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61.
This paper reports on the study of the seismic response of an urban building block located in Faial, a town of the Horta Island
of the Azores, Portugal. The work fits within the framework of studying strengthening schemes suitable for the reconstruction
process of a town damaged by an earthquake action and includes numerical modelling of all the building blocks with calibration
of material and structural parameters based on ambient vibration tests. The study aims at understanding a number of issues
that are likely to influence the global behaviour of the block and the local response of individual buildings, namely the
group effect of adjacent constructions, the in-plane stiffness of floors and/or roofs and the presence of possible localized
strengthening interventions in selected parts of the block. 相似文献
62.
The seismic assessment of the local failure modes in existing masonry buildings is currently based on the identification of the so‐called local mechanisms, often associated with the out‐of‐plane wall behavior, whose stability is evaluated by static force‐based approaches and, more recently, by some displacement‐based proposals. Local mechanisms consist of kinematic chains of masonry portions, often regarded as rigid bodies, with geometric nonlinearity and concentrated nonlinearity in predefined contact regions (unilateral no‐tension behavior, possible sliding with friction). In this work, the dynamic behavior of local mechanisms is simulated through multi‐body dynamics, to obtain the nonlinear response with efficient time history analyses that directly take into account the characteristics of the ground motion. The amplification/filtering effects of the structure are considered within the input motion. The proposed approach is validated with experimental results of two full‐scale shaking‐table tests on stone masonry buildings: a sacco‐stone masonry façade tested at Laboratório Nacional de Engenharia Civil and a two‐storey double‐leaf masonry building tested at European Centre for Training and Research in Earthquake Engineering (EUCENTRE). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
63.
Gervásio Annes Degrazia Umberto Rizza Franciano Scremin Puhales Antônio Gledson Goulart Jonas Carvalho Guilherme Sausen Welter Edson Pereira Marques Filho 《Boundary-Layer Meteorology》2009,131(2):277-292
A variable vertical mesh spacing for large-eddy simulation (LES) models in a convective boundary layer (CBL) is proposed.
The argument is based on the fact that in the vertical direction the turbulence near the surface in a CBL is inhomogeneous
and therefore the subfilter-scale effects depend on the relative location between the spectral peak of the vertical velocity
and the filter cut-off wavelength. From the physical point of view, this lack of homogeneity makes the vertical mesh spacing
the principal length scale and, as a consequence, the LES filter cut-off wavenumber is expressed in terms of this characteristic
length scale. Assuming that the inertial subrange initial frequency is equal to the LES filter cut-off frequency and employing
fitting expressions that describe the observed convective turbulent energy one-dimensional spectra, it is feasible to derive
a relation to calculate the variable vertical mesh spacing. The incorporation of this variable vertical grid within a LES
model shows that both the mean quantities (and their gradients) and the turbulent statistics quantities are well described
near to the ground level, where the LES predictions are known to be a challenging task. 相似文献
64.
65.
António Ribeiro José Munhá António Mateus Paulo Fonseca Eurico Pereira Fernando Noronha José Romão José Rodrigues Paulo Castro Carlos Meireles Narciso Ferreira 《Comptes Rendus Geoscience》2009,341(2-3):127-139
Remnants of the Cadomian basement can be found in the Iberian Variscides (IBVA) in several key sectors of its autochthonous units (composed of Neoproterozoic to Lower Palaeozoic metasedimentary sequences) and within the Continental Allochthonous Terrane (CAT). Comprehensive characterization of these critical exposures shows that the prevailing features are related to major geological events dated within the age range of 620–540 Ma. Indeed, near the Cambrian–Ordovician boundary, the IBVA Internal Zones experienced pervasive basement thinning and cover thickening, reflecting diffusive displacement of intracratonic rifting that continued until Lower Devonian times. In the thick-skinned Internal Zones, Helvetic/Penninic style nappes were generated, whereas flower upright axial structures developed along transpressive, intraplate shear zones. These features contrast with those preserved in the thin-skinned IBVA External Zones, dominated by décollements above (un-)deformed Palaeozoic and Cadomian basement. The inferred attenuation of rheological contrast between Cadomian basement and Palaeozoic cover can be explained by inherited fabrics due to thermal softening operated during the Cambrian–Lower Devonian extensional regime. Deeper décollements (and subsequent strain partitioning) are also expected to develop at the upper-lower crust (and at the Moho?) transition, as imaged by the available seismic profiling and MT surveys. The whole data implies a significant discontinuity between Cadomian and Variscan Cycles that should have constrained subsequent lithospheric evolution. 相似文献
66.
