Damage tolerance of cold drawn ferritic-austenitic stainless steels wires for prestressed concrete

Damage tolerance of high strength cold-drawn ferritic–austenitic stainless steel wires is assessed by means of tensile fracture tests of cracked wires. The fatigue crack is transversally propagated from the wire surface. The damage tolerance curve of the wires results from the empirical failure load when given as a function of crack depth. As a consequence of cold drawing, the wire microstructure is orientated along its longitudinal axis and anisotropic fracture behaviour is found at macrostructural level at the tensile failure of the cracked specimens. An in situ optical technique known as video image correlation VIC-2D is used to get an insight into this failure mechanism by tensile testing transversally fatigue cracked plane specimens extracted from the cold-drawn wires. Finally, the experimentally obtained damage tolerance curve of the cold-drawn ferritic–austenitic stainless steel wires is compared with that of an elementary plastic collapse model and existing data of two types of high strength eutectoid steel currently used as prestressing steel for concrete.

Bond Modelling of prestressed concrete during the prestressing force release

This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in a series of tests.

Bond modelling of prestressed concrete during the prestressing force release

This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

Study of bond stress-slip relationship and radial dilation in prestressed concrete

This paper presents two test procedures for evaluating the bond stress–slip and the slip–radial dilation relationships when the prestressing force is transmitted by releasing the steel (wire or strand) in precast prestressed elements. The bond stress–slip relationship is obtained with short length specimens, to guarantee uniform bond stress, for three depths of the wire indentation (shallow, medium and deep). An analytical model for bond stress–slip relationship is proposed and compared with the experimental results. The model is also compared with the experimental results of other researchers. Since numerical models for studying bond-splitting problems in prestressed concrete require experimental data about dilatancy angle (radial dilation), a test procedure is proposed to evaluate these parameters. The obtained values of the radial dilation are compared with the prior estimated by numerical modelling and good agreement is reached

An analytical model for simulating the bond of prestressed concrete during the prestressed force release

A bond analytical model is proposed in this paper. The model is capable of reproducing the bond stress developed between the steel and concrete, in precast prestressed elements, during the entire process of prestressing force release. The bond stress developed in the transmission zone, where the bond stress is not constant, is also obtained. The steel and concrete stresses as well as the slip between both materials can be also estimated by means of the relation established in the model between these parameters and the bond stress. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and it is extended to evaluate the transmission length. This has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

An analytical model for simulating the bond of prestressed concrete during the prestressed force release

A bond analytical model is proposed in this paper. The model is capable of reproducing the bond stress developed between the steel and concrete, in precast prestressed elements, during the entire process of prestressing force release. The bond stress developed in the transmission zone, where the bond stress is not constant, is also obtained. The steel and concrete stresses as well as the slip between both materials can be also estimated by means of the relation established in the model between these parameters and the bond stress. The model is validated with the results of a series of tests, considering different steel indentation depths and concrete covers and it is extended to evaluate the transmission length. This has been checked by comparing the transmission length predicted by the model and one measured experimentally in two series of tests.

Optimization of prestressed concrete bridge decks

In this paper a summary of the methods presently used for optimization of prestressed concrete bridge decks is given. By means of linear optimization the sizes of the prestressing cables with a given fixed geometry are obtained. This simple procedure of linear optimization is also used to obtain the ‘best’ cable profile, by combining a series of feasible cable profiles. The results are compared with the ones obtained by other researchers. A step ahead in the field of optimization of prestressed bridge decks is the simultaneous search of the geometry and size of the prestressing cables. A non-linear programming for optimization is used, namely, ‘the steepest gradient method’. The results obtained are compared with the ones computed previously by means of linear programming techniques. Finally, the general problem of structural optimization is considered. This problem consists in finding the sizes and geometries of the prestressing cables as well as the longitudinal variation of the concrete section.

