Correction to: Structural effects of FRC creep

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Structural effects of FRC creep

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Tensile behaviour of FRC under high strain-rate

This paper presents experimental results on two types of concrete reinforced with steel and polyvinyl-alcohol (PVA) fibres subjected to dynamic tensile loading. The tests were carried out by using a Modified Hopkinson Bar apparatus on fibre reinforced concrete notched-specimens under three different strain-rates (50, 100, and 200s−1). From the experiments it was found that there is a significant enhancement in tensile strength with increasing strain-rates. The dynamic tests on steel FRC with the smaller loading rate (50s−1) showed a strength similar to the one measured from static tests; however, for increasing loading rates, a remarkable decrease of post-peak strength and ductility occurs. In specimens with PVA fibres, an enhancement of the tensile strength was also observed and a significant reduction of fracture energy and ultimate deformation occurred. Some experimental aspects are also discussed as the specimen shape, its dimension, the loading rate as well as the different post-peak behaviour from static and dynamic test

Steel fibers for replacing minimum reinforcement in beams under torsion

AbstractThis paper concerns an investigation on six large-scale Steel Fiber Reinforced Concrete (SFRC) beams tested in pure torsion. All beams had longitudinal rebars to facilitate the well-known space truss resisting mechanism. However, in order to promote economic use of the material, the transverse reinforcement (i.e. stirrups/links) was varied in the six large scale beams. The latter contained either no stirrups, or the minimum amount of transverse reinforcement (according to Eurocode 2), or hooked-end steel fibers (25 or 50 kg/m3). Material characterization were also carried out to determine the performance parameters of SFRC. The results of this study show that SFRC with a post-cracking performance class greater than 2c (according to Model Code 2010) is able to completely substitute the minimum reinforcement required for resisting torsion. In fact, the addition of steel fibers contributes to significantly increase the maximum resisting torque and maximum twist when compared to the same specimen without fibers. Moreover, SFRC provides a rather high post-cracking stiffness and a steadier development of the cracking process as compared to classical RC elements. This phenomenon improves beam behavior at serviceability limit state. The experimental results are critically discussed and compared to available analytical models as well as with other tests available into the literature

New openings in unreinforced masonry walls under in-plane loads: a numerical and experimental study

Nowadays, existing masonry buildings are frequently modified to satisfy living demands. These modifications may require the addition of new windows or doors in walls of structural functionality. In engineering practice, such modifications are generally designed and verified for vertical loads while, for seismic loads, the changes in the walls' structural behaviour are not yet fully understood. Consequently, current design may incorrectly estimate the in-plane response of the perforated walls. This paper presents an evaluation of the effects of the introduction of new openings in masonry walls under in-plane loads by a numerical and experimental approach. Two parameters are considered for the numerical studies: opening size and eccentricity. The results show that the loss in stiffness and strength due to new openings are proportional to the opening area and that the eccentricity might change the wall response going from rocking to shear dominant behaviour, depending on the load direction

Effectiveness of a steel ring-frame for the seismic strengthening of masonry walls with new openings

The creation of new openings in masonry walls is a frequent intervention in existing buildings. Depending on their size and position, these interventions may cause a significant decrease of the wall’s original in-plane strength and stiffness, thus compromising the building seismic resistance. Therefore, in masonry buildings, strengthening techniques may be required to (i) restore as much as possible the loss of stiffness and strength, (ii) be reversible and (iii) respect the compatibility between materials, particularly in the case of historical buildings. In an attempt to comply with these requirements, engineering practitioners often introduce very stiff steel profiles forming a ring-frame inside the opening for fully restoring the stiffness and resistance without substantially increasing the building's weight. However, the effectiveness of this technique is typically quantified using linear elastic analysis and a simple sum of the flexural and shear stiffness of the masonry panels and the steel ring-frame. The present work aims to improve the knowledge and better understanding of the effectiveness of this traditional steel ring-frame technique, through experimental and numerical methods. The experimental program was designed to provide a full assessment of the effects of introducing a new door opening in brick masonry walls, from the cutting process to the application of in-plane cyclic lateral deformations. The steel ring-frame was designed using numerical tools and consisted of four profiles welded together and tied to the surrounding masonry wall by means of steel dowels dry-driven into calibrated holes of the brick. Results show that the steel ring-frame system restores the original solid wall’s in-plane strength and ductility, but not the lateral stiffness, despite the use of large steel profiles.MIUR -Ministero dell’Istruzione, dell’Università e della Ricerca(undefined

