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

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

Elevated slabs made of hybrid reinforced concrete: Proposal of a new design approach in flexure

When designing fiber‐reinforced concrete (FRC) structures, one of the basic design issues is represented by the choice of a proper combination of fibers and conventional reinforcement that allows to obtain the best structural performance with the minimum amount of materials. The combination of rebars and fibers in the concrete matrix is generally known as Hybrid Reinforced Concrete (HRC). HRC represents a feasible solution in many structures; among these, slabs are gaining an increasing interest among practitioners. In fact, slabs are the most widespread structural elements in common practice as they are typically used to construct slabs on ground (industrial floors or foundations), slabs on piles (foundations) or elevated slabs. This paper focuses on the flexural design of FRC elevated slabs by using the most recent design provisions reported in the fib Model Code 2010. A simplified design procedure based on a consolidated design practice is proposed. Emphasis is given to the use of HRC to minimize the total reinforcement (fibers + rebars) in order to get practical and economic advantages during construction (ie, construction time and costs reduction). In more detail, a procedure for proportioning the hybrid reinforcement and then verifying the structural safety will be presented and discussed. Numerical nonlinear finite element analyses will be carried out to assess the effectiveness of the proposed design method

EXPERIMENTAL STUDY ON STEEL FIBER REINFORCED CONCRETE BEAMS IN PURE TORSION

This paper concerns an experimental study on Steel Fiber Reinforced Concrete (SFRC) beams tested under pure torsion. The beams are reinforced with longitudinal rebars without any transverse reinforcement that was substituted by high strength steel fibers. Experimental results show that SFRC allows a stable torsional behavior after cracking, in terms of enhanced crack control, increased cracked stiffness and torsional resistance. In order to predict the response of SFRC beams, an analytical model reported in the literature has been used and adapted to the fib Model Code 2010 provisions. The results of the model prediction are compared against the experimental results and critically discussed