• Journal of the Korean Society for Railway
• /
• v.3 no.2
• /
• pp.51-61
• /
• 2000

In this study, field measurements of vibration on the structures supporting railroad track were performed. The vibration data obtained were analyzed to find out any correlation between its magnitude and several factors such as type of bridges, distance from the track, type of train, frequency characteristics, etc. As a result, the magnitude of vibration turned out to be the highest in the steel bridge, the concrete bridge and steel-concrete combined bridge were the next in descending order. It was also found that the dynamic characteristics of ground were the most important factors among several affecting vibration near by the railroad track. And the empirical ground vibration estimation equation for estimating ground vibration was developed. The proposed equation with respect to distances from the railroad could be easily used for the estimation of ground vibration at the residential areas nearby the track.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.03a
• /
• pp.164-178
• /
• 2009

The importance of long-term performance of reinforced earth structures has been gaining its attention as the use of reinforced earth structures as load supporting structures is increasing. When using reinforced earth structures as loading supporting structures the stability as well as serviceability requirements must be met. In that respect the time-dependent long term deformation characteristics should be well understood. In this study the applicability of power law-based creep models for modeling of creep deformation of the components of reinforced earth structures are examined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.05a
• /
• pp.859-865
• /
• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.

• Earthquakes and Structures
• /
• v.5 no.1
• /
• pp.49-65
• /
• 2013

This article presents the statistical characteristics of elastic floor acceleration spectra that represent the peak response demand of non-structural components attached to a nonlinear supporting frame. For this purpose, a set of stiff and flexible general moment resisting frames with periods of 0.3-3.6 sec. are analyzed using forty-nine near-field strong ground motion records. Peak accelerations are derived for each single degree of freedom non-structural component, supported by the above mentioned frames, through a direct-integration time-history analysis. These accelerations are obtained by Floor Acceleration Response Spectrum (FARS) method. They are statistically analyzed in the next step to achieve a better understanding of their height-wise distributions. The factors that affect FARS values are found in the relevant state of the art. Here, they are summarized to evaluate the amplification and/or reduction of FARS values especially when the supporting structures undergo inelastic behavior. The properties of FARS values are studied in three regions: long-period, fundamental-period and short-period. Maximum elastic acceleration response of non-structural component, mounted on inelastic frames, depends on the following factors: inelasticity intensity and modal periods of supporting structure; natural period, damping ratio and location of non-structural component. The FARS values, corresponded to the modal periods of supporting structure, are strongly reduced beyond elastic domain. However, they could be amplified in the transferring period domain between the mentioned modal periods. In the next step, the amplification and/or reduction of FARS values, caused by inelastic behavior of supporting structure, are calculated. A parameter called the response acceleration reduction factor ($R_{acc}$), has been previously used for far-field earthquakes. The feasibility of extending this parameter for near-field motions is focused here, suggested repeatedly in the relevant sources. The nonlinearity of supporting structure is included in ($R_{acc}$) for better estimation of maximum non-structural component absolute acceleration demand, which is ordinarily neglected in the seismic design provisions.

• Earthquakes and Structures
• /
• v.4 no.1
• /
• pp.109-132
• /
• 2013

Current codes incorporate simplified methods for the prediction of acceleration demands on secondary structural and non-structural elements at different levels of a building. While the use of simple analysis methods should be advocated, damage to both secondary structural and non-structural elements in recent earthquakes have highlighted the need for improved design procedures for such elements. In order to take a step towards the formation of accurate but simplified methods of predicting floor spectra, this work examines the floor spectra on elastic and inelastic single-degree of freedom systems subject to accelerograms of varying seismic intensity. After identifying the factors that appear to affect the shape and intensity of acceleration demands on secondary structural and non-structural elements, a new series of calibrated equations are proposed to predict floor spectra on single degree of freedom supporting structures. The approach uses concepts of dynamics and inelasticity to define the shape and intensity of the floor spectra at different levels of damping. The results of non-linear time-history analyses of a series of single-degree of freedom supporting structures indicate that the new methodology is very promising. Future research will aim to extend the methodology to multi-degree of freedom supporting structures and run additional verification studies.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.6
• /
• pp.553-561
• /
• 2009

