Results in Engineering (Sep 2022)
The orientation effect of opening and internal strengthening on shear performance of deep concrete beam using recycled tyre steel fibres
Abstract
A deep concrete beam is a structural member that transfers heavy loads from the introduced column(s) due to a change of function layout of a particular floor in the building. Due to its high depth, the service utilities are always accommodated by creating a transverse opening rather than at its soffit. However, this practice leads to a reduction of shear resistance and affects the serviceability of the beams. To reinstall this capacity, waste tyre steel fibres were used to assess their effectiveness in improving the shear resistance of the deep concrete beams with openings. Three sets of beams with, without fibres, and with fibre mesh that had openings of 160 × 86, 115 × 120, 86 × 160, and 165 × 170 mm were considered. A total of 16 beams with dimensions 150 × 400 × 1100 mm and a constant shear span-to-depth ratio of 0.8 were cast and tested. The steel fibres used had a diameter of 1.3 mm, a length of 50 mm, a fibre content of 0.5% and a fibre mesh of 110 × 100 mm. The main variables evaluated were the effect of the opening size and its orientation, the effect of stirrups, the random mixing of fibres in the matrix, and the internal strengthening of the fibre mesh in the anticipated strut line of the deep beam. The results showed that an interruption of the strut width affected the shear resistance of the beam. The beam with 160 × 86 mm had a lower capacity of 7.7% compared to 115 × 120 mm with the same opening area. The 160 × 86 mm control beam had a high shear capacity of 2.6% compared to 86 × 160 mm. The inclusion of fibre increased the compressive stiffness of the strut; The beam with fibre and opening size 165 × 170 mm had a shear capacity of 37.8% higher than the beam without fibres. The addition of mesh had a limited increase in shear capacity compared to random fibre mixes; however, the capacity was 21.6% higher than the control mix for a beam with an opening size of 165 × 170mm. Therefore, it is recommended to use recycled waste tyre steel fibres to improve the shear capacity of the deep concrete beam and less application of shear bars.
