• Structural Engineering and Mechanics
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• 제61권1호
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• pp.161-169
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• 2017

This study aimed to develop a simple and effective method to facilitate the experimental research on mechanical properties of masonry under biaxial compressive stress. A series of tests on full-scale brick masonry panels under biaxial compression have been performed in limited principal stress ratios oriented at various angles to the bed joints. Failure modes of tested panels were observed and failure features were analyzed to reveal the mechanical behavior of masonry under biaxial compression. Based on the experimental data, the failure curve in terms of two orthotropic principal stresses has been presented and the failure criterion of brick masonry in the form of the tensor polynomial has been established, which indicate that the anisotropy for masonry is closely related to the difference of applied stress as well as the orientation of bed joints. Further, compared with previous failure curves and criteria for masonry, it can be found that the relative strength of mortar and block has a considerable effect on the degree of anisotropy for masonry. The test results demonstrate the validity of the proposed experimental method for the approximation of masonry failure under biaxial compressive stress and provide valuable information used to establish experimentally based methodologies for the improvement of masonry failure criteria.

• 대한조선학회지
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• 제12권2호
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• pp.35-42
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• 1975

This paper investigates the distribution of stress and its behavior at the Root Toe in fillet welding joint. Furthermore, the stress components and principal stresses in the fillet welds are calculated by the finite element method. The distribution of stresses obtained numerically by means of the finite element method is also compared with the experimental results of two dimensional photoelasticity. A Cover plate type and Center block type of fillet welds are used as models for the numerical calculations covering the variations of 2 W/M(thickness of main plate/thickness of cover plate)=1 through 2W/M=4. The results obtained in these studies are summarized as follows; 1) When W2/M values become small, the stress concentration factors of the Root are larger than of the Toe in a C-type. Its critical value is 2W/M=3.00. However, no critical value exists in a T-type. 2) For 2W/M Values being avove 3.5 in a C-type and above 4.0 in a T-type, $K_R$ and $K_{\tau}$ become 1. 3) According to the differences of 2W/M values, the differences in stress become increasing in the Root but become decreasing in the Toe. These differences, however, disappear as the free boundary surface is approached. 4) The stress concentration factors of both the Root and Toe obtained by means of the finite element method have somewhat lower values than obtained by the photoelasiticity. But their principal stress directions coincide in either method. 5) It proves beneficial to employ the finite element method for two-dimensional plane stress analysis in front fillet welding joint.

• 지구물리
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• 제5권3호
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• pp.199-209
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• 2002

경상북도 경주시에 위치한 불국사 다보탑의 구조 안전 진단을 목적으로 탑의 각 부재에 대한 비파괴 정밀 조사가 실시되었다. 암석 부재의 역학적 성질을 추정하기 위해 255개 부재에서 641 지점에서 초음파 속도를 측정하였으며, 그 결과는 P-파 속도 범위가 $584{\sim}5169m/sec$이며 평균 속도는 2876m/sec이다. 일축압축강도는 $93{\sim}1314kg/cm^2$ 범위로 평균치가 $396kg/cm^2$이고, 풍화도지수는 $0.07{\sim}0.88$의 범위로 평균 0.43으로 중간정도의 풍화를 받은 것으로 나타났다. 각 암석부재의 파괴강도와 이에 작용하는 응력을 비교한 결과, 탑의 구조에 관계된 부재들의 상태는 비교적 양호한 상태를 보여주지만, 편하중에 의한 부분 파괴의 가능성이 남아있다. 편하중에 의한 균열이 계속 진행중인지 모니터링이 필요하며, 편하중을 제거하기 위한 대책이 중요하다. 1층 및 2층 옥신부 주변의 난간은 비교적 작은 부재들로 이루어져 있어 풍화가 많이 진전되었지만 구조적 불안정에는 직접 관련이 없다.

