Using Internal Framed Steel Stiffening Ribs as an Alternative Technique for Torsional Strengthening of RC Box Beams

Abstract

There is little research on internal torsional strengthening of box beams. This study uses internal framed steel stiffening ribs (FSSRs) as an alternative technique for torsional strengthening of reinforced self-compacting concrete (SCC) box beams. These FSSRs have been fabricated to a square shape of size equal to the internal dimensions of the box beam specimens, specified cross-section, and shear connectors on four sides. Four specimens of reinforced SCC were tested up to failure under the effect of pure torsion; one was a reference specimen without strengthening (designated as 1NR) and the other three (designated as 2N1OF, 3N3OF, and 4N5OF) were strengthened with one, three, and five FSSRs, respectively. Specimens had dimensions of 2100×300×300 mm for length (L), width (W), and height (H), respectively. The effect of FSSRs, and their number, on torsional capacity were studied, as was the application of torque-angle of twist relation at end, quarter and mid span. Results show that the ultimate torsional strength capacity is increased significantly by 32.7 %, 59.2 %, and 93.9 % for specimens 2N1OF, 3N3OF, and 4N5OF, respectively as compared with the reference specimen, 1NR. The presence of FSSRs tends to reduce deformation of specimens: deformation decreases with increase in the number of FSSRs. It is concluded that the torsional strength capacity of reinforced SCC box beams can be enhanced by use of internal FSSRs as in this study. The extent of enhancement depends mainly on the number of internal FSSRs deployed.