Cyclic behaviour of interior beam–column joints reinforced with plain bars          下载免费PDF全文

José Melo  Humberto Varum  Tiziana Rossetto 《地震工程与结构动力学》2015,44(9):1351-1371

The seismic damages commonly observed on beam–column joints of old reinforced concrete structures, built with plain bars and without proper detailing, justifies the need to further study the behaviour of this type of structures. The response of these structures when loaded cyclically, as occurs during the earthquakes, is partially controlled by the bond properties between the reinforcing bars and the surrounding concrete. This paper presents the results of an experimental campaign of unidirectional cyclic tests carried out on six full‐scale beam–column joints built with plain bars. These joint specimens are representative of existing reinforced concrete structures, that is, built without adequate reinforcement detailing for seismic demands. For comparison, an additional specimen is built with deformed bars and tested. The seven specimens are designed and detailed to allow the investigation of the influence of bond properties, lapping of the longitudinal bars in columns and beams, bent‐up bars in the beams, slab contribution and concrete strength. The lateral force–drift relationships, global dissipated energy evolution, contribution of the joint, beams and columns to the global dissipated energy, ductility, equivalent damping, final damage observed, homogenized reinforced concrete damage index, displacement components, curvature evolutions and Eurocode requirements are presented and discussed. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Assessment of seismic damage of thin and lightly reinforced concrete walls using fractal dimension of cracking          下载免费PDF全文

Julian Carrillo  William Avila 《地震工程与结构动力学》2017,46(4):661-675

Length, maximum width, and residual width of cracks are key indicators of structural damage. However, pattern and propagation of cracks on the affected structural component should be also considered. In addition, damage evaluation based on visual inspection is a subjective and capricious procedure because the damage assessment relies on the expertise and judgment of the inspector engineer. In order to assess a rapid and reliable evaluation approach of seismic damage, pattern and propagation of cracks observed in thin and lightly reinforced concrete walls for low‐rise housing subjected to seismic demands are evaluated in this study by means of fractal dimension of cracking pattern. The proposed parameters are based on the results of an experimental program that comprised 39 low‐rise RC wall specimens having typical variables of this type of housing, such as low compressive strengths of concrete, thin walls, low axial loads, low reinforcement ratios, and web shear reinforcement made of deformed bars and welded‐wire meshes. A statistical analysis is carried out for computing values of fractal dimension associated to cracking patterns at key damage conditions. Recommendations of this study can help the inspector in estimating the current limit state or performance level of the wall and the story‐drift ratio experienced by the wall during shaking. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Two simple image slicers for high resolution spectroscopy     

M. Tala  L. Vanzi  G. Avila  C. Guirao  E. Pecchioli  A. Zapata  F. Pieralli 《Experimental Astronomy》2017,43(2):167-176

We present the design, manufacturing, test and performance of two image slicers for high resolution spectroscopy. Based on the classical Bowen-Walraven concept, our slicers allow to make two slices of the image of the input fibre. We introduce the idea of a second fibre that can be cropped in half to reach the same width of the science target fibre and that can be used for simultaneous wavelength reference. The slicers presented are mirror and prism based, respectively. Both devices work within expectation, showing differences mainly in their efficiency. The prism based slicer is the solution that was adopted for the FIDEOS spectrograph, an instrument built by the AIUC for the ESO 1m telescope of La Silla. Test spectra obtained with this instrument are included as examples of a real application of the device.  相似文献   

Antarctic marine chemical ecology: what is next?     

