Behaviour of Over-reinforced Concrete Beams with Double Helix and Double Square Confinements Related to Ultimate Bending and Shear Strength

To cite this article: Horng, H. T., Al-Sanjery, K. & Choong, J. L. C. (2018). Behaviour of over-reinforced concrete beams with double helix and double square confinements related to ultimate bending and shear strength. J. Phys. Sci., 29(Supp. 2), 77–98,


Over-reinforced concrete beams with compression zones confined with double helix and double square shaped steel confinement reinforcements were studied with respect to flexural strength, shear strength and deflection. Seven reinforced concrete (RC) beams, 200 mm (width) × 300 mm (depth) × 3000 mm (length) with four incorporating 1.42 ρb and the remaining 1.64 ρb (where ρb is the balanced steel ratio) were tested under four-point static load tests. The confinements consisted of 6 mm diameter reinforcements with nominal yield stress of 275 N mm–2 and pitches of 50 mm. A previous investigation by the authors indicated that to utilise fully the ultimate bending strength of concrete beams with confinements in the compression zones, the shear strength of such beams should be enhanced by adopting the diagonal compressive strut angle (θ) of more than 22° recommended in Eurocode 2 (EC2). It was found that the failure loads are higher than the control beams’ calculated ultimate loads. Deflections of beams with confinement were less compared to the beams without confinements. Control beams failed in shear because of no shear strength enhancement whereas all confined beams failed in flexural/ compression mode and gave fair warning against failure. The cracking behaviour was the same for all beams with vertical tensile cracks at the constant moment zone and inclined cracks at the shear span. After failure, it was found that the concrete core confined was still intact. To check on the concrete compressive strength, eight concrete cylinders of diameter 100 mm were prepared, six of them were confined with helical reinforcements with 50 mm pitch, and two without confinements. It was found that with confinements, the cylindrical compressive strength increased between 1.34 and 2.22 times that of unconfined concrete cylinder strength.


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