Papers by Keyword: Frequency Content

Abstract: Liquid storage tanks are among vital structures widely used in various fields. Estimating the sloshing wave height in storage tanks during seismic events is very important to avoid seismic damage. Despite its importance, only a few studies have addressed the sloshing wave height in storage tanks considering the soil-structure and fluid-structure coupling effects. This paper used finite element numerical simulation method to study the seismic response of rectangular concrete liquid storage tanks. Three aspect ratios, three liquid heights, nine earthquake records with different frequency content, and three different topography conditions were considered. The obtained results indicated that the liquid storage tank models involved in this study were more sensitive to high-frequency earthquake events, and the step-like irregular topography could amplify the sloshing wave height of the storage tanks. Besides, Eurocode 8 underestimated the peak sloshing wave height of the storage tanks when subjected to earthquakes with high-frequency content.

Abstract: Building design codes typically specify seismic forces based on a 5-percent damped elastic design spectrum. To consider the case of structures with damping ratios other than 5%, damping correction factors are used. While these factors are determined for elastic systems, several studies have shown that the effects of damping are different for systems with nonlinear behavior. A study concerning the influence of damping on the nonlinear seismic response of building structures is presented. To separate the influence of nonlinear behavior, spectra of the ratio between the seismic strength demands corresponding to nonlinear and linear behavior, respectively, were computed, for damping ratios ranging between 2% and 10% and various constant ductility values. A database of ground motion records from the three strongest earthquakes that affected Romania during the last four decades was used in the study. The records were grouped into two sets, according to their frequency bandwidth. The spectral values computed for each set were processed statistically and results were expressed with reference to the 5%damped spectra. It was found that, for the analyzed damping range, the influence of this parameter on the nonlinear response is weak to moderate, for both considered types of frequency content.

Abstract: The paper presents the results of a study performed on a large ground motion database, containing records obtained during the three strongest earthquakes that occurred during the past four decades in the Vrancea seismogenic zone. In order to express strength demands imposed by these earthquakes, constant-ductility nonlinear acceleration spectra were computed for two sets of seismic records, selected as representative for narrow frequency band and broad frequency band ground motions, respectively. The spectra, determined for various types of bilinear hysteretic models, were normalized with respect to peak ground acceleration and mean values, as well as coefficients of variation, were computed for each analysis case. The sensitivity of spectral values to the variation of strength hardening and stiffness degradation parameters was determined, with reference to the elastic-perfectly plastic model. Conclusions were drawn, separately for the two distinct types of ground motion frequency content, on the significance of the considered hysteretic model parameters for the assessment of seismic strength demands.

Abstract: Earthquake ground motions were reasonally selected for the nonlinear dynamic time-history analysis conducted for a two-tower long-span cable-stayed bridge. The correlation between frequency content of earthquake ground motions and probabilistic seismic demands reveals that the geometric mean and dispersion of response spectra from earthquake ground motions have significant effects on probabilistic seismic demand assessment of long-span bridge stuctures and these effects are related to the difference of the shape of geometric mean spectra in the important period ranges where cumulative modal mass participation is significant. Response spectra of selected earthquake ground motions should match well with target spectra in the important period ranges. If input ground motions are reasonally selected, analytic results can be obtained more precisely and effectively and more amplitude parameters can be selected as intensity measures.

Abstract: From the perspective of fractal geometry, the irregularity and complexity of near-fault ground motions and seismic responses of single degree of freedom (SDOF) are analyzed. Based on the box-counting method, the fractal dimensions of 30 acceleration time series of near-fault ground motions from Taiwan Chi-Chi earthquake and California Northridge earthquake are calculated. It is indicated that the acceleration time series of ground motions present the statistical fractal property, and the influence of characteristics of near-fault ground motions on their box dimensions is remarkable. Moreover, the box dimensions of ground motions reflect their frequency property to a large extent, and can be regarded as alternative index to represent their frequency content. Finally, for the time histories of seismic dynamic responses of elastic and inelastic SDOF systems subjected to near-fault ground motions, their box dimensions are computed to examine the fractal property.