• Computational Structural Engineering
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• v.8 no.4
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• pp.159-171
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• 1995

The parameters describing a complete hysteresis loop include pinch force, drift offset, effective stiffness, unloading and reloading trangential stiffness. Analytical equations proposed to quantify the nonlinear, inelastic behavior of reinforced shear walls can be used to predict these parameters as a function of axial load and drift ratio. For example, drift offset, effective stiffness, and first and second unloading and reloading tangential stiffness are calculated using equations obtained from test data for a desired drift ratio or ductility level. Pinch force can also be estimated for a given drift ratio and axial load. The effective virgin stiffness at the first yield and its post yield reduction can be estimated. The load deflection response of flexural reinforced concrete shear walls can now be estimated based on the effective wall stiffness that is a function of axial force and drift ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.249-257
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• 2012

The reinforced earth method is financially viable. Furthermore, it overcomes environmental limitations and is therefore employed in retaining walls, slopes, foundations, roads, embankments, and other structures. However, in some cases, reinforced retaining walls are not strong enough in the curved sections and can collapse. Such mishaps are believed to occur because of an unsatisfactory analysis of the curved sections of a reinforced retaining wall. Accordingly, with the aim of investigating the workability and structural safety of curved sections of various types, this study investigates the differences in the estimated horizontal displacements of curved sections of various types and subsequently uses this information to study and analyze preliminary data so that appropriate measures can be taken to resolve alignment issues. The results of an experiment reveal that when a load is applied to curved sections of both concave and convex types, the largest horizontal displacement occurs at the center of the section. In the concave form, the earth pressure force is directed inward, whereas in the convex form, this force is directed outward. As a result, the horizontal displacement in convex forms is larger than that in concave forms. Convex reinforced earth structures are subjected to earth pressures as well as lateral earth pressure, therefore horizontal displacements in convex curved sections is larger than that of concave curved sections.

• Tribology and Lubricants
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• v.28 no.2
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• pp.62-69
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• 2012

Atomic force microscopy (AFM) has been widely utilized as a versatile tool not only for imaging surfaces but also for understanding nano-scale interfacial phenomena. By measuring the responses of the photo detector due to bending and torsion of the cantilever, which are caused by the interactions between the probe and the sample surface, various interfacial phenomena and properties can be explored. One of the challenges faced by AFM researchers originates in the physics of measuring the small forces that act between the probe of a force sensing cantilever and the sample. To understand the interactions between the probe and the sample quantitatively, the force calibration is essential. In this work, the procedures used to calibrate AFM instrumentation for nano-scale force measurement in normal and lateral directions are reviewed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.273-273
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• 2003

나노인덴테이션은 압자를 수 $\mu\textrm{N}$의 힘으로 시편에 압입을 시켜 재료의 경도나 탄성계수와 같은 기계적 특성을 평가하는 압입경도 시험법이다. 압입 변위를 나노미터범위로 조절할 수 있어 기존에 접근할 수 없었던 박막의 기계적 특성을 평가하는데 응용이 넓어지고 있다. 본 연구에서는 나노인덴테이션에서 제공되는 하중-변위곡선과 유한요소해석의 결과를 비교하여 유한요소해석의 신뢰성을 검증하고, 유한요소해석에서 여러 가지 재료의 특성에 따른 파일업과 싱크인 현상을 규명 하고자 한다.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.4
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• pp.1-13
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• 2003

For spatial free vibration of non-symmetric thin-walled curved beams with shear deformation, an improved formulation is proposed in the present study. The elastic strain and the kinetic energies are first derived by considering constant curvature and shear deformation effects due to shear forces and restrained warping torsion. Next equilibrium equations and force-deformation relations are obtained using a stationary condition of total potential energy. And the finite element procedures are developed by using isoparametric curved beam element with arbitray thin-walled sections. Particularly not only shear deformation and thickness-curvature effects on vibration behaviors of curved beams but also mode transition and crossover phenomena with change in curvatures of beams are parametrically investigated. In order to illustrate the accuracy and the reliability of this study, various numerical solutions for spatial free vibration are compared with results by available references and ABAQUS's shell element.

