Flexural Capacity and Stress in Unbonded Tendons of Post-Tensioned Lightweight Concrete Beams

The present study reports the effect of the amounts of mild longitudinal tensile reinforcement, effective prestress and prestressing strands on the flexural performance of the prestressed lightweight concrete (LWC) beams. Test data were compared with those compiled from the post-tensioned normal-weight concrete (NWC) beam specimens and prediction models derived based on the ACT 318-11 provision. Test results showed that the effect of the investigated parameters on the flexural behavior of the post-tensioned LWC beams was usually similar to the typical trends observed in the post-tensioned NWC concrete beams. With the increase of the reinforcing index, the incremental stress of the unbonded strands at ultimate and displacement ductility ratio of the beams decreased, while flexural capacity of the beams increased. The incremental stress of the unbonded strands at ultimate strength of the post-tensioned LWC beams was commonly higher than that of the post-tensioned NWC beams with the same reinforcing index values and the predictions obtained from the ACT code equations. Alternatively, the normalized flexural capacity of the post-tensioned LWC beams was comparable to that of the post-tensioned NWC beams and higher than the predictions based on the ACT code provision.