Behaviour of unbonded post-tensioned one-way concrete slabs

The behaviour of unbonded post-tensioned one-way concrete slabs is investigated experimentally and numerically in this paper. Two tests were conducted by the authors to measure the strains in the tendon during the post-tensioning stage and during the ultimate load test. The slabs were one-way simply-supported and reinforced with 15.7 mm nominal diameter seven-wire mono-strand tendons. Prestress losses were measured and a comparison with current design codes showed that the calculated design losses were higher than those measured. The load-deflection behaviour and modes of failure are presented for the two tests. A nonlinear finite element model, incorporating the correct load transfer from the tendon to the concrete, was developed and verified against the tests. The model also ensured that the profile of the tendon retained its correct shape during deformation. A parametric study was conducted to study the effects on the global structural behaviour due to the change in the slab's geometry, prestress load, concrete strength and boundary conditions. The experimental and numerical results were compared with values calculated using current design codes. It is shown that the ultimate loads calculated using current codes are conservative for the unbonded post-tensioned one-way concrete slabs investigated in this study. The results presented in this paper provide a valuable insight into the behaviour of unbonded post-tensioned concrete slabs during the construction phase and under ultimate load.