Analysis and Control of Cable-Stayed Bridges Subject to Seismic Action

Cable-stayed bridges are key points in transport networks and at present one of the most challenging structures for the civil engineering community. The integrity of these bridges should be guaranteed even under extremely large earthquakes. This paper begins with a discussion of the advantages of a new non-linear static “Pushover” procedure that includes the three-dimensional contribution of the governing vibration modes. The efficacy and the accuracy of the proposed Pushover in the non-linear seismic analysis of bridges with significant coupling between the towers, deck and cable system is verified. In the second part of this paper, the seismic responses of several cable-stayed bridges have been studied, verifying the influence of the tower shape, cable arrangement and the main span length on the structural behaviour under strong ground motions. Severe damage is identified at critical tower sections by means of extensive non-linear dynamic analyses. Finally, retrofit solutions with viscous dampers (VDs) and yielding metallic dampers (MDs) connecting the deck and the tower in the transverse direction are explored. The proposed connection with dampers effectively prevents yielding of the reinforcement and cracking in the tower legs

Biscarboxy-Functionalized Imidazole and Palladium as Highly Active Catalytic System in Protic Solvents: Methanol and Water

The coupling reaction between aryl bromides and boron reagents is efficiently catalyzed by an in situ generated palladium complex obtained from palladium(II) acetate (0.1 mol%) and 1,3-bis(carboxymethyl)imidazole (0.2 mol%). The catalytic system is very active in protic solvents, especially in methanol. Biaryl derivatives have been prepared in good isolated yields (up to >99%), and additionally styrene and stilbene derivatives have also been prepared by means of this protocol.Financial support from the Ministerio de Ciencia e Innovación (MICINN) of Spain (Project Nos. CTQ2007-65218, CTQ2011-24165, Consolider Ingenio 2010 CSD2007-00006), the Generalitat Valenciana (PROMETEO/2009/039 and FEDER), and the Universidad de Alicante is acknowledged

Globalization and comparative education research: misconceptions and applications of neo-institutional theory

As globalization studies have become central to comparative education research, neo-institutional theory has become the focus of many debates among comparative education researchers investigating the effects of globalization on education. Yet, in spite of this focus, many comparative education researchers have difficulty interpreting neo-institutional theory and how it frames comparative education research. In particular, misconceptions persist related to which strand of neo-institutional theory is the most relevant to comparative education research, and whether or not neo-institutional theory advocates for the homogenization of education and society worldwide. This article addresses these misconceptions by explaining the theory in relation to comparative education research using a specific empirical case as an example. The documented theoretical and methodological diversity within the field of comparative education supports the assertion that neo-institutional theory provides a productive framework for understanding and interpreting comparative education phenomena, but that complementary approaches and methods are useful as well.La teoría neo-institucionalista se ha ubicado en el centro de los debates académicos debido al avance y proliferación de los estudios en educación comparada que sitúan los análisis en el en el marco del proceso de globalización. Sin embargo, a pesar de su relevancia para la educación comparada, la teoría neo-institucionalista sigue generando incertidumbre en cuanto a su empleo e interpretación en la investigación educativa comparada. Parte de esta incertidumbre proviene de la malinterpretación de sus principios, variantes y de su capacidad explicativa. Además, aún persisten varios malentendidos sobre el neo-institucionalismo como por ejemplo, la creencia que sostiene que la versión conocida como la “cultura global” es la única variante del neo-institucionalismo relevante a la investigación educativa comparada. Otra suposición errónea es la que considera que la homogeneización cultural global es uno de los objetivos avanzados por los investigadores que aplican el marco teórico neo-institucional para explicar los fenómenos educativos comparados. Este artículo tiene como propósito abordar esos malentendidos a través de un caso de estudio que utilizaremos como ejemplo. El mismo nos permitirá no sólo clarificar los errores sobre la teoría neo-institucionalista sino también demostrar una de las tantas aplicaciones posibles a la investigación comparada en educación. Los resultados nos permiten sostener que las distintas variantes del marco teórico neo-institucionalista son útiles como acercamiento a la problemática de la educación comparada. De la misma forma también dan cuenta de la necesidad de utilizar métodos y formas de aproximación al conocimiento en forma complementaria. La probada riqueza y diversidad teórica y metodológica del neo-institucionalismo en el campo de la educación comparada asevera fehacientemente que el neo-institucionalismo nos provee de un marco teórico productivo para el entendimiento e interpretación de los fenómenos educativos comparado

