• Earthquakes and Structures
• /
• 제8권1호
• /
• pp.185-204
• /
• 2015

This study investigates the impact of the earthquake incident angle on the structural demand and the influence of ground motion selection and scaling methods on seismic directionality effects. The structural demand produced by Non-Linear Time-History Analyses (NLTHA) varies with the seismic input incidence angle. The seismic directionality effects are evaluated by subjecting four three-dimensional reinforced concrete structures to different scaled and un-scaled records oriented along nine incidence angles, whose values range between 0 and 180 degrees, with an increment of 22.5 degrees. The results show that NLTHAs performed applying the ground motion records along the principal axes underestimate the structural demand prediction, especially when plan-irregular structures are analyzed. The ground motion records generate the highest demand when applied along the lowest strength structural direction and a high energy content of the records increases the structural demand corresponding to this direction. The seismic directionality impact on structural demand is particularly important for irregular buildings subjected to un-scaled accelerograms. However, the orientation effects are much lower if spectrum-compatible combinations of scaled records are used. In both cases, irregular structures should be analyzed first with pushover analyses in order to identify the weaker structural directions and then with NLTHAs for different incidence angles.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2003년도 봄 학술발표회 논문집
• /
• pp.243-249
• /
• 2003

The characteristics of harmonic phase angles and phase angle differences contained in earthquake ground motions such as El Centre 1530 NS, Taftl 1952 NS, Hachinohe 1968 NS and Mexico 1985 are figured, which have been mostly overlooked in contrast with the importance placed on harmonic amplitudes. And, energy input spectrum of structures excited by such an earthquake motion is expressed with smoothed Fourier amplitude spectrum. In dynamic response analysis, there must be earthquake ground accelerations which contain the phase angle, the phase angle difference and energy input spectrum characteristics of the zone considered to be constructed building structures. To make clear the importance of phase angle differences, 4-earthquake ground motions are normalized by 200 gal and energy input spectrum characteristics of normalized 4-earthquake ground motions are compared.

• 한국안전학회지
• /
• 제23권2호
• /
• pp.7-13
• /
• 2008

In a long-span bridge which is constructed on soft soil, it is requested to make a plan considering soil-structure interaction, and soil-structure interaction is partially under consideration at the actual bridge plan. Many researches on dynamic behavior of a bridge affected by soil-structure interacting have been accomplished, but it is difficult to estimate dynamic behavior of a bridge on soft soil accurately because of many uncertainties. This paper presents the results about dynamic response of a long-span suspension bridge in the site composed of soft soil considering incident angle of input ground motion. The effect of soft soil was evaluated by the use o computer program SASSI and a long-span suspension bridge was modeled by finite element program MIDAS. The effect of incident angle of input ground motion was investigated on the dynamic response of a long-span bridge.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
• /
• pp.97-104
• /
• 2000

Evaluating a Review-Level Ground Motion is a key to efficiently perform Seismic Margin Assessment of nuclear power plants whose purpose is to determine a ground motion level for which a plant has high-confidence-of-a-low-probability of seismic-induced core damage and to identify any weaker-link components. In this study a method to obtain RLGMs is reviewed which is recommended by Electric Power Research Institute and implemented to be applied to Limerick site in eastern and central U. S as a case study. This method provides reasonable and site-specific RLGMs as minimum required plant HCLPF for SMA that meet a target mean seismic core-damage frequency based on seismic hazard results and generic values of uncertainty and randomness parameters of the core-damage fragility curves. In addition high-frequency RLGM is justifiably modified to reflect the increased seismic capacity of high-frequency components and spatial variation and incoherence of input ground motion on a basemat of large structures by establishing a method to obtain high0-frequency reduction factors according to EPRI guidelines.

• Geomechanics and Engineering
• /
• 제7권2호
• /
• pp.149-164
• /
• 2014

One of the most advanced classes of techniques for ground response analysis is based on the use of Transfer Functions. They represent the ratio of Fourier spectrum of amplitude motion at the free surface to the corresponding spectrum of the bedrock motion and they are applied in frequency domain usually by FFT method. However, Fourier spectrum only shows the dominant frequency in each time step and is unable to represent all frequency contents in every time step and this drawback leads to inaccurate results. In this research, this process is optimized by decomposing the input motion into different frequency sub-bands using Wavelet Multi-level Decomposition. Each component is then processed with transfer Function relating to the corresponding component frequency. Taking inverse FFT from all components, the ground motion can be recovered by summing up the results. The nonlinear behavior is approximated using an iterative procedure with nonlinear soil properties. The results of this procedure show better accuracy with respect to field observations than does the Conventional method. The proposed method can also be applied to other engineering disciplines with similar procedure.

