• Geomechanics and Engineering
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• 제14권4호
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• pp.307-314
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• 2018

Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

• Earthquakes and Structures
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• 제26권1호
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• pp.31-48
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• 2024

In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

• 대한토목학회논문집
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• 제11권1호
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• pp.9-16
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• 1991

콘크리트는 고응력 범위에서 적은 반복횟수에 의해서도 파괴에 도달할 수 있고 소성 변형에 의한 콘크리트 손상이 심각하다. 본 연구에서는 반복하중하에서의 콘크리트의 손상과정에 관하여 실험적으로 연구하였고 에너지개념에 의한 소상모델을 개발하였다. 실험은 일축압축상태의 무근콘크리트에 대해서 변위제어상태하에서 수행하였다. 콘크리트의 파괴시점은 잔여강도가 존재하지 않은 상태까지로 가정하였고, 손상도는 실험적으로 파괴시까지 구해진 에너지 발산량과 주어진 횟수의 반복하중에 의한 에너지 발산량의 비로 정의하였다. 고응력 범위에서 손상도는 변형량의 비선형함수로 누적되며, 손상비율은 초기에 높고 파괴상태에 가까울수록 점차적으로 감소하였다.

• Advances in Computational Design
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• 제8권1호
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• pp.13-36
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• 2023

The Puebla-Morelos Earthquake (Mw 7.1) occurred in Mexico in 2017 causing 44 buildings to collapse in Mexico City. This work evaluates the non-linear response of a 6-story reinforced concrete (RC) frame prototype model with masonry infill walls on upper floors. The prototype model was designed using provisions prescribed before 1985 and was subjected to seismic excitations recorded during the earthquakes of 1985 and 2017 in different places in Mexico City. The building response was assessed through a damage index (DI) that considers low-cycle fatigue of the steel reinforcement in columns of the first floor, where the steel was modeled including buckling as was observed in cases after the 2017 earthquake. Isocurves were generated with 72 seismic records in Mexico City representing the level of iso-demand on the structure. These isocurves were compared with the location of 16 collapsed (first-floor column failure) building cases consistent with the prototype model. The isocurves for a value greater than 1 demarcate the location where fatigue failure was expected, which is consistent with the location of 2 of the 16 cases studied. However, a slight increase in axial load (5%) or decrease in column cross-section (5%) had a significant detrimental effect on the cumulated damage, increasing the intensity of the isocurves and achieving congruence with 9 of the 16 cases, and having the other 7 cases less than 2 km away. Including column special detailing (tight stirrup spacing and confined concrete) was the variable with the greatest impact to control the cumulated damage, which was consistent with the absence of severe damage in buildings built in the 70s and 80s.

• Earthquakes and Structures
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• 제12권1호
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• pp.1-12
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• 2017

Historical earthquakes have shown that successive seismic events may occur in regions of high seismicity. Such a sequence of earthquakes has the potential to increase the damage level of the structures, since any rehabilitation between the successive ground motions is practically impossible due to lack of time. Few studies about this issue can be found in literature, most of which focused their attention on the seismic response of SDOF systems or planar frame structures. The aim of the present study is to examine the impact of seismic sequences on the damage level of 3D multistorey R/C buildings with various structural systems. For the purposes of the above investigation a comprehensive assessment is conducted using three double-symmetric and three asymmetric in plan medium-rise R/C buildings, which are designed on the basis of the current seismic codes. The buildings are analyzed by nonlinear time response analysis using 80 bidirectional seismic sequences. In order to account for the variable orientation of the seismic motion, the two horizontal accelerograms of each earthquake record are applied along horizontal orthogonal axes forming 12 different angles with the structural axes. The assessment of the results revealed that successive ground motions can lead to significant increase of the structural damage compared to the damage caused by the corresponding single seismic events. Furthermore, the incident angle can radically alter the successive earthquake phenomenon depending on the special characteristics of the structure, the number of the sequential earthquakes, as well as the distance of the record from the fault.