Fundamental mode estimation for modern cable-stayed bridges considering the tower flexibility

The design of cable-stayed bridges is typically governed by the dynamic response. This work provides designers with essential information about the fundamental vibration modes, proposing analytical expressions based on the mechanical and geometrical properties of the structure. Different bridge geometries are usually considered in the early design stages until the optimum solution is defined. In these design stages, the analytical formulation is advantageous, because finite-element models are not required and modifying the bridge characteristics is straightforward. The influence of the tower flexibility is included in this study, unlike in previous attempts on mode estimation. The dimensions and proportions of the canonical models proposed in the analytical study stem from the previous compilation of the dimensions of a large number of constructed cable-stayed bridges. Five tower shapes, central or lateral cable-system layouts and box- or U-shaped deck sections, have been considered. The vibration properties of more than 1,000 cable-stayed bridges with main spans ranging from 200 to 800 m long were extracted within an extensive parametric analysis. The Vaschy-Buckingham theorem of dimensional analysis was applied to the numerical results to propose the formulation for period estimation. Finally, the formulas were validated with the vibration properties of 17 real cable-stayed bridges constructed in different countries. The importance of the tower flexibility is verified, and the errors observed are typically below 15%, significantly improving the estimations obtained by previous research works. © 2014 American Society of Civil Engineers

1,2-Functionalized Imidazoles as Palladium Ligands: An Efficient and Robust Catalytic System for the Fluorine-Free Hiyama Reaction

A variety of hydroxy- and amino-functionalized imidazoles were prepared from 1-methyl- and 1-(diethoxymethyl)imidazole by means of isoprene-mediated lithiation followed by reaction with an electrophile. These compounds in combination with palladium acetate were screened as catalyst systems for the Hiyama reaction under fluorine-free conditions using microwave irradiation. The systematic study of the catalytic system showed 1-methyl-2-aminoalkylimidazole derivative L1 to be the best ligand, which was employed under solvent-free conditions with a 1:2 Pd/ligand ratio and TBAB (20 mol-%) as additive. The study has revealed an interaction between the Pd/ligand ratio and the amount of TBAB. The established catalytic system presented a certain degree of robustness, and it has been successfully employed in the coupling of a range of aryl bromides and chlorides with different aryl siloxanes. Furthermore, both reagents were employed in an equimolecular amount, without an excess of organosilane.Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN) (project numbers CTQ2007-65218, CTQ2011-24165), from Consolider Ingenio 2010 (CSD2007-00006), from the Generalitat Valenciana (PROMETEO/2009/039), from the Fondos Europeos para el Desarrollo Regional (FEDER) and from the Universidad de Alicante is acknowledged

Design of hysteretic dampers with optimal ductility for the transverse seismic control of cable-stayed bridges

Cable-stayed bridges require a careful consideration of the lateral force exerted by the deck on the towers under strong earthquakes. This work explores the seismic response of cable-stayed bridges with yielding metallic dampers composed of triangular plates that connect the deck with the supports in the transverse direction. A design method based on an equivalent single-degree of freedom approximation is proposed. This is proved valid for conventional cable-stayed bridges with 200- and 400-m main spans, but not 600 m. The height of the plates is chosen to (1) achieve a yielding capacity that limits the maximum force transmitted from the deck to the towers, and to (2) control the hysteretic energy that the dampers dissipate by defining their design ductility. In order to select the optimal ductility and the damper configuration, a multi-objective response factor that accounts for the energy dissipation, peak damper displacement and low-cycle fatigue is introduced. The design method is applied to cable-stayed bridges with different spans and deck–support connections. The results show that the dissipation by plastic deformation in the dampers prevents significant damage in the towers of the short-to-medium-span bridges under the extreme seismic actions. However, the transverse response of the towers in the bridge with a 600-m main span is less sensitive to the dampers

An Acyl-NHC Osmium Cooperative System: Coordination of Small Molecules and Heterolytic B–H and O–H Bond Activation

