Active Continuity of Hollow-Core Slabs Structural Floor by Using Iron-Based Shape Memory Alloy Re-Bars

Nowadays, the use of iron-based shape memory alloys (Fe-SMA) is a current reality in the construction sector (Cladera et al. in Constr Build Mater 63:281–293, 2014), especially in rehabilitation, which is widely extended in central European countries. The main characteristic of this type of material is the shape memory effect, which is the capacity to return to an initial shape after heating (activation process). This property allows using this alloy as a prestraining material (Shahverdi et al. in Eng Struct 117:263–273, 2016), ensuring the anchoring and heating to start the martensitic transformation. This research uses a Φ11 mm rebar Fe-SMA as a continuity prestress reinforcement in the hogging bending moment region in Hollow-Core Slab (HCS) structural floors. This paper highlights the preliminary results of the testing of four real-scale specimens. The results are part of an extensive experimental campaign where it is compared two parameters: having or not concrete topping, and prestressing (through activation), or not, of the Fe-SMA re-bars. Despite that the prestressing effect has worked correctly in both cases, with and without concrete topping, the constructive process is more straightforward using concrete topping. Moreover, it has been proved that using this technology as prestressed reinforcement improves the Service Limit State (SLS) behaviour avoiding premature cracks and improving the element stiffness. Consequently, whereas Fe-SMA has been used since now mainly in rehabilitation, considering this solution in structural designs would allow constructing slenderer structural floors, reducing the amount of concrete and the carbon footprint that this material produces. Furthermore, if an existing building needs to increase the structural stiffness, or its rehabilitation supposes an increment of loads, introducing this technology could be a satisfactory solution to consider.