• 한국농공학회논문집
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• 제46권6호
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• pp.21-28
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• 2004

This study aims to investigate the effects of partially distributed loads on the dynamic behaviour of steel parabolic arches by using the elasto-plastic finite element model based on the Von Mises yield criteria and the Prandtl-Reuss How rule. For this purpose, the vertical and the radial load conditions were considered as a distributed loading and the loading range is varied from 40% to 100% of arch span. Normal arch and arch with initial deflection were studied. The initial deflection of arch was assumed by the sinusoidal motile of ${\omega}_i\;=\;{\\omega}_O$ sin ($n{\pi}x/L$). Several numerical examples were tested considering symmetric initial deflection when the maximum initial deflection at the apex is fixed as L/1000. The analysis resluts showed that the maximum deflection at the apex of arch was occurred when 70% of arch span was loaded. The maximum deflection at the quarter point of arch span was occurred when 50% of arch span was loaded. It is known that the optimal rise to span ratio between 0.2 and 0.3 when the vertical or radial distributed load is applied. It is verified that the influence of initial deflection of radial load case is more serious than that of vertical load case.

• Geomechanics and Engineering
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• 제10권3호
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• pp.325-334
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• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

• 한국구조물진단유지관리공학회 논문집
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• 제5권3호
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• pp.233-244
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• 2001

Stress-strain behaviour of soil varies based on stress path and stress history. There has been few study on the characteristics of yielding curve which has anisotropic compression stress history in decomposed granite soil. During this study, various stress path tests in previous anisotropic compression stress history are performed on compacted decomposed granite soil sampled at Iksan, Chonbuk. Yielding points are determined from various stress-strain curves (${\eta}-{\varepsilon}$, ${\eta}$-v, and ${\eta}$-k, ${\eta}$-W curves). Stress-strain curve is certified which shows yielding point very clearly. The shape and characteristics of anisotropic compression yielding curves are examined. The main results are summarized as follows : 1) p' constant and compressive direction in stress paths, which has experienced previous anisotropic compression stress history, shows relatively dear yielding points. 2) Yielding curves defined from ${\eta}$-k and ${\eta}$-W curve show almost perfect ellipse. 3) Directions of plastic strain incremental vector($dv^p/d{\varepsilon}^p$) are not perpendicular to yielding curve.

• Journal of Welding and Joining
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• 제9권2호
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• pp.44-50
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• 1991

The use of high tensile steel plates is increasing in the fabrication of ship and offshore structures. The softening region which has lower yield stress than base metal is located to prevent cracking in the conventional high tensile steel. Also, thermo mechanical control process(TMCP) steel with low carbon equivalent has the softening region which occurs in the heat affected zone when high heat input weld is carried out. The softening region in the high tensile steel gives rise to serious effect on structural strength such as tensile strength, fatigue strength and ultimate strength. In order to make a reliable structural design using high tensile steel plates, the influence of the softening on plate strength should be evaluated in advance. In the previous paper, the authors discussed the ultimate compressive strength of 50HT steel square plates with softening region. In this paper, the ultimate compressive strength with varying the yield stress of softening region and the aspect ratio of the plate is investigated by using the elasto-plastic large deformation finite element method.

• 비파괴검사학회지
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• 제22권6호
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• pp.609-620
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• 2002

It is well known that during tensile testing, a part of the mechanical work done on the specimen is transformed into heat energy. However, the ultimate temperature rise and the rate of temperature rise is related to the nature of the material, conditions of the test and also to the deformation behaviour of the material during loading. The recent advances in infrared sensors and image/data processing techniques enable observation and quantitative analysis of the heat energy dissipated during such tensile tests. In this study, infrared imaging technique has been used to characterise the tensile deformation in AISI type 316 nuclear grade stainless steel. Apart from identifying the different stages during tensile deformation, the technique provided an accurate full-field temperature image by which the point and time of strain localization could be identified. The technique makes it possible to visualise the region of deformation and failure and also predict the exact region of fracture in advance. The effect of thermal gradients on plastic flow in the case of interrupted straining revealed that the interruption of strain and restraining at a lower strain rate not only delays the growth of the temperature gradient, but the temperature rise per unit strain decreases. The technique is a potential NDE tool that can be used for on-line detection of thermal gradients developed during extrusion and metal forming process which can be used for ensuring uniform distribution of plastic strain.

• Steel and Composite Structures
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• 제33권1호
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• pp.143-162
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• 2019

A number of desirable characteristics concerning excellent durability, aesthetics, recyclability, high ductility and fire resistance have made stainless steel a preferred option in engineering practice. However, the relatively high initial cost has greatly restricted the application of stainless steel as a major structural material in general construction. This drawback can be partially overcome by introducing composite stainless steel-concrete structures, which provides a cost-efficient and sustainable solution for future stainless steel construction. This paper presents a preliminary numerical study on stainless steel-concrete composite beam-to-column joints with bolted flush endplates. In order to ensure a consistent corrosion resistance within the whole structural system, all structural steel components were designed with austenitic stainless steel, including beams, columns, endplates, bolts, reinforcing bars and shear connectors. A finite element model was developed using ABAQUS software for composite beam-to-column joints under monotonic and symmetric hogging moments, while validation was performed based on independent test results. A parametric study was subsequently conducted to investigate the effects of several critical factors on the behaviour of composite stainless steel joints. Finally, comparisons were made between the numerical results and the predictions by current design codes regarding the plastic moment capacity and the rotational stiffness of the joints. It was concluded that the present codes of practice generally overestimate the rotational stiffness and underestimate the plastic moment resistance of stainless steel-concrete composite joints.

