• Nuclear Engineering and Technology
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• v.20 no.2
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• pp.88-104
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• 1988

The FUel Rod Analysis(FURA) code is developed using two-dimensional finite element methods for axisymmetric and plane stress analysis of fuel rod. It predicts the thermal and mechanical behavior of fuel rod during normal and load follow operations. To evaluate the exact temperature distribution and the inner gas pressure, the radial deformation of pellet and clad, the fission gas release are considered over the full-length of fuel rod. The thermal element equation is derived using Galerkin's techniques. The displacement element equation is derived using the principle of virtual works. The mechanical analysis can accommodate various components of strain: elastic, plastic, creep and thermal strain as well as strain due to swelling, relocation and densification. The 4-node quadratic isoparametric elements are adopted, and the geometric model is confined to a half-pellet-height region with the assumption that pellet-pellet interaction is symmetrical. The pellet cracking and crack healing, pellet-cladding interaction are modelled. The Newton-Raphson iteration with an implicit algorithm is applied to perform the analysis of non-linear material behavior accurately and stably. The pellet and cladding model has been compared with both analytical solutions and experimental results. The observed and predicted results are in good agreement. The general behavior of fuel rod is calculated by axisymmetric system and the cladding behavior against radial crack is used by plane stress system. The sensitivity of strain aging of PWR fuel cladding tube due to load following is evaluated in terms of linear power, load cycle frequency and amplitude.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.283-292
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• 2013

A calcareous rock slope failed during excavation of the slope for construction of a tunnel entrance. The slope is located at the construction site for widening highway in Yeongwol, Korea. Field surveys, laboratory tests, and numerical analyses were performed to determine the reason for the slope failure. The numerical analysis revealed that the safety factor of the slope before construction of the entrance was less than 1, and that this decreased after construction. After construction of the entrance, the sliding zone of the slope increased and slope stability decreased because the shear strain and plastic zone in the slope over the tunnel entrance showed an increase relative to the lower part of the slope. To enhance the stability of the slope for construction of the tunnel entrance, countermeasures such as rock bolts, rock anchors, and FRP (Fiber glass Reinforced Plastic) grouting were adopted in light of the field conditions. Serial field monitoring performed to confirm the reinforcing effects of the adopted countermeasures revealed a small amount of horizontal deformation of the slope soils, most of the elastic deformation that can regain its former value. In addition, the axial forces of the rock bolt and anchor were more strongly affected by slope excavation during construction of the tunnel entrance than by tunnel excavation or the rainy season, and the axial forces tended to converge after excavation of the tunnel. Therefore, we can confirm that the slope is currently safe.

• Journal of the Korean Wood Science and Technology
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• v.41 no.6
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• pp.535-543
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• 2013

The objective of this study was to analyse the residual stress in Larix kaempferi board during and after kiln-drying. The boards were primarily intended for using as laminar of cross laminated timber (CLT). In this study, the equivalence of moisture content by equalizing treatment was proved and reduction of residual stress by conditioning treatment was quantified. Prong test and slice test were carried out to analyse the residual stress in wood during drying. Transverse casehardening was measured immediately after making prong sample. Residual stress of four parts in wood from surface to center was analyzed quantitatively based on elastic deformation after just cutting slices from board. Tensile stress and compressive stress on the surface of board during drying did not exceed 2.2 MPa when boards were dried by kiln-drying schedule of T10-C4 and T12-D5. Because the tensile strength and compressive strength of transverse direction of Larix kaempferi lumber are 2.65 MPa and 4.60 MPa, application of more severe drying schedule can be recommended. Cup and twist were reduced by about 40% by equalizing and conditioning treatments after drying.