The hexahydride complex OsH6(PiPr3)2 (1) activates the C–OMe bond of 1-(2-methoxy-2-oxoethyl)-3-methylimidazolium chloride (2), in addition to promoting the direct metalation of the imidazolium group, to afford a five-coordinate OsCl(acyl-NHC)(PiPr3)2 (3) compound. The latter coordinates carbon monoxide, oxygen, and molecular hydrogen to give the corresponding carbonyl (4), dioxygen (5), and dihydrogen (6) derivatives. Complex 3 also promotes the heterolytic bond activation of pinacolborane (HBpin), using the acyl oxygen atom as a pendant Lewis base. The hydride ligand and the Bpin substituent of the Fischer-type carbene of the resulting complex 7 activate the O–H bond of alcohols and water. As a consequence, complex 3 is a metal ligand cooperating catalyst for the generation of molecular hydrogen, by means of both the alcoholysis and hydrolysis of pinacolborane, via the intermediates 7 and 6.Financial support from the MINECO of Spain (Projects CTQ2014-52799-P and CTQ2014-51912-REDC), the Diputación General de Aragón (E-35), and the European Social Fund (FSE) and FEDER. M.P.G. thanks the Spanish MINECO for her FPI fellowship. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva program

Concepciones de los docentes sobre la matemática. Su incidencia en la enseñanza y el aprendizaje

Los sistemas de creencias son una particular visión del mundo de la matemática e inciden en la manera en que se enfrenta un problema, en los procedimientos, el tiempo y la intensidad del trabajo que se realizará. El propósito de nuestra investigación es indagar cuál es la concepción de los docentes sobre la Matemática, su enseñanza y su aprendizaje y cómo incide esta concepción en su manera de resolver problemas y en su propia práctica docente. Los datos determinan que muy pocos docentes definen la matemática como una construcción que incluye conjeturas, pruebas y refutaciones y la mayoría tiene una visión en la que “saber matemática” es “ser hábil en desarrollar procedimientos e identificar los conceptos básicos de la disciplina”

Developmental Sex Differences in the Metabolism of Cardiolipin in Mouse Cerebral Cortex Mitochondria

Cardiolipin (CL) is a mitochondrial-specific phospholipid. CL content and acyl chain composition are crucial for energy production. Given that estradiol induces CL synthesis in neurons, we aimed to assess CL metabolism in the cerebral cortex (CC) of male and female mice during early postnatal life, when sex steroids induce sex-dimorphic maturation of the brain. Despite the fact that total amount of CL was similar, its fatty acid composition differed between males and females at birth. In males, CL was more mature (lower saturation ratio) and the expression of the enzymes involved in synthetic and remodeling pathways was higher, compared to females. Importantly, the sex differences found in CL metabolism were due to the testosterone peak that male mice experience perinatally. These changes were associated with a higher expression of UCP-2 and its activators in the CC of males. Overall, our results suggest that the perinatal testosterone surge in male mice regulates CL biosynthesis and remodeling in the CC, inducing a sex-dimorphic fatty acid composition. In male's CC, CL is more susceptible to peroxidation, likely explaining the testosterone-dependent induction of neuroprotective molecules such as UCP-2. These differences may account for the sex-dependent mitochondrial susceptibility after perinatal hypoxia/ischemia.Instituto de Investigaciones Bioquímicas de La Plat

Diseño de directrices para el tablero de un puente curvo atirantado, mediante curvas funiculares y antifuniculares de la carga concéntrica introducida por los tirantes

The aim of the following study is to optimize the layout of a curved bridge deck. The guideline proposed is intended to ensure that the entire board is free of vertical axis bending moments. Two mathematical approaches are developed for the directive, a discrete and a continuous. For both, positive and negative sign for the axial load in the deck is studied. To make the possible implementation easier, a least square approximation is made for both signs. Two examples will be developed to end the article.El presente trabajo trata de resolver la optimización del trazado del tablero para un puente en curva. La directriz que se propone pretende conseguir que todo el tablero quede exento de flexiones de eje vertical. Para este diseño se plantean dos formulaciones diferentes, una discreta mediante sumatorios y otra continua mediante ecuaciones diferenciales no lineales. En ambas se estudian los dos posibles signos de la solicitación axil que va a dominar el diseño. Para facilitar la implantación de estas formulaciones, se propone una aproximación mediante mínimos cuadrados. El trabajo de completa con dos ejemplos de aplicación