Beitrag zur Entwicklung der Querschnittsgestaltung im Verbundbrückenbau

Die grafische Darstellung des Verbundquerschnittes mit einer oberen Betonplatte und einem darunter liegenden Stahlträger war seit seiner Vorstellung in den 1950er Jahren ein Symbol, das weit über die Theorie hinausging und weite Verbreitung in der Praxis des Verbundbrückenbaus fand. Seit den 1970er bzw. 1980er Jahren hat dieses Bild – bedingt durch neue und freiere Formen, Beton und Stahl miteinander zu kombinieren – seine Symbolhaftigkeit verloren. In Deutschland und Spanien wurde der Doppelverbund mit unten liegenden Betonplatten in Bereichen mit negativen Momenten eingeführt, in Frankreich werden Stahlträger auch in vorgespannten Betonquerschnitten eingebettet. Beide Ansätze haben dazu beigetragen, dass in der Gegenwart die Materialien Stahl und Beton im Verbundbau frei miteinander kombiniert werden können. On the development of sections in composite bridges. A comprehensive theory of composite construction was established in Germany by Sattler in 1953. The theoretical image of the composite section with a superior concrete slab and a lower metallic structure was shaped in addition to the analytical resolution. Theory and graphical representation were going to be known together in Europe. This figure was repeated in all theoretical and academic publications, so becoming an authentic icon of the composite section. Its translation to the bridge deck in flexion was obvious: the superior slab defines the tread platform, while the metallic structure was left off-hook at the bottom. Nevertheless, in continuous decks the section is not optimal at all in zones of negative bending moments. But the overcoming of the graphical representation of the theory did not happen immediately. It was produced after a process in which several European countries played an active role and where different mechanisms of technological transference were developed. One approach to this overcoming is the “double composite action”, with a lower concrete slab in areas of a negative bending moment. The first accomplishments, a bridge in Orasje built in 1968 with 134 m span, as well as the publications of the system proposed by Fabrizio de Miranda in 1971 did not extend nor had continuity. Spanish bridges by Fernández Ordoñez and Martínez Calzón used double composite action for the first time in 1979. The German team of Leonhard, Andrä und partners, has used it since the end of the 1980's to solve bridges of great span. Once the technology has been well known thanks to the ASCE International Congress and the Spanish International Meetings organised by the “Colegio de Ingenieros de Caminos”, double composite action has been integrated well into the structural vocabulary everywhere. In France the approach was different. What Michel Virlogeux calls “double floor composite section” was reached as an evolution of prestressed concrete bridges. In an experimental process widely known, the external prestressing allows weight reduction by diminishing the thickness of the concrete webs. The following step, in the 1980's, was the substitution of the webs by metallic elements: stiffened plates, trusses or folded plates. A direct result of this development is the Brass de la Plaine Bridge in the Reunion Island in 2001 with 280 m span. Both approaches have contributed to a freedom of design in composite construction in steel and concrete today.

La barrera del análisis estructural y la representación gráfica en el desarrollo de los proyectos arquitectónicos: el caso de la Ópera de Sidney

