This 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.

A constitutive model for simulating the compressive response of unreinforced brick masonry subjected to cyclic loading is presented and discussed. The developed formulations are consistent with the smeared rotating crack approach and may be easily implemented in finite element codes for nonlinear analysis. The analysis approach includes different features such as nonlinear curves for capturing the shape of the unloading/reloading branches, both in case of full unloading from the envelope curve and partial unloading/reloading. A unified model for predicting the residual plastic strain as a function of the strain recovered during unloading is also proposed. Particular attention is paid to the stiffness degradation occurring during reloading and to the prediction of the stress and strain values at which the reloading branch intersects the envelope. The calibration of most of the proposed formulations is based on experimental results reported in the literature, as well as from two uniaxial cyclic compression tests carried out within the present work. Finally, the model effectiveness is tested with some verification examples.

The strength and behavior of fiber reinforced concrete (FRC) members subjected to torsion has received little attention in the literature. The primary objective of including fibers in concrete is to bridge cracks once they form, and in doing so, provide some post‐cracking resistance to the otherwise brittle concrete. This and the accompanying paper that follows present the results of a comprehensive experimental and analytical study aimed at describing the behavior and strength of FRC members subjected to torsion. In this paper, results are presented on large scale pure torsion tests which have been conducted on eighteen 2.7 m long by 0.3 m wide by 0.3 m high beams with varying transverse and longitudinal reinforcement ratios along with varying steel fiber types and dosages. The results of this study demonstrates that the addition of steel fibers significantly increases the stiffness, rigidity and the maximum resisting torque and maximum twist when compared to the same specimen without fibers. The addition of fibers substantially reduced crack widths and crack spacings induced by torsion. The complementary behavior of specimens containing fibers and stirrups is explored along with a critical discussion on members containing low amounts of conventional longitudinal and/or transverse reinforcement.

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. K E Y W O R D S design slabs, elevated slabs, fiber-reinforced concrete, hybrid-reinforced concrete, Model Code 2010, nonlinear finite element analysis

The limited tensile resistance of many existing un-reinforced masonry (URM) members may represent a matter of great concern, especially when masonry constructions are located in seismic areas. For this reason, the development of innovative strengthening and repairing techniques have been the subject of several experimental studies performed in the last few years by many researchers worldwide. The present paper concerns an experimental study based on quasi static reverse cyclic tests carried out on full-scale URM squat shear walls strengthened or repaired by means of a thin coating made of a calcium-aluminate steel fibre reinforced mortar (SFRM) containing nano-silica. This strengthening method represents a novelty with respect to both the nano-reinforced SFRM and the practical application procedure adopted. The experimental results show the enhanced performances provided by the proposed technique in terms of strength and stiffness increment

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