• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5A
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• pp.351-360
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• 2011

Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for offshore structure, there are few cases to apply structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure under changes in temperature and transverse loadings. Principal component analysis (PCA) was applied using conventional damage index to eliminate principal components sensitive to environmental change. It was found that the proposed PCA-base approach is an effective tool for long-term SHM under significant environmental changes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1082-1087
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• 2021

The propeller shaft has different pattern of behaviors at each static, dynamic, and transient condition to a ship shaft system due to the effects of propeller weight and eccentric thrust, which increases the potential risk of bearing failure by causing local load variations. To prevent this, the various research of the shafting system has been conducted with the emphasis on optimizing the relative slope and oil film retention between propeller shaft and stern tube bearing at quasi-static condition, mainly with respect to the Rules for the Classification of Steel Ships. However, to guarantee a stability of the shafting system, it is necessary to consider the dynamic condition including the transient state due to the sudden change in the stern wakefield during rudder turn. In this context, this study cross-validated the ef ect of propeller shaft behavior on the stern tube bearing during port turn operation, which is a typical transient condition, by using the strain gauge method and displacement sensor for 50,000 DWT medium class tanker. And it was confirmed that the propeller eccentric thrust change showing relief the load of the stern tube bearing.

• Journal of Korean Society of Steel Construction
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• v.26 no.2
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• pp.105-118
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• 2014

The number of the deteriorated bridge has been sharply increased due to the increase in the bridge service period in Korea. Local corrosion problem of structural member can be occurred according to atmospheric corrosion environments based on the installation location of steel bridges. Especially, in case of the plate girder bridge, corrosion damage is concentrated on the web panel and stiffener at girder end. An asymmetrical shear resistant web section in the plate girder bridge can be caused from the local corrosion of the web panel, because local corrosion is not symmetrically occurred to the bridge. In this study, therefore, the shear buckling strength and behavior of a plate girder with asymmetrically corroded web panel was numerically evaluated using FE analysis, which was considering an aspect ratio and corrosion damage level of web panel. The shear buckling strength reduction of an asymmetrical shear resistant web panel was compared and evaluated according to corroded volume ratio for a web panel and for diagonal tension field of a web panel.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.11-18
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• 2007

Seismic performance evaluation for dam safety evaluation has been continually conducted. However the behavior analysis for the spillway pier which is known as the weak point of dam is seldom reported. Therefore, this study performed the static loading tests for a prototype structures as elementary tests for the final seismic performance evaluation of dam safety. The prototype of pier structure has 1/20 scale and it adopts to strength model. And cracking loads and ultimate loads of real structures are calculated through numerical analysis using commercial FEM program (ABAQUS). The results of this study show some difference between the results of prototype tests and the results of numerical analysis. Also, the ultimate and cracking loads can be estimated through the prototype loading test and numerical analysis.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.289-301
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• 2008

Double skin composite (DSC) wall is a structural wall that is filed with concrete between two steel plate skins connected by tie bars. This type of wall was developed to enhance the structural performance of wall, to reduce wall thickness, and to enhance constructibility, eliminating the use of formwork and re-bars. In this study, cyclic tests were performed to investigate the inelastic behavior and earthquake resistance of isolated and coupled DSC walls with rectangular and T-shapedcross-sections. The DSC walls showed stable cyclic behaviors, exhibiting excellent energy dissipation capacity. The te st specimens failed by the tensile fracture of welded joints at the wall base and coupling beam and by the severe local buckling of the steel plate. The deformation capacity of the walls varied with the connection details at the wall base and their cross-sectional shapes. The specimens with well-detailed connections at the wall base showed relatively god deformation capacity ranging from 2.0% to 3.7% drift ratio. The load-carrying capacities of the isolated and coupled wall specimens were evaluated considering their inelastic behavior. The results were compared with the test results.

