• Title, Summary, Keyword: Combined Loading

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Behavior and crack development of fiber-reinforced concrete spandrel beams under combined loading: an experimental study

  • Ibraheema, Omer Farouk;Abu Bakar, B.H.;Joharib, I.
    • Structural Engineering and Mechanics
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    • v.54 no.1
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    • pp.1-17
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    • 2015
  • An experimental investigation is conducted to examine the behavior and cracking of steel fiberre-inforced concrete spandrel L-shaped beams subjected to combined torsion, bending, and shear. The experimental program includes 12 medium-sized L-shaped spandrel beams organized into two groups, namely, specimens with longitudinal reinforcing bars, and specimens with bars and stirrups. All cases are examined with 0%, 1%, and 1.5% steel fiber volume fractions and tested under two different loading eccentricities. Test results indicate that the torque to shear ratio has a significant effect on the crack pattern developed in the beams. The strain on concrete surface follows the crack width value, and the addition of steel fibers reduces the strain. Fibrous concrete beams exhibited improved overall torsional performance compared with the corresponding non-fibrous control beams, particularly the beams tested under high eccentricity.

Bone Cell Response to Neurotransmitters and Mechanical Loading (신경전달물질 및 물리적 자극에 대한 뼈 세포의 반응)

  • Kwag, J.H.;Kim, B.G.;Kim, K.H.;Kim, C.H.
    • Journal of Biomedical Engineering Research
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    • v.30 no.1
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    • pp.89-93
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    • 2009
  • Bone remodeling is a continuous process of skeletal renewal during which bone formation is tightly coupled to bone resorption. Mechanical loading is an important regulator of bone formation and resorption. In recent studies, neurotransmitters such as vasoactive intestinal peptide (VIP) were found to be present inside bone tissue and have been suggested to potentially regulate bone remodeling. In this study, our objective was to use a pre-established in vitro oscillatory fluid flow-induced shear stress mechanical loading system to quantify the effect of VIP on bone resorptive activity and investigate its combined effect with mechanical loading. VIP decreased osteoclastogenesis significantly decreased RANKL/OPG mRNA ration by approximately 90%. Combined VIP and mechanical loading further decreased RANKL/OPG ratio to approximately 95%. These results suggest that VIP present in bone tissue may synergistically act with mechanical loading to regulate bone remodeling via suppression of bone resorptive activities.

Bearing capacity of shallow footing under combined loading

  • Kusakabe, Osamu;Takeyama, Tomohide
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.3-25
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    • 2010
  • The paper deals with two bearing capacity problems of shallow footing under combined loading. The first is a FEM study of shallow strip footing on two-layer clay deposits subjected to a vertical, horizontal and moment combined loading, while the second is a centrifuge study of shallow rectangular footing on dry sand under double eccentricity. The FEM results revealed that the existence of top soft layer sensitively affects more on horizontal and moment capacity than vertical capacity for cases of footing on soft clay overlying stiff clay. Practical design charts are presented to evaluate bearing capacities of footing for various combinations of the ratio of the depth of the upper layer to the footing width and the ratio of undrained strength of the upper layer to that of the lower. The centrifuge tests indicated that current design practice of calculating failure load of rectangular surface footing under double eccentricity underestimates the centrifuge loading test data. This trend is more marked when the eccentricity becomes larger. The decreasing trend in failure load with an increase of double eccentricity is rather uniquely expressed by a single curve, using a newly defined resultant eccentricity and the diagonal length of the footing base.

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Plastic Limit Loads for Through-Wall Cracked Pipes Using 3-D Finite Element Limit Analyses (3차원 유한요소 한계해석을 이용한 관통균열 배관의 소성한계하중)

  • Huh Nam-Su;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.5
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    • pp.568-575
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    • 2006
  • The present paper provides plastic limit load solutions of axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3-D) finite element (FE) limit analysis using elastic-perfectly-plastic behavior. As a loading condition, axial tension, global bending moment, internal pressure, combined tension and bending and combined internal pressure and bending are considered for circumferential through-wall cracked pipes, while only internal pressure is considered for axial through-wall cracked pipes. Especially, more emphasis is given for through-wall cracked pipes subject to combined loading. Comparisons with existing solutions show a large discrepancy in short through-wall crack (both axial and circumferential) for internal pressure. In the case of combined loading, the FE limit analyses results show thickness effect on limit load solutions. Furthermore, the plastic limit load solution for circumferential through-wall cracked pipes under bending is applied to derive plastic $\eta\;and\;{\gamma}$-factor of testing circumferential through-wall cracked pipes to estimate fracture toughness. Being based on detailed 3-D FE limit analysis, the present solutions are believed to be meaningful fur structural integrity assessment of through-wall cracked pipes.

