Numerical analysis of concrete-filled tubes with stiffening plates under large deformation axial loading

Concrete-filled tubes have been increasingly used these recent decades thanks to their improved structural behavior, especially under compression.Concrete filling in these sections improves ¡ts compressive strength thanks to lateral pressure coming from confinement effect provided by the steel tube. At elevated percentages of loading,concrete suffers an important volumetric expansion, which is clearly restricted by the tube. Therefore, the core is subjected to a severe lateral pressure that clearly enhances the compressive response of the concrete filling. This advantageous response under compression is accompanied by a significant ductility and energy absorption, owing to crushing of the cement paste of concrete. The core is subjected to asevere damage process, while mast part of the axial load is still resisted until advanced stages of deformation, thanks to be contained by the tube. These two properties let concrete-filled tubes to play an important role in the construction of really tall buildings in seismic areas. However, confinement effect on the core and the absorption of energy in these sections is clearly different between circular and square-shaped tubes. While in circulartubes, laleral pressure over the core is clearly uniform and constant, in square-shaped tubes, the deformability of the plates implies a notorious reduction of these two mechanical capabilities. This fact can be partially solved by means of introducing stiffening plates in the core. Thus, main purpose of this investigation is to analyze and describe the influence of introducing these plates in the core of concrete-filled tubes; also the influence on circular sections is analyzed in the study. The presence of stiffening plates not only has a clear effect on the confinement effect on the core, but also on the ductility of the section. In square-shaped sections this effect is always positive,independently of the thickness of the plates and the width ofthe section; nevertheless, in circular tubes, their influence is not so significant or even negative, since circular geometry is much more effective than a cruciform shape, in terms of confinement and ductility. ln otherwords, the introduction of stiffening plates in circular concrete-filled tubes is always positive, provided that the presence of these plates does not leadn to consider thinner tubes. The proposal of concrete-filled tubes stiffened with plates, or "reticulated" concrete-filled tubes, is interesting from several points of view. These new embedded plates are normally restricted to buckling by the concrete filling, so that they could be fully loaded according to their plastic capacity, being also protected against fire. The introduction of a couple of plales in the core of these tubes not only enhances the confinement effect and ductility, but also it allows a safer response against fire. The cruciform or grid-shaped geometry is interesting also for an excellent behavior under combined states of compression with shear forces or bending -the first case corresponds exactly to those heavily loaded columns of the ground fioors in tall buildings. What is a solution with a clear structural vocation derives quickly into a new interesting sectional repertoire for designers, by analyzing the load-bearing capacity of each independent loading cell of reticulated sections and combining them in different ways. The possibility of analyzing these cells separately allows determining their compressive response depending on their location in the cross-sectional plane and on the proportion between their width and plate thickness .Las secciones tubulares mixtas se han utilizado mucho estas últimas décadas dada su magnífica respuesta estructural y su excelente comportamiento mecánico, especialmente bajo estados de compresión. El relleno de hormigón en estas secciones ve mejorada su resistencia gracias a la presión lateral procedente del efecto de confinamiento desarrollado por el tubo. En porcentajes elevados de carga el hormigón sufre una expansión volumétrica importante, quedando ésta restringida por estar embebido dentro del perfil metálico tubular. Por esta cuestión, el núcleo queda sometido a una presión triaxial muy importante, implicando a su vez una clara mejora de la respuesta a compresión Esta respuesta, muy efectiva bajo estados de compresión pura, es acompañada por una importante ductilidad y absorción de energía debido al aplastamiento del hormigón. El núcleo queda sometido a un proceso severo de daño, mientras resiste aún la mayor parte de la carga hasta porcentajes muy elevados de deformación -gracias a estar este último embebido en el tubo. Estas dos propiedades hacen que las secciones mixtas tubulares jueguen un papel muy importante en la construcción de edificios altos en zonas sísmicas. A pesar de todo, el efecto de confinamiento sobre el núcleo y la absorción de energía en estas secciones es claramente distinta entre los tubos circulares y los rectangulares. Mientras que en los circulares la presión lateral es uniforme y constante, en los rectangulares la excesiva deformabilidad de las pletinas implica una reducción importante de estas dos capacidades mecánicas. Este hecho puede ser parcialmente solucionado mediante la introducción de otras pletinas internas rigidizantes, embebidas en el hormigón. Así, el principal objetivo de esta investigación es el de analizar y describir la influencia de dichas pletinas en su respuesta a compresión; se analiza tanto su influencia sobre las circulares como sobre las rectangulares. La presencia de pletinas internas rigidizantes no tiene sólo un efecto determinante sobre el confinamiento del núcleo, sino también sobre la ductilidad de la sección. En las secciones rectangulares, esta influencia es siempre positiva, independientemente del grosor de dichas pletinas; por el contrario, en las secciones circulares, su efecto no es tan determinante, incluso puede ser negativo, dado que la geometría circular es mucho más efectiva que la cruciforme en términos de confinamiento y ductilidad. En otras palabras, la introducción de pletinas rigidizantes resulta por lo general buena, a condición que su disposición no lleve a diseños de tubos más delgados. La propuesta de secciones tubulares mixtas con pletinas rigidizantes o "reticuladas" es interesante desde distintos puntos de vista. Estas nuevas pletinas están normalmente restringidas a pandeo por el relleno de hormigón, de modo que pueden cargarse al 100% de su capacidad axil plástica, estando a su vez relativamente protegidas a incendio. La introducción de un par de pletinas en el núcleo no sólo mejora la resistencia y la ductilidad de las secciones sino que incrementa su seguridad frente a situaciones de incendio. La geometría cruciforme derivada de estas pletinas es interesante también en estados de solicitaciones combinadas (compresión y cortante o momento) -es el caso precisamente de las columnas fuertemente cargadas de las plantas bajas en edificios altos Lo que es una solución con una clara vocación de mejora estructural deriva rápidamente en un nuevo e interesante repertorio seccional disponible para arquitectos y diseñadores, analizando la capacidad de carga de cada célula independiente y combinándolas entre sí de formas muy distintas. La posibilidad de analizar estas células por separado permite determinar su capacidad resistente a compresión dependiendo de su ubicación en el plano de la sección y de la proporción entre el ancho y el grueso de las pletinas

