• Proceedings of the Korean Institute of Building Construction Conference
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• 2012.11a
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• pp.263-264
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• 2012

In this study, the ultra high strength concrete which have 100, 150, 200MPa took the heat from 20℃ to 70 0℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.221-230
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• 2004

In this paper, the dynamic response of a multi-story steel moment resisting frame equipped with viscoelastic dampers or lead rubber bearing type isolators subjected to seismic loads is investigated analytically. The objective of this study is to find the best location of viscoelastic dampers by the maximum stress method and maximum story drifts method from structure analysis. Also, a secondary objective of the study is to compare the member force, combined stress, and natural period of the structure retrofitted with viscoelastic dampers or lead rubber bearing type isolators to find effective vibration control method.

• International Journal of Korean Welding Society
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• v.5 no.1
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• pp.60-65
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• 2005

In the field of welding the mechanical behavior of a welded structure under consideration may be predicted via heat transfer and welding residual stress analysis. Usually such numerical analyses are limited to small regular mesh models or test specimens. Nevertheless, there is very few strength assessment of the whole structure that includes the effect of welded residual stress. The present work is based on the specialized finite element codes for the calculation of nonlinear heat transfer details and residual stress including the external load on the welded RHS (Rectangular Hollow Section) T-joint connections of the whole structure. First the thermal history of the combined fillet and butt-welded T-joint equal width cold-formed RHS are calculated using nonlinear finite element analysis (FEA) considering the quarter model of the joint. Then using this thermal history the residual stress around the joints has been evaluated. To validity the FEA result, the calculated residual stresses were compared with the available experimental results. The residual stress obtained from the quarter model is mapped to the full model and then to the whole structure model using FEM codes. The results from the FEM codes were exported to the commercial package for visualization and further analysis applying loads and boundary conditions on the whole structure. The residual stress redistribution along with the external applied load is examined computationally.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.598-604
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• 2010

The drilled pier foundation is widely used to support transmission line structures due to its simplicity of construction. When this foundation type is used in conjunction with a single shaft or H-frame structure, it is subjected to a high overturning moment, combined with modest vertical and shear loads. Since the length and diameter of drilled piers are often governed by a maximum permissible deflection, many drilled piers being installed today are very conservatively designed. In this study, Nine prototype field-tests (1/8 scale) have been conducted in order to determine the vertical and lateral resistance of drilled pier foundation for single pole structures. These test results reveal the test piers behaved essentially as rigid bodies in soil (6D) and the center of rotation of the pier were typically 0.6~0.4 of the pier depth below ground surface. Test results also show the relationship between the applied load and the deflection at the top of the pier is highly nonlinear.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1832-1842
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• 2014

A novel probabilistic small signal stability analysis (PSSSA) method considering load correlation is proposed in this paper. The superiority Latin hypercube sampling (LHS) technique combined with Monte Carlo simulation (MCS) is utilized to investigate the probabilistic small signal stability of power system in presence of load correlation. LHS helps to reduce the sampling size, meanwhile guarantees the accuracy and robustness of the solutions. The correlation coefficient matrix is adopted to represent the correlations between loads. Simulation results of the two-area, four-machine system prove that the proposed method is an efficient and robust sampling method. Simulation results of the 16-machine, 68-bus test system indicate that load correlation has a significant impact on the probabilistic analysis result of the critical oscillation mode under a certain degree of load uncertainty.

• Steel and Composite Structures
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• v.11 no.5
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• pp.375-390
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• 2011

Composite beam, which combined the material characteristic of the steel and concrete, has been widely used in the construction of various building and bridge system. For the effective application of the composite beam, the composite action on the composite interface between the concrete element and the steel element should be achieved by shear connectors. The behavioral characteristics of composite beam are related with the degree of interaction and the degree of shear connection according to the shear strength and shear stiffness of the stud shear connectors. These two concepts are also affected by the number of installed shear connector and the strength of composite materials. In this study, experimental and analytical evaluations of the degree of shear connection affected by stud diameter were conducted, and the relationship between structural behavior and the degree of shear connection was verified. The very small difference among the ultimate loads of the specimens depending on the change of the degree of connection was possibly because of the dependence of the ultimate load on the characteristic of plastic moment of the composite beam.

