The paper describes the experimental design and results of tests used to investigate the use of compressible EPS (geofoam) seismic buffers to attenuate dynamic loads against rigid retaining wall structures. The tests were carried out using 1-m-high models mounted on a large shaking table. Three different geofoam buffer materials retaining a sand soil were tested under idealized dynamic loading conditions. The results of these tests are compared to a nominal identical structure without a seismic buffer. The test results demonstrate that the reduction in dynamic load increased with decreasing seismic buffer density. For the best case reported here, the maximum dynamic force reduction was 31% at a peak base acceleration of 0.7g. 相似文献
Natural Hazards - One of the most widely used relationships for prediction of b-value is the Aki–Utsu relationship, which is based on the maximum likelihood estimating. This method has some... 相似文献
Techniques for soil property estimation can be categorized into two main groups, in-situ and laboratory methods. Previous investigations indicated that strong ground motions record provides a very useful tool to estimating the in-situ characteristics of soil. The main objective of the present work is to utilize the particle swarm optimization algorithm(PSOA) integrated with linear site response method to obtain the equivalent soil profile characteristics from the available surface and bedrock earthquake motion records. To demonstrate the numerical efficiency and the validity of this approach, the procedure is validated against an available case. Then this procedure is utilized to identify the soil properties profiles of the site by using strong ground motions data recorded during the Bam earthquake of December 26, 2003. The magnitude and PGA of Bam earthquake were MW 6.6 and 0.8 g respectively. 相似文献
ABSTRACTIn this study, we investigate the temporal oscillations of precipitation extremes in different climate regions of the United States. We apply quantile perturbation analysis to average daily precipitation and, to 1041 weather stations with high-quality data from 1900 to 2016. Moreover, we explore the relationship between the extreme precipitation and different well-known cyclical climate modes. Overall, the analysis of average daily precipitation identifies a drier condition in the middle decades of the twentieth century and, a wetter climate in the early century and recent decades. Moreover, the in situ analysis reveals a significant anomaly, mainly prevalent in the Central and Southern regions of the United States. We applied a finite set of linear regression models with different combinations of cyclical climate modes to inform the variability of anomalies with best performing models. Our results highlight the dominant effect of ENSO and NAO in the wide area of the United States. 相似文献
This paper presents a new clustering procedure based on K-means and self-organizing map (SOM) network algorithms for classification of earthquake ground-motion records. Six scalar indicators are used in data analysis for describing the frequency content features of earthquake ground motions, named as the average spectral period (Tavg), the mean period (Tm), the smoothed spectral predominant period (T0), the characteristic period (T4.3), the predominant period based on velocity spectrum (TgSv), and the shape factor (Ω). Different clustering validity indexes were applied to determine the best estimates of the number of clusters on real and synthetic data. Results showed the high performance of proposed procedure to reveal salient features of complex seismic data. The comparison between the results of clustering analyses recommend the smoothed spectral predominant period as an effective indicator to describe ground-motion classes. The results also showed that K-means algorithm has better performance than SOM algorithm in identification and classification procedure of ground-motion records. 相似文献
This study develops a straightforward approximate method to estimate inelastic displacement ratio, C1 for base‐isolated structures subjected to near‐fault and far‐fault ground motions. Taking into account the inelastic behavior of isolator and superstructure, a 2 degrees of freedom model is employed. A total of 90 earthquake ground motions are selected and classified into different clusters according to the frequency content features of records represented by the peak ground acceleration to peak ground velocity ratio, Ap/Vp. A parametric study is conducted, and effective factors in C1 (i.e., fundamental vibration period of the superstructure, Ts; postyield stiffness ratio of the superstructure, αs; strength reduction ratio, R; vibration period of the isolator, Tb; strength of the isolator, Q; ratio of superstructure mass to total mass of the system, γm) are recognized. The results indicate that the practical range of C1 values could be expected for base‐isolated structures. Subsequently, effective parameters are included in simple predictive equations. Finally, the accuracy of the proposed approximate equations is evaluated and verified through error measurement, and comparisons are made in the analyses. 相似文献
The characteristics of aftershocks can be quite different from those of mainshocks. However, most of the works in the past have generally focused on the aftershocks of strong earthquakes, while some moderate earthquakes can cause aftershocks with magnitudes close to the mainshocks. This paper focuses on the aftershocks characteristics of the 2012 Varzaghan–Ahar Doublet event (Mw?=?6.4, 6.2), northwest of Iran. Numerous aftershocks with magnitudes 3.7–5.5 recorded by the local seismic stations provide useful data to study the spectral characteristics at various periods. The predictive capability of the 2008 Next Generation Attenuation along with two regional models has been examined by several aftershock records obtained during these events. This paper is the first attempt made to compare the predictive capability of modern models based on significant aftershock data obtained for these two moderate events. Results confirmed that the ground motion models which have been derived based on larger-magnitude events should not directly be extrapolated to predict aftershock ground motions with magnitude smaller than 5.5, especially when we use relationships that developed without considering aftershock data. The residual analysis showed that the model of Abrahamson and Silva (Earthq Spectra, 24(1): 67–97, 2008) performed the best overall predictions in this study. However, this model performs poorly in the short period of 0.2 s at distances greater than 50 km which underestimates the spectral values for this case.
Spontaneous displacement of the non-wetting phase by a wetting phase in a porous medium, known as spontaneous imbibition, is an important mechanism of oil recovery from fractured reservoirs. In this paper, we consider the nonequilibrium model, proposed by Aryana and Kovscek, where consitutive relationships for multiphase flow in porous media are functions of a locally moving time-average saturation, and allow relaxation time to be an explicit function of local saturation. We obtain asymptotic self-similar solutions for early and late times. At very early stages, the time-scale of the process characterizing the cumulative volume of displaced fluid is a power function with an exponent of \(\frac {1}{2}+\frac {1}{2r+1}\) where r is the inverse of pore size distribution index of the medium in question. Additionally, the cumulative volume of displaced fluid at late times is independent of relaxation time, and this volume approaches the square root of time asymptotically. Finally, the late-time solution for recovery is compared with experimental observations. 相似文献