La "Catalan Vault"

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Cota 823.00

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Aprenent de l’eficiència estructural

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Anàlisi estructural i disseny de pilars mixtes tubulars per a la construcción seqüencial en alçada

S’analitza la influència del procés constructiu d'edificis en alçada en els pilars mixtes de secció tubular, a partir d'un estudi del seu comportament a compressió i de la interacció dels seus dos components. L'interès de l'estudi rau en considerar els efectes dels mètodes constructius "high-rise" utilitzats en estructures de naturalesa mixt

Mechanical characterization of a new architectural concrete with glass-recycled aggregate

Concrete is a material which is widely used in architecture, not only for structural purposes but also for architectural elements for its versatility and excellent performance. However, the manufacturing of this material as a mixture of water, cement, and ¿ne and coarse aggregate comes with a high environmental cost, such as gas emissions, among other things. This is the reason why di¿erent alternatives are being proposed in order to replace coarse aggregates with other recycled materials, as it is one of the less sustainable components of the mixture in terms of extraction. One of these alternatives is recycled glass coming from drinking bottles, crushed into small grains and mixed in the same proportions as regular aggregates. This study proposes the mechanical characterization of a new architectural concrete mixture by using white Lafarge cement and glass-recycled aggregates. This proposed concrete is made especially for architectural elements like façade panels, rather than structural elements. The mechanical evaluation of this new material is done through a set of experimental tests under compression and also bending, comparing three di¿erent ratios of glass aggregate in the mixture.Peer ReviewedPostprint (published version

Analysis of slab-column connections in CFT sections without continuity of the tube

The conference is intended to provide a forum to discuss the recent progress and advances in the research, design and practice of steel-concrete composite as well as hybrid structures. The general topics are focussed on different subjects such as beams, slabs, columns, connections, applications, case studies and new materials, earthquake, fatigue and dynamic response, design and standard developments,fire resistance, impact, blast and robustness. In addition, twelve keynote speakers will give their vision on the recent progress and advances in the research, design and practice of steel-concrete composite as well as hybrid structures. This book contains the proceedings of the conference where more than 209 abstracts were received. All papers were internationally peer-reviewed and eventually 123 papers from 24 countries were accepted for publication. Selected papers will be published ona special issue of Structures, a joint international journal launched by the Institution of Structural Engineers and Elsevier.Peer ReviewedPostprint (published version

