Simplified serviceability design of jointless structures. Experimental verification and application to typical bridge and building structures

In this article an experimental campaign aimed at validating a previously published simplified serviceability design method of the columns of long jointless structures is presented. The proposed method is also extended to include tension stiffening effects which proved to be significant in structures with small amount of reinforcement subjected to small axial loading. This extension allows significant improvement of predictions for this type of element. The campaign involved columns with different reinforcement and squashing load ratios, given that these parameters had been identified as crucial when designing columns subjected to imposed displacements. Experimental results are presented and discussed, with particular regard to cracking behaviour and structural stiffness. Considerations on tension stiffening effects are also made. Finally, the application of the method to typical bridge and building cases is presented, showing the feasibility of jointless construction, and the limits which should be respected.

Bridge windshield design to avoid aeroelastic phenomena

Since in 1940 the Tacoma Narrows Bridge was destroyed by the wind, aeroelastic instabilities have been recognized as one of the most challenging aspects of bridge design. They can produce long-term fatigue failure through vortex induced vibrations, or sudden collapse through self-excited flutter. These vibrations may also cause discomfort for the users and temporary closure of the bridge. Wind tunnel studies are a very helpful tool to understand these phenomena. By means of them, the critical wind speed at which vortex induced vibration and flutter appear can be precisely determined and the design of the bridge can be reconsidered in the early steps of the process. In this paper, an optimum design of the bridge section is sought. One of the most relevant parameters that influence the stability of a certain deck is the porosity of the barriers. Section model tests have been carried out to find whether an optimum value of the porosity of the barrier exists. This value or range of values must present neither vortex induced vibration nor flutter.

Learning from incidents during bridge erection

Bridge building is a highly uncertain endeavour that entails considerable risk, as attested to by the succession of construction-related incidents and accidents recently reported in Spain and elsewhere. While efforts are being made to improve on-site safety, many issues are still outstanding, such as the establishment of reliability requirements for the ancillary systems used. The problems that must be dealt with in everyday practice, however, are more elementary and often attributable to human error. The overall organisation of the use of bridge construction equipment is in need of improvement. Close cooperation between the bridge engineers responsible for construction planning and ancillary element suppliers is imperative, for flawed interaction between building equipment and the bridge under construction may generate structural vulnerability. External quality assurance should likewise be mandatory

Parametric analysis on bridge reinforced concrete elevated pile-cap foundations

Current design practices recommend to comply with the capacity protection principle, which pays special attention to ensuring an elastic response of the foundations under ground motion events. However, in cases such as elevated reinforced concrete (RC) pile-cap foundation typologies, this design criterion may lead to conservative designs, with excessively high construction costs. Reinforced concrete elevated pile-cap foundations is a system formed by a group of partially embedded piles connected through an aboveground stayed cap and embedded in soil. In the cases when they are subjected to ground motions, the piles suffer large bending moments that make it difficult to maintain their behavior within the elastic range of deformations. Aiming to make an in-depth analysis of the nonlinear behavior of elevated pile-cap foundations, a cyclic loading test was performed on a concrete 2x3 pile configuration specimen of elevated pile-cap foundation. Two results of this test, the failure mechanism and the ductile behavior, were used for the calibration of a numerical model built in OpenSees framework, by using a pushover analysis. The calibration of the numerical model enabled an in-depth study of the seismic nonlinear response of this kind of foundations. A parametric analysis was carried for this purpose, aiming to study how sensitive RC elevated pile-cap foundations are, when subjected to variations in the diameter of piles, reinforcement ratios, external loads, soil density or multilayer configurations. This analysis provided a set of ductility factors that can be used as a reference for design practices and which correspond to each of the cases analyzed.

