Seismic Retrofitting of Bridge Piers Using Pre-stressed Fe-SMA Rebars

The unique self-prestressing characteristics exhibited by iron-based shape memory alloys (Fe-SMA) make them a promising alternative for a wide range of retrofitting applications. Some recent studies have explored and demonstrated the effectiveness of pre-stressed Fe-SMA rebars/strips for strengthening applications, involving monotonic loading scenarios. However, their potential for applications that involve cyclic loading reversals, similar to those occurring during earthquakes, has not been investigated thus far. A useful application of pre-stressed Fe-SMA reinforcement under seismic loads can be the incorporation of a self-centering behavior into a structural element by enabling a controlled-rocking mechanism. To understand the cyclic behavior of pre-stressed Fe-SMA rebars under tension-compression reversals, this paper first presents a summary of the key Fe-SMA behavior aspects, including pre-stress loss and inelastic buckling, under cyclic loading reversals. This is followed by introducing an innovative retrofitting scheme, which utilizes pre-stressed Fe-SMA rebars for self-centering of existing reinforced concrete (RC) bridge piers. The retrofitting scheme is currently being implemented and evaluated via large-scale experiments at the Swiss Federal Laboratories for Materials Science and Technology. The outcome is expected to reduce the residual displacements of retrofitted piers significantly, enabling them to remain functional after major earthquake events.