• 한국작물학회:학술대회논문집
• /
• 한국작물학회 1999년도 추계 학술대회지
• /
• pp.80-101
• /
• 1999

Self-sufficiency ratio of food crops in Korea is estimated under $20{\%}$ in 2010 because total food consumption including feed will be increased. but food grain production will be decreased. It is necessary to maintain the optimum level of food self-sufficiency rate to secure national food demand/supply balance and non-trade and multiple function of agriculture in Korea. It will be possible to produce more food grains having the acceptable quality if the appropriate policy and cropping techniques are developed and practised in future. Breeding for high yielding varieties should be the first target to raise the production potential of food crops . Number of varieties developed during last 30 years is counted as 353 in food crops. New varieties developed in 1990s showed the higher yield potential and the improved agronomic characteristics compared with 1970s and 1980s varieties. But number of varieties planted on the farmer's field over $5{\%}$ of national planting area is less than one third of total varieties developed Breeding efforts to maintain planting area of main food crops should be focussed on consumer's demand and farmer's need. They are the best quality variety in each field of crop utilization, the newly designed variety adapting to changes of natural, rural and cropping environment, and the higher yielding variety. It is also needed to develop new quality crop varieties for inducing more consumption of crop grain produced in Korea for direct food or processing. Development of barley varieties for animal feed. high income soybean varieties, high quality wheat variety. and super yielding rice and barley varieties are also needed to keep or maximize national food production potential. In order to establish the appropriate cropping technique for domestic food security, the strong and continuous interest and financial support on crop breeding are required, and the inter-disciplinary and inter-institutionary researches should be strengthened for successful crop breeding.

• Earthquakes and Structures
• /
• 제13권5호
• /
• pp.485-496
• /
• 2017

The behavior of 8 steel reinforced high-strength concrete (SRHSC) columns, which comprised of four identical columns with cross-shaped steel and other four identical columns with square steel tube, was investigated experimentally under cyclic uniaxial and biaxial loading independently. The influence of steel configuration and loading path on the global behavior of SRHSC columns in terms of failure process, hysteretic characteristics, stiffness degradation and ductility were investigated and discussed, as well as stress level of the longitudinal and transverse reinforcing bars and steel. The research results indicate that with a same steel ratio deformation capacity of steel reinforced concrete columns with a square steel tube is better than the one with a cross-shaped steel. Loading path affects hysteretic characteristics of the specimens significantly. Under asymmetrical loading path, hysteretic characteristics of the specimens are also asymmetry. Compared with specimens under unidirectional loading, specimens subjected to bidirectional loading have poor carrying capacity, fast stiffness degradation, small yielding displacement, poor ductility and small ultimate failure drift. It also demonstrates that loading paths affect the deformation capacity or deformation performance significantly. Longitudinal reinforcement yielding occurs before the peak load is attained, while steel yielding occurs at the peak load. During later displacement loading, strain of longitudinal and transverse reinforcing bars and steel of specimens under biaxial loading increased faster than those of specimens subjected to unidirectional loading. Therefore, the bidirectional loading path has great influence on the seismic performance such as carrying capacity and deformation performance, which should be paid more attentions in structure design.

• Structural Engineering and Mechanics
• /
• 제76권3호
• /
• pp.279-291
• /
• 2020

The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (W_pi) normalized by the product of the story shear force (Q_yi) and drift (δ_yi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, W_pi/ΣW_pj, can be evaluated from the deviation of Q_yi with respect to an "optimum value" that would make the ratio W_pi/(Q_yiδ_yi) -i.e. the damage- equal in all stories. This paper investigates how the soil type and ductility demand affect the optimum lateral strength distribution. New optimum lateral strength distributions are put forth and compared with others proposed in the literature.