Embankments on Soft Soil Reinforced with Stone Columns: Numerical Analysis and Proposal of a New Design Method 总被引:5,自引:1,他引:4
José Leitão Borges Tiago Sabino Domingues António Silva Cardoso 《Geotechnical and Geological Engineering》2009,27(6):667-679
A parametric study of an embankment on soft soils reinforced with stone columns is performed using a computer program based
on the finite element method. The cylindrical unit cell formulation is used by modeling one column and its surrounding soft
soil with confined axisymmetric behaviour. The computer program incorporates the Biot consolidation theory (coupled formulation
of the flow and equilibrium equations) with constitutive relations simulated by the p–q–θ critical state model. The following parameters are analysed: the replacement area ratio, the deformability of the column
material, the thickness of the soft soil, the deformability of the fill and the friction angle of the column material. Based
on the results of this study, a new design method is proposed, relating the settlement improvement factor to the two factors
that revealed major influence: the replacement area ratio and the ratio between the deformability of the soft soil and the
deformability of the column material. 相似文献
67.
Fernando O. Marques Fernando M. S. F. Marques António Mateus Jorge Figueiras Fernando M. Santos Rogério Mota Helena Amaral 《Environmental Geology》2005,47(8):1128-1137
A sodium bentonite is being used in the basal-isolation of landfills installed on strongly fractured granitic rocks of N Portugal (NW Iberia). To evaluate the performance of this clay as the ultimate impermeable basal barrier, a detailed study was carried out of the granite fracture network; the Na-bentonite was tested to characterize its mechanical and geotechnical behavior; geophysical surveys were made to search for landfill leakage and the waters found around the landfill were geochemically characterized. Fractures in the granite are usually open and devoid of mineral infillings or clay materials and, thus, permeability of the granite is very high. Dispersal of contaminants can be further enhanced by the position of the landfill on a high steep-sided ridge. Geophysical and geochemical data show evidence for seepage and dispersion of pollutants, which means that the clay failed as an ultimate isolation barrier against seepage. This investigation shows that this can be due to fracturing of the clay under load and/or to its non-homogeneous saturation and extreme shrinking character upon drying, which are accompanied by the formation of extensive cracking. Observations and experimental results suggest that the use of synthetic clays in the safe building of landfill bottom liners needs further research, and extreme care should be taken in preventing that clay water content suffers large variations after saturation, as this process considerably degrades the mechanical behavior and sealing properties of the studied Na-bentonite. 相似文献
68.
Dr. António Júdice 《Pure and Applied Geophysics》1950,18(1):107-112
Résumé Il s'agit de la détermination de l'aplatissement de la Terre et de la pesanteur équatoriale en utilisant la définition de l'ellipsoïde de référence donnée par l'auteur dans une publication antérieure et les anomalies isostatiques moyennes calculées parL. Tanni. Les résultats obtenus,
e
=978.055, =1/296.3, sont sensiblement égaux à ceux qui proviennent de la méthode habituelle des moindres carrés; l'aplatissement calculé est compris entre les limites déduites parA. Véronnet de la précession terrestre.
Summary This article contains the numerical computation of the Earth's flattening and the equatorial gravity on the basis of the definition of the reference ellipsoid, given by the author in a former work, and the mean isostatic anomalies computed byL. Tanni. The results, e =978.055, =1/296.3, show that the method of least squares is accurate enough under the present conditions; the flattening computed is bounded by the values derived byA. Véronnet from the terrestrial precession.相似文献
69.
Arun Chawla David A. Jay António M. Baptista Michael Wilkin Charles Seaton 《Estuaries and Coasts》2008,31(2):269-288
The long-term response of circulation processes to external forcing has been quantified for the Columbia River estuary using
in situ data from an existing coastal observatory. Circulation patterns were determined from four Acoustic Doppler Profilers
(ADP) and several conductivity–temperature sensors placed in the two main channels. Because of the very strong river discharge,
baroclinic processes play a crucial role in the circulation dynamics, and the interaction of the tidal and subtidal baroclinic
pressure gradients plays a major role in structuring the velocity field. The input of river flow and the resulting low-frequency
flow dynamics in the two channels are quite distinct. Current and salinity data were analyzed on two time scales—subtidal
(or residual) and tidal (both diurnal and semidiurnal components). The residual currents in both channels usually showed a
classical two-layer baroclinic circulation system with inflow at the bottom and outflow near the surface. However, this two-layer
system is transient and breaks down under strong discharge and tidal conditions because of enhanced vertical mixing. Influence
of shelf winds on estuarine processes was also observed via the interactions with upwelling and downwelling processes and
coastal plume transport. The transient nature of residual inflow affects the long-term transport characteristics of the estuary.
Effects of vertical mixing could also be seen at the tidal time scale. Tidal velocities were separated into their diurnal
and semidiurnal components using continuous wavelet transforms to account for the nonstationary nature of velocity amplitudes.
The vertical structure of velocity amplitudes were considerably altered by baroclinic gradients. This was particularly true
for the diurnal components, where tidal asymmetry led to stronger tidal velocities near the bottom. 相似文献