• Journal of the Korean Wood Science and Technology
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• v.44 no.1
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• pp.57-66
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• 2016

In order to develop materials with a low environmental load for restoring the destroyed forest, seven types of wood-concrete hybrid laminated materials were manufactured with four softwoods, three hardwoods and concrete, and the effect of wood density on bending creep property was investigated. The bending creep curves showed a shape to considerably increase at the upper right side, and the curves were found to show a linear behavior beyond about 30 min - 1 hour, as behaviors of solid woods and wood-based materials. The initial compliances of wood-concrete hybrid-laminated materials decreased with an increase in the wood density, and those values showed 0.9 - 1.2 times of the concrete one. The creep compliances of hybrid laminated materials showed very low values, which were 0.4 - 0.8 times of the concrete ones. The relative creep were very low with a range from 8.2% to 17.0% range, which were 0.3 - 0.7 times of the concrete ones. These results indicate that these materials can be applied for restoring the destroyed forest to reduce creep deformation of the conventional concrete materials by hybrid-laminating concrete and woods.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.1
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• pp.15-29
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• 2009

Most breakwater armor blocks are designed by using Hudson's or van der Meer's formula. The minimum weight of armor blocks is calculated by equating the resistance to the load in each formula. The larger value is then chosen as the design weight. In this study, we have performed reliability analyses for thus designed breakwater armor blocks of 12 trade harbors and 8 coastal harbors in Korea. The probability of failure calculated by the reliability analysis provides a criterion for evaluating the stability of armor blocks. The calculated probability of failure was almost same for all the breakwaters so that we were able to quantitatively evaluate the safety level of armor blocks of existing breakwaters. We also found that the safety factor used in the deterministic design method and the probability of failure in the reliability design method show a linear relationship. Therefore the probability of failure of existing breakwaters can be quantitatively calculated from the safety factors. The calculated probability of failure could also be used for determining the target probability of failure in the future.

• Journal of Preventive Medicine and Public Health
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• v.13 no.1
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• pp.3-12
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• 1980

Certain heavy metals which may lead peoples to poisonous status are widely used in industry and their uses have been increasing along with rapid industrialization of this country. Such an increasement of metal uses aggravates the status of environmental pollution affecting foodstuffs which are the most important life supporting factor of animal and humanbeing. Concerning the safety measures to minimize food-borne transmission of such hazardous metals, surveillance is the backbone of them and probably more so with a potential problem such as intoxication. Theoretically, this surveillance should include the determination of levels of heavy metal toxicants in foods, the determination of food consumption patterns and typical total diet, and the estimation of total load of the metal contaminant from all sources of exposure including air, water, and occupational sources. In recent year, actually, such estimates on the total daily intake of some heavy metals from foods have been made in several developed countries and a wide variation of date by season, locality, and research method was recognized. Also in this country, this kind of research data is vitally needed to make up for the serious shortage or lack of references to estimate the total amount of heavy metal intake of the people. In this study, a modification model for estimation of the total daily intake of cadmium copper, nickel, zinc, and lead through foods was applied and concentrations of the above metals in crops cultivated in this country were measured with atomic absorption spectro photometer to get the following results. 1. Level of heavy metal concentration in crops Generally, the levels of such metals in essential crops such as rice, cucumber, radish. chinese cabbage, apple, pear, grape, and orange are similar or lower than those in Japan and other developed countries. By the way, a striking result on cadmium concentration was increasement of its concentration in rice from $0{\sim}0.035ppm$ in 1970 to 0.11ppm in this study. However, the value is still far below the. Japanese Permissible Lebel of 1.0ppm. 2. Estimation of total daily intake per capita from foods A new model for estimation was devised utilizing levels of metal concentration in foods, amount of food consumed, and other food factors. Based on the above method, the daily intake of cadmium was estimated to be $70.53{\mu}g/man/day$ in average which was as high as the Limit Value of ILO/WHO(up to $71.4{\mu}g/man/day$). Also, 3.89mg of Zinc, 1.65mg of cuppor, 0.32mg of lead were given as the total daily intake per capita by this research. 3. Efficacy of washing or skinning to decrease the amount of metals in crops After washing the crops sufficiently with commercial linear alkylate sulfonate, the concentration of heavy metals could be reduced to $50{\sim}80%$ showing decreasement rate of $20{\sim}50%$. Also, after skinning the fruits, decreasement rate of the heavy metal concentration shelved $0{\sim}50%$.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.87-95
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• 1988

