The conjecturing process: perspectives in theory and implications in practice

In this paper we analyze different types and stages of the conjecturing process. A classification of conjectures is discussed. A variety of problems that could lead to conjectures are considered from the didactical point of view. Results from a number of research studies are used to identify and investigate a number of questions related to the theoretical background of conjecturing as well as practical implications in the learning process

Experimental analysis of fiber reinforced concrete slabs

The influence of steel fibers on the behavior of concrete structures with fracture mode I is assessed by performing bending tests on slab strips reinforced with a conventional wire mesh reinforcement and different percentages of fibers. Tests performed with plain concrete slabs, steel fiber reinforced concrete slabs and wire mesh reinforced concrete slabs supported on soil are also described and the main results discussed

Model for the analysis of steel fibre reinforced concrete slabs on grade

A constitutive model is developed for material non linear analysis of steel fibre reinforced concrete slabs supported on soil. The energy absorption capacity provided by fibre reinforcement is taken into account in the material constitutive relationship. The theory of plasticity is used to deal with the elasto plastic behaviour of concrete. A smeared crack model is used for reproducing the concrete cracking behaviour. The soil non-linear behaviour is simulated by springs on orthogonal direction to the slab. The loss of contact between the slab and the soil is accounted for. The model performance is assessed using results of experimental research

Análise de elementos de parede de betão armado

O modelo desenvolvido e aplicado no presente trabalho simula o comportamento elasto-plástico do betão e das armaduras e modela o amolecimento em tracção e em compressão do betão. É possível simular com rigor adequado o comportamento de zonas de ocorrência simultânea de fendilhação e amolecimento por compressão. Um painel ensaiado experimentalmente é analisado e os resultados discutidos

Simulação numérica do comportamento de lajes de betão reforçado com fibras de aço apoiadas em solo

Neste trabalho apresenta-se os principais resultados obtidos nos ensaios efectuados com lajes de betão apoiadas em solo. Ensaiaram-se lajes de betão simples, de betão reforçado com fibras de aço e lajes armadas com rede electrossoldada. É também sucintamente descrito o modelo numérico desenvolvido para analisar este tipo de estruturas. Este modelo baseia-se nas técnicas dos elementos finitos e permite simular o comportamento não linear material da estrutura laminar e do solo de fundação. É contemplada a possibilidade da laje perder o contacto com o solo. O desempenho do modelo foi avaliado por intermédio da simulação numérica dos ensaios experimentais efectuados.In this work it is presented the main results obtained with the tests performed with slabs supported on soil. It was tested slabs of plain concrete, reinforced with steel fibers and reinforced with convencional wire mesh. It is also briefly described the numerical model developed for analyse this kind of structures. This model is based on the finite element techniques and allows to simulate the material non-linear behavior of the concrete laminate structure and the soil foundation. It is accounted the possibility of the lost contact between slab and soil. The model performance was assessed with reference to the experimental investigations carried out

Experimental and numerical analysis of steel fiber reinforced concrete slabs

Steel fiber reinforced concrete (SFRC) has proven to be an attractive material for a wide range of applications in civil construction industry. The excellent performance exhibited by this composite is essentially due to its high energy absorption capacity. This paper describes the tests performed and the numerical model developed to simulate the behavior of SFRC structures. The influence of steel fibers on the behavior of concrete structures with fracture mode I was assessed by performing bending tests on slab strips reinforced with different percentage of fibers and including a conventional wire mesh reinforcement, as well. Fiber concentration ranged from 0 to 2.5 percent by weight of concrete. The hooked-ends steel fibers, with the trademark Dramix ZX60/.80, were the fibers considered in this study. A significant increase in the load carrying capacity of the slabs and a decrease in the crack spacing were observed with the increasing of fiber content. The constitutive model developed is based on the strain decomposition concept for the cracked cement based materials. This concept is adjusted to simulate the fiber reinforcement contribution. The model performance was assessed by the experimental results obtained

Modelo de fendilhação para estruturas de betão reforçado com fibras de aço

A capacidade de absorção de energia, a ductilidade, o comportamento sob fendilhação e a resistência às acções dinâmicas e estáticas são melhoradas pela adição de fibras à composição do betão. Foi desenvolvido um modelo de fendilhação para estruturas laminares constituídas por materiais de matriz cimentícia, quer sejam ou não reforçados com armaduras convencionais e/ou fibras. Este modelo baseia-se no princípio da decomposição das deformações para o betão fendilhado. A validação do modelo é efectuado através da simulação numérica do comportamento registado em ensaios de flexão sobre prismas entalhados.The energy absorption capacity, the ductility, the cracking behavior and the dynamic and static strength of cimentitious materials are significatively improved by fibre adition. A computational code was developed for non-linear analysis of concrete structures reinforced with conventional steel bars or/and fibers. This model is based on the strain decomposition concept for cracked concrete. The model performance was assessed by comparing the numerical and experimental behavior of three-point-bending notched beams specimens