• Korean Journal of Environmental Biology
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• v.32 no.3
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• pp.225-233
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• 2014

In this study, we investigated the changes in the physiological and histological traits of a sea squirt (Halocynthia roretzi) with the emergence of the soft tunic syndrome induced by the water temperature control (6, 9, 12, 15, 18, 21, 24 and $27^{\circ}C$). It was observed that the induction rate of the soft tunic syndrome was highest at $15^{\circ}C$, but lowest at $24^{\circ}C$. Based on the tunic color condition and contraction strength, the whole process were classified into 4 stages as S0, S1, S2 and S3. Interestingly, there were significant differences in oxygen consumption and filtration rate were observed during S0-S3. The most distinctive aspects were change of blood cell composition at stage S3, whereas multi-vacuole cell ratio was decreased by 1/2 and morula cell ratio expanded about 10 times during S0-S3. Further, change of organ structure started following the syndrome such as degeneration of epithelial cells, microfilaments, increment in hemocytes and damage in muscle fiber have been detected in tunic, siphon, branchial sac, body wall musculature and pyloric gland. Briefly, our study results indicated that the normal physiological functions of the sea squirt can be affected due to the soft tunic syndrome induced by water temperature.

• Journal of the Korean Geotechnical Society
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• v.27 no.1
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• pp.77-86
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• 2011

The advanced geotechnical information has been required to determine the accurate design parameters for complex construction. However, the Standard Penetration Test (SPT), which has low reliability, has been used to estimate the subsurface condition in the field. The objective of this paper is development and application of the Static-Dynamic penetrometer, which detects the resistances in soft clay, sand and rock. The energy losses according to the rod connection methods (perfect or non-perfect connection, and number rods) are experimentally evaluated. The reflection and transmission ratios are used to investigate the energy loss by a simulation. The static-dynamic cone penetrometer, in which the accelerometers and strain gauges are installed on the cone tip and the rod head, is used to estimate the energy loss during penetration by impacts. The experimental and simulation studies show that the transferred energy through rods with non-perfect connection dramatically decreases. Furthermore, the transferred energy on the rod head is not the same as that on the cone tip. This study demonstrates that the energy loss should be evaluated on the cone tip.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.87-92
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• 2019

In this paper, we have verified a low-voltage EM(elasto-magnetic) sensing technique for tensile force management of PSC(prestressed concrete) internal tendon in order to apply the technique to actual construction sites where stable power supply is difficult. From observation of past domestic and overseas PSC structural accident cases, it was found that PS tension is very important to maintain structural stability. In this paper, we have tried to measure the tensile force from a magnetic hysteresis curve through EM sensors according to voltage value by using relation between magnetostriction and stress of ferromagnetic material based on elastic-magnetic theory. For this purpose, EM sensor of double cylindrical coil type was fabricated and tensile force test equipment for PS tendon using hydraulic tensioning device was constructed. The experiment was conducted to confirm relationship between changes of permeability and tensile force from the measurement results of the maximum / minimum voltage amount. The change of magnetic hysteresis curve with magnitude of tensile force was also measured by reducing amount of voltage step by step. As a result, the slope of estimation equation in accordance with magnitude of magnetic field decreases with the voltage reduction. But it was confirmed a similar pattern of change of magnetic permeability for the magnetic hysteresis loop. So, in this study, it is considered that it is possible to manage the tensions of PSC internal tendon using EM sensing technique in low-voltage state.

• Journal of the Korean Geotechnical Society
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• v.23 no.9
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• pp.5-16
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• 2007

The simple linear elastic-perfectly plastic model with soil parameters $s_u,\;E_u$ and n of undrained condition is usually applied to predict the displacement of a constructed diaphragm wall(DW) on soft soils during excavation. However, the application of this soil model for finite element analysis could not interpret the continued increment of the lateral displacement of the DW for the large and deep excavation area both during the elapsed time without activity of excavation and after finishing excavation. To study the characteristic behaviors of soil behind the DW during the periods without excavation, a series of tests on soft Bangkok clay samples are simulated in the same manner as stress condition of soil elements happening behind diaphragm wall by triaxial tests. Three kinds of triaxial tests are carried out in this research: $K_0$ consolidated undrained compression($CK_0U_C$) and $K_0$ consolidated drained/undrained unloading compression with periodic decrement of horizontal pressure($CK_0DUC$ and $CK_0UUC$). The study shows that the shear strength of series $CK_0DUC$ tests is equal to the residual strength of $CK_0UC$ tests. The Young's modulus determined at each decrement step of the horizontal pressure of soil specimen on $CK_0DUC$ tests decreases with increase in the deviator stress. In addition, the slope of Critical State Line of both $CK_0UC$ and $CK_0DUC$ tests is equal. Moreover, the axial and radial strain rates of each decrement of horizontal pressure step of $CK_0DUC$ tests are established with the function of time, a slope of critical state line and a ratio of deviator and mean effective stress. This study shows that the results of the unloading compression triaxial tests can be used to predict the diaphragm wall deflection during excavation.