En numerosas ocasiones a lo largo de la historia la imaginación de los creadores ha ido por delante de las posibilidades técnicas de cada momento. Así, muchas de estas nuevas ideas han requerido largos periodos de tiempo para materializarse como realidad construida, hasta que el desarrollo tecnológico e industrial hubo alcanzado un grado de madurez suficiente. En el campo de la arquitectura, estas limitaciones técnicas se han ido acotando paulatinamente hasta desembocar en la situación actual en la que cualquier planteamiento formal puede ser representado gráficamente y analizado desde un punto de vista estructural, superádose de este modo la barrera existente históricamente en el tratamiento de las formas. A lo largo del presente tesis doctoral se analiza cómo la formulación del Método de los Elementos Finitos en la década de los cincuenta y las curvas de Bézier en la década de los sesenta del siglo pasado y la posterior generalización de los ordenadores personales y de los programas informáticos asociados (C.A.D. y F.E.M. principalmente) en los estudios de arquitectura e ingeniería a partir de la década de los noventa, posibilitó el desarrollo de cualquier propuesta arquitectónica, por compleja que ésta fuese, provocando una verdadera revolución a nivel formal en el mundo de la arquitectura, especialmente en el campo de la edificación singular o icónica. Se estudia este proceso a través de ocho edificios; cuatro anteriores y otros tantos posteriores a la desaparición de la barrera anteriormente referida, establecida de forma simbólica en la década de los años ochenta del siglo XX: Frontón de Recoletos en Madrid, Edificio Seagram en Nueva York, Habitat ’67 en Montreal, Ópera de Sídney, museo Guggenheim de Bilbao, ampliación del Victoria & Albert Museum en Londres, tanatorio “Meiso no Mori” en Gifu y nueva sede de la CCTV en Pekín. De entre ellos, la Ópera de Sídney, obra del arquitecto danés Jørn Utzon, condensa gran parte de los aspectos relevantes investigados en relación a la influencia que los métodos de representación y análisis estructural ejercen en la concepción y construcción de las obras de arquitectura. Por este motivo y por considerarse un hito de la arquitectura a nivel global se toma como caso de estudio. La idea general del edificio, que data de 1956, se enmarca en una época inmediatamente anterior a la del desarrollo científico y tecnológico anteriormente referido. Esta ausencia de herramientas de diseño disponibles acordes a la complejidad formal de la propuesta planteada condicionó enormente la marcha del proyecto, dilatándose dramáticamente en el tiempo y disparándose su coste hasta el punto de que el propio arquitecto danés fue separado de las obras antes de su conclusión. Además, la solución estructural finalmente construida de las cubiertas dista mucho de la prevista por Utzon inicialmente. Donde él había imaginado unas finas láminas de hormigón flotando sobre el paisaje se materializó una estructura más pesada, formada por costillas pretensadas de hormigón con unas secciones notablemente mayores. La forma también debió ser modificada de modo ostensible respecto a la propuesta inicial. Si este edificio se pretendiese construir en la actualidad, con toda seguridad el curso de los acontecimientos se desarrollaría por senderos muy diferentes. Ante este supuesto, se plantean las siguientes cuestiones: ¿sería posible realizar un análisis estructural de la cubierta laminar planteada por Utzon inicialmente en el concurso con las herramientas disponibles en la actualidad?; ¿sería dicha propuesta viable estructuralmente?. A lo largo de las siguientes páginas se pretende dar respuesta a estas cuestiones, poniendo de relieve el impacto que los ordenadores personales y los programas informáticos asociados han tenido en la manera de concebir y construir edificios. También se han analizado variantes a la solución laminar planteada en la fase de concurso, a través de las cuales, tratando en la medida de lo posible de ajustarse a las sugerencias que Ove Arup y su equipo realizaron a Jørn Utzon a lo largo del dilatado proceso de proyecto, mejorar el comportamiento general de la estructura del edificio. Por último, se ha pretendido partir de cero y plantear, desde una perspectiva contemporánea, posibles enfoques metodológicos aplicables a la búsqueda de soluciones estructurales compatibles con la forma propuesta originalmente por Utzon para las cubiertas de la Ópera de Sídney y que nunca llegó a ser construida (ni analizada), considerando para ello los medios tecnológicos, científicos e industriales disponibles en la actualidad. Abstract On numerous occasions throughout history the imagination of creators has gone well beyond of the technical possibilities of their time. Many new ideas have required a long period to materialize, until the technological and industrial development had time to catch up. In the architecture field, these technical limitations have gradually tightened leading to the current situation in which any formal approach can be represented and analyzed from a structural point of view, thus concluding that the structural analysis and the graphical representation’s barrier in the development of architectural projects has dissappeared. Throughout the following pages it is examined how the development of the Finite Element Method in the fifties and the Bezier curves in the sixties of the last century and the subsequent spread of personal computers and specialized software in the architectural and engineering offices from the nineties, enabled the development of any architectural proposal independently of its complexity. This has caused a revolution at a formal level in architecture, especially in the field of iconic building. This process is analyzed through eight buildings, four of them before and another four after the disappearance of the above mentioned barrier, roughly established in the eighties of the last century: Fronton Recoletos in Madrid, Seagram Building in New York Habitat '67 in Montreal, Sydney Opera House, Guggenheim Museum Bilbao, Victoria & Albert Museum extension in London, Crematorium “Meiso no Mori” in Gifu and the new CCTV headquarters in Beijing. Among them, the Sydney Opera House, designed by Danish architect Jørn Utzon, condenses many of the main aspects previously investigated regarding the impact of representation methods and structural analysis on the design and construction of architectural projects. For this reason and also because it is considered a global architecture milestone, it is selected as a case study. The building’s general idea, which dates from 1956, is framed at a time immediately preceding the above mentioned scientific and technological development. This lack of available design tools in accordance with the proposal’s formal complexity conditioned enormously the project’s progress, leading to a dramatic delay and multiplying the final budget disproportionately to the point that the Danish architect himself was separated from the works before completion. Furthermore, the built structure differs dramatically from the architect’s initial vision. Where Utzon saw a thin concrete shell floating over the landscape a heavier structure was built, consisting of prestressed concrete ribs with a significantly greater size. The geometry also had to be modified. If this building were to built today, the course of events surely would walk very different paths. Given this assumption, a number of questions could then be formulated: Would it be possible to perform a structural analysis of Utzon’s initially proposed competition-free-ways roof’s geometry with the tools available nowadays?; Would this proposal be structurally feasable?. Throughout the following pages it is intended to clarify this issues, highlighting personal computers and associated software’s impact in building design and construction procedures, especially in the field of iconic building. Variants have also been analyzed for the laminar solution proposed in the competition phase, through which, trying as far as possible to comply with the suggestions that Ove Arup and his team did to Jørn Utzon along the lengthy process project, improving the overall performance of the building structure. Finally, we have started from scratch and analyzed, from a contemporary perspective, possible structural solutions compatible with Utzon’s Opera House’s original geometry and vision –proposal that was never built (nor even analyzed)-, taking into consideration the technological, scientific and industrial means currently available.

