Abstract
The article presents the results of research work aimed at testing the use of hybrid steel-polypropylene fibre as a strengthening solution to upgrade reinforced high-performance concrete (HPC) beams with openings (BO1 ÷ BO3) and without (B1 ÷ B3). A total of six simply supported beams were tested under four-point bending. The test beams had a cross section of 200 × 400 mm and a total length of 2500 mm. Two square openings in each shear span were located symmetrically about the mid-point in three BO beams. Research was carried out with regard to the quantity and type of reinforcement. Beams B1 and BO1 were constructed with traditional reinforcement made of steel bars. As regards the remaining beams, instead of stirrups and compressive bars, fibre reinforcement of varying fibre volume contents was applied. In the analysis, a non-contact system for three-dimensional measurements of strain and displacement was used. Analysis of the behaviour of the beams under static load was based on the measurements of cracks, deflections and strains. The test results show that the first diagonal crack and the ultimate shear strength increase significantly as the fibre content increases. The above study showed that the hybrid fibres have a positive effect, reducing crack width and ensuring an increase in the load-bearing capacity.
Highlights
In cases where the major tensile stresses in the shear region of a RC beam exceed the concrete tensile strength, diagonal cracks cause failure
The main purpose of this study is to investigate the mechanical behaviour at shearing of RC beams with/without openings, made of high-performance concrete (HPC), containing long steel fibres and short polypropylene fibres in order to determine the possibility of using different fibre combinations to replace the stirrups in order to improve the shear and flexural strengths, crack control, failure modes as well as ductility
The deflections were recorded by means of with shear reinforcement the form of different hybrid fibre volume contents
Summary
In cases where the major tensile stresses in the shear region of a RC beam exceed the concrete tensile strength, diagonal cracks cause failure. Research emphasizes that the strength and ductility of RC beams are increased by using fibres as an additive to plain concrete [9,10,11,12,13,14,15,16,17,18,19]. This is thanks to the greater resistance to cracking of fibre-reinforced concrete (FRC).
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