Analysis of slab-column connections in CFT sections without continuity of the tube

[EN] When dealing with concrete-filled tube columns and RC slabs, it is usual to interrupt steel tubes in slab-column connections if the column is mainly compressed. Contractors do prefer to solve these connections with independent tubes, although innerreinforcements may be continuous through the slab. In these cases, both tubes from the upper and lower levels do have base plate connections, with a set of anchor bolts. This procedure saves a lot of time of global works, by making everything easier at the same time, as tubular profiles do not intersect the formwork.However, this reasonable design for slab-column joints suggest at least some questions about the strength of the concrete at the area of connection, where the tube has been interrupted. On the one hand, the load is transferred through concrete in the slab thickness, since there is no continuity of the tube; on the other hand, concrete at that point becomes triaxially confined due to the restriction to lateral deformation.This study analyses the validity of this connection method and the differences observed depending on the relative location of the column (corner, façade –lateral- or central pillars). Needless to say that the relative location of the column leads to differentconfinement patterns in concrete.Albareda-Valls, A.; Milan, C.; Maristany Carreras, J.; Garcia Carrera, D. (2018). Analysis of slab-column connections in CFT sections without continuity of the tube. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 507-511. https://doi.org/10.4995/ASCCS2018.2018.7152OCS50751

Real Cyclic Load-Bearing Test of a Ceramic-Reinforced Slab

Ceramic-reinforced slabs were widely used in Spain during the second half of the 20th century, especially for industrial buildings. This solution was popular due to the lack of materials at that time, as it requires almost no concrete and low ratios of reinforcement. In this study, we present and discuss the results of a real load-bearing test of a real ceramic-reinforced slab, which was loaded and reloaded cyclically for a duration of one week in order to describe any damage under a high-demand loading series. Due to the design of these slabs, the structural response is based more on shear than on bending due to the low levels of concrete and the geometry and location of re-bars. The low ratio of concrete makes these slabs ideal for short-span structures, mainly combined with steel or RC frames. The slab which was analyzed in this study covers a span of 4.88 m between two steel I-beams (IPN400), and corresponds to a building from the mid-1960s in the city of Igualada (Barcelona, Spain). A load-bearing test was carried out up to 7.50 kN/m2 by using two-story sacks full of sand. The supporting steel beams were propped up in order to avoid any interference in the results of the test; without the shoring of the steel structure, deflections would come from the combination of the ceramic slab together with the steel profiles. A process of loading and unloading was repeated for a duration of six days in order to describe the cyclic response of the slab under high levels of loading. Finally, vibration analysis of the slab was also done; the higher the load applied, the higher the fundamental frequency of the cross section, which is more comfortable in terms of serviceability.Peer ReviewedPostprint (author's final draft

Implementation of buckling in the simplified method of EC4-1-1 for CFT sections

El Eurocódigo 4 sobre estructura mixta propone un método simplificado para diseñar secciones tubulares mixtas sometidas a estados combinadosde compresión y flexión, como alternativa al método analítico general. Este método se basa en determinar la validez de una sección mediantela comparación de la combinación de fuerzas actuantes con el correspondiente diagrama de interacción N-M de la sección. Con el objetivo deconsiderar la esbeltez en la resistencia de la pieza, se introduce un factor reductor de la resistencia, ¿, que afecta la respuesta a compresión y también flexión combinada. Este texto propone la integración del coeficiente ¿ en una nueva aproximación numérica basada en el método simplificado, pensada para facilitar a arquitectos e ingenieros la comprobación y diseño de este tipo de secciones. Con este objetivo, se propone una función polinómica dependiente de cuatro parámetros conocidos ¿, ¿d, ¿pm,r and µmax, las ecuaciones de los cuales se detallan también a continuación.Postprint (published version