Development of an iron-based shape memory alloy (Fe-SMA) strengthening system for steel plates

This paper presents the development of an iron-based shape memory alloy (Fe-SMA) system for the strengthening of steel plates. The shape memory effect (SME), which is the tendency of a deformed SMA to return to its original shape upon heating and subsequent cooling, was used in this study for prestressing steel plates. Five steel specimens were strengthened with different configurations (single-side, double-side, activated, and non-activated) of the Fe-SMA strips. A mechanical anchorage system was developed to anchor the prestressed Fe-SMA strips to the steel substrate. The SME in the Fe-SMA strips was then activated (i.e., the strips were prestressed) by heating to a temperature of approximately 260 °C using an electrical resistive heating technique. The test results showed that the achieved recovery stress of the Fe-SMA strips (i.e., the prestressing level after activation) was approximately in the range of 350-400 MPa, which led to a maximum compressive stress of −74 MPa in the steel plate. This compressive stress can be very beneficial and significantly increase the yield and fatigue strength of the steel plates. Finally, the strengthened specimens were subjected to static loading under a displacement-controlled condition up to failure. It was shown that the proposed strengthening technique eliminates the difficulties associated with conventional prestressing (e.g., by hydraulic jacks) and also offers a fast installation procedure as it does not require any surface preparation or curing for bond application.