Abstract:
The structural performance of reinforced concrete (RC) deep beams in both ultimate and
serviceability limit states (ULSs/SLSs) is influenced by beam size effects and the adopted
reinforcement ratios. In this study, the effects of cotton waste fibres (CWFs) and beam
depth were studied using a four-point load test on five sets of 400 mm and 500 mm CWF
high-strength RC deep beams with a 0.3% web reinforcement ratio. Control unnotched and
notched, and notched specimens with 0–0.75% CWF content in each specimen set, were
studied. The failure modes, stirrup and strut-and-tie zones’ strains, shear capacity, and
load-deflection were analyzed. It was observed that the beam failure evolved from shearcompression in unnotched specimens to the web-splitting failure phenomenon in notched
ones, coupled by 27.44% and 0.17% decline in ultimate shear capacity (Vu) in notched
400 mm and 500 mm beam sets, respectively. The notched RC deep beam specimens,
mimicking the SLS shear performance parameters, showed a 34.28% and 14.71% Vu increase
in 400 mm and 500 mm depth beams, respectively. The crack opening load increased from
13.87 kN to 44.63 k and from 11.88 kN to 35.19 kN in these beam sets, respectively. In
a similar analysis, 84.76% and 38.39% stiffness increase, and 49.15% and 39.95% shear
ductility index increase in the outer-most stirrup, were observed in the respective specimen
sets. The contribution factor of the shear reinforcement to Vu improved from 0.31 to 0.94,
and from 0.87 to 0.97 in 400 mm and 500 mm, with 0% and 0.75% CWF, respectively. These
experimental results confirm the contribution of beam size effect and fibres to the shear
performance properties of RC deep beams. The feasibility of using CWF in structural
concrete is confirmed by its improvement of the SLS properties of the studied RC deep
beam specimens with light shear reinforcement.