• Journal of the Korean Geotechnical Society
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• v.36 no.1
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• pp.5-15
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• 2020

Dynamic behavior of pile foundation is significantly influenced by the dynamic interaction between soil and pile. Especially, in the sloping ground, the soil-pile interaction becomes very complex due to different resistance according to loading direction, soil residual displacement and so on. In this study, dynamic centrifuge tests were performed on the piles in the sloping ground. The model structures consisted of a single pile and 2×2 group pile. The soil-pile interaction has been investigated considering various conditions such as slope, single and group piles, and amplitude of input motions. The phase differences between soil and pile displacement and dynamic p-y curves were evaluated. The analysis results showed that the pile behavior was largely influenced by the kinematic forces between soil and pile. In addition, the dynamic p-y curve showed the complex hysteresis loop due to the effect of slope, residual displacement, and kinematic forces.

• The korean journal of orthodontics
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• v.37 no.6
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• pp.432-439
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• 2007

The purpose of this study was to evaluate the influence of intraoral temperature changes on the orthodontic force level of a superelastic nickel-titanium alloy wire. Methods: Nickel-titanium archwires of $0.016"{\times}0.022"$ thickness were tested with a three point bending test setup, and temperature changes were applied. The force level changes according to temperature changes were measured at a 1.5 mm deflection during the loading phase and a 1.5 mm deflection during the unloading phase from a deflection to 3.1mm. Ten cycles of thermal cycling from baseline $(37^{\circ}C)$ to cold $(20^{\circ}C)$ or hot $(50^{\circ}C)$temperature were applied. Results: Alter thermal cycling, the force level during the loading phase decreased and the force level during the unloading phase increased even after the temperature was changed to the initial $37^{\circ}C$. Conclusions: The results suggest that the orthodontic force level can not return to the initial force level after temperature changes. When applying superelastic nickel-titanium archwires, we must consider that a lighter force than the loading force and a heavier force than the unloading force will be applied after intraoral temperature changes caused by eating and drinking.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.37-43
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• 2001

The energy concept has been extended to compare the hysteretic performance between various structural systems. As a result, the energy absorption efficiency is defined as the cumulative energy absorption capacity of a structural system normalized by that of the elasto-perfectly plastic system as a benchmark for comparisons. For this, the construction of energy curves from the experimental results obtained by cyclic loading tests is required. Using the proposed procedure, structures differing from each other in geometry, material and construction can be relatively and objectively compared for seismic performance. Also the beauty of this method is in its irrelevance to the structural failure mode. The proposed procedure was validated by application to the experimental results of two different specimens.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.473-484
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• 2006

The capacity spectrum method (CSM) can be used to simply estimate the maximum displacement response of the nonlinear structures. To evaluate seismic performance of multi-span bridges using the CSM, the representative response for structural system should be derived from the multi-degree-of-freedom (MDOF) responses by using the equivalent single-degree-of-freedom (ESDOF) method. The ESDOF method is used to calculate the capacity curve of the structural system from the pushover curves of all piers or structural members estimated by the pushover analysis. In order to evaluate an accuracy of ESDOF methods used in the CSM, the maximum displacements estimated by the CSM incorporating the several ESDOF methods are compared to those by the inelastic time-history analysis for several artificial earthquakes corresponding to the design spectrum.

• The korean journal of orthodontics
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• v.39 no.5
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• pp.310-319
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• 2009

Objective: NiTi closed coil springs were reported to have relatively constant unloading forces. However, the characteristics of NiTi closed coil springs from various manufacturers have not been elucidated. The purpose of this study was to compare load-deflection characteristics of various NiTi closed coil springs and to find out the optimal range of extension. Methods: Seven kinds of NiTi closed coil springs from five manufacturers were tested. Load deflection curves were obtained at extension ranges from 2 mm to 30 mm. Also, springs were kept extended during a 4 week period, and then load deflection curves were obtained again. Results: Sentalloy (Tomy) and Jinsung blue (Jinsung) showed superelasticity in every extension ranges tested and showed plastic deformation of less than 1 mm. Ni-Ti (Ormco) showed superelasticity only after the springs were extended at or more than 10 mm, thereby meaning that clinicians should extend these springs at or more than 10 mm to utilize the superelasticity. Orthonol (RMO) and Nitanium (Ortho Organizers) did not show superelasticity. After 4 weeks of extension, all springs showed plastic deformation less than 1 mm when the extension was at or under 25 mm. Conclusions: The superelastic behavior of NiTi closed springs were different among various NiTi spring products, and some NiTi closed springs failed to show superelasticity.