Shear capacity of precast half-joint beams with steel fibre reinforced self-compacting concrete

Abstract

A complex geometry of precast reinforced concrete half-joint beams has resulted from the high shear force at the recessed ends of such beams. Immense levels of reinforcements are provided close to the re-entrant corner of these beams to prevent the propagation of diagonal cracks and sudden failure. However, this condition leads to reinforcement congestion and affects the bond between concrete and reinforcing steel due to improper concrete filling around the congested bars. Hence, the use of steel fibre self-compacting concrete (SFRSCC) was found to combine the advantages of eliminating the vibration works, and reduction of secondary reinforcement. An experimental study was conducted to examine the ability of 1.0% by volume of steel fibre to partially replace the traditional reinforcements on two types of half-joint beams (short recess (SR) and deep recess (DR) beams). Other factors taken into account is the variance in shear span values and nib height, as well as the ratio of shear-span-to-depth, av/d. Observations showed that the replacement of 1.0% by volume of steel fibre volume fraction is possible only when substituting at least 50% of the vertical or horizontal reinforcement in SR beams. Meanwhile, the replacement over diagonal reinforcement is seemed to be not enough and the replacement is only promising in substituting part of stirrups in DR beams. The variance in the shear-span-to-depth av/d ratio affects the shear failure mode of the beam half-joints. Two semi-empirical equations for predicting the shear strength of precast SCC and SFSCC beam-half joints are developed based on the analysis of failure modes. The first equation, which relies on the crushing of the concrete strut, was found to suit the SR beams, while the equation for DR beams suits the theoretical of reinforcement yielding. The two equations give a good correlation with the experimental results.