• Computers and Concrete
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• v.6 no.6
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• pp.473-490
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• 2009

This paper presents a new methodology to evaluate the load carrying capacity of deteriorated non-slender concrete bridge pier columns by construction of the full P-M interaction diagrams. The proposed method incorporates the actual material properties of deteriorated columns, and accounts for amount of corrosion and exposed corroded bar length, concrete loss, loss of concrete confinement and strength due to stirrup deterioration, bond failure, and type of stresses in the corroded reinforcement. The developed structural model and the damaged material models are integrated in a spreadsheet for evaluating the load carrying capacity for different deterioration stages and/or corrosion amounts. Available experimental and analytical data for the effects of corrosion on short columns subject to axial loads combined with moments (eccentricity induced) are used to verify the accuracy of proposed model. It was observed that, for the limited available experimental data, the proposed model is conservative and is capable of predicting the load carrying capacity of deteriorated reinforced concrete columns with reasonable accuracy. The proposed analytical method will improve the understanding of effects of deterioration on structural members, and allow engineers to qualitatively assess load carrying capacity of deteriorated reinforced concrete bridge pier columns.

• Computers and Concrete
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• v.6 no.5
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• pp.357-376
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• 2009

In the design of concrete columns, it is important to provide some nominal flexural ductility even for structures not subjected to earthquake attack. Currently, the nominal flexural ductility is provided by imposing empirical deemed-to-satisfy rules, which limit the minimum size and maximum spacing of the confining reinforcement. However, these existing empirical rules have the major shortcoming that the actual level of flexural ductility provided is not consistent, being generally lower at higher concrete strength or higher axial load level. Hence, for high-strength concrete columns subjected to high axial loads, these existing rules are unsafe. Herein, the combined effects of concrete strength, axial load level, confining pressure and longitudinal steel ratio on the flexural ductility are evaluated using nonlinear moment-curvature analysis. Based on the numerical results, a new design method that provides a consistent level of nominal flexural ductility by imposing an upper limit to the axial load level or a lower limit to the confining pressure is developed. Lastly, two formulas and one design chart for direct evaluation of the maximum axial load level and minimum confining pressure are produced.

• Ocean Systems Engineering
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• v.4 no.3
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• pp.201-213
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• 2014

Wave run-up is an important issue in offshore engineering, which is tightly related to the loads on the marine structures. In this study, a series of physical experiments have been performed to investigate the wave run-up around a vertical cylinder in transitional water depth. The wave run-ups of regular waves, irregular waves and focused waves have been presented and the characteristics in frequency domain have been investigated with the FFT and wavelet transform methods. This study focuses on the nonlinear features of the wave run-up and the interaction between the wave run-up and the cylinder. The results show that the nonlinear interaction between the waves and the structures might result wave run-up components of higher frequencies. The wave run-ups of the moderate irregular waves exhibit 2nd order nonlinear characteristics. For the focused waves, the incident waves are of strong nonlinearity and the wavelet coherence analysis reveals that the wave run-up at focal moment contains combined contributions from almost all the frequency components of the focused wave sequence and the contributions of frequency components up to 4th order harmonic levels are recommended to be included.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.751-760
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• 2018

Damages in concrete structures due to aging and other factors could be a serious and immense matter. Making the best selection of the most viable and practical repairing and strengthening techniques are relatively difficult tasks using traditional methods of structural analyses. This is due to the fact that the traditional methods used for assessing aging structure are not fully capable when considering the randomness in strength, loads and cost. This paper presents a reliability-based methodology for assessing reinforced concrete members. The methodology of this study is based on probabilistic analysis, using statistics of the random variables in the performance function equations. Principles of reliability updating are used in the assessment process, as new information is taken into account and combined with prior probabilistic models. The methodology can result in a reliability index ${\beta}$ that can be used to assess the structural component by comparing its value with a standard value. In addition, these methods result in partial safety factor values that can be used for the purpose of strengthening the R/C elements of the existing structure. Calculations and computations of the reliability indices and the partial safety factors values are conducted using the First-order Reliability Method and Monte Carlo simulation.