• Journal of the Korean Geotechnical Society
• /
• v.31 no.4
• /
• pp.57-66
• /
• 2015

Empirical seismic displacement equations based on the Newmark sliding block method are widely used to develop seismic landslide hazard map. Most proposed equations have been developed for embankments and landfills, and do not consider the dynamic response of sliding block. Therefore, they cannot be applied to Korean mountain slopes composed of thin, uniform soil-layer underlain by an inclined bedrock parallel to the slope. In this paper, a series of two-dimensional dynamic nonlinear finite difference analyses were performed to estimate the permanent seismic slope displacement. The seismic displacement of mountain slopes was calculated using the Newmark method and the equivalent acceleration time history. The calculated seismic displacements of the mountain slopes were compared to a widely used empirical displacement model. We show that the displacement prediction is significantly enhanced if the slope is modeled as a flexible sliding mass and the amplification characteristics are accounted for. Regression equation, which uses PGA, PGV, Arias intensity of the ground motion and the fundamental period of soil layer, is shown to provide a reliable estimate of the sliding displacement. Furthermore, the empirical equation is shown to reliably predict the hazard category.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.9
• /
• pp.5-12
• /
• 2021

Pseudo-static slope stability analysis method is widely used in engineering practice to calculate the seismic factor of safety of slope subjected to earthquake ground motions. Although the dynamic analysis method is well recognized to have the primary advantage of simulating the stress-strain response of soils, it is not often used in practice because of the difficult in estimating the factor of safety. In this study, a procedure which utilizes the dynamic analysis method to extract the transient dynamic factor of safety is devleoped. This method overcomes the major limitation of the pseudo-static method, which uses an empirically determined seismic coefficient to derive the factor of safety. The proposed method is applied to a slope model and the result is compared with that of the pseudo-static method. It is shown that minimum dynamic factor of safety calculated by the dynamic analysis is slightly larger than that determined from the pseudo-static method. It is also demonstrated that the dynamic factor of safety becomes minimum when the horizontal seismic coefficient and horizontal average acceleration are maximum.

• Tunnel and Underground Space
• /
• v.24 no.5
• /
• pp.354-365
• /
• 2014

The horizontal response spectra using the observed ground motions from 15 Fukuoka earthquake series, including main earthquake (2005/03/20; Mw=6.5), were analysed and then were compared to both the seismic design response spectra (Regulatory Guide 1.60), applied to the domestic nuclear power plants, and the Korean Standard Design Response Spectrum for general structures and buildings (1997). 178 horizontal ground motions, without considering soil types, were used for normalization with respect to the peak acceleration value of each ground motion. The results showed that response spectrum have strong dependency on epicentral distance. The results also showed that the horizontal response spectra revealed higher values for frequency bands at two frequency bands (about 8 - 10 and 16- 20 Hz) than Regulatory Guide 1.60. The results were also compared to the Korean Standard Building Design Spectrum for the 3 different soil types and showed that thehorizontal response spectra revealed higher values for almost all period bands than the Korean Standard Response Spectrum (500 yrs; Return Period; Seismic province 1; SE soil conditions). Through the qualitative improvements and quantitative enhancement of the observed ground motions, the diversity of the observed ground motions should be considered more significantly to improve the certainty of response spectrum.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.12
• /
• pp.301-306
• /
• 2016

In bridge performance assessments, a new load carrying capacity evaluation model of simple bridges was proposed, which is based on the developed simple support impact factor spectrum. In this paper, a conservative assumption that the inner span with the both ends fixed boundary condition is ideal for applying the impact factor response spectrum for continuous bridges. The impact factor response spectrum has been proposed based on this assumption. The response spectrum by comparing the numerical analysis result and actual measurement data verified the applicability. The analysis was loading the moving load of DB-24 in a six-span continuous bridge, which was the same as the actual measurement data, the dynamic response was measured in the fourth span. The frequency of the bridge was obtained by FFT on the acceleration response and the span-frequency of sample bridge was calculated by the frequency. The impact factor of the sample bridge was determined by applying the span-frequency of the bridge to the proposed response spectrum; it was similar to the result of comparing the actual measured impact factor. Therefore, the method using the impact factor response spectrum based on the frequency response of both ends-fixed beam was found to be applicable to an actual continuous bridge.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.4
• /
• pp.55-61
• /
• 2010

This paper is concerned with an experimental research to random vibration control caused by external loads specially in bridges which tend to be structurally flexible. Experimenting on a reduced structure modelled on Seohae Grand Bridge, we inflicted a reduced form of El-centro wave on the model structure to a proper proportion. On the center of its middle span, we placed a shear type MR damper which was to control its vibration and also acquire its structural responses such as displacement and acceleration at the same site. The experiments concerning controlling vibration were performed according to a variety of theories including un-control, passive on/off control, and Lyapunov stability theory. Its control performance was evaluated in terms of the peak absolute displacements, the peak absolute accelerations and the total power required to control the bridge which differ from each different experiment method. Among all the methods applied in this paper, case of Lyapunov control method turned out to be the most effective to reduces of displacement and acceleration. Also, this method could to decrease consuming of external power for vibration control. Finally, it was noteworthy that Lyapunov control method was specially effective in the vibration control employing a semi-active damper such MR damper.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.15 no.1
• /
• pp.85-94
• /
• 2011