Influencia de la configuración geométrica de placas prefabricadas para forjados en las tensiones originadas por la transferencia del pretensado en elementos realizados con armaduras pretesas ancladas por adherencia

Las piezas pretensadas de hormigón presentan zonas muy solicitadas correspondientes a la zona de transferencia. En muchos casos se ha detectado figuración en tales zonas cuyo origen está ligado a la transferencia de la fuerza de pretensado, pudiendo llegar a causar el rechazo de la pieza. En el caso de las piezas prefabricadas con armaduras pretesas adherentes, no siempre es posible disponer armado transversal para controlar esta fisuración, ya sea por el proceso constructivo, ya sea por disponer en general de secciones transversales muy optimizadas. Recientemente se desarrolló una nueva tipología de piezas de hormigón prefabricado para forjados unidireccionales pretensadas con armadura activa pretesa y sin armadura transversal. La tipología se asimila a una sección en PI invertida, con alas de gran envergadura en comparación con el ancho de nervio, y armadura activa distribuida en las alas. Este diseño parece propenso a la aparición de fisuración en el momento de la transferencia del pretensado. Así, se han producido fallos de carácter frágil: colapso de piezas ya colocadas en obra, separándose la losa inferior de los nervios y cayendo sobre el piso. Las herramientas de análisis usuales han resultado inútiles al aplicarse a la investigación de esta patología. Para afrontar el estudio de los problemas detectados en la tipología, se ha analizado el fenómeno de las tensiones de tracción en la zona de transferencia, usualmente denominadas exfoliación y estallido, así como los métodos de análisis aplicables a elementos pretesos sin armadura transversal. En algunas ocasiones se trata del resultado de trabajos desarrollados para piezas postesadas, o para calcular cuantías de armadura transversal, adaptados a posteriori. También existen métodos desarrollados específicamente para piezas pretesas sin armadura transversal. Junto a los factores considerados en los métodos existentes se han localizado otros, no tenidos en cuenta habitualmente, pero que pueden ser determinantes en piezas no convencionales, como son: la existencia de pretensado superior e inferior, la falta de simetría de la sección transversal, el ancho variable de las piezas, una relación entre el ancho del ala y el espesor de los nervios elevada, la distribución transversal del pretensado en relación al ancho variable. Además, la mayoría de los métodos se han basado en simplificaciones bidimensionales. Para tener en cuenta la influencia de estos factores, se han modelizado piezas en las que varían tanto la geometría de la sección transversal y la cuantía de pretensado, como la ley de adherencia o la distribución de armadura activa en la sección. Estos modelos se han analizado mediante el método de elementos finitos, efectuándose u análisis elástico lineal tridimensional. En general, los métodos existentes no han predicho adecuadamente las tensiones obtenidas mediante elementos finitos. Sobre los resultados obtenidos por elementos finitos se ha desarrollado un ajuste experimental, que presentan un alto grado de correlación y de significación, así como una reducida dispersión y error relativo. En consecuencia, se propone un método de obtención de la tensión máxima de exfoliación, consistente en varias ecuaciones, que tienen en cuenta las peculiaridades de la configuración de las piezas citadas y permiten considerar cualquier ley de adherencia, manteniendo la coherencia con la longitud de transmisión. Las ecuaciones se emplean para la obtención de la tensión máxima de exfoliación en piezas de la tipología estudiada cuya armadura activa se sitúe fuera del núcleo central de la sección transversal. Respecto al estallido, se propone una modificación de los métodos existentes que, comparado con los resultados del análisis por elementos finitos, mejora el valor medio y la dispersión a valores admisibles y del lado de la seguridad. El método considera la geometría de la sección y la distribución del pretensado en la losa inferior. Finalmente, se ofrecen estrategias de diseño para piezas de la tipología o semejantes. End zones of prestressed concrete members are highly stressed. Cracking have often appeared at end zone, and its beginning is related to prestress release. Some members become rejected because of these cracks. Sometimes it is not possible having transverse reinforcement in order to control cracking, when referring to pretensioned precast members. The reason may be the construction process or highly optimized crosssections. A new typology of precast concrete members designed for one-way composite floors was recently developed. The members, without transverse reinforcement, are prestressed with pretensioned wires or strands. This typology is similar to an inverted TT slab, with a large flange related to the web thickness and prestressing reinforcement spread across the flange. This design is highly susceptible to appear cracking at prestress release. Therefore, brittle failures have been reported: fail of slabs laid in place on a construction site, resulting in the separation of the flange from the webs,, and the subsequent fall on the lower floor. Usual analytical methods have been useless to study the failure. End zone tensile stresses have been analysed to study the detected typology problems. These tensile stresses are usually called spalling and bursting (also called splitting in the U.S.). Analysis methods applicable to pretensioned members without transverse reinforcement have been analysed too. Some methods were originally developed for postensioned concrete or for obtaining the amount of transverse reinforcement. In addition, there are methods developed specifically for pretensioned members without transverse reinforcement. Some factors, frequently ignored, have been found, such as lower and upper prestress, lack of symmetry in the cross section, variable width, a high ratio between flange width and web thickness or prestressing reinforcement location related to variable width. They can play a decisive role in non-conventional members. In addition, most methods are based on 2D simplifications. Finite Element modelling has been conducted in order to consider the influence of these factors. A linear 3D approach has been used. The modelled members vary according to cross section geometry, bond behaviour, or prestressing reinforcement location. In general, the obtained tensile stresses don’t agree with existing methods. An experimental adjustment has been conducted on the obtained results, with a high correlation ratio and significance level as well as a low dispersion and relative error. Therefore, a method to obtain the maximum spalling stress is proposed. The proposal consists on some equations that consider the special features of the typology and bond behaviour. Consistency between transmission length and bond behaviour is considered too. The equations are used to calculate maximum spalling stress for the studied typology members whose prestressing reinforcement is located out of the core of the cross section. In relation to bursting, a modification of existing methods is proposed. Compared to finite element results, the proposal improves mean value and dispersion, whose ranges are considered acceptable and secure. The method takes into account cross section geometry and location of prestressing reinforcement across the lower flange. Finally, strategies to design members of this typology or similar are proposed.

