58 resultados para bars
em Universidad Politécnica de Madrid
Resumo:
The aim of this work is to study the evolution of the corrosion rate of reinforcements embedded in mortar specimens that have been partly or fully replaced by the sand ladle furnace white slag. Prisms are manufactured mortar 6cm x 8cm x 2cm in which are embedded reinforcing steel bars of 6mm diameter B500SD. At the time of mixing were added varying amounts of chloride ion content by weight of cement (0%, 0.4%, 0.8%, 1.2%, 2%). The specimens were made totally or partially replacing the white slag, getting four different mixes depending on the degree of substitution. After curing the specimens for 28 days in moist chambers proceeded to dry up naturally. Here are gradually dampened by its conservation in a moist chamber, periodically measuring the corrosion rate of the bars using the technique of polarization curve. The results, in terms of corrosion current and corrosion potential, were compared with those obtained on standard samples, without replacement by slag aggregate. The analysis of results allows us to know, depending on the type of mortar used, the chloride threshold with the depassivation produced steel and the corrosion rates achieved in steels in the active state in terms of mortar moisture, obtained from qualitatively using gravimetric techniques. The results achieved to date support the conclusion that no significant differences in the behavior against corrosion induced by chloride ions, between the steel bars embedded in standard samples and the steel bars embedded in samples including with aggregates from slag. Both the chloride threshold resulting in the depassivation steel as the corrosion rate reached through the bars in an active state are very similar in both types of mortars when they have the same moisture content.
Resumo:
Three broken steel bars from a sewed crack in a dam are reported. The inspection of the fracture surfaces of the prestressed bars suggests that fractures were triggered by small cracks and by the inherent brittleness of the bars, as fracture toughness was about 40 MPa m1/2. The analysis of the failures shows that the usual design requirements for prestressing bars fail to warn against brittle failures if some damage exists. Some recommendations, based on the concept of damage tolerance, are suggested to avoid similar unfortunate incidents.
Resumo:
The fracture of ductile materials, such as metals, is usually explained with the theory of nucleation, growth and coalescence of microvoids. Based on this theory, many numerical models have been developed, with a special mention to Gurson-type models. These models simulate mathematically the physical growth of microvoids, leading to a progressive development of the internal damage that takes place during a tensile test. In these models, the damage starts to develop in very early stages of the test. Tests carried out by the authors suggest that, in the case of some eutectoid steels such as those used for manufacturing prestressing steel wires, the internal damage that takes place as a result of the growth of microvoids is only noticeable in very late stages of the tensile test. In the authors’ opinion, using a cohesive model as a failure criterion may be interesting in this case; a cohesive model only requires two parameters to be defined, with the fracture energy being one of them, which can be obtained experimentally. In addition to this, given that it is known that the stress triaxiality has a strong influence on the fracture of ductile materials, a cohesive model whose parameters are affected by the value of the stress triaxiality can be considered. This work presents a fracture model for steel specimens in a tensile test, based on a cohesive behaviour and taking into account the effect of stress triaxiality, which is different at each point of the fracture plane.
Resumo:
This paper presents seventy new experimental results from PMMA notched specimens tested under torsion at 60 C. The notch root radius ranges from 0.025 to 7.0 mm. At this temperature the non-linear effects previously observed on specimens of the same material tested at room temperature strongly reduce. The averaged value of the strain energy density over a control volume is used to assess the critical loads to failure. The radius of the control volume and the critical strain energy density are evaluated a priori by using in combination the mode III critical stress intensity factor from cracked-like specimens and the critical stress to failure detected from semicircular notches with a large notch root radius
Resumo:
Congreso internacional celebrado en Praga sobre modelos numéricos de fractura en el campo de la ciencia de materiales y estructuras.
Resumo:
Steel is, together with concrete, the most widely used material in civil engineering works. Not only its high strength, but also its ductility is of special interest, since it allows for more energy to be stored before failure. A better understanding of the material behaviour before failure may lead to better structural safety strategies.
