1,721,118 research outputs found
Experimental and numerical analysis of advanced cementitious composites for sustainable roof elements
No full textThe use of Ultra High Performance Fibre Reinforced Composites (UHPFRC) allows the designer to reduce the dead weight of roofing keeping concrete covering structures still more competitive in relation to steel structures in terms of costs, thermal and acoustic insulation and fire resistance. Thin plates can be used as tertiary elements in roof floors beside the border beams and the simply supported prestressed precast roof elements. The high performances of the 2m wide elements are mainly used for bending along the 2,5m span and in order to drastically simplify the detailing of the support regions. The sandwich technology potential is maximized by coupling the exceptional mechanical characteristics of Textile Reinforced Mortars (TRM) and UHPFRC with the insulation capability of a polystyrene layer. It is expected that the coupling of a low stiffness material with concrete layers brittle at the specific level, could give back a composite panel characterized by multi-cracking phenomena and high inertia.
Due to the internal actions acting on the horizontal bearing component, the insulating core should ensure an adequate shear transfer, able to keep the TRM layer mainly in tension and the FRC plate mainly in compression. This configuration makes lighter structures possible because it fully exploits the material used and, secondly, makes them more environmental friendly because recycled materials can be used.
In this paper, the attention will be focused on the problems inherent with the experimental evaluation of individual materials constitutive relations and on the non-linear finite elements modelling of the bending behaviour of the composite
Elementi di copertura sostenibili: un'indagine teorico-sperimentale
No full textIn this paper, a sustainable solution for roofing is investigated. It con The concerns the use of High Performance Fibre Reinforced Cementitious Composites to allows the designer the reduction of the dead weight and improving at the same time thermal, acoustic insulation and fire resistance. Thin slabs can be used as tertiary elements in roof decks beside the spandrel beams and the simply supported prestressed precast roof elements. The idea is that of coupling textile and UHPFRC technology, by means of an interposed polystyrene layer. A wide experimental investigation is in progress to mechanically characterize the materials in uniaxial tension and compression, in order to identify all the data needed for design like toughness, bending resistance, fire resistance and durability. With reference to textile materials, they are reinforced with glass fabric. The mechanical characteristics are deduced in uniaxial tension, while the structural behaviour of the composite will be tested in bending. The attention is here focused on the problems inherent with the experimental evaluation of individual materials constitutive relations and on the non-linear finite elements modelling of the bending behaviour of the composite
On site assessment of Azzone Visconti bridge in Lecco: Limits and reliability of current techniques
No full textPonte Azzone Visconti is a strategic middle age bridge built at north of Milan astride river Adda, along the road towards the centre of Europe passing from the Valtellina, the lordship of Milan and the Serenissima Republic. An on-site assessment of the bridge was carried out starting from the requirement expressed by the municipality of Lecco, consisting in the evaluation of the actual bearing capacity of the infrastructure with reference to the bridge classes defined in the national standards. The investigation used several approaches to quantify the bridge structural safety with reference to the vertical loads due to traffic and accidental seismic events and to highlight any critical issue. The paper is aimed at suggesting the most convenient analysis and maintenance choices, in order to conjugate the very significant historical value of the bridge to a sustainable evolution of its function
Mechanical characterization and modelling of Ultra High Performance Fiber Reinforced Concrete
Full text linkIn the last two decades the use of Ultra High Performance Fiber Reinforced Concrete (UHPFRC) for the construction of structural and non-structural elements has increased, but there is still a strong need to establish a complete method for its mechanical characterization, especially of its tensile behavior. In this paper, a mechanical investigation carried out on four UHPFRC specimens with a fiber volume fraction of 3.3% is presented. The fiber content resulted to be sufficient to cause strain hardening behavior, characterized by a multicracking phase. The tensile constitutive law provided by Model Code 2010 for the inverse analysis from bending tests is hereby discussed. In particular, the size of the mul-ticrack diffusion zone is investigated with vision-based measurement tools and used as a characteristic length
Comportamento Flessionale di Lastrine a matrice cementizia con rinforzi ibridi
No full textRecently, the interest in the use of high
performance cement-based materials (HPC) has
been increased due to the need to intervene on
existing buildings no longer meeting the structural
and seismic requirements imposed by the revised
national codes. A retrofitting strategy that might be
successfully adopted in precast structures is
represented by the substitution of the unsafe
roofing elements with innovative composites
characterized by lightness and high structural
performances. The significant self-weight
reduction might play a positive role on both the
static and the dynamic building behavior.
The paper investigates the flexural response
of three sets of cement-based plates (400 mm
long, 70 mm wide, 15 mm thick); the first set was
reinforced with unoriented high carbon steel
microfibers, the second one with two layers of
glass fabrics and the third one with a combination
of steel fibers and textiles.
