Long-term behaviour of simply-supported post-tensioned composite slabs

• Long-term behaviour of post-tensioned composite slabs
• Occurrence of non-uniform shrinkage gradients
• Influence of the steel deck on the service response of composite slabs

Post-tensioned composite steel-concrete slabs represent an economical form of construction commonly used in Australia. This paper presents three full-scale tests aimed at the evaluation of the influence of the steel deck on the time-dependent response. These consisted of one post-tensioned solid slab and two post-tensioned composite ones using Stramit Condeck HP® and Stramit PrimeForm® profiled sheeting. These samples were cast at the same time in a simply-supported static configuration. Long-term deformations were monitored for a period of 239 days while the samples were subjected to their own sustained self-weight and to the development of shrinkage. Standard tests were carried out to obtain the material properties of the components forming the cross-section. In the case of the composite samples, a non-uniform shrinkage distribution developed over time through the slab thickness due to the presence of the steel deck which prevented moisture egress to occur from its underside. For this purpose, separate concrete specimens were prepared and used to monitor the development of this shrinkage gradient. A theoretical model was developed to account for the time-dependent behaviour of post-tensioned composite slabs with particular attention devoted to the development of the non-uniform shrinkage component. Comparisons between numerical results and experimental measurements showed good agreement, highlighting the importance of considering the non-uniform shrinkage profile for an adequate prediction of the deflections induced by shrinkage. It is expected that further comparisons with experimental results need to be carried out to properly validate the adequacy of the proposed approach for its use in routine design.