In the arctic offshore regions, massive offshore gravity platforms are recommended to be construced because of severe environments. In such structures which is so large that its characteristic length is of the order of the wave length, wave-structure interaction problem has been solved using linear diffraction theory. Structural analysis of the large scale offshore structures requires wave force distribution along depth and wave pressure distribution on the body surface. In this study, existing computer program which calculates the total wave force acting on axisymmetric bodies has been modified to calculate wave force distribution along depth and wave pressure distribution on the body surface. Numerical results of pressure distribution for a fixed vertical cylinder obtained from this analysis has been compared with the results of an analytic solution of MacCamy-Fuchs, and good agreements has been obtained. It is desirable to use 6 in the case of analytic solution, and 5 in the case of numerical solution as the Fourier Mode of Green function. The results in this study are expected to be utilized for structural analysis such as pseudo-static analysis, dynamic analysis and fatigue analysis.

• Journal of Korean Society of Steel Construction
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• v.14 no.6
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• pp.735-746
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• 2002

The task of plastic theory is twofold: first, to set up relationships between stress and strain that adequately describe the observed plastic deformation of metals, and second, to develop techniques for using these relationships in studying of the mechanics of metal forming processes, and the anlaysis and design of structures. One of the major problems in the theory of plasticity is to describe the behavior of work-hardening materials in the plastic range for complex loading histories. This can be achieved by formulating constitutive laws either in the integral or differential forms. To adequately predict the response of steel members during cyclic loading, the hardening rule must account for the features of cyclic stress-strain behavior. Neithe of the basic isotropic and kinematic hardening rules is suitable for describing cyclic streess-strain behavior, although a kinematic hardening rule describes the nearly linear portions of the stabilized hystersis loops. There is also a limited expansion of the yield surface as predicted by the isotropic hardening rule. Strong ground motions or wind gusts affect the complex and nonproportional loading histories in the inelastic behavior of structues rather than the proportional loading. Nonproportional loading is defined as externally applied forces on the structure, with variable ratios during the entire loading history. This also includes the rate of time-dependency of the loads. For nonproportional loading histories, unloading may take place along a chord instead of the radius of the load surface. In such cases, the shape of the stress-strain curve has to be determined experimentally for all non-radial loading conditions. The plasticity models including two surface models ae surveyed based on a yield surface and a bound surface that represent a state of maximum stress. This paper is concerned with the improvement of a plasticity models of the two-surface type for structural steel. This is follwed by an overview of plasticity models on structural steel. Finally the need for further research is identified.

• Journal of the Korean Wood Science and Technology
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• v.12 no.3
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• pp.15-24
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• 1984

The $3{\times}3{\times}30\;cm^3$ sized specimens of Douglas-fir(Pseudotsuga menziesii) and western hemlock(Tsuga heterophylla) in this study were soaked in four fire-retardant solutions of ammonium sulfate, monoammonium phosphate, diammonium phosphate, and aluminium chloride for 1, 24, 72, 168, and 336 hours. Subsequently they were air-dried and burned at high temperature of ca. $1,800^{\circ}C$ and for short time of 5 minutes. This study estimated the relationship between the adsorbed chemicals and the residual weight ratio or residual bending strength of these partly burned lumbers. The results were as follows; 1) In average amount of chemical adsorption, diammonium phosphate showed the largest and aluminium chloride the smallest regardless of species but monoammonium phosphate was larger in Douglas-fir than that of western hemlock. 2) The amount of chemical adsorption was larger in western hemlock than Douglas-fir on the whole. 3) The amount of chemical adsorption was increased with the increase of soaking time but the rate of increase began to decrease at 200hrs. 4) Residual weight ratios showed no difference between species but showed differences among the chemicals treated i.e. monoammonium phosphate, diammonium phosphate, ammonium sulfate and aluminium chloride in turn from the largest to the smallest. 5) MOR values showed linear increase with the increase of residual weight ratios but showed no difference in species and chemicals respectively. 6) In the relationship between amount of chemical adsorption and MOR, only diammonium phosphate showed the curve of secondary degree with significance in Douglas-fir. 7) The MOE value of burned Douglas-fir lumber increased and showed significance of 99% as the adsorbed chemical amount increased, but among the chemicals only monoammonium phosphate showed significance. The MOE value of burned western hemlock lumber didn't show significance. 8) In only Douglas-fir, the correlation between adsorbed chemical amount and work to proportional limit showed significance in only monoammonium phosphate. And in both Douglas-fir and western hemlock, the correlation between adsorbed chemicals and work to maximum load showed significance in monoammonium phosphate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.251-257
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• 2011