Performing four point bending tests, it was find
out that the combination of high-carbon steel
microfibers and alkali-resistant glass textiles
(hybrid reinforcement) is capable of increasing the
structural performances in terms of tensile
strength, ductility and crack pattern
Role of the tensile constitutive modeling on the structural response of fiber reinforced concrete flat slabs: A numerical study
Full text linkFor decades, fiber reinforced concrete (FRC) has been primarily used in elements for which the consequences of potential failure are minor, like slabs on grade and precast tunnel segments, just to name a few examples. With reference to slabs supported on walls and/or columns, the use of fibers as partial or main reinforcement has increased over the last 15 years. Despite the existence of advanced design codes like the fib Model Code 2010, experimental data, and standing buildings that prove the technical feasibility of FRC, there are still barriers for its use at a wider scale. Technical aspects such as the uncertainties in the identification procedure of FRC uniaxial tensile laws and the influence of the FRC post-cracking strength class on the serviceability and ultimate limit states response are among the factors that prevent a larger diffusion of FRC. In this paper, the role played by several tensile post-cracking constitutive models—among those most commonly used both in research and in design practice—on the structural response of FRC flat slabs is investigated. The effect of numerical modeling choices such as (i) the influence of shell or brick elements and (ii) the influence of material homogeneity or heterogeneity along the slab thickness on the structural response of FRC flat slabs is also examined
Advancing construction techniques: Textile reinforced concrete shells and high-performance fiber-reinforced concrete beams for partially prefabricated elevated slabs
Full text linkInnovative high-performance cementitious materials lead the way for the development of advanced structural systems, characterized by improved durability, mechanical performance, and construction efficiency. In this paper, we introduce a partially precast unidirectional ribbed slab system, featuring very high-performance fiber-reinforced concrete (VHPFRC) I-beams, textile-reinforced concrete (TRC) stay-in-place formworks, and ordinary steel fiber-reinforced concrete (SFRC) finishes. Engineered to maximize the advantages of these innovative materials, the system achieves a lightweight configuration, minimizing the need for on-site steel reinforcement placement. After outlining the conceptual design of the proposed structural system, the paper thoroughly examines the characterization of materials and details the prototyping procedures employed. The theoretical framework is substantiated by an extensive experimental campaign on individual components, offering insights into the full-scale response of the precast elements, and is supplemented by simplified sectional analyses aimed at estimating the flexural behavior of the full composite slab. Additionally, a preliminary assessment of the environmental sustainability of the solution is provided
FLEXURAL BEHAVIOR OF FIBER AND TEXTILE REINFORCED HPC THIN PLATES
No full textThe interest in the use of high performance cement-based materials (HPC) has been recently increased due to the need to intervene on existing buildings that do not meet the structural and seismic requirements imposed by the revised national codes.
A retrofitting strategy that might be successfully applied to several precast buildings in Northern Italy is represented by the substitution of the unsafe roofing elements with innovative multilayer panels characterized by lightness and high structural performances. The significant self-weight reduction might play a positive role on both the static and the dynamic building behavior.
The paper investigates the flexural behavior of three sets of prismatic specimens (400 mm long, 70 mm wide, 15 mm thick); the first set was reinforced with unoriented high carbon steel microfibers, the second one with two layers of glass fabrics and the third one with a combination of steel fibers and textiles.
Performing four point bending tests, it was find out that the addition of high-carbon steel microfibers is capable of increasing the structural performances of the composites, in terms of tensile strength, ductility and crack pattern
HPFRCC BEAMS IN INNOVATIVE ELEVATED SLABS: EXPERIMENTAL CHARACTERIZATION AND MODELING
No full textIn the field of precast structures, the need to ensure robustness, ductility, fire resistance and rapid assembly, moves designers and researchers towards the development of innovative structural solutions, making use of high-performance materials [1, 2] which allow to optimize the elements sections, while reducing the total masses and the execution costs. This is the case of a semi-precast slab floor composed by HPFRCC beams coupled with TRC disposable formworks and a SFRC finishing casting, which is actually the topic of a research project held at Politecnico di Milano [3].
In this framework, the secondary HPFRCC beams were designed according to the fib Model Code 2010, paying attention on both the transient and the service conditions. Following the experimental characterization of the plain material (by means of bending tests on notched beam specimens and compressive tests on cylindrical specimens), two full-scale beams (3.4 m long) were cast and experimentally validated by means of four-point bending and shear tests. The results were finally compared with simplified analytical models based on plane-section hypotheses, proving the predictive capability of the available design tools
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