Behavior of one-way slabs reinforced with deformed wire and deformed wire fabric /

Mode of access: Internet.

An experimental study of a reinforced concrete two-way floor slab /

Mode of access: Internet.

Abrasion resistance of fibre reinforced concrete floors

This thesis focuses on the investigation of the abrasion resistance of fibre reinforced concrete floors at both the macro and micro levels. A literature review of the available literature concerning subjects allied to the current project is included. This highlights themes relevant to wear mechanisms and the factors influencing it: factors that affect the abrasion resistance of concrete and several test methods for assessing it; and the historical development of fibres and the properties of different fibre types and their influence on concrete. Three accelerated abrasion testers were compared and critically discussed for their suitability for assessing the abrasion resistance of concrete floors. Based on the experimental findings one accelerated abrasion apparatus was selected as more appropriate to be used for carrying out the main investigations. The laboratory programme that followed was undertaken to investigate the influence of various material and construction factors on abrasion resistance. These included mix variations (w/c ratio), fibre reinforcement, geometry, type and volume, curing method and superplasticizing agents. The results clearly show that these factors significantly affected abrasion resistance and several mechanisms were presumed to explain and better understand these observations. To verify and understand these mechanisms that are accountable for the breakdown of concrete slabs, the same concrete specimens that were used for the macro-study, were also subjected to microstructutural investigations using techniques such as Microhardness examination, Mercury intrusion porosimetry and Petrographic examination. It has been found that the abrasion resistance of concrete is primarily dependent on the microstructure and porosity of the concrete nearest to the surface. The feasibility of predicting the abrasion resistance of fibre reinforced concrete floors by indirect and non-destructive methods was investigated using five methods that have frequently been used for assessing the quality of concrete. They included the initial surface absorption test, the impact test, ball cratering, the scratch test and the base hardness test. The impact resistance (BRE screed tester) and scratch resistance (Base hardness tester) were found to be the most sensitive to factors affecting abrasion resistance and hence are considered to be the most appropriate testing techniques. In an attempt to develop an appropriate method for assessing the abrasion resistance of heavy-duty industrial concrete floors, it was found that the presence of curing/sealing compound on the concrete surface at the time of accelerated abrasion testing produces inappropriate results. A preliminary investigation in the direction of modifying the Aston accelerated abrasion tester has been carried out and a more aggressive head has been developed and is pending future research towards standardisation.

Cathodic protection of reinforced concrete:anodic processes in cements and related electrolytes

The nature and kinetics of electrode reactions and processes occurring for four lightweight anode systems which have been utilised in reinforced concrete cathodic protection systems have been studied. The anodes investigated were flame sprayed zinc, conductive paint and two activated titanium meshes. The electrochemical properties of each material were investigated in rapidly stirred de-oxygenated electrolytes using anodic potentiodynamic polarisation. Conductive coating electrodes were formed on glass microscope slides, whilst mesh strands were immersed directly. Oxygen evolution occurred preferentially for both mesh anodes in saturated Ca (OH)2/CaC12 solutions but was severely inhibited in less alkaline solutions and significant current only passed in chloride solutions. The main reactions for conductive paint was based on oxygen evolution in all electrolytes, although chlorides increased the electrical activity. Self-corrosion of zinc was controlled by electrolyte composition and the experimental set-up, chlorides increasing the electrical activity. Impressed current cathodic protection was applied to 25 externally exposed concrete slabs over a period of 18 months to investigate anode degradation mechanisms at normal and high current densities. Specimen chloride content, curing and reinforcement depth were also variables. Several destructive and non-destructive methods for assessing the performance of anodes were evaluated including a site instrument for quantitative "instant-off- potential measurements. The impact of cathodic protection on the concrete substrate was determined for a number of specimens using appropriate methods. Anodic degradation rates were primarily influenced by current density, followed by cemendtious alkalinity, chloride levels and by current distribution. Degradation of cementitious overlays and conductive paint substrates proceeded by sequential neutralisation of cement phases, with some evidence of paint binder oxidation. Sprayed zinc progressively formed an insulating layer of hydroxide complexes, which underwent pitting_ attack in the presence of sufficient chlorides, whilst substrate degradation was minimal. Adhesion of all anode systems decreased with increasing current density. The influence of anode material on the ionic gradients which can develop during cathodic protection was investigated. A constant current was passed through saturated cement paste prisms containing calcium chloride to central cathodes via anodes applied or embedded at each end. Pore solution was obtained from successive cut paste slices for anion and cation analyses. Various experimental errors reduced the value of the results. Characteristic S-shaped profiles were not observed and chloride ion profiles were ambiguous. Mesh anode specimens were significantly more durable than the conductive coatings in the high humidity environment. Limited results suggested zinc ion migration to the cathode region. Electrical data from each investigation clearly indicated a decreasing order of anode efficiency by specific anode material.