• 한국지진공학회논문집
• /
• 제24권2호
• /
• pp.59-65
• /
• 2020

The empirical Green's function method is applied to the foreshock and the mainshock of the 2016 Gyeongju earthquake to simulate strong ground motions of the mainshock and scenario earthquake at seismic stations of seven metropolises in South Korea, respectively. To identify the applicability of the method in advance, the mainshock is simulated, assuming the foreshock as the empirical Green's function. As a result of the simulation, the overall shape, the amplitude of PGA, and the duration and response spectra of the simulated seismic waveforms are similar with those of the observed seismic waveforms. Based on this result, a scenario earthquake on the causative fault of Gyeongju earthquake with a moment magnitude 6.5 is simulated, assuming that the mainshock serves as the empirical Green's function. As a result, the amplitude of PGA and the duration of simulated seismic waveforms are significantly increased and extended, and the spectral amplitude of the low frequency band is relatively increased compared with that of the high frequency band. If the empirical Green's function method is applied to several recent well-recorded moderate earthquakes, the simulated seismic waveforms can be used as not only input data for developing ground motion prediction equations, but also input data for creating the design response spectra of major facilities in South Korea.

• 한국지진공학회논문집
• /
• 제25권2호
• /
• pp.59-69
• /
• 2021

Historical records of earthquakes are generally used as a basis to extrapolate the instrumental earthquake catalog in time and space during the probabilistic seismic hazard analysis (PSHA). However, the historical catalogs' input parameters determined through historical descriptions rather than any quantitative measurements are accompanied by considerable uncertainty in PSHA. Therefore, quantitative assessment to verify the historical earthquake parameters is essential for refining the reliability of PSHA. This study presents an approach and its application to constrain reliable ranges of the magnitude and corresponding epicenter of historical earthquakes. First, ranges rather than specific values of ground motion intensities are estimated at multiple locations with distances between each other for selected historical earthquakes by reviewing observed co-seismic natural phenomena, structural damage levels, or felt areas described in their historical records. Based on specific objective criteria, this study selects only one earthquake (July 24, 1643), which is potentially one of the largest historical earthquakes. Then, ground motion simulations are performed for sufficiently broadly distributed epicenters, with a regular grid to prevent one from relying on strong assumptions. Calculated peak ground accelerations and velocities in areas with the historical descriptions on corresponding earthquakes are converted to intensities with an empirical ground motion-intensity conversion equation to compare them with historical descriptions. For the ground motion simulation, ground motion prediction equations and a frequency-wavenumber method are used to consider the effects of possible source mechanisms and stress drop. From these quantitative calculations, reliable ranges of epicenters and magnitudes and the trade-off between them are inferred for the earthquake that can conservatively match the upper and lower boundaries of intensity values from historical descriptions.

• Earthquakes and Structures
• /
• 제23권2호
• /
• pp.115-128
• /
• 2022

One common method to select input ground motions to predict dynamic behavior of structures subjected to seismic excitation requires spectral acceleration (S_a) match target mean response spectrum. However, dispersion of ground motions, which explicitly affects the structural response, is rarely discussed in this method. Generally, selecting ground motions matching target mean and variance has been utilized as an appropriate method to predict reliable seismic response. The goal of this paper is to investigate the impact of target spectra variance of ground motions on structural seismic response. Two sets of ground motions with different target variances (zero variance and minimum variance larger than inherent variance of the target spectrum) are selected as input to two different structures. Structural responses at different heights are compared, in terms of peak, mean and dispersion. Results show that increase of target spectra variance tends to increase peak floor acceleration, peak deformation and dispersions of response of interest remarkably. To short-period structures, dispersion increase ratios of seismic response are close to that of S_a of input ground motions at the first period. To long-period structures, dispersions of floor acceleration and floor response spectra increase more significantly at the bottom, while dispersion increase ratios of IDR and deformation are close to that of S_a of input ground motions at the first period. This study could further provide useful information on selecting appropriate ground motion to predict seismic behavior of different types of structures.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2007년 가을학술발표회
• /
• pp.305-316
• /
• 2007

Free field ground motion during earthquake is significantly affected by the local soil conditions and it is essential for the seismic design to perform the site specific ground response analysis. So, Round Robin Test (RRT) on ground response analysis was performed for three sites in Korea. A total of 12 teams presented the results of ground response analysis with used input soil properties based on own judgement. In this paper, the results of one dimensional equivalent linear analysis presented by 11 teams were compared to evaluate the effect of input soil properties on ground response analysis. Additionally, 4 influence factors on ground response analysis, that is shear wave velocity of soil layer, nonlinear dynamic deformational characteristics, bedrock depth and bedrock velocity were studied for assumed simple soil conditions.

• Structural Monitoring and Maintenance
• /
• 제6권4호
• /
• pp.347-364
• /
• 2019

Two seismic response data from the CSMIP strong motion instrumentation of Pacoima dam are selected: San Fernando earthquake (Jan 13, 2001; ML=4.3) and Newhall earthquake (Sept. 1, 2011; ML=4.2), for the identification of the dam system. To consider the spatially nonuniform input ground motion along the dam abutment, the subspace identification technique with multiple-input and multiple-output is used to extract the dynamic behavior of the dam-reservoir interaction system. It is observed that the dam-reservoir interaction is significant from the identification of San Fernando earthquake data. The influence of added mass (from the reservoir) during strong ground motion will create a tuned-mass damper phenomenon on the dam body. The fundamental frequency of the dam will be tuned to two different frequencies but with the same mode shapes. As for the small earthquake event, the dam-reservoir interaction is insignificant.