Numerical modeling for the rebar bond behaviour in normal and high strength concrete

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.This paper presents a finite element model for the analysis of the bond behavior between steel rebars and concrete. This behavior is defined by the bond vs. slip curve in European standards (e.g. the CEB- 90) for normal strength concrete (NSC). Pull-out tests have been performed on both NSC and high strength concrete (HSC) specimens and the resulting curves are compared to numerical models implemented in a FEM software. In these models the contact behavior has been defined according to the Model Code CEB-2010 and a position controlled loading has been performed in order to trace the load-slip curve for comparison with experiments. The FEM model has been calibrated with basic mechanical parameters from both types of concrete (compressive and tensile stress, elastic moduli). The numerical modelling has proven suitable for the NSC bond behaviour. However, the CEB standard should be improved to account for the HSC bond behaviour

Dynamic behavior of masonry chimney with different reinforcement schemes

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.This paper presents a structural analysis of a masonry chimney built in the 1950’s, which is currently being catalogued as local interest heritage. These structures exhibit insufficient tensile strength to resist the seismic action because the masonry is not reinforced. For this reason, the aim of this work is to analyze different structural reinforcement schemes so the chimney is capable of withstanding seismic actions. Ten numerical models, for nine reinforcement configurations, have been defined using Ansys software. A glass fiber reinforced cement composite was always used as reinforcement. For each model, a modal analysis and time history analyses were made. Five different synthetic accelerograms were used for the structural analysis, according to NCSE02 Spanish standard. The final reinforcement, capable of resisting the seismic action, consisted of a helicoid wrap and eight longitudinal stripes along the shaft, and the inner and outer reinforcement of all masonry walls of the base

Dynamic load tests on the North-South axis cable-stayed bridge with a non-symmetric central pylon.

Abstract The new cable-stayed bridge built for the North-South axis road of Bari in order to overpass the railway of RFI and Ferrotramviaria s.p.a. has been recently built and opened to the traffic. The bridge is 626 m long and the central cable-stayed bays have a total length of 225 m. They are supported by cables connected to a central upside down Y-shaped pylon. The peculiarity is that this column is about 60° rotated with respect to the axis of the bridge deck. A dynamic load tests was developed previously to open the bridge to conventional traffic. 26 piezoelectric accelerometers have been utilized in different positions of the cables-stayed bays to record the accelerations produced by environmental forces and by the impact produced by a loaded truck passing over a bump. Operational Modal Analysis has been applied by mean of Artemis software to determine the first fundamental frequencies and the mode shapes. The main frequency of this non-symmetric pylon is the main frequency of all the stayed bridge

In-plane shear cyclic behavior of windowed masonry walls reinforced with textile reinforced mortars

The current experimental study is focused on the mechanical performance of masonry walls under in-plane cyclic shear forces. All specimens were fabricated with a central window, in which the geometry considered the recommendations of the Spanish structural seismic design code. Windows represent a weak area in the masonry structure, in which there are stress concentrations responsible for crack initiation. In order to improve the mechanical strength and ductility, a reinforcement with a Textile Reinforced Mortar (TRM) was used on both sides of the wall. The performance of the unreinforced and reinforced masonry has been discussed in terms of strength and ductility gain, stiffness degradation and energy dissipation capacity. The experimental tests comprised an initial vertical preload, and shear cycles with increasing amplitude. All tests were monitored by means of traditional displacement transducers, and digital image correlation. The analysis of the images showed the time evolution of the overall crack distribution. The TRM effect could be observed as an increase of the mechanical strength (maximum shear from 120 kN to more than 300 kN), higher displacements (drift from 9 to 35 mm), and more energy dissipation (the cumulative energy loss from 2.7 to 12.7 kN·m). In addition, the TRM reinforcements were capable of controlling the crack initiation and growth. The widespread crack along mortar joints observed in the unreinforced masonry became localized cracks (from the window’s corners mainly), in which crack growth direction was not determined by masonry joints.The authors would like to acknowledge Mapei Spain S.A. for the materials supplied in this research. This research was funded by Spanish Ministry of Economy and Competitiveness, grant number BIA2015-69952-R and Spanish Ministry of Science, Innovation and Universities, grant number RTI2018-101148-B-I00