• 콘크리트학회논문집
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• 제24권5호
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• pp.585-596
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• 2012

이 연구는 교량이나 주차장 건물 등에 적용이 가능한 GFRP 보강 철근 폴리머 콘크리트 T형 보의 휨 특성에 관한 연구로서 GFRP 보강 수준에 따른 압축파괴(compression failure: CF), 인장파괴(tension failure: TF) 및 GFRP 보강재의 파괴(fiber sheet failure: FF) 등 파괴모드의 판단과 결정방법을 제시하고, 파괴모드별 설계휨강도 산정식을 제시하였다. GFRP 보강 철근콘크리트 보에서는 FF, TF, CF 등 3가지 파괴모드 중에서 철근항복 ${\rightarrow}$ GFRP 파단 ${\rightarrow}$ 압축측 콘크리트 파괴의 순으로 진행되는 FF 파괴모드가 가장 이상적이다. FF 파괴모드의 경우 압축측 폴리머 콘크리트가 극한변형률(${\varepsilon}_{cu}$)에 도달하기 전에 GFRP가 먼저 파단되므로 콘크리트의 극한상태를 기반으로 하는 기존의 등가직사각형 응력블럭의 개념을 적용할 수 없다. 따라서 이 연구에서는 폴리머 콘크리트의 특성에 부합되는 이상화된 폴리머 콘크리트의 압축응력-변형률 곡선을 제안하고, 폴리머 콘크리트의 변형률을 기반으로 하여 응력블럭 매개변수 ${\alpha}$, ${\beta}$를 도출하였다. 또한 T형 보의 형상비에 따른의 압축응력 분포 및 설계휨강도 특성을 규명하고 적정한 형상비를 2.5로 제시하였으며, GFRP 보강재의 두께 및 높이에 따른 설계휨강도 산정식을 제시하고 그 식의 적정성을 실험과 이론해석에 의해 입증하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.97-97
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• 2009

The use of thin plate increases due to the need for light weight in large ship. Thin plate is easily distorted and has residual stress by welding heat. Therefore, the thin plate should be carefully joined to minimize the welding deformation which costs time and money for repair. For one effort to reduce welding deformation, it is very useful to predict welding deformation before welding execution. There are two methods to analyze welding deformation. One is simple linear analysis. The other is nonlinear analysis. The simple linear analysis is elastic analysis using the equivalent load method or inherent strain method from welding experiments. The nonlinear analysis is thermo-elastic analysis which gives consideration to the nonlinearity of material dependent on temperature and time, welding current, voltage, speed, sequence and constraint. In this study, the welding deformation is analyzed by using thermo-elastic method for PCTC(Pure Car and Truck Carrier) which carries cars and trucks. PCTC uses thin plates of 6mm thickness which is susceptible to welding heat. The analysis dimension is 19,200mm(length) * 13,825mm(width) * 376mm(height). MARC and MENTAT are used as pre and post processor and solver. The boundary conditions are based on the real situation in shipyard. The simulations contain convection and gravity. The material of the thin block is mild steel with $235N/mm^2$ yield strength. Its nonlinearity of conductivity, specific heat, Young's modulus and yield strength is applied in simulations. Welding is done in two pass. First pass lasts 2,100 second, then it rests for 900 second, then second pass lasts 2,100 second and then it rests for 20,000 second. The displacement at 0 sec is caused by its own weight. It is maximum 19mm at the free side. The welding line expands, shrinks during welding and finally experiences shrinkage. It results in angular distortion of thin block. Final maximum displacement, 17mm occurs around welding line. The maximum residual stress happens at the welding line, where the stress is above the yield strength. Also, the maximum equivalent plastic strain occurs at the welding line. The plastic strain of first pass is more than that of second pass. The flatness of plate in longitudinal direction is calculated in parallel with the direction of girder and compared with deformation standard of ${\pm}15mm$. Calculated value is within the standard range. The flatness of plate in transverse direction is calculated in perpendicular to the direction of girder and compared with deformation standard of ${\pm}6mm$. It satisfies the standard. Buckle of plate is calculated between each longitudinal and compared with the deformation standard. All buckle value is within the standard range of ${\pm}6mm$.

• Journal of Cardiovascular Imaging
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• 제31권1호
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• pp.26-38
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• 2023

BACKGROUND: Dobutamine and adenosine stress cardiac magnetic resonance (CMR) imaging is relatively contraindicated in patients with moderate to severe aortic valve stenosis (AS). We aimed to determine the safety of dobutamine and adenosine stress CMR in patients with moderate to severe AS. METHODS: In this retrospective study patients with AS who underwent either dobutamine or adenosine stress CMR for exclusion of obstructive coronary artery disease were enrolled. We recorded clinical data, CMR and echocardiography findings, and complications as well as minor symptoms. Patients with AS were compared to matched individuals without AS. RESULTS: A total of 187 patients with AS were identified and compared to age-, gender- and body mass index-matched 187 patients without AS. No severe complications were reported in the study nor the control group. The reported frequency of non-severe complications and minor symptoms were similar between the study and the control groups. Nineteen patients with AS experienced non-severe complications or minor symptoms during dobutamine stress CMR compared to eighteen patients without AS (p = 0.855). One patient with AS and two patients without AS undergoing adenosine stress CMR experienced minor symptoms (p = 0.562). Four examinations were aborted because of chest pain, paroxysmal atrial fibrillation and third-degree atrioventricular block. Inducible ischaemia, prior coronary artery bypass grafting, prior stroke and age were associated with a higher incidence of complications and minor symptoms. CONCLUSIONS: Moderate to severe AS was not associated with complications during CMR stress test. The incidence of non-severe complications and minor symptoms was greater with dobutamine.