Modelo para calcular a contribuição da fibra na resistência à punção de lajes em concreto reforçado com fibra de aço

Neste artigo, formulações analíticas são desenvolvidas para calcular a resistência à punção de lajes lisas de concreto reforçado com fibras de aço (CRFA) e que também são reforçadas à flexão por barras de aço (reforço convencional). A partir de análises estatísticas sobre um banco de dados que reúne resultados experimentais de caracterização do comportamento pós-fissuração do CRFA, equações são estabelecidas para avaliar parâmetros da resistência residual à tração na flexão (fRi) a partir de informações fundamentais que caracterizam a fibra de aço. O parâmetro de resistência fRi, proposto pelo ModelCode10 foi usado para definir a lei tensão-abertura da fissura (σ-w) que simula o mecanismo de reforço da fibra em um material cimentício. A segunda parte do artigo descreve uma formulação analítica baseada nos conceitos propostos por Muttoni e Ruiz, onde a lei σ-w é convenientemente integrada para simular a contribuição da fibra de aço na resistência à punção de lajes em CRFA. A partir de um banco de dados, composto de 154 ensaios de punção, o bom desempenho da proposta apresentada é demonstrado. O desempenho do modelo também é evidenciado comparando-se os seus resultados a outros modelos.

Modelo para calcular a resistência à punção de lajes lisas simétricas reforçadas com fibras de aço

O presente artigo discute a metodologia de um novo modelo para calcular a resistência à punção simétrica de lajes de concreto reforçado com fibras de aço (CRFA). O modelo é fundamentado na teoria da fissura crítica de cisalhamento de Muttoni e seus coautores e na proposta do ModelCode10 para simular o comportamento pós-fissuração do CRFA. O desempenho do modelo é avaliado a partir de um banco de dados (BD), coletado da literatura técnica, que totaliza 154 lajes. Os resultados são avaliados em função da precisão, da dispersão e do nível de conservadorismo, a partir do parâmetro λ=Vexp/Vteo, sendo Vexp e Vteo, respectivamente, os resultados obtidos do BD e do modelo. Finalmente, para confirmar o desempenho do modelo, os seus resultados são comparados a outros 7 modelos da literatura técnica e ambos são classificados segundo o critério modificado de Collins, o Demerit Points Classifications – DPC.

Comportamento de lajes de betão armado pré-fendilhadas e reforçadas à flexão com laminados de CFRP inseridos pré-tensionados

Dissertação de mestrado integrado em Engenharia Civil

Efeito do carregamento cíclico e da pré-fendilhação do betão no comportamento de lajes de betão armado reforçadas à flexão com laminados de CFRP inseridos

Dissertação de mestrado integrado em Engenharia Civil

Reforço à flexão de lajes de betão armado com laminados de CFRP pré-esforçados

Dissertação de mestrado integrado em Engenharia Civil (área de especialização em Estruturas e Geotecnia)

Dowel Bar Optimization: Phases I and II, October 2001

America’s roadways are in serious need of repair. According to the American Society of Civil Engineers (ASCE), one-third of the nation’s roads are in poor or mediocre condition. ASCE has estimated that under these circumstances American drivers will sacrifice $5.8 billion and as many as 13,800 fatalities a year from 1999 to 2001 ( 1). A large factor in the deterioration of these roads is a result of how well the steel reinforcement transfers loads across the concrete slabs. Fabricating this reinforcement using a shape conducive to transferring these loads will help to aid in minimizing roadway damage. Load transfer within a series of concrete slabs takes place across the joints. For a typical concrete paved road, these joints are approximately 1/8-inch gaps between two adjacent slabs. Dowel bars are located at these joints and used to transfer load from one slab to its adjacent slabs. As long as the dowel bar is completely surrounded by concrete no problems will occur. However, when the hole starts to oblong a void space is created and difficulties can arise. This void space is formed due to a stress concentration where the dowel contacts the concrete. Over time, the repeated process of traffic traveling over the joint crushes the concrete surrounding the dowel bar and causes a void in the concrete. This void inhibits the dowel’s ability to effectively transfer load across the joint. Furthermore, this void gives water and other particles a place to collect that will eventually corrode and potentially bind or lock the joint so that no thermal expansion is allowed. Once there is no longer load transferred across the joint, the load is transferred to the foundation and differential settlement of the adjacent slabs will occur.

