• Smart Structures and Systems
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• 제20권1호
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• pp.11-22
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• 2017

The long-term effect of ambient temperature on bridge strain is an important and challenging problem. To investigate this issue, one year data of strain and ambient temperature of a long-span cable-stayed bridge is studied in this paper. The measured strain-time history is decomposed into two parts to obtain the strains due to vehicle load and temperature alone. A linear regression model between the temperature and the strain due to temperature is established. It is shown that for every $1^{\circ}C$ increase in temperature, the stress is increased by 0.148 MPa. Furthmore, the extreme value distributions of the strains due to vehicle load, temperature and the combination effect of them during the remaining service period are estimated by the average conditional exceedance rate approach. This approach avoids the problem of declustering of data to ensure independence. The estimated results demonstrate that the 95% quantile of the extreme strain distribution due to temperature is up to $1.488{\times}10^{-4}$ which is 2.38 times larger than that due to vehicle load. The study also indicates that the estimated extreme strain can reflect the long-term effect of temperature on bridge strain state, which has reference significance for the reliability estimation and safety assessment.

• 한국기계가공학회지
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• 제18권9호
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• pp.100-105
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• 2019

In wire drawing, aterial deformation is concentrated on the surface of the drawn wire because of surface contact with the drawing die. Therefore, strain varies from the center to the surface of the drawn wire. In this study, based on the upper bound method, an effective strain prediction method from the center to the surface of a drawn wire was proposed. Using the proposed method, the effective strain of the drawn wire was calculated verify the proposed prediction method, the predicted effective strain was compared with the result of finite element analysis.

• ALGAE
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• 제36권1호
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• pp.61-72
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• 2021

Increased proliferation of bacterial resistance to antibiotics is a critical issue that has increased the demand for novel antibacterial compounds. Antibacterial activities have been evaluated in extracts from photosynthetic green microalgae, with varying levels of subsequent potential for development based on the strain of algae, strain of bacterial pathogen, and solvent used to extract the metabolites. Green microalgae from extreme environmental conditions have had to adapt to conditions that exclude many other organisms. The production of antibacterial compounds aids directly or indirectly in the survival of green microalgae in these extreme environments, as well as potentially serve other roles. This review investigates antibacterial activities of green microalgae from both extreme in-situ environmental conditions and induced extreme laboratory conditions and highlights.

• 한국압력기기공학회 논문집
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• 제14권2호
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• pp.11-15
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• 2018

A development plan for seismic capacity verification procedures of nuclear components based on the elastic-plastic strain (EPS) features is explained in this paper. The EPS methodology is more realistic to assess seismic responses of components to extreme seismic events beyond the safe shutdown earthquake (SSE) than current practices with the criteria of stress limits. The EPS based approach to analyze the seismic capacity of components can reduce over-conservatism in the current stress-based criteria and can incorporate the seismic responses of components deformed in plastic behavior by the motion of extreme earthquake.

• Geomechanics and Engineering
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• 제22권3호
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• pp.219-226
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• 2020

Unconfined compression test (UCT) is widely conducted in laboratories to evaluate the mechanical behavior of frozen soils. However, its results are sensitive to the initial conditions of sample creation by freezing as well as the end-surface conditions during loading of the specimen into the apparatus for testing. This work compared ice samples prepared by three-dimensional and one-dimensional freezing. The latter created more-homogenous ice samples containing fewer entrapped air bubbles or air nuclei, leading to relatively stable UCT results. Three end-surface conditions were compared for UCT on ice specimens made by one-dimensional freezing. Steel disc cap with embedded rubber was found most appropriate for UCT. Three frozen materials (ice, frozen sand, and frozen silt) showed different failure patterns, which were classified as brittle failure and ductile failure. Ice and frozen sand showed strain-softening, while frozen silt showed strain-hardening. Subsequent investigation considered the influence of fines content on the unconfined compression behavior of frozen soil mixtures with fines contents of 0-100%. The mixtures showed a brittle-to-ductile transition of failure patterns at 10%-20% fines content.