Characterization of Combined Sewer Overflows from a Small Urban Watershed and Determination of Optimum Detention Volume (소규모 도시유역 합류식 하수관거 월류수 특성화 및 최적 저류지 용량 결정)

  • Jo, Deokjun;Kim, Geonha
    • Journal of Korean Society on Water Environment
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    • v.22 no.2
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    • pp.314-320
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    • 2006
  • Diffuse pollution from an urban area contributes to the significant pollution loading to a receiving water body. In this paper, rainfall runoffs from an urban basin with combined sewer systems located in the city of Daejeon were monitored to measure the rainfall runoff discharge rates and pollutant concentrations. Strong first flush effects were observed for all monitored rainfall runoffs. The first flush effects were closely related to rainfall intensity, while suspended solids were closely related to pollutant constituents. The observed averaged Event Mean Concentrations (EMCs) of Combined Sewer Overflows (CSOs) were 536.1 mg SS/L, 467.7 mg CODcr/L, 142.7 mg BOD/L, 16.5 mg TN/L, and 13.5 mg TP/L. Storage volumes for containing the first flush to improve water quality of the receiving stream can be estimated based on suspended solid concentration. In this study, retainment of the first flush equivalent to 5mm of precipitation could reduce diffuse pollution loading induced by CSOs to a receiving water body by up to 80% of suspended solid loading.

Numerical Studies on Combined VH Loading and Inclination Factor of Circular Footings on Sand (모래지반에서 원형기초의 수직-수평 조합하중 지지력과 경사계수에 대한 수치해석 연구)

  • Kim, Dong-Joon;Youn, Jun-Ung;Jee, Sung-Hyun;Choi, Jaehyung;Lee, Jin-Sun;Choo, Yun Wook
    • Journal of the Korean Geotechnical Society
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    • v.30 no.3
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    • pp.29-46
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    • 2014
  • For circular rigid footings with a rough base on sand, combined vertical - horizontal loading capacity was studied by three-dimensional numerical modelling. A numerical model was implemented to simulate the swipe loading and the probe loading methods and an interpretation procedure was devised in order to eliminate the numerical error from the restricted mesh density. Using the Mohr-Coulomb plasticity model, the effect of friction angle was studied under the associated flow-rule condition. The swipe loading method, which is efficient in that the interaction diagram can be drawn with smaller number of analyses, was confirmed to give similar results with the probe loading method, which follows closely the load-paths applied to real structures. For circular footings with a rough base, the interaction diagram for combined vertical (V) - horizontal (H) loading and the inclination factor were barely affected by the friction angle. It was found that the inclination factors for strip and rectangular footings are applicable to circular footings. For high H/V ratios, the results by numerical modelling of this study were smaller than the results of previous studies. Discussions are made on the factors affecting the numerical results and the areas for further researches.

Numerical Studies on Combined VM Loading and Eccentricity Factor of Circular Footings on Sand (모래지반에서 원형기초의 수직-모멘트 조합하중 지지력과 편심계수에 대한 수치해석 연구)

  • Kim, Dong-Joon;Youn, Jun-Ung;Jee, Sung-Hyun;Choo, Yun Wook
    • Journal of the Korean Geotechnical Society
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    • v.30 no.3
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    • pp.59-72
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    • 2014
  • For circular rigid footings with a rough base on sand, combined vertical - moment loading capacity was studied by three-dimensional numerical modelling. Mohr-Coulomb plasticity model with the associated flow-rule was used for the soil. After comparing the results of the swipe loading method, which can construct the interaction diagram with smaller number of analyses, and those of the probe loading method, which can simulate the load-paths in the conventional load tests, it was found that both loading methods give similar results. Conventional methods based on the effective width or area concept and the results by eccentricity factor ($e_{\gamma}$) were reviewed. The results by numerical modelling of this study were compared with those of previous studies. The combined loading capacity for vertical (V) - moment (M) loading was barely affected by the internal friction angle. It was found that the effective width concept expressed in the form of eccentricity factor can be applied to circular footings. The numerical results of this study were smaller than the previous experimental results and the differences between them increased with the eccentricity and moment load. Discussions are made on the reason of the disparities between the numerical and experimental results, and the areas for further researches are mentioned.