• Composites Research
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• 제26권2호
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• pp.91-98
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• 2013

복합재 이중-겹침 볼트 체결부의 파손을 예측하기 위해 손상계수를 고려한 강성저하 방법과 Hashin의 3차원 파손판정식에 근거한 3차원 유한요소해석 방법을 제안하였다. 기지 혹은 면내(In-plane) 전단 손상을 고려하기 위해 손상변수를 이용하는 Ladeveze 이론을 섬유방향 강성저하와 연계하여 사용하였고, 수지 압축/전단, 수지 인장/전단, 섬유압축, 섬유 인장 등 4가지 파손모드를 고려하였다. 상업용 유한요소 프로그램인 ABAQUS를 이용하여 마찰력과 볼트 체결력을 고려하였고, 강성저하모델 처리를 위해 ABAQUS의 사용자 정의 부프로그램을 이용하였다. 제안된 유한요소해석 방법을 검증하기 위해 복합재 이중겹침 볼트 체결부 시험 결과와 파손강도를 비교한 결과 7~16% 오차를 보임을 확인하였다.

• Steel and Composite Structures
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• 제42권4호
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• pp.501-511
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• 2022

Earthquake Resistant Design Philosophy seeks (a) no damage, (b) no significant structural damage, and (c) significant structural damage but no collapse of normal buildings, under minor, moderate and severe levels of earthquake shaking, respectively. A procedure is proposed for seismic design of low-rise reinforced concrete special moment frame buildings, which is consistent with this philosophy; buildings are designed to be ductile through appropriate sizing and reinforcement detailing, such that they resist severe level of earthquake shaking without collapse. Nonlinear analyses of study buildings are used to determine quantitatively (a) ranges of design parameters required to assure the required deformability in normal buildings to resist the severe level of earthquake shaking, (b) four specific limit states that represent the start of different structural damage states, and (c) levels of minor and moderate earthquake shakings stated in the philosophy along with an extreme level of earthquake shaking associated with the structural damage state of no collapse. The four limits of structural damage states and the three levels of earthquake shaking identified are shown to be consistent with the performance-based design guidelines available in literature. Finally, nonlinear analyses results are used to confirm the efficacy of the proposed procedure.

• The Plant Pathology Journal
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• 제39권6호
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• pp.548-565
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• 2023

Armillaria root disease affects forests around the world. It occurs in many habitats and causes losses in the infested stands. Weather conditions are important factors for growth and development of Armillaria species. Yet, the relation between occurrence of damage caused by Armillaria disease and weather variables are still poorly understood. Thus, we used generalized linear mixed models to determine the relationship between weather conditions of current and previous year (temperature, precipitation and their deviation from long-term averages, air humidity and soil temperature) and the incidence of Armillaria-induced damage in young (up to 20 years old) and older (over 20 years old) coniferous stands in selected forest districts across Poland. We used unique data, gathered over the course of 23 years (1987-2009) on tree damage incidence from Armillaria root disease and meteorological parameters from the 24-year period (1986-2009) to reflect the dynamics of damage occurrence and weather conditions. Weather parameters were better predictors of damage caused by Armillaria disease in younger stands than in older ones. The strongest predictor was soil temperature, especially that of the previous year growing season and the current year spring. We found that temperature and precipitation of different seasons in previous year had more pronounced effect on the young stand area affected by Armillaria. Each stand's age class was characterized by a different set of meteorological parameters that explained the area of disease occurrence. Moreover, forest district was included in all models and thus, was an important variable in explaining the stand area affected by Armillaria.

• Tribology and Lubricants
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• 제21권6호
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• pp.272-277
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• 2005

Continuously variable transmission (CVT) of toroidal type has a elliptical shape of contact zone under the elastohydrodynamic lubrication (EHL) condition, where the power is transmitted only by shearing the lubricant. Due to the small contact area of elliptical shape, the traction of the shear behaviors of lubricant over the contact zone is under extremely high contact pressure over 1.0GPa. During the power transmission by shearing the fluid, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spin. Among the movements, the spin effect that is the most undesirable contact behavior in transmitting the power frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of EHL with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.310-315
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• 2001

The most general feature of contact zone among the mechanical components is elliptical circle. In particular, continuously variable transmission (CVT) of toroidal type has elliptical shape of contact zone under the elastohydrodynamic lubrication condition, where the power is transmitted by the shearing the efluid. Due to the traction of the shear behaviors of lubricant over the small elliptical contact zone, high power of torque is transmitted. During the power transmission, many kinds of mechanical movements occur such as squeezing, sliding, rolling and spinning. The spinning effect that is not common contact behavior in tribological components frequently makes significant abnormal wear damage. In this work, the analysis of elliptical contact of elastohydrodynamic lubrication with spin effect is performed, which will give very useful information to understand the traction behaviors in toroidal type of CVT system.