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981.
982.
The evaluation of shear strains under multi-directional shaking is an important issue in interpreting dynamic soil behavior for both laboratory physical modeling and in situ monitoring. Shear strain components evaluated from Cartesian coordinates in undrained conditions have limitations to fully capture the coupled shear strain-pore pressure responses with an individual expression. In the present study, radial and rotational shear strain components derived from particle motions described with cylindrical polar coordinates are proposed. The proposed radial and rotational shear strains are verified with data from a bi-directional laminar shear box and a free field downhole array. Comparison results show that the proposed expressions of shear strain effectively capture the coupled strain-pore pressure responses in terms of the frequency content, amplitude variation, phase difference, and oscillation behavior. Comparison results reveal that the radial shear strain is the dominant shearing mode and the amplitude of the rotational shear strain is only 6.5–14.5% of the radial component. This provides quantitative data for the correction factor for multi-directional shaking and suggests that a simple shear system capable of inducing the radial shear strain on the vertical plane is a better approach than other shearing modes for physically modeling the behavior of soil subjected to undrained seismic loadings. 相似文献
983.
984.
985.
广州天誉大厦采用型钢混凝土框架一钢筋混凝土筒体的混合结构体系,地面以上结构采用抗震缝兼伸缩缝分隔为南、北塔两个独立结构体系,南塔高186.5 m,北塔高159.5 m.两塔的核心筒总宽度与核心筒总高的比值均超出了规范限值.为研究这种超限高层混合结构的抗震性能,对其进行了缩尺(1/30)模型的振动台试验,并建立了有限元计... 相似文献
986.
Paola Bordoni John Haines Giuliano Milana Sandro Marcucci Fabrizio Cara Giuseppe Di Giulio 《Bulletin of Earthquake Engineering》2011,9(3):761-781
This is the first part of a study on the seismic response of the L’Aquila city using 2D simulation and experimental data.
We have studied two velocity-depth models with the aim of outlining the behavior of a velocity reversal in the top layer,
which is associated with the stiff Brecce de L’Aquila unit (BrA). In this setting, the SMTH model is topped by a layer with
about 2:1 impedance contrast with the underlying layer while the NORV model has no velocity reversal. We have simulated the
propagation of SH and P-SV wavefields in the range 0–10 Hz for incidence 0°–90°. Earthquake spectral ratios of the horizontal
and vertical components at six sites in L’Aquila downtown are compared to corresponding synthetics spectral ratios. The vertical
component of P-SV synthetics enables us to investigate a remarkable amplification effect seen in the vertical component of
the recorded strong motion. Sites AQ04 and AQ05 are best matched by synthetics from the NORV model while FAQ5 and AQ06 have
a better match with synthetics spectral ratios from the SMTH model. All simulations show this behavior systematically, with
horizontal and near-horizontal incident waves predicting the overall pattern of matches more clearly than vertical and near-vertical
incidence. The model inferences are in agreement with new geological data reporting lateral passages in the top layer from
the stiff BrA to softer sediments. Matches are good in terms of frequency of the first amplification peak and of spectral
amplitude: the horizontal components have spectral ratio peaks predominantly at 0.5 Hz in the simulations and at 0.7 Hz in
the data, both with amplitudes of 4, while the vertical component spectral ratios reach values of 6 at frequencies of about
1 Hz in both data and simulations. The vertical component spectral ratios are very well matched using Rayleigh waves with
incidence at 90°. The NORV model without the velocity reversal predicts spectral ratio peaks for the horizontal components
at frequencies up to 6 Hz. The reversal of velocity acts as a low-pass frequency filter on the horizontal components reducing
the amplification effect of the sediment filled valley. 相似文献
987.
The Aterno valley strong-motion array: seismic characterization and determination of subsoil model 总被引:1,自引:1,他引:0
G. Lanzo M. Tallini G. Milana G. Di Capua F. Del Monaco A. Pagliaroli S. Peppoloni 《Bulletin of Earthquake Engineering》2011,9(6):1855-1875
The paper focuses on the strong motion array deployed in the upper Aterno River Valley, in the immediate outskirts north-west
of the town of L’Aquila, which is part of the Italian Strong Motion Network operated by the Department of Civil Protection.