Comparison of Meperidine and Meperidine Combined with 0.08% Bupivacaine for the pain Relief after Cesarean Section (제왕절개술후 통증조절을 위해 경막외 PCA를 이용한 Meperidine 단독투여와 Meperidine과 저농도 Bupivacaine병합투여의 제통효과 비교)

  • Lee, Byung-Ho;Lee, Chul-Woo;Kim, Chang-Jae;Chung, Mee-Young;Son, Woong;Chea, Jun-Seuk
    • The Korean Journal of Pain
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    • v.9 no.1
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    • pp.172-177
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    • 1996
  • We performed a study of epidural patient controlled analgesia of meperidine with or without 0.08% bupivacaine for 48 hours after Cesarean section. 51 parturients were randomly assigned to one of two treatment groups : 1) epidural 0.2% meperidine group(n:24) and 2) epidural combined group with 0.2% meperidine and 0.08% bupivacaine(n:27). All parturients used patient controlled analgesia with loading dose, 2 ml/hour continuous infusion, 1 ml bolus infusion and lockout time, 8 minutes. visual analog scales after loading doses were not significantly different in either groups. The total quantity of meperidine consumption and hourly consumption were significantly lower in the combined group than meperidine group(P<0.05). The cumulative amount of meperidine consumption were also significantly lower in the combined group than meperidine group at 6, 12, 24 and 48 hours. In combined group the hourly consumption of meperidien from 3 hours to 12 hours after loading dose was significantly lower than those of meperidine group. Above 90% of parturients were satisfied in both groups. Side effects were: numbness (2), thigh weakness (1), nausea (1), headache (1) and back pain (2) in epidural meperidine group. There were no case needed specific treatment in both groups. We conclude that analgesic effects were similar in both groups, however the amount of meperidine consumption was less for meperiding group than combined group.

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Engineering Elastic-Plastic Fracture Analysis for Semi-Elliptical Surface Cracked Plates Under Combined Bending and Tension (복합하중을 받는 평판에 존재하는 반타원 표면균열의 공학적 탄소성 파괴해석법)

  • Shim, Do-Jun;Kim, Yun-Jae;Choi, Jae-Boong;Kim, Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.6
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    • pp.1127-1134
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    • 2002
  • The present paper provides an engineering J estimation equation for surface cracked plates under combined bending and tension. The proposed equation is based on the reference stress approach, and the most relevant normalising loads to define the reference stress for accurate J estimations are given for surface cracked plates under combined bending and tension. Comparisons with J results from extensive 3-D FE analyses, covering a wide range of crack geometry, plate geometry and loading combination, show overall good agreement not only at the deepest point but also at arbitrary points along the crack front. for pure tension, agreement between the estimated J and the FE results is excellent, even at the surface point. On the other hand, for pure bending and combined bending and tension, the estimated J values become less accurate for locations close to the surface point. Thus the results in this paper will be useful to assess short-term fracture or low cycle fatigue of surface defects in plates under combined bending and tension.

Crack-tip Stress Field of Fully Circumferential Surface Cracked Pipe Under Combined Tension and Thermal Loads (원주방향 부분 관통 균열이 존재하는 직관에 인장하중과 열하중의 복합하중이 가해지는 경우의 균열 선단 응력장)

  • Je, Jin Ho;Kim, Dong Jun;Kim, Yun Jae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.11
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    • pp.1207-1214
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    • 2014
  • Under excessive plasticity, the fracture toughness of a material depends on its size and geometry. Under fully yielded conditions, the stresses in a material near its crack tip are not unique but rather depend on the geometry. Therefore, the single-parameter J-approach is limited to a high-constraint crack geometry. The JQ theory has been proposed for establishing the crack geometry constraints. This approach assumes that the crack-tip fields have two degrees of freedom. In this study, the crack-tip stress field of a fully circumferential surface-cracked pipe under combined loads is investigated on the basis of the JQ theory by using finite element analysis. The combined loads are a tensile axial force and the thermal gradient in the radial direction. Q-stresses of the crack geometry and its loading state are used to determine the constraint effects. The constraint effects of secondary loading are found to be greater than those of primary loading. Therefore, thermal shock is believed to be the most severe loading condition of constraint effects.