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

El pretensado : la disolución de las tipologías constructivas en la arquitectura del siglo XX

La traslación de la tecnología del pretensado desde la ingeniería civil al campo de la arquitectura da lugar a una nueva reinterpretación de las tipologías estructurales utilizadas con anterioridad, tales como los arcos, bóvedas, grandes vigas, etc. El comportamiento resistente de estos elementos estructurales se podrá desligar de su geometría, mediante la interposición de sistemas de fuerzas, escogidos por el proyectista, que se superpongan a los determinados la gravedad, de forma que el proyectista tendrá el control sobre la geometría propuesta y por tanto sobre la forma final. Estas nuevas configuraciones finales, conseguidas mediante la técnica del pretensado en el ámbito arquitectónico, tendrán a su vez un carácter formal también nuevo. Posibilitarán la construcción a grandes escalas, así como la reinterpretación de los materiales y las formas de la construcción empleadas hasta ese momento. La libertad de diseño y de escala pasa a ser entonces mucho más amplia y rica. Con el empleo de esta tecnología constructiva se puede conseguir un control estructural de tal impacto que, en relación a las tipologías estructurales tradicionales, de lugar a que la geometría de éstas no responda, con carácter necesario, a su trabajo resistente, de tal manera que se genere un nuevo conjunto de soluciones estructurales, constructivas y arquitectónicas, dando lugar con ello a la transformación o disolución de las tipologías estructurales de la tradición arquitectónica del SXX. ABSTRACT The transfer of the technology of the prestressed concrete from civil engineering to architecture has produced a new interpretation of the constructivestructural typologies traditionally used, such as bows, vaults, large beams, etc. As a result of the application of this technology the resistant behavior of such structural elements may be released from their constructive requirements as they were understood in the past. The designer will choose a system of forces, combined with the gravity, so it will be possible to control the geometry proposal and therefore the final form of the construction. These new configurations, achieved thanks to prestressing technique applied in architectural field, will also have a new formal definition, because they are detached from their structural requeriments. They will enable construction on large scales as well as the reinterpretation of materials, structures and construction forms used so far. Thereby freedom in design and scale will be broader and richer. The geometry of the structural forms, released from traditional construction types, can be controlled by this technology. So the traditional link with a priori types is broken and a new set of structural, constructive and architectural solutions appears. That is why, technology of prestressing gives the possibility of transformation, or even dissolution, of constructive typologies of the architectural tradition in the twentieth century.

Espacios máximos con recursos mínimos : edificio Central Lechera CLESA, Alejandro de la Sota

