Experimental investigation of RC beams with rectangular spiral reinforcement in torsion

Recently, the use of continuous spiral reinforcement has been extended in reinforced concrete elements with rectangular cross-sections. The behaviour of reinforced concrete beams with rectangular cross-section and continuous rectangular spiral reinforcement as transverse reinforcement under pure torsion is experimentally investigated. The presented experimental program comprises 11 beams. Test results of this study clearly indicated that the use of rectangular spiral reinforcement provided enhanced torsional capacity and improved post peak performance in the examined beams. Compared to beams with equal quantity of the commonly used stirrups the measured increase of the torsional strength for the tested beams under imposed twist that locks the spirals was 18%, 16% and 14% for the beams with transverse reinforcement spacing at 200 mm, 150 mm and 100 mm, respectively. However, it is stressed that when spirals are unlocked due to the direction of the external twist the torsional capacity of the beams is decreased and considerable concrete spalling is observed compared to beams with equal quantity of the commonly used stirrups.