Función de calefacción en pastas de cemento con adición de nanofibras de carbono

The viability of carbon nanofiber (CNF) composites in cement matrices as a self-heating material is reported in this paper. This functional application would allow the use of CNF cement composites as a heating element in buildings, or for deicing pavements of civil engineering transport infrastructures, such as highways or airport runways. Cement pastes with the addition of different CNF dosages (from 0 to 5% by cement mass) have been prepared. Afterwards, tests were run at different fixed voltages (50, 100 and 150V), and the temperature of the specimens was registered. Also the possibility of using a casting method like shotcrete, instead of just pouring the fresh mix into the mild (with no system’s efficiency loss expected) was studied. Temperatures up to 138 °C were registered during shotcrete-5% CNF cement paste tests (showing initial 10 °C/min heating rates). However a minimum voltage was required in order to achieve a proper system functioning.En este artículo se estudia la viabilidad del uso de matrices cementicias con adición de nanofibras de carbono (NFC) como elementos calefactores. Esto permitiría aumentar la temperatura de estancias en edificación o el deshielo de pavimentos en obras civiles. Se han fabricado pastas de cemento con distintas dosificaciones de NFC (0, 1, 2 y 5% respecto masa del cemento) y sometidas al paso de corriente continua a distintos potenciales fijos (50, 100 y 150 V), mientras se controlaba la temperatura en distintos puntos. Se ha estudiado la viabilidad de utilizar la proyección de la pasta fresca como método de puesta en obra, sin perjudicar la eficiencia del sistema. Se consiguieron temperaturas de hasta 138 °C (con velocidades iniciales de 10 °C/min) para pasta proyectada con 5% NFC. Además se ha detectado la necesidad de un potencial mínimo para que la densidad de corriente resultante sea suficiente para producir el efecto esperado.The authors would like to thank the Spanish Ministerio de Ciencia e Innovación for its financial support (ref: Mat2009-10866)

Seismic behavior of 1960's RC buildings exposed to marine environment

Steel rebars corrosion is one of the most important problems of reinforced concrete (RC) structures. The mechanical performance loss of RC elements because of steel corrosion can be aggravated under horizontal loads (e.g. wind pressure or seismic actions). This paper presents a methodology for the study of the seismic behavior of a residential typology of the Mediterranean coast, which was widely spread during the 1960's. These RC frame structures are usually 10 to 15 stories high, located very close to the coast and are exempt buildings, which made them specially exposed to chloride corrosion. Besides, there are some design conditions that should be taken into account: (i) these structures were designed only under gravity loads, especially seismic actions were not considered. (ii) The raw materials had lower quality than those considered in current design codes, e.g. structural concrete strength was around 15 MPa, and made with natural beach sand as fine aggregates (hence including chlorides into the concrete mass). Therefore, two important aspects converge in these buildings, fifty years of marine exposure (i.e. degradation by corrosion) and the omission of the seismic loads in the original design, making them especially vulnerable to earthquakes (in an area with a moderate-high seismicity). Hence, a methodology for the seismic analysis of the corroded structure is proposed, in order to determine the structural safety factor of this type of structures, and evaluate the effectiveness of a retrofitting if necessary

Desarrollo de aplicaciones interactivas para la docencia de estructuras en Ingeniería Civil

Las nuevas tecnologías aplicadas a la enseñanza permiten la visualización de fenómenos físicos y su relación con la base matemática utilizada en la modelización de los mismos. En este trabajo se ha utilizado el programa Mathematica para realizar una aplicación ilustrativa del oscilador con un grado de libertad en funcionamiento libre, amortiguado y forzado armónicamente. El oscilador de 1 GL forma parte del conocimiento de base en el análisis de estructuras bajo cargas dinámicas (sismos), y la comprensión de sus fundamentos teóricos, así como la influencia de los parámetros implicados, deben ser objetivo didáctico prioritario en las asignaturas relacionadas con el cálculo avanzado de estructuras. En la aplicación desarrollada se pueden variar las características intrínsecas del oscilador (rigidez, constante de amortiguación y masa) y la fuerza aplicada (amplitud y frecuencia). El resultado se visualiza en forma de gráfico animado del movimiento permanente resultante. Las ecuaciones resultantes y los parámetros característicos (frecuencia natural, coeficiente de amortiguamiento, razón de frecuencias, factor de amplificación dinámica, ángulo de desfase…) también están disponibles de una forma interactiva. Las constantes de integración que definen las condiciones iniciales, y la ventana de tiempos mostrada pueden variarse asimismo. La aplicación puede ejecutarse desde cualquier navegador

Residual Compressive Strength of Recycled Aggregate Concretes after High Temperature Exposure