Resumo:
Corrosion can affect the bond between reinforcing bars and concrete and hence the transfer of longitudinal stresses. Although a number of experimental studies on bond failure have been conducted in recent years, the findings have diverged rather widely, due primarily to differing test conditions. The present paper reports on an experimental programme consisting of eccentric pull-out tests run on corroded steel bars in specimens subjected to accelerated or natural corrosion. An axisymmetric bi-dimensional FE model with finite deformations initially developed to study bond mechanics with sound steel bars, has been enhanced to consider bond effects in corroded steel bars. The model simulation is compared to some of the experimental results for corroded and sound bars and the findings are analysed.
Resumo:
In order to reduce costs and time while improving quality, durability and sustainability in structural concrete constructions, a widely used material nowadays, special care must be taken in some crucial phases of the project and execution, including the structure design and calculation, the dosage, dumping and curing of concrete: another important aspect is the proper design and execution of assembly plans and construction details. The framework, a name designating the whole reinforcement bars cage already assembled as shown in the drawings, can be made up of several components and implies higher or lower industrialization degree. The framework costs constitute about one third of the price per cubic meter placed in concrete works. The best solutions from all points of view are clearly those involving an easier processing to achieve the same goal, and consequently carrying a high degree of industrialization, meaning quality and safety in the work. This thesis aims to provide an indepth analysis of a relatively new type of anchoring by plate known as headed reinforcement bars, which can potentially replace standard or L-shaped hooks, improving the cleaning of construction details and enabling a faster, more flexible, and therefore a more economical assembly. A literature review on the topic and an overview of typical applications is provided, followed by some examples of specific applications in real projects. Since a strict theoretical formulation used to provide the design plate dimensions has not yet been put forward, an equation is proposed for the side-face blowout strength of the anchorage, based on the capacity of concrete to carry concentrated loads in cases in which no transverse reinforcement is provided. The correlation of the calculated ultimate load with experimental results available in the literature is given. Besides, the proposed formulation can be expanded to cases in which a certain development length is available: using a software for nonlinear finite element analysis oriented to the study of reinforced concrete, numerical tests on the bond-bearing interaction are performed. The thesis ends with a testing of eight corner joints subjected to a closing moment, held in the Structures Laboratory of the Polytechnic University of Madrid, aiming to check whether the design of such plates as stated is adequate for these elements and whether an element with plate-anchored reinforcement is equivalent to one with a traditional construction detail.
Resumo:
El presente trabajo se refiere al estudio teórico-experimental del comportamiento de pilares y vigas de hormigón armado reforzados con fibra de carbono o CFRP. El análisis se realiza considerando que los pilares se refuerzan mediante la técnica de adhesión de tejidos de fibra de carbono, generando un efecto de confinamiento. Las vigas se refuerzan mediante la incorporación de barras del mismo material, con refuerzos a cortante. El objetivo es poder comparar el estudio analítico de este tipo de refuerzos con resultados experimentales obtenidos con anterioridad a la realización de este documento, y así poder obtener conclusiones de las posibles diferencias. Hay que señalar que los modelos experimentales no forman parte de este estudio. Los ensayos en pilares fueron realizados en sección cuadrada y circular evaluando la rotura a compresión de las piezas, habiendo sido éstas escaladas con un factor de reducción de 2,3. Los ensayos correspondientes a vigas se realizaron en sección rectangular, centrándose en la evaluación de la rotura a flexión y habiendo sido escaladas igualmente, pero con un factor de reducción de 1:2. El documento se estructura en cuatro capítulos, cuyo contenido se expone de forma concisa a continuación. En el capítulo uno o marco teórico se exponen los principios de comportamiento y tipologías de los pilares y vigas de hormigón armado, las bases teóricas de su refuerzo y confinamiento, así como las diversas técnicas de refuerzo existentes. Se detalla la técnica con FRP, comparando y analizando sus ventajas e inconvenientes. En el capítulo dos se expone el proceso de fabricación, refuerzo y resultados de los modelos experimentales realizados para ambos elementos estructurales. La obtención de los modelos teóricos forma parte del capítulo tres, comparándose con los resultados experimentales en el cuarto capítulo. Finalmente, en el último capítulo se presentan las conclusiones obtenidas al realizar esta comparativa en el refuerzo de vigas y pilares con fibra de carbono. This work refers to the theoretical and experimental study of the behavior of CFRP reinforced concrete columns and beams. The analysis was done considering that the pillars are reinforced by CFRP wrapping technique, resulting in a confinement effect. The beams are reinforced by the addition of bars of the same material, with shear