• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.1
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• pp.43-50
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• 2008

The analysis and results of flexural behavior for steel composite beam with built-up cross-section considering bolt deformation are presented in this paper. The bolt deformation and the restrict effect due to bolt-connection and friction are considered to investigate the flexural behavior of steel composite beam. Nonlinear spring element in ABAQUS is used to consider bolt deformation, also the results are compared with those in case bolt deformations are ignored. The displacement, bending stresses and shear stresses are calculated by F.E. model, and these results are compared with the analytical value of no interaction beam, partial interaction beam and full interaction beam. As a result of analysis, the behavior of composite beam is more dependant on the composite rate than the friction of the steel. When the composite rate is more than 50%, the behavior of composite beam considering the effects of bolt deformation is similar to that of fully composite beam.

• Journal of the Korean GEO-environmental Society
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• v.14 no.4
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• pp.59-66
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• 2013

The foundation of offshore wind energy system is generally assumed to be fixed-ended in system analysis for the convenience of calculation and, correspondingly, it might lead a conservative design. If soil-foundation interaction get involved with the analysis, the system characteristics such as natural frequency, shear force, moment and displacement are expected to differ from those of fixed-ended case. In this study, the analysis have been conducted to identify how the response of offshore wind turbine varies upon considering the foundation flexibility with soil-foundation interaction. The model taking account of the flexibility of foundation was compared with fixed-ended model at the seabed. The flexibilities of foundation were obtained by coupled spring model at the seabed and Winkler Spring Model with soil depth. As a result, the first mode of the whole system with the Winkler Spring Model was decreased relative to that with the fixed-ended model. The results showed that the effect of foundation flexibility should be considered when designing the offshore wind energy system.

• Computers and Concrete
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• v.23 no.1
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• pp.61-68
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• 2019

This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.147-157
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• 2006

This paper represents a numerical study of the flow field due to the interactions between a pair of vortices produced by vortex generators in a rectangular channel flow. In order to analyze longitudinal vortices induced by the vortex generators, the pseudo-compressibility method is introduced into the Reynolds-averaged Navier-Strokes equations of a 3-dimensional unsteady, incompressible viscous flow. A two-layer $k-{\epsilon}$ turbulence model is applied to a flat plate 3-dimensional turbulence boundary to predict the flow structure and turbulence characteristics of the vortices. The computational results predict accurately the vortex characteristics related to the flow field, the Reynolds shear stresses and turbulent kinetic energy. Also, in the prediction of skin friction characteristics the computational results are reasonably close to those of the experiment obtained from other researchers.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2879-2884
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• 2007

Dynamic responses of electrorheological (ER) fluids in steady pressure flow to stepwise electric field excitations are investigated experimentally. The transient periods under various applied electric fields and flow velocities were determined from the pressure behavior of the ER fluid in the flow channel with two parallel-plate electrodes. The pressure response times were exponentially decreased with the increase of the flow velocity, but increased with the increase of the applied electric field strength. In order to investigate the cluster structure formation of the ER particles, it was verified using the flow visualization technique that the transient response of ER fluids in the flow mode is assigned to the densification process in the competition of the electric field-induced particle attractive interaction forces and the hydrodynamic forces, unlike that in the shear mode determined by the aggregation process.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.513-520
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• 2003

A numerical comparison or predictions by limit equilibrium analysis and 3n analysis is presented for slope/pile system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a pile-reinforced slope according to shear strength reduction technique. The case of coupled analyses was performed for stabilizing piles in slope in which the pile response and slope stability are considered simultaneously and subsequently the factors of safety are compared to uncoupled analysis (limit equilibrium analysis) solution for a homogeneous slope. Based on a limited parametric study, it is shown that in the free-head condition the factor of safety in slope is more conservative for a coupled analysis than for an uncoupled analysis and a definitely larger value represents when piles are installed in the middle of the slopes and are restrained in the pile head.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.2
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• pp.63-71
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• 1992

A solution method is developed for computing the bed shear stress driven by combined wave and current flow on a natural mobile coastal beach. An empirical equation is introduced to determine the shape of ripples formed on the natural sandy beach. The model being based on the Prandtl's mixing length theory, the effect of arbitrarily-angled interaction is included in the estimation of current velocity reduction and all numerical integrations are expressed by explicit approximate equations to improve the computation speed. In addition the computed sediment transport rates were compared with the measured values reported in literature. using the refined bottom friction model considering the ripple formation.

• Interaction and multiscale mechanics
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• v.6 no.3
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• pp.301-316
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• 2013

The influence of indenter geometry on nanoindentation was studied using a static molecular dynamics simulation. Dislocation nucleation, dislocation locks, and dislocation movements during nanoindentation into Al (001) were studied. Spherical, rectangular, and Berkovich indenters were modeled to study the material behaviors and dislocation activities induced by their different shapes. We found that the elastic responses for the three cases agreed well with those predicted from elastic contact theory. Complicated stress fields were generated by the rectangular and Berkovich indenters, leading to a few uncommon nucleation and dislocation processes. The calculated mean critical resolved shear stresses for the Berkovich and rectangular indenters were lower than the theoretical strength. In the Berkovich indenter case, an amorphous region was observed directly below the indenter tip. In the rectangular indenter case, we observed that some dislocation loops nucleated on the plane. Furthermore, a prismatic loop originating from inside the material glided upward to create a mesa on the indenting surface. We observed an unusual softening phenomenon in the rectangular indenter case and proposed that heterogeneously nucleating dislocations are responsible for this.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.71-71
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• 2012

Chemically modified graphene has been great interest for the application of printed electronics using solution prossesable technique. Here, we demonstrate a large area graphene exfoliation method with fewer defects on the basal plane by application of shear stress in solution to obtain high quality reduced graphene oxide (RGO). Moreover, we introduce a novel route to preparing highly concentrated and conductive RGO in various solvents by monovalent cation-${\pi}$ interaction. Noncovalent binding forces can be induced between a monopole (cation) and a quadrupole (aromatic ${\pi}$ system). The stability of this RGO dispersion was more sensitive to the strength of the cation-${\pi}$ interactions than to the cation-oxygen functional group interactions. The RGO film prepared without a post-annealing process displayed superior electrical conductivity of 97,500 S/m. Our strategy can facilitate the development of large scalable production methods for preparing printed electronics made from high-quality RGO nanosheets.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.04a
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• pp.73-81
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• 1995

In Korea, the pilot construction of the first high-speed railroad on the Seoul-Pusan has already started 2 years ago. In the thesis, an attempt is made to develop reliability-based integrity-assessment models for the computer-aided control and maintenance of high-speed railroad bridges. The strength limit state models for PC railroad bridges encompass the bending and shear strengths as well as the strength interaction equations which simultaneously take into the element and system reliablities of the proposed limit states and reliability models. Then, the actual load carrying capacity and the realistic safety of bridges are evaluated using the system reliability-based equivalent strength, and the results are compared with those of the element reliability-based or conventional methods. Various parametric studies are performed for the proposed reliability-based safety and integrity-assessment models using the actual PC box girder bridges used in the pilot construction. And the sensitivity analyses are performed for the basic random variables included in strength limit state models. It is concluded that proposed models may be practically applied for the rational assessment of safety and integrity of high speed railroad bridges.