• Smart Structures and Systems
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• 제17권6호
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• pp.995-1015
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• 2016

In the design and condition assessment of bridges, it is usually necessary to take into consideration the extreme conditions which are not expected to occur within a short time period and thus require an extrapolation from observations of limited duration. Long-term structural health monitoring (SHM) provides a rich database to evaluate the extreme conditions. This paper focuses on the extrapolation of extreme traffic load effects on bridges using long-term monitoring data of structural strain. The suspension Tsing Ma Bridge (TMB), which carries both highway and railway traffic and is instrumented with a long-term SHM system, is taken as a testbed for the present study. Two popular extreme value extrapolation methods: the block maxima approach and the peaks-over-threshold approach, are employed to extrapolate the extreme stresses induced by highway traffic and railway traffic, respectively. Characteristic values of the extreme stresses with a return period of 120 years (the design life of the bridge) obtained by the two methods are compared. It is found that the extrapolated extreme stresses are robust to the extrapolation technique. It may owe to the richness and good quality of the long-term strain data acquired. These characteristic extremes are also compared with the design values and found to be much smaller than the design values, indicating conservative design values of traffic loading and a safe traffic-loading condition of the bridge. The results of this study can be used as a reference for the design and condition assessment of similar bridges carrying heavy traffic, analogous to the TMB.

• 지질공학
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• 제26권4호
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• pp.583-591
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• 2016

극한지에 매설된 파이프라인의 안정성 평가를 위해서는 진동현식 변형률게이지가 널리 사용되고 있다. 외국에서는 극한지용 변형률 게이지가 상용화되어 있으나 상당히 고가이므로 국내 기술에 의한 게이지 개발이 필요하다. 국내의 서미스터(thermistor)가 내장된 일반 진동현식 변형률 게이지와 본 연구를 위해 제작된 PT 100이 내장된 변형률 게이지의 온도 측정에 대한 신뢰성을 검증하였다. 기존 서미스터는 $-15^{\circ}C$ 이하의 저온에서는 신뢰성이 매우 떨어지므로 극한지에서는 PT 100의 사용이 권장된다. 또한 일반 진동현식 변형률 게이지의 경우 저온에서 변형률 측정의 오차가 증가하였으나 인코넬을 이용하여 제작된 진동현식 변형률 게이지는 저온에서 일반 게이지보다 더 높은 신뢰성을 보였다. 현재 진행 중인 연구를 통하여 신뢰성 있는 극한지용 변형률 게이지를 개발할 계획이다.

• Journal of Mechanical Science and Technology
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• 제17권1호
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• pp.1-10
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• 2003

This paper summarizes the results of the fatigue test of four composite bridge decks in extreme temperatures (-30$^{\circ}C$ and 50$^{\circ}C$ ). The work was performed as part of a research program to evaluate and install multiple FRP bridge deck systems in Dayton, Ohio. A two-span continuous concrete deck was also built on three steel girders for the benchmark tests. Simulated wheel loads were applied simultaneously at two points by two servo-controlled hydraulic actuators specially designed and fabricated to perform under extreme temperatures. Each deck was initially subjected to one million wheel load cycles at low temperature and another one million cycles at high temperature. The results presented in this paper correspond to the fatigue response of each deck for four million load cycles at low temperature and another four million cycles at high temperature. Thus, the deck was subjected to a total of ten million cycles. Quasi-static load-deflection and load-strain responses were determined at predetermined fatigue cycle levels. Except for the progressive reduction in stiffness, no significant distress was observed in any of the composite deck prototypes during ten million load cycles. The effects of extreme temperatures and accumulated load cycles on the load-deflection and load-strain response of FRP composite and FRP-concrete hybrid bridge decks are discussed based on the experimental results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.501-506
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• 1998

This paper is an experimental study on the flexural strength and ductility capacity of reinforced high performance concrete beams with the concrete which has compressive strength of 600~700kg/$\textrm{cm}^2$, slump value of 20~25cm and slump-flow value of 60~70cm. Total 8 beams with different tensile reinforcement ratio and pattern of loading were tested. Form the results of reinforced high performance concrete beams, the equivalent stress block parameters proposed by MacGregor et al. or New Zealand code are recommended to use. Also, an extreme fiber concrete compressive strain of reinforced high performance concrete beams are distributed 0.0033~0.0048. In reinforced high performance concrete beams, reinforcement ratio in order to insure curvature ductility index 2 and 4 propose by ACI code should be less than those of reinforced normal strength concrete beams.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.891-896
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• 2001

The determination of compressive zone at the critical section of concrete walls under in-plane flexure is important in both assessing the ductility and designing the seismic retrofit. Recognizing this, the once-predominated code approach to determine the compressive zone was advanced by considering concrete rectangular stress block parameters varying with the extreme fiber strain in compression. It is shown that the major factors influencing the magnitude of compressive zone are axial load ratio, concrete strength, longitudinal steel ratio, yield strength and the level of strain at extreme compression fiber of wall sections. The present paper closes with the discussion for the research agenda requiring further study to investigate the behavior of reinforced concrete walls.