This paper deals with the statistical properties of parameters B and q in the creep crack growth rate (CCGR) law, da/dt=B$(C^*)^q$, in Mod. 9Cr-1Mo (ASME Gr.91) steel which is considered a candidate materials for fabricating next generation nuclear reactors. The CCGR data were obtained by creep crack growth (CCG) tests performed on 1/2-inch compact tension (CT) specimens under an applied load of 5000N at a temperature of $600^{\circ}C$. The CCG behavior was analyzed statistically using the empirical equation between CCGR, da/dt and the creep fracture mechanics parameter, $C^*$. The B and q values were determined for each specimen by the least-squares fitting method. The probability distribution functions for B and q were investigated using normal, log-normal, and Weibull distributions. As far as this study is considered, it can be appeared that B and q followed the log-normal and Weibull distributions. Moreover, a strong positive linear correlation was found between B and q.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.2
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• pp.164-171
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• 2002

In this study, a mass-spring model is used to dynamically describe and calculate the shape and movement of a mid-water trawl system. This mathematical model theorizes that the factors constituting the system are the material points and the external forces such as hydrodynamic load, gravity, and buoyancy act on these material points. In addition, it surmises that these material points are connected to each other by springs, the springs do not have any mass, and the internal force acts on these springs. The non-linear differential equations are implicitly integrated with time for guaranteeing a stable solution. The dynamic simulation by the mass-spring model shows the status of the gear such as fishing gear depth, distance between doors, shape of the gear, and tension of each line. It depends on the parameters such as towing force, warp length, force of a sinker, buoyancy of a float, type of door and netting materials. The validity of the model is verified by comparing simulation motions of a trawl system obtained from computed values to those from an actual experiment.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.59-66
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• 2002

Long-rails in railways and high-speed railway are subjected to additional stresses resulted from the displacements inconsistence between upper structures, and this phenomenon is more remarkable in continuous bridges than in simple bridges. For the sake of safety, railways have to guarantee trains to stop safely without derailment even in the event of earthquake. The influences of acceleration, braking, and temperature were analyzed by static nonlinear method. But earthquake loads that require dynamic nonlinear analysis are not considered in these methods. Because linear relation between relative displacements of decks and rail stresses is not guaranteed at the nonlinear systems such as long rails on the bridges, it is required compute to rail stresses considering both braking and earthquake load by nonlinear dynamic analysis method. In this study, dynamic analysis method with material non-linearity for rails on continuous bridges according to the Taiwan High Speed Railway(THSR) Design Specification volume 9 was developed. And additional stresses and displacements of long rails for acceleration, braking, and earthquake loads were analyzed by this method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.171-185
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• 2006

A sophisticated reliability analysis method is proposed to evaluate the reliability of real nonlinear complicated dynamic structural systems excited by short duration dynamic loadings like earthquake motions by intelligently integrating the response surface method, the finite element method, the first-order reliability method, and the iterative linear interpolation scheme. The method explicitly considers all major sources of nonlinearity and uncertainty in the load and resistance-related random variables. The unique feature of the technique is that the seismic loading is applied in the time domain, providing an alternative to the classical random vibration approach. The four-parameter Richard model is used to represent the flexibility of connections of real steel frames. Uncertainties in the Richard parameters are also incorporated in the algorithm. The laterally flexible steel frame is then reinforced with reinforced concrete shear walls. The stiffness degradation of shear walls after cracking is also considered. The applicability of the method to estimate the reliability of real structures is demonstrated by considering three examples; a laterally flexible steel frame with fully restrained connections, the same steel frame with partially restrained connections with different rigidities, and a steel frame reinforced with concrete shear walls.