Conxita Avila  Sergi Taboada  & Laura Núñez-Pons 《Marine Ecology》2008,29(1):1-71

Antarctic ecosystems are exposed to unique environmental characteristics resulting in communities structured both by biotic interactions such as predation and competition, as well as abiotic factors such as seasonality and ice‐scouring. It is important to understand how ecological factors may trigger chemical mechanisms in marine Antarctic organisms as a response for survival. However, very little is known yet about the evolution of chemical compounds in Antarctic organisms. Investigations in chemical ecology have demonstrated over the last several years that defensive metabolites have evolved in numerous representative Antarctic species. This contradicts earlier theories concerning biogeographic variation in predation and chemical defenses. As reviewed here, a number of interesting natural products have been isolated from Antarctic organisms. However, we believe many more are still to be discovered. Currently, many groups such as microorganisms, planktonic organisms and deep‐sea fauna remain almost totally unknown regarding their natural products. Furthermore, for many described compounds, ecological roles have yet to be evaluated. In fact, much of the research carried out to date has been conducted in the laboratory, and only in a few cases in an ecologically relevant context. Therefore, there is a need to extend the experiments to the field, as done in tropical and temperate marine ecosystems, or at least, to test the activity of the chemicals in natural conditions and ecologically meaningful interactions. Defense against predators is always one of the main topics when talking about the roles of natural products in species interactions, but many other interesting aspects, such as competition, chemoattraction, fouling avoidance and ultraviolet (UV) protection, also deserve further attention. In our opinion, challenging future developments are to be expected for Antarctic marine chemical ecology in the years to come.  相似文献   

Reproduction and feeding of Sagitta enflata in the Humboldt Current system off Chile     

Giesecke  Ricardo; Gonzalez  Humberto E. 《ICES Journal of Marine Science》2008,65(3):361-370

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First evidence of complex dental practice about 1300 BP in Mesoamerica revealed by absolute geomagnetic intensity     

Avto Goguitchaichvili  Juan Morales  Ramiro Aguayo Haro  Humberto Quiroz Castañon  Jasinto Robles Camacho 《Studia Geophysica et Geodaetica》2017,61(2):310-317

Deliberated dental modifications and mutilations are known since prehistoric times. The Mayas and other ancient cultures in Mesoamerica were considered pioneers of such practice. The evidences of therapeutic intervention, however, are still poorly documented and credible examples are extremely scarce. One of the burials excavated at the locality of La Mina (Michoacan, Mexico) corresponds to a 30-35 year old male individual named Alvaro, who presented a well-marked dental deformation. Moreover, Alvaro had a quite deep and symmetrical perforation in the upper right canine–a treatment similar to the procedure of endodontics or root canal. The archaeological context of Alvaro’s habitat was dated using the archaeomagnetic method applied to pottery samples unambiguously correlated to the burial. The analysis supplied a time interval between 647 and 825 AD suggesting the first evidence of complex dental practice in the Americas.  相似文献   

Seismic vulnerability and loss assessment of the Nepalese Pagoda temples     

Manjip Shakya  Humberto Varum  Romeu Vicente  Aníbal Costa 《Bulletin of Earthquake Engineering》2015,13(7):2197-2223

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Preface to special issue on numerical modelling of URM buildings: benchmark project     

Dolce  Mauro  Lagomarsino  Sergio  Varum  Humberto 《Bulletin of Earthquake Engineering》2022,20(4):1897-1900

Bulletin of Earthquake Engineering -  相似文献   

An efficient matrix-free algorithm for the ensemble Kalman filter     

Humberto C. Godinez  J. David Moulton 《Computational Geosciences》2012,16(3):565-575

In this work, we present an efficient matrix-free ensemble Kalman filter (EnKF) algorithm for the assimilation of large data sets. The EnKF has increasingly become an essential tool for data assimilation of numerical models. It is an attractive assimilation method because it can evolve the model covariance matrix for a non-linear model, through the use of an ensemble of model states, and it is easy to implement for any numerical model. Nevertheless, the computational cost of the EnKF can increase significantly for cases involving the assimilation of large data sets. As more data become available for assimilation, a potential bottleneck in most EnKF algorithms involves the operation of the Kalman gain matrix. To reduce the complexity and cost of assimilating large data sets, a matrix-free EnKF algorithm is proposed. The algorithm uses an efficient matrix-free linear solver, based on the Sherman–Morrison formulas, to solve the implicit linear system within the Kalman gain matrix and compute the analysis. Numerical experiments with a two-dimensional shallow water model on the sphere are presented, where results show the matrix-free implementation outperforming an singular value decomposition-based implementation in computational time.  相似文献   

Erratum to: Downward longwave radiation estimates for clear and all-sky conditions in the Sertãozinho region of São Paulo, Brazil     

Nadiane Smaha Kruk  Íria Fernandes Vendrame  Humberto Ribeiro da Rocha  Sin Chan Chou  Osvaldo Cabral 《Theoretical and Applied Climatology》2010,102(3-4):483-483

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