1,720,968 research outputs found
Fibre-reinforced concrete in fib Model Code 2010: principles, models and test validation
No full textIn the fib Model Code for Concrete Structures 2010, fibre-reinforced concrete (FRC) is recognized as a new material for structures. This introduction will favour forthcoming structural applications because the need of adopting new design concepts and the lack of international building codes have significantly limited its use up to now. In the code, considerable effort has been devoted to introducing a material classification to standardize performance-based production and stimulate an open market for every kind of fibre, favouring the rise of a new technological player: the composite producer. Starting from standard classification, the simple constitutive models introduced allow the designer to identify effective constitutive laws for design, trying to take into account the major contribution in terms of performance and providing good orientation for structural uses. Basic new concepts such as structural characteristic length and new factors related to fibre distribution and structural redistribution benefits are taken into account. A few examples of structural design starting from the constitutive laws identified are briefly shown. FRC can be regarded as a special concrete characterized by a certain toughness after cracking. For this reason, the most important constitutive law introduced is the stress-crack opening response in uniaxial tension. A wide discussion of the constitutive models introduced to describe this behaviour, which controls all the main contributions of fibres for a prevailing mode I crack propagation, is proposed. The validity of the models is discussed with reference to ordinary cross-sections as well as thin-walled elements by adopting plane section or finite element models
Thin-webbed open cross-section roof elements: modelling of second order effects up to failure
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Prefabricated roof elements: knowledge and experience accumulated in over twenty years
No full textRoof elements are a highly technological prefabricated product of Italian industry. Though a large variety of shapes are offered on the market, almost all production is characterized by thin-webbed open cross-section profiles. In the last twenty years, both the design and the technological aspects have evolved the production of these structural elements. A wide experimental experience on their structural behaviour has highlighted the effectiveness of beam theory in the prediction of serviceability and ultimate limit states, but also a significant interaction between the longitudinal and the transversal bending at failure. The interaction is due to second order effects, and becomes not negligible when the longitudinal bending curvature approaches the onset of yielding in the pre-stressed reinforcement. Owing to the open cross-section and to the reduced thickness of the inclined wings, a shape loss can anticipate the longitudinal bending collapse. A simple design model is proposed to predict this collapse. An extensive experimental investigation was also carried out on the use of Steel Fibre Reinforced Concrete to substitute the diffused reinforcement in prefabricated long-span covering roof elements. In the paper the mechanical behaviour up to failure of a traditional R/C element with that of SFRC elements with reference to a shed shape are discussed. The SFRC elements are characterized by two types of fibre and two concrete matrix strengths
On the connections between fresh state behavior, fiber dispersion and toughness properties of steel fiber reinforced concrete
No full textThe connections between fresh and hardened state properties of fiber reinforced concrete and issues related to fiber dispersion have been a research challenge in the very last years. The topic is addressed in this work with reference to “self compacting” concretes with three different types of steel fiber reinforcement.
Fresh state properties have been measured through the slump flow, V funnel and L-box tests. Plate specimens 1000x500x70 mm have been cast in such a way that the concrete flow was parallel to their long side. Beams 150 mm wide and 600 mm long and disks with a 150 mm diameter were sawn from the plates and tested respectively in 4 point bending and splitting. Beams have been cut with their axis either parallel or normal to the flow direction of the fresh concrete in the plate and the same happened for the diameter axis of preferential fracture in split disks.
The results show a strong correlation between the fresh state properties, the dispersion and orientation of fibers, as influenced by the casting process, and the mechanical properties of the composite. An omni-comprehensive approach to the problem is currently under development aiming at a “design” of the material and of the casting process tailored to the dedicated application and to the anticipated structural performance
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