Sustainability requirements are gaining importance in the construction industry, which needs to take specific measures in the design and construction of concrete structures. The use of recycled aggregates in concrete may be of special interest. Recycling a construction waste will close the life cycle of the original materials (e.g., concrete). Thus, environmental benefits would come from the lower waste generation, and from a lower necessity of raw materials for new structures. The current Spanish code for structural concrete considers the use of recycled aggregates in replacement rates up to 20% by aggregate mass, assimilating their properties with those of concretes without aggregate replacement. Higher substitution percentages would require further testing. In this work, substitution of coarse aggregate for recycled aggregates (with replacement percentages of 25%, 50% and 100%) has been studied, and the concrete’s residual properties after exposure to high temperatures (between 350 °C and 850 °C) have been assessed. Compressive strength and capillary water absorption tests were made after heating, and the experiments showed higher residual strength in concretes with the greatest content of recycled aggregates. However, a statistical analysis made with additional data available in the literature seemed to predict otherwise, and the recycled aggregate replacement would have a negative effect on the residual strength.This research was funded by Generalitat Valenciana, grant number GV/2018/015

FRP Confinement of Stone Samples after Real Fire Exposure

The mechanical properties of stone materials can be severely affected by exposure to high temperatures. The effect of fire on stone buildings could cause irreversible damage and make it necessary to retrofit the affected elements. Particularly, the strengthening of columns by confinement with composites has been widely improved during the last decades. Today, fiber reinforced polymer (FRP) confinement represents a very interesting alternative to traditional steel solutions. This work studied the behavior of cylindrical stone specimens subjected to real fire action and confined by means of CFRP or GFRP jackets, with the aim of assessing the effectiveness of these reinforcement systems applied to a material that has previously been seriously damaged by high temperature exposure. In general, the strengthened samples showed notable increases in strength and ductility. The response seemed to depend basically on the FRP properties and not on the degree of damage that the stone core may have suffered. Finally, the results obtained experimentally were compared with the confinement models proposed by the available design guides, in order to evaluate the accuracy that these models can offer under the different situations addressed in this research.This research was funded by the Spanish Ministry of Science, Innovation and Universities, grant number RTI2018‐101148‐B‐I00. The APC was funded by University of Alicante, grant number VIGROB 212

Experimental analysis of the loss of bond between rebars and concrete exposed to high temperatures

En el conjunto de materiales de construcción habituales en la edificación y las obras de ingeniería, el hormigón destaca entre otras razones por su excelente comportamiento frente a las altas temperaturas y la exposición al fuego. El presente estudio se centra en la adherencia residual entre el hormigón y las barras de acero corrugado soldable tras exponer probetas a altas temperaturas y enfriarlas hasta temperatura ambiente por convección natural. El estudio incluye hormigones de resistencia convencional, hormigones de alta resistencia y hormigones reforzados con fibras de polipropileno y fibras de acero. La adherencia hormigón-acero se ha medido mediante el conocido ensayo de pull-out. La campaña experimental también ha incluido la resistencia a compresión y la resistencia a tracción indirecta. Parte de las probetas se han ensayado a 28 días de edad a temperatura ambiente. A 60 días de edad se han repetido los ensayos a temperatura ambiente y se han realizado esos mismos ensayos en probetas calentadas en un horno industrial hasta tres rangos de temperatura: 450°C, 650°C y 825°C. Previo al proceso de calentamiento han sido sometidas durante 3 horas a un escalón de secado a 120°C. Mediante la metodología propuesta ha sido posible caracterizar la evolución de la pérdida de adherencia residual entre el acero y el hormigón conforme se exponen los especímenes a temperaturas más elevadas. La adición de fibras no tiene una influencia clara en la adherencia a temperatura ambiente. Sin embargo, sí se ha conseguido determinar una mejora sustancial de la adherencia residual en los hormigones, reforzados con fibras de acero sometidos a altas temperaturas.Within the context of the most usual construction materials for building and civil infrastructures, concrete stands out because of its excellent behaviour when exposed to high temperatures and fire condition. The present study focuses on the residual bond strength between concrete and steel rebars after exposure to elevated temperatures and natural cooling to room temperature. Normal strength and high strength concretes have been tested, as well as polypropylene and steel fibre reinforced concretes. The bond strength has been measured using the pull-out test. Compressive and tensile strength have also been determined. Some specimens have been tested at an age of 28 days and at room temperature. At 60 days the tests have been repeated at room temperature and after heating up to three temperature ranges: 450°C, 650°C and 825°C. Before each of the three heating phases, the specimens were pre-heated during 3 hours at 120 °C. After these experiments it has been possible to assess the loss of steel-concrete bonding for higher temperatures. The addition of fibres has no clear influence on the bonding at ambient condition. However, an improvement on the residual bonding strength has been observed for steel fibre reinforced concrete under high temperatures