reinforcements. The objective is to compare the analytical study of this type of reinforcement with experimental results obtained prior to the performance of this document, and draw conclusions for any differences. Notice that experimental models are not part of this study. The tests were performed on circular and square section pillars, evaluating compression fracture of the pieces, having been scaled down with a factor of 2.3. The tests were performed on rectangular section beams, focusing on evaluation of the bending fracture and being scaled down equally, but with a factor of 1:2. The document is divided into four chapters, whose content is set out concisely below. The chapter one or theoretical framework sets out the principles of behavior and types of columns and beams of reinforced concrete, the theoretical basis of its reinforcement and confinement, as well as various existing reinforcement techniques. CFRP technique it’s detailed, comparing and analyzing their advantages and disadvantages. Chapter two describes the process of manufacture, reinforcement and results of experimental models made for both structural elements. Chapter three shows the obtaining of the theoretical models, comparing them with the experimental results in the fourth chapter. Finally, the last chapter presents the conclusions to make this comparison in the strengthening of beams and columns with carbon fiber.
Resumo:
The pathogenicity of seven strains of Fusarium equiseti isolated from seabed soil was evaluated on different host plants showing pre and post emergence damage. Radial growth of 27 strains was measured on culture media previously adjusted to different osmotic potentials with either KCl or NaCl (-1.50 to - 144.54 bars) at 15º, 25º and 35º C. Significant differences and interactive effects were observed in the response of mycelia to osmotic potential and temperature.
Resumo:
The inner oval dome of the Basílica de la Virgen los Desamparados, built in 1701, is one of the most slender masonry vaults ever built. It is a tile dome with a total thickness of 80 mm and a main span of 18.50 m. It was built without centering with great ingenuity and economy of means, thirty three years after the termination of the building in 1667. The dome is in contact with the external dome only in the inferior part with the projecting ribs of the intrados, the lunettes of the windows, and, in the upper part, through 126 inclined iron bars. This unique construction was revealed in the 1990's in the studies previous to the restoration of the Basílica, and has given rise to different theories about the mode of construction and the structural behaviour and safety of the dome. The present contribution aims to provide a plausible hypothesis about the mode of construction and to explain the safety of the inner dome which has stood, without need of repairs or reinforcement, for 300 hundred years.
Resumo:
The threat of impact or explosive loads is regrettably a scenario to be taken into account in the design of lifeline or critical civilian buildings. These are often made of concrete and not specifically designed for military threats. Numerical simulation of such cases may be undertaken with the aid of state of the art explicit dynamic codes, however several difficult challenges are inherent to such models: the material modeling for the concrete anisotropic failure, consideration of reinforcement bars and important structural details, adequate modeling of pressure waves from explosions in complex geometries, and efficient solution to models of complete buildings which can realistically assess failure modes. In this work we employ LS-Dyna for calculation, with Lagrangian finite elements and explicit time integration. Reinforced concrete may be represented in a fairly accurate fashion with recent models such as CSCM model [1] and segregated rebars constrained within the continuum mesh. However, such models cannot be realistically employed for complete models of large buildings, due to limitations of time and computer resources. The use of structural beam and shell elements for this purpose would be the obvious solution, with much lower computational cost. However, this modeling requires careful calibration in order to reproduce adequately the highly nonlinear response of structural concrete members, including bending with and without compression, cracking or plastic crushing, plastic deformation of reinforcement, erosion of vanished elements etc. The main objective of this work is to provide a strategy for modeling such scenarios based on structural elements, using available material models for structural elements [2] and techniques to include the reinforcement in a realistic way. These models are calibrated against fully three-dimensional models and shown to be accurate enough. At the same time they provide the basis for realistic simulation of impact and explosion on full-scale buildings
Resumo:
This paper is a first step of a research about the analysis of the richness of the existing sounds in the Plaza Mayor, due to the old and traditional shops and bars under its porticoes together with the huge daily affluence of people. In this paper we study the sound preferences of the salesmen and bar tenders at those traditional shops. These sound preferences include particular sounds, time of occurrence and date of specific annoying and pleasant sounds perceived at the square and the shops surrounding it. To carry out this study, several noise level measurements and socio-acoustic surveys were held. We will also try to correlate sound preferences and annoyance with noise levels of specific events existing at this particular square.