• 대한기계학회논문집
• /
• 제17권9호
• /
• pp.2223-2233
• /
• 1993

An engineering method is suggested to calculate the applied load versus crack extension in the elastic-plastic fracture. The condition for an increment of crack extension is set by a critical increment of crack-up opening displacement(CTOD). The ratio of the CTOD increment to the incremental crack extention is a critical crack-tip opening angle(CTOA), assumed to be constant for a material of a given thickness. The Dugdale model of crack-tip deformation in an infinite plate is applied to the method, and a complete solution for crack extension and crack instability is obtained. For finite-size specimens of arbitrary geometry in general yielding, an approximate generalization of the Dugdale model is suggested so that the approximation approaches the small-scale yielding solution in a low applied load and the finite-element solution in a large applied load. Maximum load is calculated so that an applied load attains either a limit load on an unbroken ligament or a peak load during crack extension. The proposed method was applied to three-point bend specimens of a carbon steel SM45C in various sizes. Reasonable agreements are found between calculated maximum loads and experimental failure loads. Therefore, the method can be a viable alternative to the J-R curve approach in the elastic-plastic fracture analysis.

• 열처리공학회지
• /
• 제28권4호
• /
• pp.171-180
• /
• 2015

The variation in microstructure and texture during continuous annealing was examined in a series of 1.6% Mn-0.1% Cr-0.3% Mo-0.005% B steels with carbon contents in the range of 0.010 to 0.030%. It was found that microstructure of hot band consisted of ferrite and pearlite as a consequence of high coiling temperature, and eutectoid carbon content was between 0.011% and 0.016%. Martensite ranged in volume fraction from 1.5% to 4.0% when annealed at $820{\circ}C$ according to the typical continuous annealing cycle. The critical martensite content for the continuous yielding was about 4% from stress-strain curves. The continuous yielding was obtained in the 0.030% carbon steel and 0.010% to 0.020% carbon steels revealed some yield point elongation ranging from 0.8% to 2.2% in as-annealed conditions. Higher tensile strength in the higher carbon steel is due to both increase in the martensite volume fraction and ferrite grain refinement. Decreasing the carbon content to 0.01% strengthened the intensities of ${\gamma}$-fiber textures, resulting in the increase in the $r_m$ value, which was caused by the lower volume fraction of martensite. The higher carbon steels showed the lower $r_m$ value of about 1.0.

• 한국작물학회지
• /
• 제43권3호
• /
• pp.161-167
• /
• 1998

Root and shoot development of two rice (Oryza sativa L.) cultivars with different genetic backgrounds was studied with reference to their relative growth. Tongil type (indica-japonica hybrid) cultivar 'Kuemkangbyeo' and japonica cultivar 'Koshihikari' were grown in $5000^{-1}$ a Wagnar pots under flooded condition. Three plants with roots of both cultivars were taken in every phyllochron through the heading stage to record morphological characteristics of shoot and root system. Compared to Koshihikari, Kuemkangbyeo produced more tillers and had greater shoot weight and leaf area per hill. Length and weight of the root system in both cultivars increased exponentially with time. At the same time, root system development was significantly faster in Kuemkangbyeo than in Koshihikari after the panicle initiation stage. As a result, Kuemkangbyeo has a vigorous root system which consists of larger number of nodal roots compared to Koshihikari. Also, the root length and weight per unit leaf area of Kuemkangbyeo were larger than those of Koshihikari in the later half of growing period, which suggests possible higher physiological activity of the root system of Kuemkangbyeo which is known as a high-yielding cultivar. The relationship between root traits (crown root number, total root length, and root dry weight) and shoot traits (leaf area and leaf+culm dry weight) in both cultivars closely showed allometry until the flag leaf stage.

• 한국안전학회지
• /
• 제23권6호
• /
• pp.38-43
• /
• 2008

Significant portion of the fire accident is caused by some troubles in electric circuits. To prevent the fire induced by those electric trouble, some indications of electric fire need to be suitably detected at the first stage of the fire development. With this background, the characteristics of soot yielding of electric cables have been investigated using a light extinction method. In this study, a light scattering method was compared with the light extinction method. A slot-type premixed-flame combustor was traversed to bum three types of electric cables by compulsion, then the mass decrease rate and the soot densities were measured. According to the experimental results, the light scattering method is preferred to the light extinction method when the soot yield ratio is relatively small. Thus the former method is more suitable to detect the occurrence of an electric fire in a power distributer box.

