The effect of helical pitch on the behaviour of helically confined HSC beams

The strength and ductility of HSC beams are enhanced through the application of helical reinforcement located in the compression region of the beams. The pitch of helix is an important parameter controlling the level of strength and ductility enhancement of over-reinforced high strength concrete beams. This paper presents an experimental investigation of the effect of helix pitch on the beam behaviour through testing five helically confined full-scale beams. The helix pitches were 25, 50, 75, 100 and 160 mm. Beams’ cross section was 200 × 300 mm, and with a length of 4 m and a clear span 3.6 m subjected to four point loading, with emphasis placed on the mid-span deflection. The main results indicate that the helical effectiveness is negligible when the helical pitch is 160 mm (helix diameter), the concrete cover spalling off load increases linearly as the helical pitch increased, and the ultimate load decreases as the helical pitch increases. Finally, there is a considerable release of strain energy responsible for spalling off the concrete cover.