Experimental behaviour of fibre concrete slabs on soil

The cracking control of plain concrete slabs on soil foundation requires the execution of joints with mechanisms of load transfer between adjacent panels. These joints increase the construction costs and, often, are the source of local damage and loss of service performance. Slabs reinforced with steel wire mesh have been used in order to increase the load carrying capacity and to enhance the cracking control. However, the use of this conventional reinforcement increases the costs, mainly due to labor time spent on the arrangement and positioning of the reinforcement. Fiber reinforced concrete is a recent material well fitted for applications in industrial floors on soil foundation. The cost of fibers is compensated by a faster construction process and a reduction in the number of expansion joints. The fatigue, impact and flexural strength are significantly improved when steel fibers are added to the concrete mix. The work developed aims to contribute to the on going research effort to clarify the behavior of fiber reinforced concrete slabs on soil foundation. For this purpose, an experimental and numerical investigation were carried out. The present article deals basically with the experimental work developed, describing the tests performed and discussing the main results obtained

Comportamento de elementos estruturais de betão reforçado com fibras de aço

O betão reforçado com fibras (BRF) é um material compósito relativamente recente em aplicações de Engenharia Civil. A capacidade de absorção de energia, a ductilidade, o comportamento sob fendilhação e a resistência às acções dinâmicas e estáticas são melhoradas pela correcta adição de fibras à composição dos materiais de matriz cimentícia. Neste trabalho são analisados os aspectos essenciais das técnicas de fabrico e as propriedades dos betões reforçados com fibras de aço (BRFA). Ensaios de compressão e flexão com controle de deformações sobre provetes reforçados com fibras de aço permitiram verificar um aumento substancial da capacidade de absorção de energia. Ensaios sobre vigas e faixas de laje revelaram que os mecanismos de reforço introduzidos pelas fibras aumentam a ductilidade e a resistência à flexão e corte do material. É efectuada uma análise comparativa entre resultados experimentais e numéricos com vista à aferição do modelo numérico desenvolvido.The fibre reinforced concrete is a composite material with a increasing number of applications on engineering structures. The fracture energy, the ductility, the cracking behaviour and the strength characteristics under dynamic loads are significatively improved by adding steel fibres to the concrete composition. In the present work, the mix techniques and the properties of fibre reinforced concrete are analysed. Uniaxial compression tests and three-point bending notched tests carried out with displacement control have shown a significative improvement in the fracture energy when steel fibres are present. The ductility and strength characteristics of beams and slabs experimentally tested were also improved with the presence of fibres. The experimental results obtained are used to appraise a numerical model developed for the analysis of fibre reinforced concrete structures

Experimental analysis of concrete slabs on grade

Nos pavimentos industriais assentes num maciço terroso as acções cíclicas e de impacto são, na maior parte dos casos, aquelas que condicionam o dimensionamento. Nos pavimentos de betão simples o controlo da fendilhação requer a execução de juntas com mecanismos de transferência de carga entre os bordos de painéis adjacentes. As juntas além de encarecer a solução são por vezes fonte de perda de funcionalidade dos pavimentos. Para resistir às acções actuantes e controlar a fendilhação, os pavimentos têm sido reforçados com armaduras convencionais. Os custos da armadura e principalmente os encargos associados à mão de obra no corte e montagem das armaduras conduz a que esta solução seja bastante mais onerosa do que a solução em betão simples. O betão reforçado com fibras tem nos pavimentos a sua aplicação por excelência, dado que o custo associado às fibras é largamente compensado pela economia de tempo de execução, pelo aumento do desempenho do material e pela diminuição do número de juntas. A resistência à fadiga, ao impacto e à flexão são substancialmente melhoradas pela correcta adição de fibras ao betão. O comportamento de lajes de betão apoiadas em solo tem vindo a ser investigado na FEUP, ensaiando-se à rotura lajes de betão simples, armado com rede electrossoldada e reforçado com fibras de aço. As características mecânicas dos betões foram analisadas por meio de ensaios de compressão e flexão sobre provetes cilíndricos e prismáticos, respectivamente, em equipamento com controlo de deformações. O comportamento do solo foi analisado através de ensaio de placa sob controlo automático de força. A presente publicação é dedicada à descrição da investigação experimental desenvolvida e à apresentação de alguns resultados já obtidos.In the design of industrial floors on grade the cyclic and impact loading effects are mandatory. The cracking control of plain concrete slabs on grade requires the execution of joints with mechanisms of load transfer between adjacent panels. These joints increase the construction price and often are the source of local damage and lost of the floor performance. Slabs reinforced with wire meshes have been used in order to improve the strength to applied loads and cracking control. However, the use of this conventional reinforcement increases the solution price mainly due to labour time spent on the reinforcement arrangement. Fibre reinforced concrete is a high performance material well fitted for applications on industrial floors on grade. The cost of fibres is compensated by faster construction time and reduction in the number of expansion joints. The fatigue, impact and flexural strength are significantly improved when steel fibres are added to the concrete mix. The behaviour of concrete slabs on grade are being investigated in Civil Engineering Dept. of University of Porto. The response up to collapse of plain concrete, wire mesh and fibre reinforced concrete slabs on grade have been studied. The concrete properties are determined by performing uniaxial compression and three-pointbending notched beams tests under displacement control. The soil behaviour was analysed carrying out automatic plate loading tests. The present work is devoted to describe the experimental research and to present some results already obtained