Abstract
Fibre reinforced concrete shows enhanced performance in statistically redundant bi-dimensional structural elements that undergo biaxial bending. However, the lack of reinforcing rebars in fibre reinforced structural elements may affect the structural ductility which may further affect the overall load bearing capacity of these structures. To investigate the influence of fibres in such elements, six concrete plates of 2000 × 2000 × 150 mm reinforced with steel fibres and/or reinforcing rebars are tested under a central concentrated load. Two of the elements are reinforced with only 35 kg/m3 of steel fibres, two are reinforced with 2-way conventional reinforcing rebars (35 kg/m3, in each direction) and two are reinforced with both steel fibres and rebars. The specimens are simply supported at the middle of each side by means of a bilateral restraint; the deflection response and cracking behaviour of all the specimens are recorded and compared. Moreover, the methodology introduced in the fib Model Code 2010 for design of steel fibre reinforced concrete is implemented to predict the ultimate load bearing capacity of these elements and its reliability is determined in comparison with the experimental values. The comparison of the behaviour of the specimens reinforced only with steel fibres, with those reinforced with steel rebars, shows the higher efficiency of steel fibres in terms of load carrying capacity, but with a lower ductility. The combination of steel fibres and rebars allows for a better exploitation of the capacity of both reinforcement solutions. Finally, the reliability of the approach implemented for the ultimate load prediction is shown and the need of rebars in providing ductility in fibre reinforced concrete members is underlined.
Highlights
The addition of steel fibres in concrete to prevent the brittle tensile behaviour shown by plain concrete has been studied for over half a century after the observation of the crack arrest mechanism by Romualdi and Batson [1]
While classifying the steel fibre reinforced concrete (SFRC) according to provisions of Model Code 2010 (MC 2010) at 34 days leads to a ‘‘3c’’ material, taking into account the specimens tested at 167 and 220 days, a ‘‘5b’’ material is obtained
Unlike the results presented here, the deflection of the R/fibre reinforced concrete (FRC) slabs, tested by Pujadas et al was only slightly smaller than the R/C ones in the SLS range
Summary
The addition of steel fibres in concrete to prevent the brittle tensile behaviour shown by plain concrete has been studied for over half a century after the observation of the crack arrest mechanism by Romualdi and Batson [1]. While in a conventionally reinforced concrete member tensile stresses are transferred to concrete between the cracks by stretched rebars through the steel–concrete bond, in fibre reinforced concrete (FRC), due to the presence of fibres, concrete is able to carry tensile stresses along the cracks. This stiffening effect brought by fibres is responsible for closer crack spacing and narrower crack widths in a structural system containing both reinforcing bars and fibres (R/FRC) [8,9,10,11,12]
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