• Structural Engineering and Mechanics
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• 제82권5호
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• pp.611-628
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• 2022

Energy-dissipative rocking (EDR) columns are a class of seismic mitigation device capable of dissipating seismic energy and preventing weak-story failure of moment resisting frames (MRFs). An EDR consists of two hinge-supported steel columns interconnected by steel dampers along its height. Under earthquakes, the input seismic energy can be dissipated by plastic energy of the steel dampers in the EDR column. However, the unrecoverable plastic deformation of steel dampers generally results in residual drifts in the structural system. This paper presents a proof-of-concept study on an innovative device, namely self-centring energy-dissipative rocking (SC-EDR) column, aiming at enabling self-centring capability of the EDR column by installing a set of shape memory alloy (SMA) tension braces. The working mechanism of the SC-EDR column is presented in detail, and the feasibility of the new device is carefully examined via experimental and numerical studies considering the parameters of the SMA bar diameter and the steel damper plate thickness. The seismic responses including load carrying capacities, stress distributions, base rocking behaviour, source of residual deformation, and energy dissipation are discussed in detail. A rational combination of the steel damper and the SMA tension braces can achieve excellent energy dissipation and self-centring performance.

• Steel and Composite Structures
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• 제49권6호
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• pp.685-699
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• 2023

In recent years, Carbon Fibre Reinforced Plastic (CFRP) strengthening is found to be one of the best methods to strengthen steel structures. The fibrous bond can also influence the vibration characteristics of the strengthened element apart from its static strength enhancement property. The main objective of this study is to understand the influence of CFRP strengthening on the dynamic Behaviour of Thin-Webbed Castellated Beams (TWCBs). A detailed experimental investigation was carried out on five sets of beams with varying parameters such as domination of shear (Shear Dominant, Moment Dominant and Moment and Shear Dominant), sectional classification (Plastic and Semi-compact) and perforation geometries (h_o/d_wratio 0.65 and e/h_o ratio 0.3). Free vibration analysis was carried out by exciting the simply supported TWCBs with an impact force generated by a ball dropped from a specific height. Logarithmic decrement method was used to obtain the damping ratio and natural frequencies of vibration were found by Fast Fourier Transform (FFT). Natural frequency showed an increase in a range of 10.5 - 55% for the different sets of castellated beams. An increase of 62.30% was noted in the damping ratio of TWCBs after strengthening which is an indication of improvement in the vibration characteristics of the beam.

• 비파괴검사학회지
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• 제29권5호
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• pp.473-478
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• 2009

본 연구에서는 비파괴법을 이용하여 압력용기 강 다층용접부에서 채취한 표준 샤르피 시험편의 균열선단에서 형성되는 소성변형 거동을 평가하였다. 모재, 후열처리재 및 용접재를 대상으로 시험편에 기계적인 노치를 가공한 후 예균열(pre-crack)을 낸 다음 4점 굽힘실험과 음향방출(acoustic emission: AE)실험을 동시에 실시하였다. 균열선단은 용접재외 후열처리재의 경우 용융선 근처에 위치하도록 하였다. 하중이 가해짐에 따라 균열선단에서 형성되는 소성영역의 크기는 응력확대계수를 이용하여 구했으며, 각 시험편에 대한 소성역의 크기와 음향방출 특성과의 관계는 축적된 AE 에너지 관점에서 고찰하였다. 시험편에 관계없이 탄성역역에서는 거의 AE신호가 감지되지 않았으며, 대부분의 AE신호는 소성변형 과정에서 발생하였다. 또한, 용접재가 모재와 후열처리재에 비해 AE신호가 훨씬 많이 발생하였다. 모재와 후열처리재 및 용접재의 균열선단에서 소성영역 크기와 축적된 AE에너지와의 관계는 현저히 다르게 나타났으며, 용접재의 AE counts는 모재와 후열처리재에 비해 많이 발생하였다.

• 한국지진공학회논문집
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• 제1권1호
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• pp.57-67
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• 1997

본 논문의 목적은 보-전단벽식 고층아파트의 단소성 지진응답해석을 수행하여 내진성능을 검토하는 것이다. 이를 위해 우선 구조물을 3차원 입체모델화하여 정적 탄소성해석을 수행하고 층 강성을 평가한 후, 그 결과를 이용하여 집중질량계모델을 사용한 시간이력 응답해석을 수행한다. 이때 탄소성 이력모델로는 modified Clough 모델을, 입력하중으로는 3종류의 기록 지진동 El-Centro 1940 NS, Taft 1952 EW, Hachinohe 1968 NS를 사용하되, 최대 지반가속도를 0.12g, 0.24g로 조절하여 사용한다. 해석모델로 장변 방향을 배치된 전단벽의 단면적이 단변의 0.5배이고, 동일한 평면을 가진 2세대가 일자형으로 배치된 25층의 아파트를 선정한다. 층간 변형각, 소성율등을 구하고 우리나라 및 미국, 일본의 내진규준에서 정하고 있는 제한사항과 비교검토한다.