Transversal load distribution on bridge decks

An orthotropic rectangular plate is analysed. The plate has been considered simply supported in two opposite edges and general boundary conditions along the remainder edges. Matrix formulation, very convenient for programming on a digital computer, is used through the text. This technique is applied to an actual bridge deck and the results are compared with those obtained by means of the Guyon-Massonet-Rowe method

A procedure to track vibration modes under changing external factors: application to a pedestrian bridge

A low-cost vibration monitoring system has been developed and installed on an urban steel- plated stress-ribbon footbridge. The system continuously measures: the acceleration (using 18 triaxial MEMS accelerometers distributed along the structure), the ambient temperature and the wind velocity and direction. Automated output-only modal parameter estimation based on the Stochastic Subspace Identification (SSI) is carried out in order to extract the modal parameters, i.e., the natural frequencies, damping ratios and modal shapes. Thus, this paper analyzes the time evolution of the modal parameters over a whole-year data monitoring. Firstly, for similar environmental/operational factors, the uncertainties associated to the time window size used are studied and quantified. Secondly, a methodology to track the vibration modes has been established since several of them with closely-spaced natural frequencies are identified. Thirdly, the modal parameters have been correlated against external factors. It has been shown that this stress-ribbon structure is highly sensitive to temperature variation (frequency changes of more than 20%) with strongly seasonal and daily trends

Doubling the width of the platform of the San Pedro bridge in Spain

The San Pedro Bridge has six spans and is 750 m (2460 ft) long, 88 m (290 ft) high, 12 m (39 ft) wide, and curved with a radius of 700 m (2300 ft). It was built in 1993 using the cantilever method. Its super - structure is a prestressed concrete box girder with main spans of 150 m (490 ft). In 2008 and 2009, the width of the platform was enlarged to 23 m (75 ft) using five movable sets of scaffolding. The bridge remained open to traffic during construction. The original platform was widened 6 m (20 ft) on each side by connecting a new lightweight concrete cantilever to the original upper slab. These cantilevers were supported by steelstruts. The tie into the upper slab was made with new transverse post-tensioned tendons. The original superstructure was strengthened to resist the additional dead load of the expansion and live loads of the extra traffic. An additional new central web and a composite concrete-steel section were constructed and connected to the concrete box and central web using vertical high-strength post-tensioning bars. Also, external post-tensioning cables were implemented. It was also necessary to strengthen the connection of the original concrete box section to the piers. Detailed calculations were performed to evaluate the load distribution transmitted to the piers by the webs and by the original inclined concrete walls of the box girder. Finally, a detailed second-order-analysis of the complete structure was made to guarantee the resistance of the piers compared with actual loads

Minimum volume for a liquid bridge between equal disks

The lower stability limit for axisymmetric floating zones at rest between equal coaxial disks has been experimentally verified for several disk-separation/disk-diameter ratios by using the neutral buoyancy technique. Results show a close agre ment with theory in the case of bridge disruption and a wide scatter in the case of bridge etachment.

IDR/UPM facilities for liquid bridge experimentation on earth under microgravity conditions

Besides space laboratories for in-orbit experimentation, Earth based facilities for laboratory experimentation are of paramount importance for the enhancement on liquid bridge knowledge. In spite of the constraints imposed by simulated microgravity (which force to work either with very small size liquid bridges or by using the Plateau tank technique, amongst other techniques), the availability and accessibility of Earth facilities can circumvent in many cases the drawbacks associated with simulated microgravity conditions. To support theoretical and in orbit experimental studies on liquid bridges under reduced gravity conditions, several ground facilities were developed at IDR. In the following these ground facilities are briefly described, and main results obtained by using them are cited.

Underbridge: relocalización del Gujari Bazaar bajo el Ellis Bridge, Ahmedabad, India

Underbridge: relocalización del Gujari Bazaar bajo el Ellis Bridge, Ahmedabad, India

