Undrained instability detection under general stress conditions     

Leguizamón-Barreto  Luis C.  Ramos-Cañón  Alfonso M.  Andrade  José E. 《Acta Geotechnica》2021,16(10):3041-3059

Acta Geotechnica - This work proposes a criterion for the detection of undrained instability under multiaxial stress conditions at elemental level. To do so, it develops the application of the...  相似文献   

Editorial to the topical collection in Environmental Earth Sciences “Stone in the architectural heritage: from quarry to monuments—environment,exploitation, properties and durability”     

Siegfried Siegesmund  Luís Sousa  Rubén Alfonso López-Doncel 《Environmental Earth Sciences》2018,77(21):730

  相似文献   

In situ and nondestructive characterization of mechanical properties of heritage stone masonry     

Orenday-Tapia Edith Estefanía  Pacheco-Martínez Jesús  Padilla-Ceniceros Raudel  López-Doncel Rubén Alfonso 《Environmental Earth Sciences》2018,77(7):286

The necessity of conserving and preserving the heritage is nowadays a developing study line for several researchers. From a civil engineering perspective, one of the most important issues for the conservation of historical buildings is to ensure the structural stability. For this purpose, it is necessary to determine the mechanical properties of the ancient construction materials. However, these structures cannot be evaluated by destructive tests due to politics and restrictions for preserving the heritage built. As a consequence, new methods that do not put in risk the integrity of the materials and the structure are becoming useful tools for researchers who work on structural engineering of heritage buildings. This paper presents a nondestructive method (NDM) that has been used to characterize the mechanical properties of different constructive systems of the San Antonio de Padua Temple, which is a religious icon in Aguascalientes, Mexico. This method includes the measuring of seismic waves’ travel time in order to obtain shear and compressional velocity waves. Results show that with this method mechanical properties of masonry can be obtained such as Young’s modulus, Poisson ratio and bulk density, which are needed for the structural analysis using numerical simulation models.  相似文献   

Effect of Weather-Related Episodic Events over Chlorophyll-a In a Shallow Lake: an Analysis Based on High-Frequency Data     

Zunino  Josefina  Alfonso  María Belén  Vitale  Alejandro José  Piccolo  María Cintia 《Water Resources》2021,48(4):614-623

Water Resources - With conventional monitoring at low-frequency, biological responses to weather-related events are missed. In this paper, we examine the chlorophyll-a concentrations in a shallow...  相似文献   

Temporal distribution of heavy metal concentrations in oysters Crassostrea rhizophorae from the central Venezuelan coast     

Juan A. Alfonso  Helga Handt  Abrahan Mora  Yaneth Vásquez  José Azocar  Eunice Marcano 《Marine pollution bulletin》2013

The oyster Crassostrea rhizophorae is a bivalve abundant in Venezuelan estuaries and consumed by local populations. No known values have been reported on trace metals in oysters from the central Venezuelan coast. We report the concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V and Zn in the soft parts of C. rhizophorae, which were collected bimonthly between March 2008 and March 2009, at two sampling areas from the Central Venezuelan Coast: Buche estuary and Mochima estuary. Our results show that for each metal there is a similar temporal variation pattern. The concentrations of the heavy metals reported in this work are useful as reliable baselines and can be used for comparison in future environment studies. Concentrations in C. rhizophorae from the Buche estuary can be interpreted to be high on a global scale for Cd, Cu, Ni and Mn, indicating atypically raised bioavailabilities.  相似文献   

Criterion for flow liquefaction instability     

José E. Andrade  Alfonso M. Ramos  Arcesio Lizcano 《Acta Geotechnica》2013,8(5):525-535

This study describes a general liquefaction flow instability criterion for elastoplastic soils based on the concept of loss of uniqueness. We apply the criterion to the general case of axisymmetric loading and invoke the concepts of effective stresses and loss of controllability to arrive at a general criterion for the onset of liquefaction flow. The criterion is used in conjunction with an elastoplastic model for sands to generate numerical simulations. The numerical results are compared with experimental evidence to give the following insights into predicting liquefaction. (1) The onset of liquefaction flow is a state of instability occurring under both monotonic and cyclic tests, and coincides with loss of controllability. (2) The criterion proposed herein clearly and naturally differentiates between liquefaction flow (instability) and cyclic mobility. (3) Flow liquefaction not only depends on the potential of the material to generate positive excess pore pressures, but more importantly, it also depends on the current state of the material, which is rarely predicted by phenomenology.  相似文献   

Explaining global patterns and trends in marine protected area (MPA) development     

Helen E. Fox  Carrie S. Soltanoff  Michael B. Mascia  Kelly M. Haisfield  Alfonso V. Lombana  Christopher R. Pyke  Louisa Wood 《Marine Policy》2012

