Response of post-tensioned concrete beams with unbonded tendons including serviceability and ultimate state

The model proposed in this paper calculates the structural response of post-tensioned prestressed beams with unbonded tendons, including both the deflections under service loading, before or after cracking, and the ultimate bearing capacity. Both monotonic and repeated load effects are considered. The originality of the model appears in the calculation of prestressed concrete serviceability after cracking, based on a non-linear macro finite element (M.F.E.). This is a beam finite element for bending problems characterized mainly by its homogeneous average inertia. A second innovation is the prediction of the overall lengthening of the unbonded tendons at all loading stages: cracking, serviceability, ultimate. Results show that the model gives very good predictions of the bending stiffness of the beam in the loading cycles, and the permanent residual deflection after unloading due to crack propagation. The calculations of the bearing capacity and the deflection at failure are also very accurate.