This paper is concerned to constitute a semi-active realtime feedback vibration control system and evaluate it through experiments in order to control in realtime the vibration externally generated, specially on the bridges which is structurally flexible. For the experiment of vibration control, we built a model bridge structure of Seohae Grand Bridge in a 1/200 reduced form and inflicted El-centro wave on the model structure also in a reduced force considering the lab condition. The externally excited vibration was to be controled by placing a shear type MR damper vertically on the center of bridge span, and the response (displacement and acceleration) of structure was to be acquired by placing LVDT and Accelerometer at the same time. As for the experiment concerning controlling vibration, a realtime feedback vibration control experiments were performed under each different condition largely such as un-control, passive on/off control, Lyapunov stability theory control, and Clipped-optimal control. Its control performance under different condition was quantitatively evaluated in terms of the peak absolute displacements, the peak absolute accelerations and the power required for control on the center of span. The results of experiments proved that the Lyapunov control and clipped-iptimal control were effective to decrease the displacement and acceleration of the structure, and also to decrease the power consumption to a great extent. Finally, the semi-active realtime feedback vibration control system constituted in this research was proven to be an effective way to control and manage the vibration generated on bridge structure.

• Journal of Korean Association for Spatial Structures
• /
• v.9 no.1
• /
• pp.87-94
• /
• 2009

This paper presents dynamic behavior of double-layer barrelvault systems subjected to earthquake loadings. In order to investigate different seismic behaviors according to Time History Analysis (THA), six open angles were employed and different fundamental frequencies corresponding to each open angle were considered. A total of 24 double-layer structures were developed by using Midas Gen., which is a computer analysis program and then THA with three different earthquakes with 5% damping ratio was performed. This study investigated the characteristics of the dynamic response for X-, Y- and Z- directions, both subjected to the horizontal earthquake (H) and applied to the vertical earthquake (V) with respect to the each variable, which assumed to be important aspects for spatial structure. In order to examine the dynamic characteristics, the ratio of acceleration in specific nodes of barrelvaults was evaluated at the time with maximum response. The main purpose of this study is to obtain equations of the equivalent earthquake loading with respect to the barrelvault systems.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.10 no.2
• /
• pp.59-67
• /
• 2006

The aim of this study is to evaluate the design table for envelope curve analysis of base isolated buildings, which represent the period of base isolated buildings and the lateral displacement of base isolation devices. For the construction of design table, $V_E$ spectrum, which represents the energy, is developed instead of acceleration of seismic hazard. Based on the seismic coefficient of UBC 97, boundary period $T_G$ and maximum velocity response $V_0$ are proposed considering Korea seismic hazard. Using $T_G$ and $V_0$, finally, $V_E$ spectrum is developed for the four types of soil conditions. Base on the $V_E$ spectrum, design table for envelope curve analysis is also developed for soil types.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.3
• /
• pp.13-23
• /
• 2008

In a nonlinear site response analysis which is performed in time domain, small strain damping is modeled as viscous damping through use of various forms of Rayleigh damping formulations. Small strain damping of soil is known to be independent of the loading frequency, but the viscous damping is greatly influenced by the loading frequency. The type of Rayleigh damping formulation has a pronounced influence on the dependence. This paper performs a series of nonlinear analyses to evaluate the degree of influence of the viscous damping formulation on Korean soil profiles. Analyses highlight the strong influence of the viscous damping formulation for soil profiles exceeding 30 m in thickness, commonly used in simplified Rayleigh damping formulation overestimating energy dissipation at high frequencies due to artificially introduced damping. When using the full Rayleigh damping formulation and carefully selecting the optimum modes, the artificial damping is greatly reduced. Results are further compared to equivalent linear analyses. The equivalent linear analyses can overestimate the peak ground acceleration even for shallow profiles less than 20 m in thickness.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.1 no.1
• /
• pp.31-39
• /
• 1997

This paper is on the vibration control of access floor on the frames of reinforced structure. In this study, the horizontal anti-vibration system using precise spring damper was developed and modeling and vibration analysis of the RC structure was performed for the control of horizontal vibration coused by machinery and worker's moving. Experiment was done in three cases, no damper at the RC structures, dampers connecting pedestal to pedestal and pedestal to the structure, for the investigation of the effect of the system on disigned RC structure. For each experiment, the occeleration responses on slab and access floor after giving impact wave and external vibration were measured. It was shown that the magnitude of resonance response of the system with dampers are smaller than without damper and the resonance peak also partly moved to low-frequency range. Furthermore. It was shown that the acceleration components of the system with domoers decreased greatly in high-frequency range and the system was very much effective especially for external vibration. In order to verify the anti-vibration effect of the developed system, the vibration analysis was also done for the system by using the finite element modelling. The analysis results was in good agreement with experimental results. Thus, It is concluded that this study is useful for the design of precise anti-vibration system and micro-vibration control of concrete structures.