Technical and environmental characterisation of recycled aggregate for reuse in bricks

Waste mud coming from an aggregate washing plant was formerly used as filling material for a pond, aimed at the recovery of an abandoned quarry. Once completed the filling capacity of the pond, the need for identifying a possible reuse of mud produced by the plant arose in order to avoid landfill disposal. Therefore, mud has been geometrically, physically and chemically characterised for its recovery as construction material. A variety of tests was carried out on mud samples as required by EN technical specifications and by Italian environmental standards, focusing particularly on leaching behaviour. The tested material showed satisfactory physical and chemical properties and a release of pollutants below the limits set by the Italian code. Many mix-designs for the production of unfired bricks made of waste mud, sand and straw, stabilised and non-stabilised with lime, gypsum or cement, were developed. The bricks were tested in order to evaluate mechanical properties and leaching behaviour. Mud bricks provided remarkable compressive strength, even if not suitable for structural elements. The use as interior design to minimise humidity changes and to facilitate a thermal insulation is fostered, thus strengthening the so-called green building economy

Retrofitting unreinforced masonry by steel fiber reinforced mortar coating: uniaxial and diagonal compression tests

AbstractThin layers of mortar reinforced with steel fibers can be applied on one or both sides of bearing walls as an effective seismic strengthening of existing masonry buildings. To assess the effectiveness of this technique, an experimental study on masonry sub-assemblages was carried out at the University of Brescia. This paper summarizes and discusses the main results of the investigation, which included mechanical characterization tests on masonry and its components as well as on the Steel Fiber Reinforced Mortar (SFRM) used to retrofit the masonry samples. Uniaxial and diagonal compression tests were carried out on both unstrengthened wallets and masonry samples retrofitted with 25 mm thick SFRM coating. Both single-sided and double-sided retrofitting configurations for application on wall surfaces were considered. The results highlighted the ability of the technique to improve the compressive and the shear behavior of masonry, even in case of single-sided strengthening. Moreover, no premature debonding of coating was observed. Lastly, the manuscript presents the results of a numerical investigation that was performed both to simulate the diagonal compression tests described in the first part of the paper and to predict the response of panels with different strengthening configurations

Fiber reinforced mortar and concrete for seismic retrofitting of masonry and RC structures

Many countries are currently facing the problem of the evaluation and retrofitting of existing buildings and infrastructures, due to structural deficiencies and durability issues. With the aim of avoiding expensive demolition and reconstruction interventions, excellent retrofitting techniques have been developed over the years, using new composite materials like fibre reinforced mortar (FRM) and ultra-high performance fibre reinforced concrete (UHPFRC). The present paper describes the most significant experiences carried out at the University of Brescia, leading to the development of innovative retrofitting techniques for masonry buildings and RC bridges, including characterization tests of materials, tests on full-scale elements and experimental investigations performed on full-scale structures

Sustainable Recycling of Electric Arc Furnace Steel Slag as Aggregate in Concrete: Effects on the Environmental and Technical Performance

The aim of this research work was the evaluation of the feasibility to utilize industrial by-products, such as electric arc furnace steel slags, for sustainable concrete production. The paper evaluated the environmental and mechanical properties of steel slags and concrete, respectively. Specifically, the release of contaminants from steel slags was investigated by leaching test and the properties of fresh and hardened concrete were evaluated for a concrete mixture designed with a partial substitution (30%) of natural coarse aggregates with electric arc furnace steel slags. The results show that the concentrations of pollutants were lower than the legal limits imposed by the Ministerial Decree 186/2006 and the addition of steel slag can enhance the mechanical performance of concrete. The compressive strength of cubic specimens was also measured after different cycles of alternate wetting–drying. The steel slag incorporation results in a stiffness comparable to that of a traditional concrete. Overall, the mechanical and leaching characterization has shown that the reuse of electric arc furnace steel slags for sustainable concrete production is feasible and reliable