• Title/Summary/Keyword: stress regions

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Splitting of reinforced concrete panels under concentrated loads

  • Foster, Stephen J.;Rogowsky, David M.
    • Structural Engineering and Mechanics
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    • v.5 no.6
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    • pp.803-815
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    • 1997
  • It is well understood that concentrated forces applied in the plane of a beam or panel (such as a wall or slab) lead to splitting forces developing within a disturbed region forming beyond the bearing zone. In a linearly elastic material the length of the disturbed region is approximately equal to the depth of the member. In concrete structures, however, the length of the disturbed region is a function of the orthotropic properties of the concrete-steel composite. In the detailing of steel reinforcement within the disturbed regions two limit states must be satisfied; strength and serviceability (in this case the serviceability requirement being acceptable crack widths). If the design requires large redistribution of stresses, the member may perform poorly at service and/or overload. In this paper the results of a plane stress finite element investigation of concentrated loads on reinforced concrete panels are presented. Two cases are examined (i) panels loaded concentrically, and (ii) panels loaded eccentrically. The numerical investigation suggests that the bursting force distribution is substantially different from that calculated using elastic design methods currently used in some codes of practice. The optimum solution for a uniformly reinforced bursting region was found to be with the reinforcement distributed from approximately 0.2 times the effective depth of the member ($0.2D_e$) to between $1.2D_e$ and $1.6D_e$. Strut and tie models based on the finite element analyses are proposed herein.

Numerical modeling and analysis of RC frames subjected to multiple earthquakes

  • Abdelnaby, Adel E.;Elnashai, Amr S.
    • Earthquakes and Structures
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    • v.9 no.5
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    • pp.957-981
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    • 2015
  • Earthquakes occur as a cluster in many regions around the world where complex fault systems exist. The repeated shaking usually induces accumulative damage to affected structures. Damage accumulation in structural systems increases their level of degradation in stiffness and also reduces their strength. Many existing analytical tools of modeling RC structures lack the salient damage features that account for stiffness and strength degradation resulting from repeated earthquake loading. Therefore, these tools are inadequate to study the response of structures in regions prone to multiple earthquakes hazard. The objective of this paper is twofold: (a) develop a tool that contains appropriate damage features for the numerical analysis of RC structures subjected to more than one earthquake; and (b) conduct a parametric study that investigates the effects of multiple earthquakes on the response of RC moment resisting frame systems. For this purpose, macroscopic constitutive models of concrete and steel materials that contain the aforementioned damage features and are capable of accurately capturing materials degrading behavior, are selected and implemented into fiber-based finite element software. Furthermore, finite element models that utilize the implemented concrete and steel stress-strain hysteresis are developed. The models are then subjected to selected sets of earthquake sequences. The results presented in this study clearly indicate that the response of degrading structural systems is appreciably influenced by strong-motion sequences in a manner that cannot be predicted from simple analysis. It also confirms that the effects of multiple earthquakes on earthquake safety can be very considerable.

Numerical Analysis of Iceberg Impact Interaction with Ship Stiffened Plates Considering Low-temperature Characteristics of Steel (강재의 저온 특성을 고려한 선체 보강판과 빙하의 충격 상호 작용에 대한 수치 해석)

  • Nam, Woongshik
    • Journal of Ocean Engineering and Technology
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    • v.33 no.5
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    • pp.411-420
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    • 2019
  • It is essential to design crashworthy marine structures for operations in Arctic regions, especially ice-covered waters, where the structures must have sufficient capacity to resist iceberg impact. In this study, a numerical analysis of a colliding accident between an iceberg and stiffened plates was carried out employing the commercial finite element code ABAQUS/Explicit. The ice material model developed by Liu et al. (2011) was implemented in the simulations, and its availability was verified by performing some numerical simulations. The influence of the ambient temperature on the structural resistance was evaluated while the local stress, plastic strain, and strain energy density in the structure members were addressed. The present study revealed the risk of fracture in terms of steel embrittlement induced by ambient temperature. As a result, the need to consider the possibility of brittle failure in a plate-stiffener junction during operations in Arctic regions is acknowledged. Further experimental work to understand the structural behavior in a plate-stiffener junction and HAZ is required.