Objetos tenaces : adaptive reuse en Meatpacking, 1970–1985

OBJETOS TENACES versa sobre la práctica del adaptive reuse (la “reutilización adaptativa”, la reconversión) explicado a través del fenómeno de ruptura, suspensión y reconfiguración de vínculos que el objeto arquitectónico tiene con respecto a su medio económico, sociocultural, normativo y de utilitas. Se trata de un fenómeno en tres fases, muy próximo al mecanismo empleado por el readymade y por el display, que en arquitectura parte de la crisis que supone un cambio de circunstancias, un desarraigo del objeto respecto de su ámbito anterior. El mecanismo tiene vocación de intervención mínima, desde un posicionamiento actual que comprende el mundo construido como una realidad “ya hecha”, y donde las operaciones de proyecto son acciones de transformación que llevan de una situación de obsolescencia a otra de vigencia renovada, es decir, de una realidad completa a otra igualmente completa. Para ello, la investigación se sirve de tres ejemplos de un mismo entorno geográfico (el área en torno a Meatpacking, en el lado oeste del bajo Manhattan, Nueva York) y temporal (las últimas décadas del siglo XX, en las que los casos se solapan a pesar de tener desarrollos cronológicos diversos). Bell Telephone Laboratories, The West Side Improvement y The National Biscuit Company, reconvertidos a Westbeth, a The High Line y a Chelsea Market, construyen juntos el argumento por suma de conceptos, por adición de fenómenos, estudiando las cualidades y las circunstancias que hacen posible la continuidad de las estructuras, es decir, su supervivencia. El texto forma un corpus que proporciona algunas de las claves del objeto denominado como tenaz a través del análisis sincrónico del antes y el después de su puesta en crisis. A tal efecto, se exponen una serie de figuras razonadas entre las cuales figuran el lijado del barniz, los hilos compartidos, la máscara, la momificación y la vitrina, el puente sobre le desfiladero, el enfriamiento, o las reliquias, incrustaciones y adherencias, todas ellas encaminadas a explicar el proceso de renovación del artefacto como un cambio en el sentido, en el significado, y no tanto en lo material. Entre las consideraciones de la tesis está, por un lado, el carácter relativo del término tenacidad, concepto que define a los objetos que se encuentran y se reconocen en su idoneidad, que tienen capacidad de adaptación, y que precisan finalmente de grandes dosis de pragmatismo para su reconfiguración, siendo todas éstas condiciones necesarias pero sólo suficientes a posteriori. Por otro lado, el texto reflexiona acerca del intangible que comparten todos los objetos así llamados y que consiste en la condición, quizá formidable, de ser reconocibles por parte de los sucesivos intervinientes de su historia, convencidos de que su renovación supone una oportunidad; su desaparición, una pérdida. Finalmente, la investigación apunta hacia el concepto de anacronismo como justificación para los objetos que se demuestran adaptables a épocas sucesivas, y que encajan en el tiempo de forma compleja. ABSTRACT TENACIOUS OBJECTS deals with the practice of the adaptive reuse explained by means of the phenomenon of rupture, suspension and reconfiguration of links that the architectural object has vis-à-vis its economic, socio-cultural and regulatory environment, and its utilitas. It is a phenomenon structured in three stages, very close to the mechanism used by the readymade and by the display, which in architecture arise from the crisis that leads to a change in circumstances, an alienation of the object regarding its previous environment. The mechanism aims to the minimum intervention, from a current positioning which understands the world built as a reality “already made”, and where the operations of the project are transformative actions that take us from a situation of obsolescence to a situation of renewed validity, that is, from a complete reality to one just as complete. For this purpose, the research makes use of three examples in the same geographical area (the Meatpacking Discrict, in the Lower West Side of Manhattan, New York) and the same period (the last decades of the 20th century, in which the cases overlap in spite of their diverse chronological developments). Bell Telephone Laboratories, The West Side Improvement and The National Biscuit Company, reconverted into Westbeth, The High Line and Chelsea Market, make up, together, the argument as a sum of concepts, and addition of phenomena, studying the qualities and circumstances which make the continuity of the structures possible, that is, their survival. The text forms a corpus that provides some of the keys of the so-called tenacious object by means of the synchronic analysis of before and after its crisis. To this end, a series of reasoned figures is presented, including the sanding of varnish, the shared threads, the mask, the mummification and the display cabinet, the bridge over the gorge, cooling, or the relics, incrustations and adherences, all of them aimed at explaining the renovation process of the artifact as a change in the sense and the meaning, rather than the material. The considerations of this dissertation include, on the one hand, the relative nature of the term tenacity, a concept which defines the objects found and recognized in their suitability, that are capable of adapting and which finally require large doses of pragmatism for their reconfiguration, all these conditions being necessary but only sufficient a posteriori. On the other hand, the text reflects on the intangible shared among all the so-called objects, and which consists of the condition, perhaps extraordinary, of being recognized by the subsequent interveners of their history, convinced that their renovation represents an opportunity; their disappearance, a loss. Finally, the dissertation studies the concept of anachronism as a justification for the objects that prove to adapt to subsequent periods, and which fit in time in a complex manner.