• Journal of the Korean Geotechnical Society
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• v.26 no.7
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• pp.49-58
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• 2010

This paper presents experimental results of a series of 1-g shaking table model tests performed on end-bearing single piles and pile groups to investigate the effect of particle size on the dynamic behavior of soil-pile systems. Two soil-pile models were tested twice: first using Jumoonjin sand, and second using Australian Fine sand. In the case of single-pile models, the lateral displacement was almost within 1% of pile diameter which corresponds to the elastic range of the pile. The back-calculated p-y curves show that the subgrade reaction of the Jumoonjin-sand-model ground was larger than that of the Australian Fine-sand-model ground at the same displacement. This phenomenon means that the stress-strain behavior of Jumoonjin sand was initially stiffer than that of Australian Fine sand. This difference was also confirmed by resonant column tests and compression triaxial tests. And the single pile p-y backbone curves of the Australian fine sand were constructed and compared with those of the Jumoonjin sand. As a result, the stiffness of the p-y backbone curves of Jumunjin sand was larger than those of Australian fine sand. Therefore, using the same p-y curves regardless of particle size can lead to inaccurate results when evaluating dynamic behavior of soil-pile system. In the case of the group-pile models, the lateral displacement was much larger than the elastic range of pile movement at the same test conditions in the single-pile models. The back-calculated p-y curves in the case of group pile models were very similar in both sands because the stiffness difference between the Jumoonjin-sand-model ground and the Australian Fine-sand-model ground was not significantly large at a large strain level, where both sands showed non-linear behavior. According to a series of single pile and group pile test results, the evaluation group pile effect using the p-multiplier can lead to inaccurate results on dynamic behavior of soil-pile system.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.119-133
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• 2020

Underground utility tunnel, the most representative cut and cover structure, is subjected to seismic force by displacement of the surrounding soil. In 2020, Korea Infrastructure Safety Corporation has published "Seismic Performance Evaluation Guideline for Existing Utility Tunnel." This paper introduces two seismic evaluation methods, RDM (Response Displacement Method) and RHA (Response History Analysis) adopted in the guide and compares the methods for an example of an existing utility tunnel. The test tunnel had been constructed in 1988 and seismic design was not considered. RDM is performed by single and double cosine methods based on the velocity response spectrum at the base rock. RHA is performed by finite difference analysis that is able to consider nonlinear behavior of soil and structure together in two-dimensional plane strain condition. The utility tunnel shows elastic behavior for RDM, but shows plastic hinge for RHA under the collapse prevention level earthquake.

• Magazine of the Korea Concrete Institute
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• v.6 no.2
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• pp.97-107
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• 1994

The objective of this study is to develop polymer-impregnated concrete(PIC), which is a newly developed composite material made by impregnating polymer impregnanls into hardened normal concrete, and to develop analytical techniques for its proper applications. Crystalline methyl methacrylate(MMA) is chosen as a monomer of polymer impregnants. The corrlpositions of polymer impregnants and producing processes are developed by analyzing the effects of penetration, polymerization, thermal safety, and strengthening characteristics. On t he basis of experimental results of this study, various strength characteristics and stress strain constitutive relations are formulated in terms of the compressive strength of normal concrete and the polymer loadings, which can be applied for analysis and design of PIC members. In order to provide a model for fracture analysis of flexural members, fracture toughness, fracture energy, critical crack width, and tension softening relations near crack tip are also formulated in terms of member depth, initial notch depth, and the flexural strength of normal concrete. The structural analysis procedure and the finite element computer program developed in the study are applicable to evaluate elastic behavior, ultimate strength, and tension softening behavior of MMA type PIC structural members subject to various loading conditions. The accuracy and effectiveness of the developed computer program is examined by comparing the anal ytical results with the experimental results. Therefore, it is concluded that the developed structural analysis procedure and the finite element computer program are applicable to analysis and design of in-situ and precast PIC structural members.