• 한국지반공학회논문집
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• 제21권6호
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• pp.5-18
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• 2005

본 연구에서는 배수면으로부터의 거리에 따라 점진적으로 진행되는 압밀이 차후의 압밀 거동에 미치는 영향에 대하여 고찰하였다. 이를 위해 압밀진행에 따른 위치 별 투수계수 및 부피압축계수의 변화를 고려할 수 있는 유한차분 압밀해석기법 및 프로그램을 개발하였다. 개발된 해석 프로그램을 이용하여 간극비 변화에 따른 투수계수와 부피압축 켸수의 변화 정도가 다른 다양한 특성의 지반에 대하여 연직배수재가 설치된 모형지반의 압밀거동을 분석하였다. 또한 실제 지반조건에서의 영향 정도를 살펴보기 위하여, 낙동강 하구의 정규압밀 점성토 및 재성형 카올리나이트의 지반 특성을 근간으로 입력치를 결정, 해석을 수행하여 위치 별 점진적 압밀에 의한 영향을 분석하였다. 해석 결과 점진적 압밀 진행에 따른 압밀 지체가 현장의 압밀 거동 이해에 매우 중요하며, 또한 압밀 초기에, 소성성이 크고, 재하하중이 클수록 현저하게 나타남을 알 수 있었다.

• Computers and Concrete
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• 제14권1호
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• pp.73-90
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• 2014

The traditional destructive tests in damage detection require high cost, long consuming time, repairing of damaged members, etc. In addition to these, powerful equipments with advanced technology have motivated development of global vibration based damage detection methods. These methods base on observation of the changes in the structural dynamic properties and updating finite element models. The existence, location, severity and effect on the structural behavior of the damages can be identified by using these methods. The main idea in these methods is to minimize the differences between analytical and experimental natural frequencies. In this study, an application of damage detection using model updating method was presented on a one storey reinforced concrete (RC) building model. The model was designed to be 1/2 scale of a real building. The measurements on the model were performed by using ten uni-axial seismic accelerometers which were placed to the floor level. The presented damage identification procedure mainly consists of five steps: initial finite element modeling, testing of the undamaged model, finite element model calibration, testing of the damaged model, and damage detection with model updating. The elasticity modulus was selected as variable parameter for model calibration, while the inertia moment of section was selected for model updating. The first three modes were taken into consideration. The possible damaged members were estimated by considering the change ratio in the inertia moment. It was concluded that the finite element model calibration was required for structures to later evaluations such as damage, fatigue, etc. The presented model updating based procedure was very effective and useful for RC structures in the damage identification.

• Earthquakes and Structures
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• 제14권3호
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• pp.273-283
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• 2018

Previous experimental researches indicate that reinforced concrete beam-column joints play an important role in the mechanical properties of moment resisting frame structures, so as to require proper design. In order to get better understanding of the beam-column joint performance, a rational model needs to be developed. Based on the former considerations, two typical models for calculating the shear carrying capacity of the beam-column joint including the inelastic reinforced concrete joint model and the softened strut-and-tie model are selected to be introduced and analyzed. After examining the applicability of two typical models mentioned earlier to interior beam-column joints, several adjustments are made to get better predicting of the test results. For the softened strut-and-tie model, four adjustments including modifications of the depth of the diagonal strut, the inclination angle of diagonal compression strut, the smeared stress of mild steel bars embedded in concrete, as well as the softening coefficient are made. While two adjustments for the inelastic reinforced concrete joint model including modifications of the confinement effect due to the column axial load and the correction coefficient for high concrete are made. It has been proved by test data that predicted results by the improved softened strut-and-tie model or the modified inelastic reinforced concrete joint model are consistent with the test data and conservative. Based on the test results, it is also not difficult to find that the improved beam-column joint model can be used to predict the joint carrying capacity and cracks development with sufficient accuracy.

• Earthquakes and Structures
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• 제15권4호
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• pp.369-382
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• 2018

A free vibration analysis and wave propagation of functionally graded porous beams has been presented in this work using a high order hyperbolic shear deformation theory. Unlike other conventional shear deformation theories, a new displacement field that introduces indeterminate integral variables has been used to minimize the number of unknowns. The constituent materials of the beam are assumed gradually variable along the direction of height according to a simple power law distribution in terms of the volume fractions of the constituents. The variation of the pores in the direction of the thickness influences the mechanical properties. It is therefore necessary to predict the effect of porosity on vibratory behavior and wave velocity of FG beams in this study. A new function of the porosity factor has been developed. Hamilton's principle is used for the development of wave propagation equations in the functionally graded beam. The analytical dispersion relationship of the FG beam is obtained by solving an eigenvalue problem. Illustrative numerical examples are given to show the effects of volume fraction distributions, beam height, wave number, and porosity on free vibration and wave propagation in a functionally graded beam.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.193-209
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• 2020

This paper presents a new hyperbolic shear deformation plate theory including the stretching effect for free vibration of the simply supported functionally graded plates in thermal environments. The theory accounts for parabolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. This theory has only five unknowns, which is even less than the other shear and normal deformation theories. The present one has a new displacement field which introduces undetermined integral variables. Material properties are assumed to be temperature-dependent, and graded in the thickness direction according to a simple power law distribution in terms of the volume power laws of the constituents. The equation of motion of the vibrated plate obtained via the classical Hamilton's principle and solved using Navier's steps. The accuracy of the proposed solution is checked by comparing the present results with those available in existing literature. The effects of the temperature field, volume fraction index of functionally graded material, side-to-thickness ratio on free vibration responses of the functionally graded plates are investigated. It can be concluded that the present theory is not only accurate but also simple in predicting the natural frequencies of functionally graded plates with stretching effect in thermal environments.

