۱- Introduction

۲- Research aim and novelty

۳- Experimental investigation

۴- Experimental results and discussion

۵- Prediction of crack spacing

۶- Conclusions

References

Abstract

The load-deformation response of Fiber Reinforced Concrete (FRC) elements subjected to pure shear is still matter of strong debate within the scientific community. In this paper, the tests on six fiber reinforced concrete panels under pure shear are presented and discussed. The tests were conducted under displacement control and a peculiar loading frame was designed to ensure that a pure shear state of stress was established. Steel fibers were added in relatively low amounts (20 and 50 kg/m3), and two steel reinforcements (0.21% and 0.74%) were selected, aiming at simulating lightly reinforced elements. A critical discussion on the influence of fibers on both global and local behavior (tension stiffening, cracking formation and propagation, post-cracking stiffness and residual strength) is presented. Finally, a novel crack spacing formulation, extended to FRC, is proposed and compared against available experimental data.

Introduction

The prediction of the shear behavior of Fiber Reinforced Concrete (FRC) elements still represents a challenging issue. To improve the knowledge of mechanisms related to shear, a large number of studies involving FRC members has been carried out and reported by literature. One of the first experimental studies focusing on the shear behavior of fiber reinforced concrete beams without stirrups was performed by Li et al in 1992 [1]. It was observed that the shear strength increases in the range 100–۲۰۰% when adopting a volume fraction of 1% of polyethylene, aramid or steel fibers. Later, in 1997, Adebar et al. [2] carried out tests on large-scale beams without stirrups proving that the use of a sufficient amount of fibers is able to prevent brittle shear failure in favor of a more ductile response. Lower volume fractions of steel fibers (0.5–۰٫۷۵%) were adopted by Kwak et al. [3], whose tests on shear critical beams showed that the increment of the shear strength was particularly large (69–۸۰%) especially for beams with shear span-todepth ratios equal or lower than 2. These observations were further supported by the research carried out in 2006 by Parra-Montesinos et al. [4], who performed some shear tests on beams and then collected a database containing the results from tests performed by different researchers. The analysis of the database led to the conclusion that fibers are potentially able to replace minimum conventional shear reinforcement; anyway, the authors recommended the use of a fiber volume fraction higher than 0.75%. Unlike usual studies, Meda et al. adopted quite low amounts (0.38–۰٫۷۶%) of steel fibers to investigate the effect of fiber reinforcement on the flexural response of slender beams. The authors concluded that fibers do not significantly improve the flexural resistance and the overall ductility strongly depends on the FRC toughness over the reinforcement ratio. On the contrary, they pointed out that fibers considerably enhance the behavior of the beam at service conditions by increasing the stiffness in the cracked stage and by limiting both the deformations and crack widths. More recently, other studies [6,8] were carried out to investigate the effect of different parameters (i.e., concrete class, fiber content, mixture of different fibers and sectional height-to-width ratio) on both the shear, torsional and flexural response of FRC beams without shear reinforcement.