ENHANCEMENT OF TORSIONAL RESISTANCE IN FIBROUS NORMAL STRENGTH CONCRETE BEAMS

Abstract

This paper highlights the influence of thickness of concrete cover on the torsional resistance in the fibrous rectangular solid concrete beams under pure torsion. In this investigation, thickness of concrete cover vary between 18 and 53 mm. To study the influence of concrete cover in under-reinforced fibrous normal strength concrete, four fibrous concrete beams were cast and test under pure torsion. The under-reinforced concrete beams was designed based on ACI-318-14. The transverse and longitudinal reinforcement indexes are kept constant in the beams. While the aspect ratio of the beam cross section and span to depth ratio of the beams are 1.22 and 5.75, respectively. The test results were claimed that the torsional resistance provided by concrete and reinforcements plus fibre were enhanced at crack and peak loads up to 76.4% and 64.4%, respectively. In contrast, twisting angle, shear strain in concrete, strain in transverse and longitudinal reinforcements were reduced up to 57.8%, 65%, 89.3% and 95.6%, respectively. The spacing between cracks and the angle of inclination of crack at failure was increased whereas the number of cracks reduced. The dimensional analysis was used to proposed equations to predict torsional resistance at crack and peak loads including the contribution of concrete cover. In addition, the Buckingham П theorem was used for this purpose. Based on the 34 data from previous researches and the data in this research, nonlinear multiple regressions in Minitab software version 16 was used to predict the coefficients of the proposed П-groups equations. The proposed models have shown a good agreement with test results.