The relative paucity and heterogeneous distribution of marine protected areas (MPAs) indicates the need for better understanding of factors that foster MPA establishment at local, sub-national, and national levels. The relationship between national-level MPA establishment and geographic, ecological, social, and political factors that may drive patterns and trends in MPA establishment were assessed. A country's coastline length is the strongest predictor of both the number and spatial extent of MPAs. Controlling for coastline, the Human Development Index (HDI) and spatial overlap with designated conservation priority areas are positively correlated with MPA establishment. Surprisingly, some factors influencing MPA establishment in case studies, such as percentage of fishers within a population, were not correlated with MPA establishment on a national scale. These national dynamics explain a relatively small proportion of variation, however, indicating that other biological or social factors, as well as sub-national processes, also influence MPA establishment. Positive and negative outliers illuminate the importance of policy engagement at both national and local levels. Ensuring a supportive enabling environment at the national or even multi-national level can enhance success at the local level.  相似文献   

Effects of near‐fault ground motions on the nonlinear dynamic response of base‐isolated r.c. framed buildings     

Fabio Mazza  Alfonso Vulcano 《地震工程与结构动力学》2012,41(2):211-232

Near‐fault ground motions are characterized by long‐period horizontal pulses and high values of the ratio between the peak value of the vertical acceleration, PGA_V, and the analogous value of the horizontal acceleration, PGA_H, which can become critical for base‐isolated (BI) structures. The objective of the present work is to check the effectiveness of the base isolation of framed buildings when using High‐Damping‐Rubber Bearings (HDRBs), taking into consideration the combined effects of the horizontal and vertical components of near‐fault ground motions. To this end, a numerical investigation is carried out with reference to BI reinforced concrete buildings designed according to the European seismic code (Eurocode 8). The design of the test structures is carried out in a high‐risk region considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones and assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDRBs. The nonlinear seismic analysis is performed using a step‐by‐step procedure based on a two‐parameter implicit integration scheme and an initial‐stress‐like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub‐elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment–curvature law is adopted; the effect of the axial load on the ultimate bending moment (M‐N interaction) of the columns is also taken into account. The response of an HDRB is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Transient response to well-mixed greenhouse gas changes     

Isabella Bordi  Klaus Fraedrich  Alfonso Sutera  Xiuhua Zhu 《Theoretical and Applied Climatology》2012,109(1-2):245-252

A change in CO₂ concentration induces a direct radiative forcing that modifies the planetary thermodynamic state, and hence the surface temperature. The infrared cooling, by assuming a constant temperature lapse-rate during the process, will be related to the surface temperature through the Stefan–Boltzmann law in a ratio proportional to the new infrared opacity. Other indirect effects, such as the water vapor and ice-albedo feedbacks, may amplify the system response. In the present paper, we address the question of how a global climate model with a mixed layer ocean responds to different rates of change of a well-mixed greenhouse gas such as CO₂. We provide evidence that different rates of CO₂ variation may lead to similar transient climates characterized by the same global mean surface temperature but different values of CO₂ concentration. Moreover, it is shown that, far from the bifurcation points, the model’s climate depends on the history of the radiative forcing displaying a hysteresis cycle that is neither static nor dynamical, but is related to the memory response of the model. Results are supported by the solutions of a zero-dimensional energy balance model.  相似文献   

Surface evolution of salt‐encrusted playas under extreme and continued dryness          下载免费PDF全文

Octavio Artieda  Alfonso Davila  Jacek Wierzchos  Peter Buhler  Rafael Rodríguez‐Ochoa  Juan Pueyo  Carmen Ascaso 《地球表面变化过程与地形》2015,40(14):1939-1950

Miocene continental saltpans are scattered in the Central Valley of the Atacama Desert, one of the driest regions on Earth. These evaporitic deposits are hydrologically inactive, and are detached from groundwater brines or aquifers. The surface of the saltpans, also known as salars, comprises desiccation polygons, commonly with nodular salt structures along their sides. The morphology and bulk mineralogy of salt polygons differs between and within salars, and the shape and internal structure of salt nodules varies between different polygon types. Based on field observation, and mineralogy and crystallography data, we generated a conceptual model for the genesis and evolution of these surface features, whereby rare rainfall events are responsible for the transformation of desiccation salt polygons and the initial formation of salt nodules along polygon borders. In addition, frequent, but less intense, deliquescence events further drive the evolution of salt nodules, resulting in a characteristic internal structure that includes laminations, and changes in porosity and crystal morphologies. As a result, and despite the extreme dryness, the surfaces of fossil salars are dynamic on timescales of several years to decades, in response to daily cycles in atmospheric moisture, and also to rare and meager rainfall events. We propose that fossil salars in the Atacama Desert represent an end stage in the evolution of evaporitic deposits under extreme and prolonged dryness. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献