• Structural Engineering and Mechanics
• /
• 제81권3호
• /
• pp.317-333
• /
• 2022

Visco-Plastic Damper (VPD) as a passive energy dissipation device with dual behavior has been recently numerically studied. It consists of two bent steel plates and segments with a viscoelastic solid material in between, combining and improving characteristics of both displacement-dependent and velocity-dependent devices. In order to trust the performance of VPD, for the 1st time this paper experimentally investigates prototype damper behavior under a wide range of frequency and amplitude of dynamic loading. A high-axial damping rubber is innovatively proposed as the viscoelastic layer designed to withstand large axial strains and dissipate energy accordingly. Test results confirmed all assumptions about VPD. The behavior of VPD subjected to low levels of excitation is elastic while with increasing levels of excitation, a significant source of energy dissipation is provided through the yielding of the steel elements in addition to the viscoelastic energy dissipation. The results showed energy dissipation of 99.35 kN.m under a dynamic displacement with 14.095 mm amplitude and 0.333 Hz frequency. Lateral displacement at the middle of the device was created with an amplification factor obtained ranging from 2.108 to 3.242 in the rubber block. Therefore, the energy dissipation of viscoelastic material of VPD was calculated 18.6 times that of the ordinary viscoelastic damper.

• Structural Engineering and Mechanics
• /
• 제27권4호
• /
• pp.425-438
• /
• 2007

Large changes in stiffness associated with cracking and yielding of reinforced concrete sections may be expected to occur during the dynamic response of reinforced concrete frames to earthquake ground shaking. These changes in stiffness in stories that experience cracking might be expected to cause relatively large peak interstory drift ratios. If so, accounting for such changes would add complexity to seismic design procedures. This study evaluates changes in an index parameter to establish whether this effect is significant. The index, known as the coefficient of distortion (COD), is defined as the ratio of peak interstory drift ratio and peak roof drift ratio. The sensitivity of the COD is evaluated statistically for five- and nine-story reinforced concrete frames having either uniform story heights or a tall first story. A suite of ten ground motion records was used; this suite was scaled to five intensity levels to cause varied degrees of damage to the concrete frame elements. Ground motion intensity was found to cause relatively small changes in mean CODs; the changes were most pronounced for changes in suite scale factor from 0.5 to 1 and from 1 to 4. While these changes were statistically significant in several cases, the magnitude of the change was sufficiently small that values of COD may be suggested for use in preliminary design that are independent of shaking intensity. Consequently, design limits on interstory drift ratio may be implemented by limiting the peak roof drift in preliminary design.

• 한국강구조학회 논문집
• /
• 제12권3호통권46호
• /
• pp.281-290
• /
• 2000

본 연구에서는 강구조물에 자주 사용되고 있는 용접구조용강재를 대상으로 강재검사성적증명서를 수집하고 이를 통계적으로 분석, 정리해서 기계적 성질의 특성을 정량적으로 평가하였다. 본 연구결과 현재 국내에서 생산되는 용접구조용강재의 기계적 성질은 현행 KS에서 규정하고 있는 기준값을 만족하였으며, 판두께 및 강도등급과 일정한 상관관계가 있음을 알 수 있었다. 강종별 판두께 및 강도등급과 기계적 성질 사이에는 선형적인 비례관계가 성립, 본 연구결과는 기존 연구결과와 유사한 경향이 있음을 알 수 있었다. 현행 KS에서는 강재의 기계적 성질 중 항복점 응력에 대한 상한값이 규정되어 있지 않는데, 강재의 변형성능을 충분하게 확보하기 위해서는 항복비 (또는 항복강도)의 상한값을 규정 할 필요가 있을 것으로 생각된다.