• Journal of the Korean GEO-environmental Society
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• v.2 no.2
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• pp.13-22
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• 2001

In this study, centrifuge model tests were fulfilled to investigate the characteristics of bearing capacity of paper ash as a filling material. The model tests were done varying the footing width and gravity level. The settlement and vertical soil pressure by loading were measured. The results from the tests were compared with the one from FLAC program using finite difference method and bearing capacity theory. After all, it was shown that the characteristics of load-settlement represented the local shear failure, which the settlement ratio s/B showed inflection point around 25~30%. As g-level and footing width were increasing, the load strength was increasing. The ultimate bearing capacity from the tests was very closed the results from Terzaghi's theory. As the distance from footing center was increasing, the vertical soil pressure was decreasing. If E/B is higher than 7, the stress by loading was almost increasing. The vertical displacement from loading was the largest one around under the footing and was almost occurred when the depth>4cm and E/B is higher than 5.0.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.8 s.251
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• pp.873-879
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• 2006

To investigate applicability of the reference stress approach as simplified inelastic stress analysis to estimate local creep rupture, detailed finite element stress analyses of a T-piece pipe with different inner pressure and system loading levels are performed. The reference stresses are obtained from the finite element (FE) limit analysis based on elastic-perfectly-plastic materials, from which the local reference stress for creep rupture is determined from R5. The resulting inelastic stresses are compared with elastic stresses resulting from linear elastic FE calculations. Furthermore they are also compared with the stresses from full elastic-creep FE analyses. It shows that the stresses estimated from the reference stress approach compare well with those from full elastic-creep FE analysis, which are significantly lower than the elastic stress results. Considering time and efforts for full inelastic creep analysis of structures, the reference stress approach is shown to be a powerful tool for creep rupture estimates and also to reduce conservatism of elastic stress analysis significantly.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.5
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• pp.433-441
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• 2009

Generally, the events in nature have multi-disciplinary characteristics. To solve this problems, these days loosely coupled methods are widely applied because of advantage of solvers which are already developed and well proved. Those solvers use different mesh system, so transformation and mapping of data are vital in the field of fluid-structure interaction(FSI). In this paper, the interpolation of deformation which is used globally and compactly supported radial basis functions(RBF), and mapping of force which use principle of virtual work are examined for computing time and accuracy to compare ability with simple 3-D problem. As the results, interpolation scheme of compactly supported radial basis functions are useful to interpolation and mapping for large-scale airplane in FSI with a k-dimensional tree(kd-tree) which is a space-partitioning data structure for organizing points in a k-dimensional space.

• Journal of Korean Society of Steel Construction
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• v.26 no.3
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• pp.169-176
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• 2014

This paper presents the experimental results of behavior of square CFT columns with large the width-ro thickness ratio strengthened with carbon fiber reinforced polymers (CFRP) sheets subjected to concentrated axial loading. The main parameters were b/t ratio and the number of CFRP layers and 6 specimens were fabricated. The values of b/t were ranged from 60 to 100. From the tests, Maximum increase of 16% was also achieved in axial-load capacity with three transverse layered CFRP applied on four sides of steel tubes. The load capacity decreased up to 41% comparing with nominal load capacity of unstrengthened CFT column. However, for CFRP strengthened CFT, the load capacity decreased up to 32%. Finally, from the load-strain relationships, the local buckling occurred before yield point of steel tubes. Also, from the load-strain relationships, it was observed that local buckling were delayed on CFT columns by CFRP sheets retrofitting.

• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.25-31
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• 2003

This research aimed to experimentally and theoretically investigate the moment strength of deck plates. A moment experiment was carried out using a full-scale 14 specimen. To prevent local buckling, the point load was applied at 1/4 points. After the experiment, theoretical analysis was conducted and the differences between various codes were identified. The experimental results were compared with AISI (the American Iron and Steel Institute), EC (Euro Code) 3, and KS (Korea Standard) codes. Analysis results are summarized as follows: (1) the failure mode was influenced by local buckling at the midpoint of the beam and/or at the intermediate loading point: (2) if yielding first occurred at the tension side, the moment strength would increase as the plastic reservation of the tension zone acted: (3) the experimental results were closest to the EC3 codes in which the partial plastic reservation was considered; (4) statistical evaluation based on the EC3 Annex Z showed that the partial resistance safety coefficient calculated applying to the EC3 formula, $^{\circ}{_M}$, was placed within 1.1 which was the target value of EC3 code; and (5) the analytical power of AISI and KS codeswere expected to improve into the level of EC3 codes if the concept of plastic reservation of the tension side would be introduced to them.