Experimental study on recovery stress losses in Fe-SMA rebars under semi-cyclic loads considering different activation temperatures and multiple activations

Iron-based Shape Memory Alloys (Fe-SMAs) offer a promising and cost-effective solution for strengthening existing concrete structures. When heated to temperatures of 160 °C or higher and subsequently cooled while properly anchored, Fe-SMA bars generate recovery stresses through the Shape Memory Effect (SME), allowing them to function as prestressing elements. However, recent research has shown that Fe-SMA rebars can experience a reduction in recovery stress when subjected to semi-cyclic loading. These loading conditions, which do not involve reversals between tension and compression, may reflect the effects of different types of live loads. This study presents an experimental campaign aimed at quantifying recovery stress losses under semi-cyclic loading. The results indicate that Fe-SMA bars are highly sensitive to semi-cyclic loading, with complete recovery stress loss occurring even at moderate strain levels. However, it was also observed that successive activations can restore the initial recovery stresses, highlighting the potential of multiple activations as a viable strategy for maintaining long-term performance under service conditions. • Iron-based SMA rebars of different diameters and manufacturing dates were characterized. • Recovery stresses generated at activation are lost under significant semi-cyclic loading. • Stress losses in Fe-SMA rebars may reduce their effectiveness in concrete strengthening. • Higher activation temperatures slightly reduce the magnitude of stress losses. • Multiple activations can help mitigate recovery stress losses in Fe-SMA rebars.