La tesis aborda el estudio de la Central lechera CLESA, uno de los edificios industriales de Alejandro de la Sota más significativos de la década de los años cincuenta en España. Las centrales lecheras fueron abordadas por Sota en distintas ocasiones entre 1955 y 1969, siendo CLESA la única de todas ellas que llega a construirse. Se trata de uno de los exponentes más brillantes de la arquitectura moderna industrial española de la posguerra, incluido en "La arquitectura de la industria, REGISTRO DOCOMOMO IBÉRICO”1 entre la veintena de edificios seleccionados de la arquitectura madrileña de este periodo. Plantea una solución singular para alcanzar la diafanidad exigida en la implantación del proceso de producción. La estructura de las naves se realiza con hormigón pretensado, siendo uno de los pioneros en la utilización de esta técnica. La hipótesis de partida considera la realidad del proyecto construido como respuesta desde la arquitectura a un programa industrial resuelto con sencillez, que partiendo de una economía de recursos que le es inherente, consigue desde la coherencia del planteamiento, soluciones donde la complejidad espacial constituye una respuesta eficaz y del máximo interés. Los objetivos de esta tesis son contribuir a un conocimiento riguroso del edificio, que permita descubrir la particularidad de su entramado espacial y el interés de las soluciones adoptadas en su configuración final, en aras de contrastar su calidad arquitectónica. El edificio de la Central Lechera CLESA, si bien es un edificio muy conocido, lo es de una manera superficial. Aparece en numerosas publicaciones, en muchas ocasiones formando parte de un relato extenso de la obra de su autor. El libro monográfico publicado en 2007 por la Fundación Alejandro de la Sota, cuya edición está a cargo de Teresa Couceiro, es la única publicación específica sobre él. Tras una breve introducción, en la que se destaca la intensa dedicación de Sota a esta obra, reúne una colección de planos, fotografías y croquis, junto a la memoria del proyecto. Ofrece una visión fragmentada, que permite vislumbrar el interés de esta obra, pero no facilita comprenderla en su integridad. Es importante destacar la publicación de CLESA en el libro editado por Pronaos (1989), que incluye una selección, realizada por el autor, de plantas, alzados y secciones que corresponden al proyecto construido junto a fotografías de la obra terminada, además de un breve texto tan conciso como esclarecedor. Sobre Alejandro de la Sota se han escrito, tesis doctorales, numerosos artículos, varios libros así como realizado exposiciones que recogen su obra global, reflejados en este documento en las consiguientes bibliografías específicas. Cabe destacar la exposición realizada en la sede del COAM en 2014, con ocasión de su centenario, que el edificio CLESA protagoniza en cierto modo, por su riesgo de desaparición.2 La tesis se estructura en cuatro capítulos: descripción, análisis, síntesis y conclusiones. El primer capítulo contempla la descripción del edificio objeto de la tesis, con una introducción que nos sitúa en el contexto histórico, económico, cultural y social en el que se desarrolla el encargo, proyecto y obra de la central lechera. La descripción propiamente dicha del conjunto industrial, partiendo del encargo de la central lechera al autor del proyecto, pasando por el anteproyecto, el proyecto visado y llegando a la obra realizada. Se compara el proyecto visado, la obra terminada y la CLESA publicada, así como el devenir del edificio. La segunda parte corresponde al análisis, en primer lugar desde el programa como planteamiento general, estudiando las circulaciones, relaciones espaciales, geométricas, esqueléticas, geográficas -parte a parte- que integran el conjunto de la central. La estructura, introducción explicativa de las soluciones adoptadas por Alejandro de la Sota; análisis del sistema esquelético del edificio por partes, operaciones geométricas y espaciales. Construcción, análisis de la materialización de la obra, sistemas constructivos empleados en cerramientos, cubiertas, lucernarios; de lo general a lo particular, estudiando los sistemas. Finalmente a través de la pequeña escala se compendian elementos singulares que forman parte de sistemas complejos, como las múltiples escaleras, barandillas, carpinterías, miradores. Se recapitula en una síntesis que configura un todo con la suma de las partes, mediante la utilización de recursos de enlace de esa arquitectura aditiva, como es el módulo, los recorridos y los enlaces visuales. El capítulo final de Conclusiones contrasta la hipótesis de partida de la tesis en cuanto a una arquitectura de espacios máximos con recursos mínimos. Recoge también diversas reflexiones como la dialéctica entre el espacio fragmentado y el espacio único; crecimiento expansivo o inclusivo; imagen singular y representación; escala doméstica y escala industrial; renuncias estructurales o limitaciones de medios. Quizás, el mayor interés de esta tesis reside los dibujos realizados en axonométrica del complejo CLESA, que han permitido restituir y reconstruir idealmente la fábrica al inicio de su actividad. Teniendo en cuenta su posible desaparición total o