Discovery of a New Mechanism of Dust Destruction in Strong Radiation Fields and Implications

  • Hoang, Thiem;Tram, Le Ngoc;Lee, Hyseung;Ahn, Sang-hyeon
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.1
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    • pp.44.3-44.3
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    • 2019
  • Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the universe. Observations usually show near- to mid-infrared (NIR-MIR, 1-5~micron) emission excess from H II regions around young massive star clusters (YMSCs) and anomalous dust extinction and polarization towards Type Ia supernova (SNe Ia). The popular explanation for such NIR-MIR excess and unusual dust properties is the predominance of small grains (size a<0.05micron) relative to large grains (a>0.1micron) in the local environment of these strong radiation sources. The question of why small grains are predominant in these environments remains a mystery. Here we report a new mechanism of dust destruction based on centrifugal stress within extremely fast rotating grains spun-up by radiative torques, namely the RAdiative Torque Disruption (RATD) mechanism, which can resolve this question. We find that RATD can destroy large grains located within a distance of ~ 1 pc from a massive star of luminosity L~ 10^4L_sun and a supernova. This increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR-MIR excess and anomalous dust extinction/polarization. We show that small grains produced by RATD can also explain the steep far-UV rise in extinction curves toward starburst and high redshift galaxies, as well as the decrease of the escape fraction of Ly-alpha photons observed from HII regions surrounding YMSCs.

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Influences of hands-only cardiopulmonary resuscitation on lumbar muscle tone, stiffness, and fatigue in emergency medical technicians (가슴압박소생술이 구조자의 허리근육의 근긴장도, 경직, 피로에 미치는 영향)

  • Wang, Joong-San;Shin, Sang-Yol
    • The Korean Journal of Emergency Medical Services
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    • v.24 no.3
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    • pp.79-87
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    • 2020
  • Purpose: This study sought to determine how the act of performing cardiopulmonary resuscitation (CPR) affects the rescuer's muscle tone, stiffness, and fatigue in the lumbar region. Methods: The research subjects were 30 healthy men in their twenties in possession of a Basic Life Support (BLS) provider certificate. In this study, the CPR rescuer's muscle tone and stiffness in the upper and lower lumbar regions were measured in the resting position, starting position, and position after 10 min. Their level of fatigue was measured before and after performing CPR. Results: Muscle tone and stiffness in the upper and lower lumbar regions of the research subjects significantly increased throughout the CPR process and lasted up to 10 min after the process (p<.001). The subjects' fatigue also significantly increased post-CPR (p<.001). Conclusion: This study suggests that performing CPR creates muscular and physiological stress, fatigue, and ultimately, lower back pain.

Design charts for consolidation settlement of marine clays using finite strain consolidation theory

  • Jun, Sang-Hyun;Lee, Jong-Ho;Park, Byung-Soo;Kwon, Hyuk-Jae
    • Geomechanics and Engineering
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    • v.24 no.3
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    • pp.295-305
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    • 2021
  • In this study, design charts for estimating consolidation settlement are proposed according to finite strain consolidation theory using a nonlinear constitutive relationship equation. Results of parametric sensitivity analysis shows that the final settlement, initial height, and initial void ratio exerted the greatest effect, and the coefficients of the void ratio-effective-stress. Proposed design charts were analyzed for three regions using a representative constitutive relationship equation that enables major dredged-reclaimed construction sites in Korea. The regional design charts can be calculated accurately for the final settlement because it is applied directly to the numerical analysis results, except for reading errors. A general design chart applicable to all marine clays is proposed through correlation analysis of the main parameters. A final self-weight consolidation settlement with various initial void ratios and initial height conditions should be estimated easily using the general design chart and constitutive relationship. The estimated final settlement using the general design chart is similar to the results of numerical analysis obtained using finite strain consolidation theory. Under an overburden pressure condition, design charts for estimating consolidation settlement are proposed for three regions in Korea.

Effects of Economic Strain and Family Conflict on Children's Adjustment : Focused on Interaction Effects of Children's Stress and Coping Strategies (경제적 곤란과 가족갈등이 아동의 적응에 미치는 영향: 아동의 스트레스와 스트레스 대처방식의 상호작용을 중심으로)

  • Yoon, Hye-Mee
    • Korean Journal of Social Welfare
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    • v.57 no.3
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    • pp.133-164
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    • 2005
  • This study examined the effects of children's perceived stress of economic strain, resulting family conflict, and stress coping strategies on their adjustment. Dimensions of children's adjustment studied in this research were problem behaviors (aggression, delinquency, withdrawal and anxiety depression) and school adjustment. Interaction effects between children's stress variables and coping strategies on the adjustment were also explored. 1,115 fifth to eighth graders from Chungbuk regions participated in self-administered structured questionnaires. Data were processed with SPSS PC 10.0 statistical package. Results were: First, the level of children's problem behaviors and school adjustment indicated differences according to their academic achievement, gender, and their age. Middle schoolers with rather low grade average reported higher level of aggression, delinquency, withdrawal and that of depression/anxiety. Boys tended to be more prone to external problems while girls to internal problems. Second, stresses originated from children's perceived economic strain and family conflicts showed consistent meaningful explanatory power on adjustment. Boys' adjustment was influenced by stress from economic strain and family conflict while girls by family conflict and academic achievements. The support seeking coping strategy among others was the most popularly employed coping strategy of children followed by aggressive coping strategy. In boys' cases, interaction effects of stress and coping strategies were significant in all of the adjustment variables, the more frequent the use of support seeking coping strategies, the lower the problem behavior, while interaction effect of family conflict stress and support seeking coping strategies played the opposite significant role in girls' cases. Further research efforts are required. Research results suggest; when developing a program facilitating children's adjustment, training on stress coping strategies should be considered as a potent new arena of interest.