Bridge damage identification from moving load induced deflection based on wavelet transform and Lipschitz exponent

The wavelet transform and Lipschitz exponent perform well in detecting signal singularity.With the bridge crack damage modeled as rotational springs based on fracture mechanics, the deflection time history of the beam under the moving load is determined with a numerical method. The continuous wavelet transformation (CWT) is applied to the deflection of the beam to identify the location of the damage, and the Lipschitz exponent is used to evaluate the damage degree. The influence of different damage degrees,multiple damage, different sensor locations, load velocity and load magnitude are studied.Besides, the feasibility of this method is verified by a model experiment.

Functional transitions in myosin: Formation of a critical salt-bridge and transmission of effect to the sensitive tryptophan

For analyzing the mechanism of energy transduction in the “motor” protein, myosin, it is opportune both to model the structural change in the hydrolytic transition, ATP (myosin-bound) + H2O → ADP⋅Pi (myosin-bound) and to check the plausibility of the model by appropriate site-directed mutations in the functional system. Here, we made a series of mutations to investigate the role of the salt-bridge between Glu-470 and Arg-247 (of chicken smooth muscle myosin) that has been inferred from crystallography to be a central feature of the transition [Fisher, A. J., Smith, C. A., Thoden, J. B., Smith, R., Sutoh, K., Holden, H. M., & Rayment, I. (1995) Biochemistry 34, 8960–8972]. Our results suggest that whether in the normal, or in the inverted, direction an intact salt-bridge is necessary for ATP hydrolysis, but when the salt-bridge is in the inverted direction it does not support actin activation. Normally, fluorescence changes result from adding nucleotides to myosin; these signals are reported by Trp-512 (of chicken smooth muscle myosin). Our results also suggest that structural impairments in the 470–247 region interfere with the transmission of these signals to the responsive Trp.

Full Bridge MMC Converter Optimal Design to HVDC Operational Requirements

This project is funded by RTE, Paris, France

Structure of the glycosylphosphatidylinositol anchor of an arabinogalactan protein from Pyrus communis suspension-cultured cells

Arabinogalactan proteins (AGPs) are proteoglycans of higher plants, which are implicated in growth and development. We recently have shown that two AGPs, NaAGP1 (from Nicotiana alata styles) and PcAGP1 (from Pyrus communis cell suspension culture), are modified by the addition of a glycosylphosphatidylinositol (GPI) anchor. However, paradoxically, both AGPs were buffer soluble rather than membrane associated. We now show that pear suspension cultured cells also contain membrane-bound GPI-anchored AGPs. This GPI anchor has the minimal core oligosaccharide structure, d-Manα(1–2)-d-Manα(1–6)-d-Manα(1–4)-d-GlcN-inositol, which is consistent with those found in animals, protozoa, and yeast, but with a partial β(1–4)-galactosyl substitution of the 6-linked Man residue, and has a phosphoceramide lipid composed primarily of phytosphingosine and tetracosanoic acid. The secreted form of PcAGP1 contains a truncated GPI lacking the phosphoceramide moiety, suggesting that it is released from the membrane by the action of a phospholipase D. The implications of these findings are discussed in relation to the potential mechanisms by which GPI-anchored AGPs may be involved in signal transduction pathways.