parcial, esta restitución cobra relevancia como testimonio de lo que fue. ABSTRACT The thesis deals with the study of CLESA's Dairy Plant, one of the most significant industrial buildings of the Decade of the fifties in Spain, by Alejandro de la Sota. The Dairies were addressed by Sota at various occasions between 1955 and 1969, being the CLESA plant the only one that is has been built. This is one of the most brilliant exponents of Spanish industrial post-war modern architecture, included in "The architecture industry, IBERIAN DOCOMOMO RECORD"3 between the score of selected buildings of Madrid architecture of this period. It poses a singular solution to achieve the openness of the space required in the implementation of the manufacturing process. The structure of the nave is done with prestressed concrete, being one of the pioneers in the use of this technique. The initial hypothesis considers the reality of the project built from the architecture in response to an industrial program solved with simplicity, that from a resource economy that is inherent, gets from the consistency of the approach, solutions where the space complexity is an effective response of great interest. The objectives of this thesis are to contribute to a rigorous knowledge of the building, which allows to discover the particularity of its space lattice and the interest of the solutions adopted in its final configuration, in order to contrast its architectural quality. The building of the Central Lechera CLESA, despite it is a well known building, is in a superficial way. It appears in several publications, often as part of an extensive account of the work of its author. The monograph published in 2007 by the Foundation Alejandro de la Sota, whose edition is run by Teresa Couceiro, is the only specific publication about it. After a brief introduction, in which Sota's intense dedication to this work stands out, it brings together a collection of drawings, photographs and sketches, along with the project report. It offers a fragmented view, which enable to glimpse the interest of this work, but not helps to understand it in full. It is important to highlight the publication of CLESA in the book edited by Pronaos (1989), which includes a selection made by the author of plants, elevations and sections corresponding to the project built, next to photographs of the finished construction, in addition to a brief text as concise as enlightening. About Alejandro de la Sota have been written doctoral thesis, numerous articles, several books as well as held exhibitions collecting his global work, which have been reflected in this document in the resulting specific bibliographies. It should be noted the exhibition in COAM headquarters in 2014, on the occasion of its Centennial, where the building CLESA has a leading role, in a certain way, because of its risk of disappearance.4 The thesis is structured in four chapters: description, analysis, synthesis, and conclusions. The first chapter provides the description of the building object of this thesis. Includes an introduction that puts us in the historic, economic, cultural and social context in which it is developed the commission, the project and construction of the dairy building. The description itself of the industrial complex, starts with the order of the dairy to the author of the project, moves through the draft, the visa project and reaches the completion of the work. The visa project, CLESA's finished and published work, as well as the future of the building is compared. The second part corresponds to the analysis, first from the program as a general approach, studying the circulations, geometric, spatial, skeletal, geographical relations - bit by bit - comprising the manufacturing plant ("la central"). The structure, explanatory introduction of the solutions adopted by Alejandro de la Sota; analysis of the skeletal system of the building by parts, geometric and spatial operations. Construction, analysis of the realization of the work, constructive systems used in the building enclosures, roofs, skylights; from the general to the particular and studying the systems. Finally through small scale unique elements that are part of complex systems, such as multiple stairs, railings, carpentry, viewpoints are summarized. It is recapitulated in a synthesis which forms a whole with the sum of the parts, using linking resources that belongs to the additive architecture, such as the module, tours and visual links The final chapter of Conclusions contrast the hypothesis of the thesis regarding the maximum space architecture with minimal resources. It also includes various reflections as the dialectic between the fragmented space and the single space; expansive or inclusive growth; unique image and representation; domestic and industrial scale; structural abandonment or limitation of means. Perhaps the greatest interest of this thesis lies in the axonometric drawings made of the CLESA complex, which ideally have allowed to restore and rebuild the factory back to the beginning of its activity. Considering its potential full or partial disappearance, such recovery becomes relevant as a testimonial evidence of what it was.