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Salinity Stress Resistance Offered by Endophytic Fungal Interaction Between Penicillium minioluteum LHL09 and Glycine max. L

  • Khan, Abdul Latif;Hamayun, Muhammad;Ahmad, Nadeem;Hussain, Javid;Kang, Sang-Mo;Kim, Yoon-Ha;Adnan, Muhammad;Tang, Dong-Sheng;Waqas, Muhammad;Radhakrishnan, Ramalingam;Hwang, Young-Hyun;Lee, In-Jung
    • Journal of Microbiology and Biotechnology
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    • v.21 no.9
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    • pp.893-902
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    • 2011
  • Endophytic fungi are little known for their role in gibberellins (GAs) synthesis and abiotic stress resistance in crop plants. We isolated 10 endophytes from the roots of field-grown soybean and screened their culture filtrates (CF) on the GAs biosynthesis mutant rice line - Waito-C. CF bioassay showed that endophyte GMH-1B significantly promoted the growth of Waito-C compared with controls. GMH-1B was identified as Penicillium minioluteum LHL09 on the basis of ITS regions rDNA sequence homology and phylogenetic analyses. GC/MS-SIM analysis of CF of P. minioluteum revealed the presence of bioactive $GA_4$ and $GA_7$. In endophyte-soybean plant interaction, P. minioluteum association significantly promoted growth characteristics (shoot length, shoot fresh and dry biomasses, chlorophyll content, and leaf area) and nitrogen assimilation, with and without sodium chloride (NaCl)-induced salinity (70 and 140 mM) stress, as compared with control. Field-emission scanning electron microcopy showed active colonization of endophyte with host plants before and after stress treatments. In response to salinity stress, low endogenous abscisic acid and high salicylic acid accumulation in endophyte-associated plants elucidated the stress mitigation by P. minioluteum. The endophytic fungal symbiosis of P. minioluteum also increased the daidzein and genistein contents in the soybean as compared with control plants, under salt stress. Thus, P. minioluteum ameliorated the adverse effects of abiotic salinity stress and rescued soybean plant growth by influencing biosynthesis of the plant's hormones and flavonoids.

Coupled Distinct Element and Boundary Element Analysis of Problems Having Infinite or Semi-infinite Boundaries (개별요소와 경계요소 조합에 의한 무한 및 반무한 영역문제의 해석)

  • Huh, Taik Nyung;Kim, Moon Kyum;Hwang, Hak Joo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.12 no.4
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    • pp.81-93
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    • 1992
  • Numerical modeling of problems having infinite and semi-infinite boundaries is studied using a coupled method of distinct elements and boundary elements. The regions which are restricted on stress concentration area of loading points, excavation surface, and geometric discontinuity in the underground structures, are modeled using distinct elements, while the infinite and semi-infinite regions are modeled using linear boundary elements. Linear boundary elements for infinite and semi-infinite region are respectively composed using the Kelvin's and the Melan's solution, respectively. For the completeness, the boundary element method, the distinct element, and the coupled method of distinct elements and boundary elements are studied independently. The coupled method is verified and is applied to underground structures of infinite and semi-infinite regions. Through the comparison of the results, it is concluded that the coupled analysis may be used for discontinuous underground structures in the effective manner.

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Seismic Performance of Precast Infill Walls with Strain-Hardening Cement Composite (변형경화형 시멘트 복합체를 사용한 프리캐스트 끼움벽판의 내진성능)

  • Kim, Sun-Woo;Jeon, Esther;Kim, Yun-Su;Ji, Sang-Kyu;Jang, Gwang-Soo;Yun, Hyun-Do
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.11a
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    • pp.89-92
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    • 2008
  • The seismic behavior of the lightly reinforced concrete frames (LRCFs) was controlled by the nonductile behavior of the critical regions. These critical regions require retrofit to improve the seismic behavior of the lightly reinforced concrete frames. Critical column end regions must be retrofit to increase the global ductility capacity. The objective of this research is to evaluate structural strengthening performance of lightly reinforced concrete frame with Strain hardening cement composite(SHCC) experimentally. The experimental investigation consisted of a cyclic load tests on 1/3-scale models of precast infill walls. Reinforcement detail of infill wall was variables in the experiment. The experimental results, as expected, show that the multiple crack pattern, strength, ductility and energy dissipation capacity are superior for specimen with SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.

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