Effects of Ordinary Tension Reinforcement on the Response of Beams with Unbonded Tendons

Abstract

This paper describes an analytical investigation of the flexural response of unbonded prestressed beams and the ultimate stress increase in unbonded tendons, with particular emphasis on the effects of bonded ordinary tension reinforcement. A numerical model, based on the finite element method incorporating an arc-length solution technique, is developed to predict the entire nonlinear response of concrete beams prestressed with unbonded tendons. The reliability of the proposed analysis is verified by comparing the analytical predictions with the experimental results. Two parameters relating to bonded ordinary tension reinforcement are analytically investigated. The analytical results show that an unbonded prestressed concrete beam without any ordinary tension reinforcement exhibits very poor behaviour. However, with the minimum amount of ordinary tension reinforcement provided, the flexural behaviour of the beam is greatly improved. The variable yield strength of ordinary reinforcement in combined reinforcing index is inappropriate in its current form since the calculated prediction is inconsistent with the actual trend of the variation of ultimate stress increase in tendons.