization has been carried out under only El Centro earthquake results and after obtained the optimal parameters, more two earthquakes (California and Northridge) has been performed to investigate the performance of optimal damper. The obtained results also compared with the different conventional TMD's designed by Den Hartog's, Sadek et al.'s and Warburton's method. From the results, it was found that the optimal TMD based on RSM shows better response than the conventional damper. It is concluded that the proposed response model offers an efficient approach regarding the TMD optimization.

• Smart Structures and Systems
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• 제19권2호
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• pp.213-224
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• 2017

The electromagnetic field can cause an essential change of the dynamic behavior of the railgun. The evaluation of the dynamics performance of railgun is a mandatory task. Here, a nonlinear electromagnetic force equation of the railgun is given in which the clearance, the thickness and the width of the rail are considered. Based on it, the nonlinear electromechanical coupled dynamics equations of Euler beam rails for the railgun are proposed. Using the equations, the nonlinear free vibration frequency of the railgun is investigated and the effects of the system parameters on the frequency are analyzed. The nonlinear forced responses of the rail to the electromagnetic excitation are investigated as well. The results show that as the nonlinearity of the railgun system is considered, the vibration frequencies of the railgun system increase; as the current in the rail increases, the difference between the natural frequencies and the nonlinear vibration frequencies increases significantly; the nonlinearity of the railgun system is more obvious for smaller distance between the two rails, smaller rail thickness, and smaller stiffness of the elastic foundation; the unstable dynamics state of the rail system occurs when the armature runs to the exit of the railgun. The results are useful for design and application of the railgun system.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.607-614
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• 2000

Settlement with crack on the hardened liners may occur in the weak clay due to waste load since the stiffness of the hardened liner is greater than that of the clay layers. Way of reducing deformation crack in the hardened liner is investigated using two computer programs, CONSOL and FLAC. The computer program CONSOL estimates the magnitude of settlement with time in clay layers and FLAC analyses the stress and deformation relationship between the foundation of landfill and waste load. The results show that a representative block of the analyzed area reaches the consolidation settlement of 1.32m, 8.8 years after the disposal of waste started with the degree of consolidation U=90%. The stress within the hardened liner exceeds the allowable vertical stress of 5kg/$\textrm{cm}^2$ and horizontal stress of 1.67kg/$\textrm{cm}^2$ at the concave part of the liner where the main and branch drainage pipes of leachate are located. It was recognized that the thickness of the interested area should be enlarged or the strength of the same area should be improved to tolerate the planned waste load.

• Steel and Composite Structures
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• 제36권2호
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• pp.229-247
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• 2020

This study analyzed stresses in concrete and its reinforcement, computing the additional loading transferred by concrete creep. The loading varied from zero, structure exclusively under its self-weight, up to the critical buckling load. The studied structure was a real, tapered, reinforced concrete pole. As concrete is a composite material, homogenizing techniques were used in the calculations. Due to the static indetermination for determining the normal forces acting on concrete and reinforcement, equations that considered the balance of forces and compatibility of displacement on cross-sections were employed. In the mathematical solution used to define the critical buckling load, all the elements of the structural dynamics present in the system were considered, including the column self-weight. The structural imperfections were linearized using the geometric stiffness, the proprieties of the concrete were considered according to the guidelines of the American Concrete Institute (ACI 209R), and the ground was modeled as a set of distributed springs along the foundation length. Critical buckling loads were computed at different time intervals after the structure was loaded. Finite element method results were also obtained for comparison. For an interval of 5000 days, the modulus of elasticity and critical buckling load reduced by 36% and 27%, respectively, compared to an interval of zero days. During this time interval, stress on the reinforcement steel reached within 5% of the steel yield strength. The computed strains in that interval stayed below the normative limit.

• Wind and Structures
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• 제14권2호
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• pp.85-112
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• 2011

Wind turbine structures are long slender columns with a rotor and blade assembly placed on the top. These slender structures vibrate due to dynamic environmental forces and its own dynamics. Analysis of the dynamic behavior of wind turbines is fundamental to the stability, performance, operation and safety of these systems. In this paper a simplied approach is outlined for free vibration analysis of these long, slender structures taking the soil-structure interaction into account. The analytical method is based on an Euler-Bernoulli beam-column with elastic end supports. The elastic end-supports are considered to model the flexible nature of the interaction of these systems with soil. A closed-form approximate expression has been derived for the first natural frequency of the system. This new expression is a function of geometric and elastic properties of wind turbine tower and properties of the foundation including soil. The proposed simple expression has been independently validated using an exact numerical method, laboratory based experimental measurement and field measurement of a real wind turbine structure. The results obtained in the paper shows that the proposed expression can be used for a quick assessment of the fundamental frequency of a wind turbine taking the soil-structure interaction into account.

• Structural Engineering and Mechanics
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• 제61권6호
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• pp.775-784
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• 2017

This study is devoted to developing many new substructure models for ballasted railway track by using the pyramid model philosophy. As the effect of railway embankment has been less considered in the previous studies in the field of vehicle/track interaction, so the present study develops the pyramid models in the presence of railway embankment and implements them in vehicle/track interaction dynamic analyses. Considering a moving car body as multi bodies with 10 degrees of freedom and the ballasted track including rail, sleeper, ballast, subgrade and embankment, two categories of numerical analyses are performed by considering the new substructure systems including type A (initiation of stress overlap areas in adjacent sleepers from the ballast layer) or type B (initiation of stress overlap areas in adjacent sleepers from the subgrade layer). A comprehensive sensitivity analyses are performed on effective parameters such as ballast height, sleepers spacing and sleeper width. The results indicate that the stiffness of subgrade, embankment and foundation increased by increasing the ballast height. Also, by increasing the ballast height, rail and ballast vertical displacement decreased.

• 한국농공학회지
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• 제30권2호
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• pp.44-54
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• 1988

This study was carried out to investigate the applicability of the conventional design method for ground supported circular cylindrical shell structures. For this purpose, the ensiled farm silo was adopted as a model structures. Herein, the conventional design method was based on the assumption that such structures are clamped at the bottom edges or the ground pressure is independent of the deflection at the surface. In the present paper, the applicability of above assumption was checked out by comparison with an exact method considering soil-structure interaction. Some results of numerical calculation show us ; When the ground is very hard, for example Winkler's constant k is larger than 100 kg / cm$^2$ / cm, or the bottom plate of structures has a infinitely stiffness, for example the bottom plate thickness is larger than 100 cm, the sectional forces, obtained from the conventional method at any wall of structures resting on an elastic foundation, can used for design purpose. Therefore, if the above condition is satisfied then the conventional assumptions can be justified for the design purpose. In this case, the assumption that such structures are fixed at the lower edges was more realistic than the assumption that the reaction pressure acting on structures is uniformly disributed since the accuracy of results of the analysis by the former assumption was higher than that obtained from the latter assumption. But the sectional forces in the bottom plate resting on ground directly could not be evaluate correctly by the conventional method.