Risk analysis of highway sign supporting structures and sound barriers was done. Stochastic wind load was modeled by using extreme value distribution from site measurement and the variability of structural parameters was considered. Limit state functions were defined to assess structural stability by wind and risk of highway facilities was analyzed by combining wind hazard. According to the numerical analysis results, sound barrier post shows significantly higher risk than highway sign supporting structures. This is caused by the fact that the design codes of the structures are different. To distribute wind induced risk in highway structures, unification and improvement of design codes are required based on risk assessment.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.4
• /
• pp.319-327
• /
• 2017

In this study, characteristics of seismic behaviors of offshore wind turbine systems using concrete-suction-type supporting structures are investigated. Applying hydrodynamic pressure from the surrounding sea water and interaction forces from the underlying soil to the structural system which is composed of RNA, the tower, and the supporting structure, a governing equation of the system is derived and its earthquake responses are obtained. It can be observed from the analysis results that the responses are significantly influenced by soil-structure interaction because dynamic responses for higher natural vibration modes are increased due to the flexibility of soil. Therefore, the soil-structure interaction must be taken into consideration for accurate assessment of dynamic behaviors of offshore wind turbine systems using concrete-suction-type supporting structures.

• Wind and Structures
• /
• v.34 no.3
• /
• pp.291-301
• /
• 2022

Although mostly used in wind turbine market, single rotor wind turbines have problems with transportation and installation costs due to their large size. In order to solve such problems, multi-rotor wind turbine is being proposed; however, light weight design of multi-rotor wind turbine is required considering the installation at offshore or deep sea. This study proposes the systematic design process of the multi-rotor wind turbine focused on its supporting structure with simultaneous consideration of static and dynamic behaviors in an ideal situation. 2D and successive 3D topology optimization process based on the density method were applied to minimize the compliance of supporting structure. To realize the conceptual design obtained by topology optimization for manufacturing feasibility, the derived 3D structure was modified to have shell structures and optimized again through parametric design using the design of experiments and the response surface method for detail design of their thicknesses and radii. The resultant structure was determined to satisfy the stress and the buckling load constraint as well as to minimize the weight and the resultant supporting structure were verified numerically.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1185-1191
• /
• 2000

In general, the strength of hull structures can be estimated from stress evaluation considering static and hydro-dynamic load due to sea-wave. However, war ships such as submarine, have frequently experienced the underwater explosion and local structures of ship as well as hull girder can be damaged by the dynamic response excited from underwater non-contact explosion. When explosion happens at underwater, shock wave is radiated In early short time, then gas bubbles are generated, and expansion and contraction are repeated as they float to the surface. The shock wave causes the damage of equipment and its supporting structures, on the other hand, the hull girder strength can be lost by resonance between bubble pulsation and lowest ship natural vibration period. In this paper, the hydro-Impulse force due to bubble was calculated. Based on these results the hull girder strength of submarine was estimated from transient response analysis by using NASTRAN. Also, shock analysis for some equipment supporting structures was carried out by using DDAM. In order to evaluate the strength of these local structures due to shock wave.

• Earthquakes and Structures
• /
• v.7 no.3
• /
• pp.349-365
• /
• 2014

The dynamic response of structures under extremely short duration dynamic loads is of great concern nowadays. This paper investigates structures' response as well as the associated structural damage to explosive loads considering and ignoring the supporting soil flexibility effect. In the analysis, buildings are modeled by two alternate approaches namely, (1) building with fixed supports, (2) building with supports accounting for soil-flexibility. A lumped parameter model with spring-dashpot elements is incorporated at the base of the building model to simulate the horizontal and rotational movements of supporting soil. The soil flexibility for various shear wave velocities has been considered in the investigation. In addition, the influence of variation of lateral natural periods of building models on the obtained response and peak response time-histories besides damage indices has also been investigated under blast loads with different peak over static pressures. The Dynamic response is obtained by solving the governing equations of motion of the considered building model using a developed Matlab code based on the finite element toolbox CALFEM. The predicted results expressed in time-domain by the building model incorporating SSI effect are compared with the corresponding model results ignoring soil flexibility effect. The results show that the effect of surrounding soil medium leads to significant changes in the obtained dynamic response of the considered systems and hence cannot be simply ignored in damage assessment and response time-histories of structures where it increases response and amplifies damage of structures subjected to blast loads. Moreover, the numerical results provide an understanding of level of damage of structure through the computed damage indices.