• 한국지반신소재학회논문집
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• 제18권2호
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• pp.23-36
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• 2019

본 논문에서는 블록식 보강토옹벽의 현장계측을 통해 곡선부 보강영역의 변형특성을 분석하였다. 보강토공법은 설계 및 시공이 증가하여 실생활에서 쉽게 접할 수 있게 되었으나, 곡선부의 균열 및 붕괴사례가 빈번히 발생하여 안전에 대한 중요성이 대두되고 있다. 이러한 붕괴원인은 곡선부에 대한 연구 부족과 설계기준의 미흡, 경제성과 공기단축에 의한 시공성 결여, 충분하지 못한 다짐 공간 등에 있다고 할 수 있다. 이에 본 연구에서는 기존 설계 및 시공 기준을 검토하고 블록형 보강토옹벽 곡선부 사고사례를 통해 원인을 분석하였으며, 실제 시공된 블록형 보강토옹벽의 현장계측을 통해 직선부와 곡선부의 거동을 비교 분석하고 곡선부 보강영역의 변형특성을 확인하였다. 그 결과, 먼저 곡선부의 수평변위가 직선부와 비교하여 볼록형에서 최대 90%, 오목형에서 최대 60% 높게 나타났으며, 다음으로 곡선부 보강영역에서 볼록형의 경우 보강토옹벽 중심에서 수평방향으로 H/2구간에서 최대변위를 보이며 H까지의 영향범위를 나타내었으며, 오목형의 경우 중심에서 최대변위를 보이며 수평방향으로 H/4구간에서 최소변위를 확인하였다. 이러한 결과로 형태에 따른 곡선부의 영향범위와 현장적용을 위한 보강영역의 재정립이 필요하다고 판단되며, 본 연구결과가 이를 위한 기초 자료로서 활용 가능할 것으로 판단된다.

• Computers and Concrete
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• 제10권1호
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• pp.1-18
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• 2012

This paper presents the details of studies conducted on hollow concrete block masonry (HCBM) units and wall panels. This study includes, compressive strength of unit block, ungrouted and grouted HCB prisms, flexural strength evaluation, testing of HCBM panels with and without opening. Non-linear finite element (FE) analysis of HCBM panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and then lateral load is applied in incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response reduction factors have been evaluated based on experimental results. From the study, it is observed that fully grouted and partially reinforced HCBM panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved towards the compression toe of the wall. The force reduction factor of a wall panel with opening is much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by non-linear FE analysis are found to be in good agreement with the corresponding experimental values. The influence of mortar joint has been included in the stress-strain behaviour as a monolith with HCBM and not considered separately. The derived response reduction factors will be useful for the design of reinforced HCBM wall panels subjected to lateral forces generated due to earthquakes.

• International Journal of Ocean System Engineering
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• 제3권2호
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• pp.95-101
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• 2013

This study is mainly interested in roundness of a circular moonpool structure in FPSO. Because this structure needs abrasion-resistance on inner wall, we should do buttering widely and deeply by using Inconel. But a general buttering can cause a severe distortion at structures. If someone can analyze the roundness by thermal distortion under Inconel over-lay, an erection policy can be established. In this study, shrinkage methodology by designed stress-strain curve was used and the result allowed deciding an appropriate block size.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.529-532
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• 1999

With increasing use of high-strength concrete tied columns in structural engineering, it becomes necessary to examine the applicability of related sections of the current design codes. This experimental study was conducted to investigate the behavior of eccentrically loaded high-strength concrete columns. Column specimens with concrete strength 234, 437, 703kgf/㎠ were tested under monotonically increasing eccentric compression. The test parameters included the longitudinal reinforcement ratio, eccentric distance and concrete compressive strength. The analytical results obtained from the stress-strain relationship and the ACI's equivalent rectangular stress block are compared with experimental test results.