Resumo:
Commercial aluminium foam filled structures and sandwich panels are available for structural applications. As alternative to these materials, small granular foamed pieces are proposed to fill structures as well as sandwich panels. On the present work, foam precursors are obtained by Powder Metallurgy (PM) route, using natural calcium carbonate as foaming agent instead of titanium hydride. Extruded precursor bars were cut into small pieces (around 4.5 mm long and 5mm in diameter). Foaming treatment was carried out on two different ways: electrical preheated furnace and by solar furnace. Foamed nodules presented a low cell size, density e.g. 0.67 g/cm3 to 0.88 g/cm3 and a height/diameter ratio between 0.72 and 0.84 as a function of precursor size. These properties depend on the foaming particle size, foaming cycle and precursor dimensions. Carbonate precursors are easily foamed by concentrated solar energy, due to the lower risk of cell collapse than with hydride precursors, resulting from cell stabilization by oxide skin formation into cells and a low degree of foamed nodules bonding.
Resumo:
Este estudio aborda la recopilación de nuevas tendencias del diseño sismorresistente, enfocándose en la técnica del aislamiento de base, por ser la más efectiva, difundida y utilizada; y el análisis de las ventajas que puede tener una edificación que aplica dicha técnica, desde el punto de vista estructural y económico. Se elige la tipología más frecuente o común de edificios de hormigón armado propensos a ser aislados, que en este caso es un hospital, cuyo modelo empotrado se somete a varias normas sismorresistentes comparando principalmente fuerzas de cortante basal, y considerando la interacción suelo-estructura; para asistir a este cálculo se desarrolla un programa de elementos viga de 6 gdl por nodo en código Matlab. El modelo aislado incluye el análisis de tres combinaciones de tipos de aisladores HDR, LPR y FPS, alternando modelos lineales simplificados de 1 y 3 gdl por piso, evaluando diferencias de respuestas de la estructura, y procediendo a la elección de la combinación que de resultados más convenientes; para la modelación no lineal de cada sistema de aislamiento se utiliza el método explícito de diferencias centrales. Finalmente, se realiza un análisis comparativo de daños esperados en el caso de la ocurrencia del sismo de diseño, utilizando el método rápido y tomando como referencia el desplazamiento espectral del último piso; llegando a dar conclusiones y recomendaciones para el uso de sistemas de aislamiento. This study addresses the collection of new seismic design trends, focusing on base isolation technique, as the most effective and widely used, and the analysis of the advantages in buildings that apply this technique, from the structurally and economically point of view. Choosing the most common types of concrete buildings likely to be isolated, which in this case is a hospital, the fix model is subjected to various seismic codes mainly comparing base shear forces, and considering the soil-structure interaction; for this calculation attend a program of bars 6 dof per node is made in Matlab code. The isolated model includes analysis of three types of isolators combinations HDR, LPR and FPS, alternating simplified linear model of 1 and 3 dof per floor, evaluating differences in the response of the structure, and proceeding to the choice of the combination of results more convenient; for modeling nonlinear each insulation system, the explicit central difference method is used. Finally, a comparative analysis of expected damage in the case of the design earthquake, using a fast combined method and by reference to the spectral displacement of the top floor; reaching conclusions and give recommendations for the use of insulation systems.