The array is composed of six accelerometric stations located along a cross section of the valley. The importance of this array
relies on the fact that a large amount of high-quality records were obtained during the 2009 L’Aquila seismic sequence, from
both the mainshock and several aftershocks. These data are especially important to investigate site effects in sediment-filled
valleys during moderate earthquakes in epicentral area because well-documented observational studies are very limited in the
literature. However, the main drawback for the study of site effects in the Aterno valley is the lack of a detailed knowledge
of the geometry of the valley, soil layering and dynamic properties of materials. The main motivation for this study stems
from the need to provide a reliable subsoil model of the valley coupled with high-quality strong motion data. Based on the
above, in the framework of S4 project, a major effort was undertaken to get a trustworthy cross section of the valley by an
ad hoc investigation, comprising geological and geotechnical surveys as well as an extensive geophysical campaign, characterized
by both active and passive measurements. These results were complemented by additional geological and geotechnical data available
in the literature. By merging all the information acquired, a 2D subsoil model of the transversal section of the upper Aterno
valley has been produced. The valley is characterised by an asymmetric shape with a shallower rock basement at the western
edge of the valley that deepens at the valley centre. Moreover, based on the results of geophysical tests, representative
Vs values were assigned to the different lithologic units forming the alluvial deposits filling the valley. Shear wave velocity
is a fundamental parameter for ground response studies and it is also effective in classifying the accelerometric station
from a seismic point of view. The 2D model may be therefore, considered a benchmark model for future studies of site effects.
It will offer the possibility to examine site effects with a complex underlying geology and to validate the results of numerical
simulations of site response analyses with the numerous observations from earthquake recordings, both for weak and strong
ground motion conditions. 相似文献
988.
E. Bertrand A.-M. Duval J. R��gnier R. M. Azzara F. Bergamashi P. Bordoni F. Cara G. Cultrera G. Di Giulio G. Milana J. Salichon 《Bulletin of Earthquake Engineering》2011,9(3):809-823
During the microzonation studies of the April 6th, 2009 L??Aquila earthquake, we observed local seismic amplifications in the Roio area??a plane separated from L??Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the ground motion from these events to determine relative site amplification within the plain and on surrounding ridges. Horizontal over vertical spectral ratio on noise data (HVSRN), aftershock recordings (HVEQ) and standard spectral ratio (SSR) showed amplifications at 1.3 and 4.0?Hz on quaternary deposits. Seismic amplifications in the frequency range of 4 and 6?Hz were also observed on a carbonate ridge of Colle di Roio, on the northwestern border of the plateau. A small amplification was noticed near the top of mount Luco, another rocky site. Large discrepancies in the amplification levels between methods have been observed for these sites, but the HVSRN, HVEQ and SSR gave similar results at the stations located in the Roio plain. On the rocky sites, the SSR was more reliable than the HVSRN at estimating the transfer function of the site, even if the resonance frequency seemed to be well detected by the latter method. 相似文献
989.
Cheol-Hee Kim Lim-Seok Chang Jeong-Soo Kim Fan Meng Mizuo Kajino Hiromasa Ueda Yuanhang Zhang Hye-Young Son Youjiang He Jun Xu Keiichi Sato Chang-Keun Song Soo-Jin Ban Tatsuya Sakurai Zhiwei Han Lei Duan Suk-Jo Lee Shang-Gyoo Shim Young Sunwoo Tae-Young Lee 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(4):399-411
Three comprehensive acid deposition models were used to simulate the sulfur concentrations over northeast Asia over the period covering entire year of 2002, and discussed the aggregated uncertainties and discrepancies of the three models. The participating models are from the countries participating in the project of Longrange Transboundary Air Pollutants in Northeast Asia (LTP): China, Japan and Korea. The Eulerian Model-3/CMAQ (by China), Regional Air Quality Model (RAQM, by Japan), and Comprehensive Acid Deposition Model (CADM, by Korea) were employed by each country with common emissions data established by the administrative agencies of China, Japan and Korea. The episodic simulation results between 1 to 15, March 2002 are also presented, during which aircraft measurements were carried out over the Yellow sea. The episodic results show both a wide short-term variability in simulations against measurements, and maximum concentration differences of 3~5 times among the three models, requiring that further attention before confidence among the three models can be claimed for short-term simulations. However, the year-long cumulative simulations showed almost the same general features, with lower aggregated uncertainties between the three models, produced by the long term integration over northeast Asia. 相似文献
990.