• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.295-304
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• 2008

This paper comprises two specific objectives. The first is to examine the applicability of Ordinary Kriging interpolation(OK) to finite element method that is based on variogram modeling in conjunction with different allowable limits of separation distance. The second is to investigate the accuracy according to theoretical variograms such as polynomial, Gauss, and spherical models. For this purpose, the weighted least square method is applied to obtain the estimated new stress field from the stress data at the Gauss points. The weight factor is determined by experimental and theoretical variograms for interpolation of stress data apart from the conventional interpolation methods that use an equal weight factor. The validity of the proposed approach has been tested by analyzing two numerical examples. It is noted that the numerical results by Gauss model using 25% allowable limit of separation distance show an excellent agreement with theoretical solutions in literature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2939-2944
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• 2011

The performance and efficiency of a Molten Carbonate Fuel Cell system will improve with the aids of numerical simulations such as finite element analysis. For best simulation results, the virtual model must accurately reflect the actual model including the material properties. It is very difficult, however, to make a detailed numerical model of the stack that consists of hundreds of layers of unit cells composed of various materials like metal, ceramics, polymer, etc. Instead, a practical approach is to find a homogenized material property of the stack as a whole as an approximate replacement. In this paper, the compression ratio of a unit cell is introduced, and a new method is proposed to estimate the homogeneous material properties for both the active and the manifold regions of the stack under the assumption that the compressive deformation occurs only at the separators and matrices in the unit cells. The estimated properties are applied successfully to simulating an actual stack.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.197-215
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• 2021

Under a severe environment of multiple hazards such as earthquakes and winds, the life-cycle performance of engineering structures may inevitably be deteriorated due to the fatigue effect caused by long-term exposure to wind loads, which would further increase the structural vulnerability to earthquakes. This paper presents a framework for evaluating the lifetime structural seismic performance under the effect of wind-induced fatigue considering different sources of uncertainties. The seismic behavior of a high-rise steel-concrete composite frame with buckling-restrained braces (FBRB) during its service life is systematically investigated using the proposed approach. Recorded field data for the wind hazard of Fuzhou, Fujian Province of China from Jan. 1, 1980 to Mar. 31, 2019 is collected, based on which the distribution of wind velocity is constructed by the Gumbel model after comparisons. The OpenSees platform is employed to establish the numerical model of the FBRB and conduct subsequent numerical computations. Allowed for the uncertainties caused by the wind generation and structural modeling, the final annual fatigue damage takes the average of 50 groups of simulations. The lifetime structural performance assessments, including static pushover analyses, nonlinear dynamic time history analyses and fragility analyses, are conducted on the time-dependent finite element (FE) models which are modified in lines with the material deterioration models. The results indicate that the structural performance tends to degrade over time under the effect of fatigue, while the influencing degree of fatigue varies with the duration time of fatigue process and seismic intensity. The impact of wind-induced fatigue on structural responses and fragilities are explicitly quantified and discussed in details.

• Earthquakes and Structures
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• v.24 no.4
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• pp.259-274
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• 2023

In this paper, mechanical properties of periodic foundation made of concrete and rubber are investigated by a parametric study using the finite element method (FEM). Periodic foundation is a special type of seismic isolation foundation used in civil engineering, which is inspired by the meso-scale structure of phononic crystals in solid-state physics. This type of foundation is capable of reducing the seismic wave propagating though the foundation, therefore providing additional protection for the structures. In the FEM analysis, layered periodic foundation is frequently modelled due to its simplicity in numerical modeling. However, the isolation effect of periodic foundation on nuclear power plant has not been fully discussed to the best knowledge of authors. In this work, we construct four numerical models of nuclear power plant with different foundations to investigate the seismic isolation effects of periodic foundations. The results show that the layered periodic foundation can increase the natural period of the nuclear power plant like traditional base isolation systems, which is beneficial to the structures. In addition, the seismic response of the nuclear power plant can also be effectively reduced in both vertical and horizontal directions when the frequencies of the incident waves fall into some specific frequency bandgaps of the periodic foundation. Furthermore, it is demonstrated that the layered periodic foundation can reduce the amplitude of the floor response spectrum, which plays an important role in the protection of the equipment.

• Structural Engineering and Mechanics
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• v.90 no.4
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• pp.371-390
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• 2024

Investigating the impact of openings on the structural behavior of ferrocement I-beams with two distinct types of reinforcing metallic and non-metallic meshes is the primary goal of the current study. Up until failure, eight 250x200x2200 mm reinforced concrete I-beams were tested under flexural loadings. Depending on the kind of meshes used for reinforcement, the beams are split into two series. A control I-beam with no openings and three beams with one, two, and three openings, respectively, are found in each series. The two series are reinforced with three layers of welded steel meshes and two layers of tensar meshes, respectively, in order to maintain a constant reinforcement ratio. Structural parameters of investigated beams, including first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were reported. The number of mesh layers, the volume fraction of reinforcement, and the kind of reinforcing materials are the primary factors that vary. This article presents the outcomes of a study that examined the experimental and numerical performance of ferrocement reinforced concrete I-beams with and without openings reinforced with welded steel mesh and tensar mesh separately. Utilizing ANSYS-16.0 software, nonlinear finite element analysis (NLFEA) was applied to illustrate how composite RC I-beams with openings behaved. In addition, a parametric study is conducted to explore the variables that can most significantly impact the mechanical behavior of the proposed model, such as the number of openings. The FE simulations produced an acceptable degree of experimental value estimation, as demonstrated by the obtained experimental and numerical results. It is also noteworthy to demonstrate that the strength gained by specimens without openings reinforced with tensar meshes was, on average, 22% less than that of specimens reinforced with welded steel meshes. For specimens with openings, this value is become on average 10%.

• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.51-63
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• 2023

Numerical analysis was conducted to determine the effect of soil behavior by thawing and freezing of seasonal frozen soil on pile foundations. The analysis was performed using the finite element method (FEM) to simulate soil-pile interaction based on the atmosphere temperature change. Thermomechanical coupled modeling using FEM was applied with the temperature-dependent nonlinear properties of the frozen soil. The analysis model cases were applied to the MCR and HDP models to simulate the elastoplastic behavior of soil. The numerical analysis results were analyzed and compared with various conditions having different length and width sizes of the pile. The results of the numerical analysis showed t hat t he HDP model was relat ively passive, and t he aspect and magnit ude of t he bearing capacit y and displacement of the pile head were similar depending on the length and width of the pile conditions. The vertical displacement of the pile head by thawing and freezing of the ground showed a large variation in displacement for shorter length conditions. In the MCR model, the vertical displacement appeared in the maximum thaw settlement and frost heaving of 0.0387 and 0.0277 m, respectively. In the HDP model, the vertical displacement appeared in the maximum thaw settlement and frost heaving of 0.0367 and 0.0264 m, respectively. The results of the pile bearing capacity for the two elastoplastic models showed a larger difference in the width condition than the length condition of the pile, with a maximum of about 14.7% for the width L condition, a maximum of about 5.4% for M condition, and a maximum of about 5.3% for S condition. The significance of the effect on the displacement of the pile head and the bearing capacity depended on the pile-soil contact area, and the difference depended on the presence or absence of an active layer in the soil and its thickness.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.288-296
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• 2003

Generally, application of steel pipe pile as deep foundation member needs special requirement for the connection method between steel pipe pile and concrete footing. Even though two types of connection method are suggested in the related specification, type B-method is provident. To investigate real structural behavior of type B connection, several load tests are done with carefully designed experimental system. The purpose of this experiment is mainly focused on the understanding of actual behavior which can be predicted by design theory. At this research stage, vertical and lateral loading test are done for three types of specimen to review stress concentration, formation and behavior of imaginary RC column in the footing and effect of non-slip device installed in the steel pipe pile. The load resistance mechanism in these specific connection method is predicted based on both experimental results. The three-dimensional finite element modeling is also done for the purpose of comparison between numerical and experimental result. With all the results gained from experiment the structural behavior of imaginary RC column in the design concept is confirmed. The role of non-slip device is very important and it affects the resistance capacity with help of composite action of concrete and steel pipe pile.

• Geophysics and Geophysical Exploration
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• v.11 no.2
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• pp.85-92
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• 2008

Magnetotelluric (MT) methods are widely applied as an effective exploration technique to geothermal surveys. Two-dimensional (2-D) analysis is frequently used to investigate a complicated subsurface structure in a geothermal region. A 2-D finite-element method (FEM) is usually applied to the MT analysis, but we must pay attention to the accuracy of so-called auxiliary fields. Rodi (1976) proposed an algorithm of improving the accuracy of auxiliary fields, and named it as the MOM method. Because it introduces zeros into the diagonal elements of coefficient matrix of the FEM total equation, a pivoting procedure applied to the symmetrical band matrix makes the numerical solution far less efficient. The MOM method was devised mainly for the inversion analysis, in which partial derivatives of both electric and magnetic fields with respect to model parameters are required. In the case of forward modeling, however, we do not have to resort to the MOM method; there is no need of modifying the coefficient matrix, and the auxiliary fields can be elicited from the regular FEM solution. The computational efficiency of the MOM method, however, can be greatly improved through a sophisticated rearrangement of the total equation.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.281-290
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• 2005

This paper presents experimental and analytical studies on long-term behavior of square CFT columns under central axial loading. Two loading cases are considered; (1) the load applied only at the inner concrete of the column and (2) the load applied simultaneously on both the concrete and the steel tube. Four specimens of square CFT columns were tested under the two loading cases, and basic creep test for two concrete specimens was performed to find out the creep properties of the inner concrete. Three-dimensional finite element analysis models were established and verified with the experimental results. The verification shows that the prediction for the long-term behavior of actual square CFT columns is possible from the three dimensional finite element modeling considering the bond behavior between steel tube and inner concrete. Also, experimental results and numerical calculations revealed that the bond stress Induced by the confinement pressure as well as the slip between inner concrete and steel tube were increased with time In the first loading case. However, the confinement by the loading Plate was decreased with time while increasing confinement effect by the steel tube was observed over time. In contrast no confinement effects occur in the second loading case.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.3
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• pp.167-174
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• 2021

Recent investigation into the integrity of nuclear containment buildings has highlighted the importance of developing an elaborate diagnostic method to evaluate the distribution and size of cavities inside concrete walls. As part of developing such a method, this paper presents a finite element approach to modeling elastic waves propagating in the containment building walls of a nuclear power plant. We introduce a perfectly matched layer (PML) wave-absorbing boundary to limit the large-scale nuclear containment wall to the region of interest. The formulation results in a semi-discrete form with symmetric damping and stiffness matrices. The transient elastic wave equations for a mixed unsplit-field PML were solved for displacement and stresses in the time domain. Numerical results show that the sensitivity of displacement, velocity, acceleration, and stresses is large depending on the size and location of the cavity. The dynamic response of the wall slightly differs depending on the existence of the containment liner plate. The results of this study can be applied to a full-waveform inversion approach for characterizing cavities inside a containment wall.