Influence of Different European Code Provisions for Capacity Design on the Seismic Performance of Reinforced Concrete Frames

Performance-based seismic codes ensure proper inelastic behaviour of reinforced concrete frames through capacity design, among others. This strategy relies not only on avoiding brittle failures and providing ductility to plastic hinges but also in their distribution within the frame aimed at a greater number of storeys involved in the eventual collapse mechanism. Although codes are generally in agreement to some basic principles in order to ensure capacity design, they show some discrepancies regarding the specific strategies. In this paper, capacity design provisions proposed by some European current codes—Eurocode 8, Italian NTC, and Spanish NCSE-02—are compared, and their effectiveness is discussed. The alternative formulation proposed by Italian code for “strong column–weak beam” turns out to be not suitable under specific circumstances, such as with large gravity loads or significant cantilever deformation in lower storeys. Regarding the value of axial load in columns to be considered for the calculation of shear and moment capacities, provisions in the three codes could eventually cause unconservative design for perimeter columns. The Spanish whole set of provisions is proved to not be effective due to their different fundamentals—they are based on overstrength instead of capacity. For all the three cases, some alternative procedures are suggested in this work

Numerical evaluation of the Green's functions for arbitrarily shaped cylindrical enclosures and their optimization by a new spatial images method

IIn this paper, a spatial image technique is used to efficiently calculate the mixed potential Green’s functions associated with electric sources, when they are placed inside arbitrarily shaped cylindrical cavities. The technique is based on placing electric dipole images and charges outside the cavity region. Their strength and orientation are thencalculated by imposing the appropriate boundary conditions for the fields at discrete points on the metallic wall. A method for the assessment of the potentials accuracy is proposed, and several optimization techniques are presented. Three cavities are analyzed to demonstrate the usefulness of the techniques. The cutoff frequencies and potentials patterns are compared to those obtained by a standard finite elements technique, showing excellent agreement. Finally, a band-pass filter based on coupled lines is analyzed, demonstrating the practical value of the technique.This work has been developed with support from the Spanish National Project (CICYT) with reference TEC2004-04313-C02-02/TCM, and the Regional Seneca Project with reference 02972/PI/0

A Rich Morphological Diversity of Biosaline Drying Patterns Is Generated by Different Bacterial Species, Different Salts and Concentrations: Astrobiological Implications

Biosaline formations (BSFs) are complex self-organized biomineral patterns formed by ‘‘hibernating’’ bacteria as the biofilm that contains them dries out. They were initially described in drying biofilms of Escherichia coli cells + NaCl. Due to their intricate 3-D morphology and anhydrobiosis, these biomineralogical structures are of great interest in astrobiology. Here we report experimental data obtained with various alkali halide salts (NaF, NaCl, NaBr, LiCl, KCl, CsCl) on BSF formation with E. coli and Bacillus subtilis bacteria at two saline concentrations: 9 and 18 mg/mL. Our results indicate that, except for LiCl, which is inactive, all the salts assayed are active during BSF formation and capable of promoting the generation of distinctive drying patterns at each salt concentration. Remarkably, the BSFs produced by these two bacterial species produce characteristic architectural hallmarks as the BSF dries. The potential biogenicity of these biosaline drying patterns is studied, and the astrobiological implications of these findings are discusse

Natural structures: strategies for geometric and morphological optimization

p. 893-906For centuries, architects and engineers have been searching the most efficient structural arrangements for their projects. Some of them have founded their proposals on the principle of biomimesis. The aim of their approach was to check how useful were 'for structural purposes' some geometrical patterns displayed by Nature on organic or inorganic bodies. Nature develops its structures in order to reach always optimal energetic solutions on a long term basis. The most usual arrangements are: pneus, shells, trees, webs and skeletons. All of them are controlled by four main factors: nature of forces, global form, local design and quality of material. Additional parameters, like pattern or material lightening, sometimes changes substantially the resulting geometry, and also some other general features as flexibility, integration, continuity, or self-straining are surrounding in most examples. This paper presents the achieved results on this topic by relevant authors of diverse fields: from the drawings of micro-organisms by the naturalist Häckel and the descriptive studies of the biologist Thompson, through the topological analysis of the patterns by the engineer Wester, the studies of natural lightweight structures by the architect F. Otto, to the final applications to light mega-structures by the engineers R. Le Ricolais or Buckminster Fuller.Pérez García, AJ.; Gómez Martínez, F. (2010). Natural structures: strategies for geometric and morphological optimization. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/695