Estudio de la tolerancia al daño de los materiales y sistemas de pretensado

La mayoría de las estructuras de hormigón pretensadas construidas en los últimos 50 años han demostrado una excelente durabilidad cuando su construcción se realiza atendiendo las recomendaciones de un buen diseño así como una buena ejecución y puesta en obra de la estructura. Este hecho se debe en gran parte al temor que despierta el fenómeno de la corrosión bajo tensión típico de las armaduras de acero de alta resistencia. Menos atención se ha prestado a la susceptibilidad a la corrosión bajo tensión de los anclajes de postensado, posiblemente debido a que se han reportado pocos casos de fallos catastróficos. El concepto de Tolerancia al Daño y la Mecánica de la Fractura en estructuras de Ingeniería Civil ha empezado a incorporarse recientemente en algunas normas de diseño y cálculo de estructuras metálicas, sin embargo, aún está lejos de ser asimilado y empleado habitualmente por los ingenieros en sus cálculos cuando la ocasión lo requiere. Este desconocimiento de los aspectos relacionados con la Tolerancia al Daño genera importantes gastos de mantenimiento y reparación. En este trabajo se ha estudiado la aplicabilidad de los conceptos de la Mecánica de la Fractura a los componentes de los sistemas de postensado empleados en ingeniería civil, empleándolo para analizar la susceptibilidad de las armaduras activas frente a la corrosión bajo tensiones y a la pérdida de capacidad portante de las cabezas de anclajes de postensado debido a la presencia de defectos. Con este objeto se han combinado tanto técnicas experimentales como numéricas. Los defectos superficiales en los alambres de pretensado no se presentan de manera aislada si no que existe una cierta continuidad en la dirección axial así como un elevado número de defectos. Por este motivo se ha optado por un enfoque estadístico, que es más apropiado que el determinístico. El empleo de modelos estadísticos basados en la teoría de valores extremos ha permitido caracterizar el estado superficial en alambres de 5,2 mm de diámetro. Por otro lado la susceptibilidad del alambre frente a la corrosión bajo tensión ha sido evaluada mediante la realización de una campaña de ensayos de acuerdo con la actual normativa que ha permitido caracterizar estadísticamente su comportamiento. A la vista de los resultados ha sido posible evaluar como los parámetros que definen el estado superficial del alambre pueden determinar la durabilidad de la armadura atendiendo a su resistencia frente a la corrosión bajo tensión, evaluada mediante los ensayos que especifica la normativa. En el caso de las cabezas de anclaje de tendones de pretensado, los defectos se presentan de manera aislada y tienen su origen en marcas, arañazos o picaduras de corrosión que pueden producirse durante el proceso de fabricación, transporte, manipulación o puesta en obra. Dada la naturaleza de los defectos, el enfoque determinístico es más apropiado que el estadístico. La evaluación de la importancia de un defecto en un elemento estructural requiere la estimación de la solicitación local que genera el defecto, que permite conocer si el defecto es crítico o si puede llegar a serlo, si es que progresa con el tiempo (por fatiga, corrosión, una combinación de ambas, etc.). En este trabajo los defectos han sido idealizados como grietas, de manera que el análisis quedara del lado de la seguridad. La evaluación de la solicitación local del defecto ha sido calculada mediante el empleo de modelos de elementos finitos de la cabeza de anclaje que simulan las condiciones de trabajo reales de la cabeza de anclaje durante su vida útil. A partir de estos modelos numéricos se ha analizado la influencia en la carga de rotura del anclaje de diversos factores como la geometría del anclaje, las condiciones del apoyo, el material del anclaje, el tamaño del defecto su forma y su posición. Los resultados del análisis numérico han sido contrastados satisfactoriamente mediante la realización de una campaña experimental de modelos a escala de cabezas de anclaje de Polimetil-metacrilato en los que artificialmente se han introducido defectos de diversos tamaños y en distintas posiciones. ABSTRACT Most of the prestressed concrete structures built in the last 50 years have demonstrated an excellent durability when they are constructed in accordance with the rules of good design, detailing and execution. This is particularly true with respect to the feared stress corrosion cracking, which is typical of high strength prestressing steel wires. Less attention, however, has been paid to the stress corrosion cracking susceptibility of anchorages for steel tendons for prestressing concrete, probably due to the low number of reported failure cases. Damage tolerance and fracture mechanics concepts in civil engineering structures have recently started to be incorporated in some design and calculation rules for metallic structures, however it is still far from being assimilated and used by civil engineers in their calculations on a regular basis. This limited knowledge of the damage tolerance basis could lead to significant repair and maintenance costs. This work deals with the applicability of fracture mechanics and damage tolerance concepts to the components of prestressed systems, which are used in civil engineering. Such concepts have been applied to assess the susceptibility of the prestressing steel wires to stress corrosion cracking and the reduction of load bearing capability of anchorage devices due to the presence of defects. For this purpose a combination of experimental work and numerical techniques have been performed. Surface defects in prestressing steel wires are not shown alone, though a certain degree of continuity in the axial direction exist. A significant number of such defects is also observed. Hence a statistical approach was used, which is assumed to be more appropriate than the deterministic approach. The use of statistical methods based in extreme value theories has allowed the characterising of the surface condition of 5.2 mm-diameter wires. On the other hand the stress corrosion cracking susceptibility of the wire has been assessed by means of an experimental testing program in line with the current regulations, which has allowed statistical characterisasion of their performances against stress corrosion cracking. In the light of the test results, it has been possible to evaluate how the surface condition parameters could determine the durability of the active metal armour regarding to its resistance against stress corrosion cracking assessed by means of the current testing regulations. In the case of anchorage devices for steel tendons for prestressing concrete, the damage is presented as point defects originating from dents, scratches or corrosion pits that could be produced during the manufacturing proccess, transport, handling, assembly or use. Due to the nature of these defects, in this case the deterministic approach is more appropriate than the statistical approach. The assessment of the relevancy of defect in a structural component requires the computation of the stress intensity factors, which in turn allow the evaluation of whether the size defect is critical or could become critical with the progress of time (due to fatigue, corrosion or a combination of both effects). In this work the damage is idealised as tiny cracks, a conservative hypothesis. The stress intensity factors have been calculated by means of finite element models of the anchorage representing the real working conditions during its service life. These numeric models were used to assess the impact of some factors on the rupture load of the anchorage, such the anchorage geometry, material, support conditions, defect size, shape and its location. The results from the numerical analysis have been succesfully correlated against the results of the experimental testing program of scaled models of the anchorages in poly-methil methacrylate in which artificial damage in several sizes and locations were introduced.

Structural behaviour and design criteria of under-deck cable-stayed bridges subjected to seismic action

Under-deck cable-stayed bridges are very effective structural systems for which the strong contribution of the stay cables under live loading allows for the design of very slender decks for persistent and transient loading scenarios. Their behaviour when subjected to seismic excitation is investigated herein and a set of design criteria are presented that relate to the type and arrangement of bearings, the number and configuration of struts, and the transverse distribution of stay cables. The nonlinear behaviour of these bridges when subject to both near-field and far-field accelerograms has been thoroughly investigated through the use of incremental dynamic analyses. An intensity measure that reflects the pertinent contributions to response when several vibration modes are activated was proposed and is shown to be effective for the analysis of this structural type. The under-deck cable-stay system contributes in a very positive manner to reducing the response when the bridges are subject to very strong seismic excitation. For such scenarios, the reduction in the stiffness of the deck because of crack formation, when prestressed concrete decks are used, mobilises the cable system and enhances the overall performance of the system. Sets of natural accelerograms that are compliant with the prescriptions of Eurocode 8 were also applied to propose a set of design criteria for this bridge type in areas prone to earthquakes. Particular attention is given to outlining the optimal strategies for the deployment of bearings