Dowel Bar Optimization: Phases I and II, October 2001

America’s roadways are in serious need of repair. According to the American Society of Civil Engineers (ASCE), one-third of the nation’s roads are in poor or mediocre condition (1). ASCE has estimated that under these circumstances American drivers will sacrifice $5.8 billion and as many as 13,800 fatalities a year from 1999 to 2001 ( 1). A large factor in the deterioration of these roads is a result of how well the steel reinforcement transfers loads across the concrete slabs. Fabricating this reinforcement using a shape conducive to transferring these loads will help to aid in minimizing roadway damage. Load transfer within a series of concrete slabs takes place across the joints. For a typical concrete paved road, these joints are approximately 1/8-inch gaps between two adjacent slabs. Dowel bars are located at these joints and used to transfer load from one slab to its adjacent slabs. As long as the dowel bar is completely surrounded by concrete no problems will occur. However, when the hole starts to oblong a void space is created and difficulties can arise. This void space is formed due to a stress concentration where the dowel contacts the concrete. Over time, the repeated process of traffic traveling over the joint crushes the concrete surrounding the dowel bar and causes a void in the concrete. This void inhibits the dowel’s ability to effectively transfer load across the joint. Furthermore, this void gives water and other particles a place to collect that will eventually corrode and potentially bind or lock the joint so that no thermal expansion is allowed. Once there is no longer load transferred across the joint, the load is transferred to the foundation and differential settlement of the adjacent slabs will occur.

Chloride Penetration Into LSDC (Iowa System) Resurfacing Mixes, MLR-77-05 and R-267, 1977

The purpose of this investigation was to determine the comparative effectiveness of standard D-57 concrete and Iowa system Low Slump Dense Concrete in preventing threshold levels of chloride from penetrating the concrete slabs to the reinforcing steel.

Shear behaviour of reinforced cconcrete slab under concentrated load: an investigation through non-linear and sequentially linear analysis

English: The assessment of safety in existing bridges and viaducts led the Ministry of Public Works of the Netherlands to finance a specific campaing aimed at the study of the response of the elements of these infrastructures. Therefore, this activity is focused on the investigation of the behaviour of reinforced concrete slabs under concentrated loads, adopting finite element modeling and comparison with experimental results. These elements are characterized by shear behaviour and crisi, whose modeling is, from a computational point of view, a hard challeng, due to the brittle behavior combined with three-dimensional effects. The numerical modeling of the failure is studied through Sequentially Linear Analysis (SLA), an alternative Finite Element method, with respect to traditional incremental and iterative approaches. The comparison between the two different numerical techniques represents one of the first works and comparisons in a three-dimensional environment. It's carried out adopting one of the experimental test executed on reinforced concrete slabs as well. The advantage of the SLA is to avoid the well known problems of convergence of typical non-linear analysis, by directly specifying a damage increment, in terms of reduction of stiffness and resistance in particular finite element, instead of load or displacement increasing on the whole structure . For the first time, particular attention has been paid to specific aspects of the slabs, like an accurate constraints modeling and sensitivity of the solution with respect to the mesh density. This detailed analysis with respect to the main parameters proofed a strong influence of the tensile fracture energy, mesh density and chosen model on the solution in terms of force-displacement diagram, distribution of the crack patterns and shear failure mode. The SLA showed a great potential, but it requires a further developments for what regards two aspects of modeling: load conditions (constant and proportional loads) and softening behaviour of brittle materials (like concrete) in the three-dimensional field, in order to widen its horizons in these new contexts of study.

Análisis mediante elementos finitos del comportamiento de losas de hormigón armado sometidas a explosiones