Application of composite spectrum in agricultural machines

Producción CientíficaComposite spectrum (CS) is a data-fusion technique that reduces the number of spectra to be analyzed, simplifying the analysis process for machine monitoring and fault detection. In this work, vibration signals from five components of a combine harvester (thresher, chopper, straw walkers, sieve box, and engine) are obtained by placing four accelerometers along the combine-harvester chassis in non-optimal locations. Four individual spectra (one from each accelerometer) and three CS (non-coherent, coherent and poly-coherent spectra) from 18 cases are analyzed. The different cases result from the combination of three working conditions of the components—deactivated (off), balanced (healthy), and unbalanced (faulty)—and two speeds—idle and maximum revolutions per minute (RPM). The results showed that (i) the peaks can be identified in the four individual spectra that correspond to the rotational speeds of the five components in the analysis; (ii) the three formulations of the CS retain the relevant information from the individual spectra, thereby reducing the number of spectra required for monitoring and detecting rotating unbalances within a combine harvester; and, (iii) data noise reduction is observed in coherent and poly-coherent CS with respect to the non-coherent CS and the individual spectra. This study demonstrates that the rotating unbalances of various components within agricultural machines, can be detected with a reduced number of accelerometers located in non-optimal positions, and that it is feasible to simplify the monitoring with CS. Overall, the coherent CS may be the best composite spectra formulation in order to monitor and detect rotating unbalances in agricultural machines

Enfoque técnico-económico para el dimensionamiento de transformadores de distribución

In colombia, distribution transformer ratings are selected upon the rated current flowing through circuits and branches feeding low-voltage networks. As a result, transformers turn out oversized. This paper shows a methodology for selecting distribution transformers based on technical and technoeconomical criteria as an alternative to current methodologies complying with NTC 2050. Whereas, technical criteria assure the operation of transformer within its maximum efficiency without loss of shelf life, the technoeconomical criteria balance a reasonable reduction of shelf life with a lower investment and service cost, even though the transformer is operating out of its maximun efficiency point. As a matter of fact, this later approach is of bigger interest for power distribution utilities. The proposed methodology, added to the overload capability of the transformers, allow to find the most suitable ratings in order to supply the expected demand, with lower investment and service costs and higher efficiency through the assets shelf life.En Colombia, la selección de la capacidad de los transformadores de distribución se realiza con base en la corriente con la que se calculan las acometidas y ramales alimentadores de las redes de baja tensión, lo cual trae como consecuencia un sobredimensionamiento. Este artículo presenta una metodología para la selección de los transformadores de distribución basada en criterios técnicos y técnico-económicos como una alternativa a las metodologías tradicionales derivadas de los lineamientos de la NTC 2050. Por el criterio técnico se asegura que el transformador operará en la zona de máxima eficiencia sin pérdida de vida útil por encima de la normal esperada. El criterio técnico-económico asegura una pérdida de vida dentro de lo normal esperado y un costo de inversión y operación del equipo menor, aunque el transformador opere por fuera de la zona de máxima eficiencia. Esta última alternativa es más atractiva para las empresas distribuidoras. La evaluación que realiza la metodología, sumada a la capacidad inherente de sobrecarga temporal de los transformadores, posibilita encontrar la capacidad del transformador con la cual se pueda atender de manera adecuada la demanda esperada con un menor costo de inversión y operación, además de mayor eficiencia a lo largo de la vida útil esperada del activo

La valoración del Greco por los críticos y escritores del 98.

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