Project Abstract

Abstract
Steel fibre reinforced concrete (SFRC) has gained popularity in various structural applications due to its enhanced mechanical properties. This study investigates the shear capacity of SFRC beams without conventional shear reinforcement. A series of experiments were conducted on simply supported beams to evaluate the effectiveness of steel fibres in enhancing the shear capacity of concrete beams. The test program included beams with varying steel fibre content and aspect ratios to analyze their impact on shear behavior. The results indicate that the inclusion of steel fibres in concrete beams significantly improves their shear capacity. Beams with higher steel fibre content exhibited increased shear resistance compared to plain concrete beams. Additionally, the aspect ratio of steel fibres influenced the shear behavior of the beams, with longer fibres providing better crack control and shear strength. Furthermore, the test results were compared with theoretical predictions from existing models for shear capacity of SFRC beams without conventional shear reinforcement. The findings demonstrated good agreement between the experimental and theoretical values, validating the accuracy of the developed models. The study also investigated the failure modes of SFRC beams under shear loading. It was observed that beams with steel fibres predominantly exhibited ductile failure characteristics, with multiple diagonal cracks forming before final failure. This ductile behavior is crucial for ensuring structural safety and integrity even after the initiation of cracks. Moreover, the influence of steel fibres on the crack width development in SFRC beams was examined. The results showed that the use of steel fibres effectively reduced crack widths in the beams, thereby improving their durability and serviceability. In conclusion, the experimental investigation highlighted the significant enhancement in shear capacity of concrete beams achieved through the addition of steel fibres without conventional shear reinforcement. The study provides valuable insights into the behavior of SFRC beams under shear loading and contributes to the development of design guidelines for utilizing steel fibre reinforcement in structural applications. The findings underscore the potential of SFRC as a reliable and effective alternative for enhancing the shear capacity of concrete beams in various construction projects.

Project Overview

While the increase in shear strength of Steel Fibre Reinforced Concrete (SFRC) is well recognized, it has yet to be found common application of this material in building structures and there is no existing national standard that treats SFRC in a systematic manner.

The aim of the diploma work is to investigate the shear strength of fibre reinforced concrete beams and the available test data and analyse the latter against the mostpromising equations available in the literature. The equations investigated are: Narayanan and Darwish’s formula, the German, the RILEM and the Italian guidelines.

Thirty articles, selected among over one hundred articles taken from literature, have been used to create the database that contains almost 600 beams tested in shear. This large number of beams has been decreased to 371 excluding all those beams and test that do not fall within the limitation stated for this thesis. Narayanan and Darwish’s formula can be utilized every time that the fibre percentage, the type of fibres, the beam dimensions, the flexural reinforcement and the concrete strength class have been defined.

On the opposite, the parameters introduced in the German, the RILEM and the Italian guidelines always require a further characterization of the concrete (with bending test) in order to describe the post‐cracking behaviour. The parameters involved in the guidelines are the residual flexural tensile strengths according to the different test set-ups.

A method for predicting the residual flexural tensile strength from the knowledge of the fibre properties, the cylindrical compressive strength of the concrete and the amount of fibres percentage is suggested. The predictions of the shear strength, obtained using the proposed method for the residual flexural tensile strength, showed to be satisfactory when compared with the experimental results.

A comparison among the aforementioned equations corroborate the validity of the empirical formulations proposed by Narayanan and Darwish nevertheless only the other equations provide a realistic assessments of the strength, toughness and ductility of structural elements subjected to shear loading.

Over the three investigated equations, which work with the post‐cracking characterization of the material, the Italian guideline proposal is the one that, due to its wide domain of validity and the results obtained for the gathered database of beams, has been selected as the most reliable equation.