Journal of Seismology and Earthquake Engineering
Volume:17 Issue: 2, Summer 2015

Recent advances made in forecasting Earthquakes using clustering analysis techniques are being run by numerical simulations. In this paper, the Gaussian Copula clustering technique is used to obtain Earthquake patterns such as the Doughnut Earthquake pattern to better predict medium and large events. Copulas methods can involve recognizing precursory seismic patterns before a large earthquake within a specific region occurs. The observed data represent seismic activities situated around IRAN in the 1980-2014 time intervals. This technique is based on applying cluster analysis of earthquake patterns to observe and synthetic seismic catalog. Earthquakes are first classified into different clusters, and then, patterns are discovered before large earthquakes via Copulas simulation. The results of the experiments show that recognition rates achieved within this system are much higher than those achieved only during the feature map is used on the seismic silence and the Doughnut pattern before large earthquakes.

This paper presents the results of a numerical parametric study on the seismic behavior of 2D triangular-shaped valleys subjected to vertically propagating incident SV waves. The medium is assumed to have a linear elastic constitutive behavior. All calculations are executed in time-domain utilizing the spectral finite element method. Clear perspectives of the amplification patterns of the valley are presented by investigation of the frequency-domain responses. It is shown that the amplification pattern of the valley and its frequency characteristics depend strongly on its shape ratio. The maximum amplification ratio along the ground surface occurs at the centre of the valley. A simple formula has been proposed for making initial estimation of the natural period of the valley in site effect microzonation studies. The natural frequency of the alluvial valley decreases as the shape ratio of the valley decreases; moreover, the value of the natural frequency of the triangular alluvial valley is bigger than the natural frequency of the corresponding rectangular alluvial valley.

In the field of soil-structure interaction (SSI), kinematic interaction (KI) can potentially be a source of notable influence on dynamic response. Such influence takes place through alternation in free field motion (FFM) and results in new foundation input motions (FIM). In this paper, first, the effect of KI on horizontal input motion for the case of single rigid strip embedded foundation with incomplete contact between sidewall and nearby soil under vertical propagation of shear waves is investigated. Then, it is discussed that how this input-change would be reflected in peak horizontal input acceleration (PHIA). Results for different embedment depths and various soil-wall contact lengths are depicted. In this research, numerical analysis was conducted by ABAQUS finite element software. It is shown that the effects of kinematic interaction are significant for high frequencies of excitation. Besides, it is illustrated that foundation shape and its contact area to surrounding soil alter the PHIA usually conservatively with some exceptions in the case of zero contact lengths.

The first objective of this paper is to consider asymmetric location of braces in steel structures. For this purpose, eccentricity effect of the center of stiffness toward the center of mass and the torsion caused by that is considered. For that, a building, which has been constructed in the past, is investigated by changing the arrangement of braces and the amount of steel consumption, as an important economic indicator, is considered in each items. Then the displacement parameter, which is the suitable criterion for detection of structural damages, was evaluated. Finally, changes of base shear toward eccentricity are examined. It is shown that with closing the center of mass and stiffness and reducing the eccentricity using the appropriate location of braces, how much base shear and structure weight (steel consumption) is reduced. Then, the sensitivity of the asymmetric structure under torsion to analysis type is investigated. For this purpose, two types of analysis included pseudo-static and dynamic spectral analysis are studied. As well, in the second objective, the effect of considering the accidental eccentricity is evaluated in designing phase of buildings. For this purpose, two asymmetric structures in plan are designed with and without considering the accidental eccentricity (ea) equal to 5%. Whereas according to Iranian Seismic Code No. 2800, considering ea is not necessary for the structures. These structures are analyzed by nonlinear time history and results indicate that ea can reduce the response of structure considerably.

Liquefaction is one of the most essential causes of failure of transportation infrastructures, especially the road and railroad based on saturated fine sand substrates under seismic conditions. Meanwhile, applying stone columns in a group form is considered as a method to control this phenomenon. To do so, Model No (1) of VELACS project, including NEVADA sand with relative density of %40, was first evaluated numerically using FLAC3D, in which finite difference and sufficiency of Finn constitutive model in liquefaction simulation was shown. Then, sensitivity analysis was performed to examine its radius and depth of influence on reducing excess pore water pressure by imposing a stone column in the center of the model and changing its diameter. In the final step, sensitivity analysis was performed on their efficiency to control liquefaction by simulating the group stone column with square layout and changing diameter of columns and their center-to-center distance. The results of numerical analyses show that the performance of the single stone column increases in reducing excess pore water pressure by increasing depth. Generally, it can be stated that at the depth of 1.25 m and 2.5 m the effective area of the column is 3 and 4 times bigger than the stone column diameter. Columns distance proportion to stone columns diameter (s/d= 2, 3, 4, 5) was evaluated for the group stage. Moreover, the single manner in the group forms more effective than a single column. The group performance of columns appeared to be better than the singular ones.

Recent seismic codes include design requirements in order to take soil-structure interaction (SSI) into account for realistic modelling of structures. The paper investigates the performance of multi-story building-foundation systems through a Winkler-based approach. A set of 4-, 8-, 12- and 16-story steel moment resisting frame buildings on three soil types with shear wave velocities less than 600m/s subjected to actual earthquake records with a probability of exceedance of 10% in 50 years are modeled with and without SSI. It is observed that the performance level of frames supported by flexible foundation, particularly at soft soil sites, may alter significantly in comparison to fixed-base structures. Moreover, the nonlinear foundation is found to have a significant effect on the force and displacement demands. A comparison and brief discussion on the design guidelines for consideration of flexible foundation behavior is also included.