Se presenta en este trabajo una investigación sobre el comportamiento de losas de hormigón armado sometidas a explosiones y la simulación numérica de dicho fenómeno mediante el método de los elementos finitos. El trabajo aborda el estudio de la respuesta de dichos elementos estructurales por comparación entre los resultados obtenidos en ensayos reales a escala 1:1 y los cálculos realizados mediante modelos de ordenador. Este procedimiento permite verificar la idoneidad, o no, de estos últimos. Se expone en primer lugar el comportamiento mecánico de los modelos de material que son susceptibles de emplearse en la simulación de estructuras mediante el software empleado en la presente investigación, así como las diferentes formas de aplicar cargas explosivas en estructuras modeladas mediante el método de los Elementos Finitos, razonándose en ambos casos la elección llevada a cabo. Posteriormente, se describen los ensayos experimentales disponibles, que tuvieron lugar en las instalaciones del Laboratorio de Balística de Efectos, perteneciente al Instituto Tecnológico de la Marañosa (ITM), de Madrid, para estudiar el comportamiento de losas de hormigón armado a escala 1:1 sometidas a explosiones reales. Se ha propuesto un método de interpretación del nivel de daño en las losas mediante el martillo de Schmidt, que posteriormente permitirá comparar resultados con los modelos de ordenador realizados. Asimismo, se propone un método analítico para la determinación del tamaño óptimo de la malla en las simulaciones realizadas, basado en la distribución de la energía interna del sistema. Es conocido que el comportamiento de los modelos pueden verse fuertemente influenciados por el mallado empleado. Según el mallado sea “grosero” o “fino” el fallo puede no alcanzarse o hacerlo de forma prematura, o excesiva, respectivamente. Es más, algunos modelos de material contemplan una “regularización” del tamaño de la malla, pero en la presente investigación se evidencia que dicho procedimiento tiene un rango de validez limitado, incluso se determina un entorno óptimo de valores. Finalmente, se han elaborado los modelos numéricos con el software comercial LS-DYNA, contemplando todos los aspectos reseñados en los párrafos anteriores, procediendo a realizar una comparación de los resultados obtenidos en las simulaciones con los procedidos en los ensayos reales a escala 1:1, observando que existe una muy buena correlación entre ambas situaciones que evidencian que el procedimiento propuesto en la investigación es de todo punto adecuado para la simulación de losas de hormigón armado sometidas a explosiones. ABSTRACT This doctoral thesis presents an investigation on the behavior of reinforced concrete slabs subjected to explosions along with the numerical simulation of this phenomenon by the finite elements method. The work involves the study of the response of these structural elements by comparing the results of field tests at full scale and the calculations performed by the computer model. This procedure allows to verify the appropriateness or not of the latter. Firstly, the mechanical behavior of the material models that are likely to be used in the modelling of structures is explained. In addition, different ways of choosing explosive charges when conducting finite element methods are analyzed and discussed. Secondly, several experimental tests, which took place at the Laboratorio de Balística de Efectos at the Instituto Tecnológico de la Marañosa (ITM), in Madrid, are described in order to study the behavior of these reinforced concrete slabs. A method for the description of the slab damage level by the Schmidt hammer is proposed, which will make possible to compare the modelling results extracted from the computation experiments. Furthermore, an analytical method for determining the optimal mesh size to be used in the simulations is proposed. It is well known that the behavior of the models can be strongly influenced by the mesh size used. According to this, when modifiying the meshing density the damaged cannot be reached or do it prematurely, or excessive, respectively. Moreover, some material models include a regularization of the mesh size, but the present investigation evidenced that this procedure has a limited range of validity, even an optimal environment values are determined. The method proposed is based on the distribution of the internal energy of the system. Finally, several expecific numerical models have been performed by using LS-DYNA commercial software, considering all the aspects listed in the preceding paragraphs. Comparisons of the results extracted from the simulations and full scale experiments were carried out, noting that there exists a very good correlation between both of them. This fact demonstrates that the proposed research procedure is highly suitable for the modelling of reinforced concrete slabs subjected to blast loading.

Comportamiento, para el terremoto de Lorca de 11-05-2011, de edificios de vigas planas proyectados sin tener en cuenta la acción sísmica

(SPA) El terremoto de Lorca (11-05-2011) fue el movimiento sísmico más destructivo registrado en España, a pesar de su moderada magnitud. Este artículo describe la simulación numérica de la respuesta dinámica, al registro principal del terremoto de Lorca, de seis edificios de tres y seis plantas con forjados unidireccionales de hormigón con vigas planas; estos edificios fueron proyectados sin tener en cuenta la acción sísmica. Se ha elegido esta tipología constructiva por presentar, potencialmente, una elevada vulnerabilidad sísmica. Los seis edificios han sido seleccionados para representar un número importante de edificios de este tipo existentes en zonas de sismicidad baja o media (como Lorca) de España y correspondientes a los años 1974-1994, posteriores a la PDS-1 1974 y previos a la NCSE-94. Los resultados obtenidos muestran que estos edificios, aun contando con la cooperación de los muros, no poseen capacidad para resistir la componente más intensa del registro de Lorca. (ENG)The recent earthquake in Lorca (11-05-2011) was the most destructive recorded event in Spain, despite its moderate magnitude. This paper describes the numerical simulation of the dynamic response to the main record of the Lorca earth-quake of six 3 and 6-story buildings with one-way concrete slabs with wide beams; these buildings were designed without any seismic consideration. We have chosen this type of construction because it is potentially highly vulnerable. The six considered buildings were selected to represent a large number of buildings of this type in areas of low-to-medium seismicity (as Lorca) of Spain along the period 1974-1994. The results show that these buildings, even with the cooperation of the walls, do not have sufficient capacity to withstand the most severe component of the Lorca record.