• International Journal of Fluid Machinery and Systems
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• 제10권3호
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• pp.240-253
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• 2017

Latin hypercube sampling is widely used design-of-experiment technique to select design points for simulation which are then used to construct a surrogate model. The exploration/exploitation properties of surrogate models depend on the size and distribution of design points in the chosen design space. The present study aimed at evaluating the performance characteristics of various surrogate models depending on the Latin hypercube sampling (LHS) procedure (sample size and spatial distribution) for a diverse set of optimization problems. The analysis was carried out for two types of problems: (1) thermal-fluid design problems (optimizations of convergent-divergent micromixer coupled with pulsatile flow and boot-shaped ribs), and (2) analytical test functions (six-hump camel back, Branin-Hoo, Hartman 3, and Hartman 6 functions). The three surrogate models, namely, response surface approximation, Kriging, and radial basis neural networks were tested. The important findings are illustrated using Box-plots. The surrogate models were analyzed in terms of global exploration (accuracy over the domain space) and local exploitation (ease of finding the global optimum point). Radial basis neural networks showed the best overall performance in global exploration characteristics as well as tendency to find the approximate optimal solution for the majority of tested problems. To build a surrogate model, it is recommended to use an initial sample size equal to 15 times the number of design variables. The study will provide useful guidelines on the effect of initial sample size and distribution on surrogate construction and subsequent optimization using LHS sampling plan.

• 복합신소재구조학회 논문집
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• 제2권1호
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• pp.15-22
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• 2011

펄트루젼 FRP 구조용 부재는 많은 유용한 역학적, 물리적 성질 때문에 토목분야에서 구조부재의 매력적인 대체부재로 고려될 수 있다. 그러나 펄트루젼 FRP는 탄성계수가 상대적으로 낮고, 부재의 단면이 복부와 플렌지 등의 얇은 판요소로 구성되어 있기 때문에 압축재로 설계할 때 구조적인 안정성은 매우 중요한 고려사항이 된다. 따라서, 압축을 받는 구조용 부재의 설계를 위해, 판요소의 좌굴 및 후좌굴강도를 고려해야 한다. AISC/LRFD의 강구조 설계기준에서는, 후좌굴강도에 추가적인 단면 내 일정하지 않은 응력분포의 영향을 형상계수(form factor)를 사용하여 고려하고 있다. 이 논문에서는 압축력을 받는 펄트루젼 FRP 구조용 부재의 형상계수를 해석적으로 연구하였으며, 형상계수를 설정하는 과정에 대하여 제안하였다.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.649-658
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• 1997

강관에 콘크리트를 충전하는 경우, 콘크리트 충전강관 기둥은 뛰어난 내력과 변형성능을 발휘한다. 그리고 콘크리트의 축열효과에 의해서 일정시간은 내화피복 없이도 내력을 유지할 수 있다. 화재발생동안 콘크리트 충전강관 기둥의 거동을 알아보고자 강관과 콘크리트의 온도에 따른 특성치 변화를 가정하고 온도 해석 및 축력-모멘트관계에 대한 수치해석을 수행하여 시간변화에 따른 변수별로 비교평가하였다. 온도에 따른 특성치는 기존문헌의 데이터를 이용하였으며 온도해석은 범용 해석프로그램인 ANSYS로 유한요소해석을 하였고 이를 바탕으로 내력에 대한 수치해석을 수행하였다.

• Journal of Welding and Joining
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• 제26권2호
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• pp.62-68
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• 2008

Effects of gravitational orientation on gas tungsten arc welding (GTAW) for 304 stainless steel were studied to determine the critical factors for weld pool formation, such as weld surface deformation and weld pool shape. This study was accomplished through an analytical study of weld pool stability as a function of primary welding parameters (arc current and arc holding time), material properties (surface tension and density), and melting efficiency (cross-sectional area). The stability of weld pool shape and weld surface deformation was confirmed experimentally by changing the welding position. The arc current and translational velocity were the major factors in determining the weld pool stability as a function of the gravitational orientation. A 200A spot GTAW showed a significant variation of the weld pool formation as the arc held longer than 3 seconds, however the weld pool shape and surface morphology for a 165A spot GTAW were 'stable', i.e., constant regardless of the gravitational orientation. The cross-sectional area of the weld (CSA) was one of the critical factors in determining the weld pool stability. The measured CSA ($13.5mm^2$) for the 200A spot GTAW showed a good agreement with the calculated CSA ($14.9mm^2$).

• 한국강구조학회 논문집
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• 제10권2호통권35호
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• pp.201-209
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• 1998

강섬유보강 적층복합구조물에서 온도의 변화는 구조물의 응답에 중요한 영향을 미칠수 있다. 온도의 급작스런 변화는 재료의 강도와 성질을 현저히 저하시켜 구조물의 대변형, 좌굴, 고응력상태를 유발하는 중요한 인자가 된다. 본 연구에서는 등분포로 재하된 온도하중에 의한 적층복합판의 온도좌굴에 관한 해석을 수행하였다. 전단변형의 효과를 정확히 고려하기위해 5개의 변수로 구성된 고차전단변형이론을 적용하였다. 적층판의 배열각도, 적층판의 수, 폭-두께비의 변화, 형상비의 변화에 따른 임계좌굴온도를 구하여 1차전단변형이론에 의한 결과와 고전적이론에 의한 결과와 비교분석하였다.