Proactive Enhancement on Bending Behavior of Steel–Concrete Composite Beams with Fe-SMA Plates

Shape memory alloy (SMA) is a material with a unique shape memory effect, capable of returning to its original shape upon reaching a critical activation temperature. Through four-point bending tests, this paper describes the experimental study conducted on steel–concrete composite beams enhanced using iron-based shape memory alloy (Fe-SMA) plates. Additionally, the performance of carbon fiber reinforced polymer (CFRP)-strengthened beams is studied for comparison. The experimental results show that, following high-temperature activation, no prestress loss is exhibited by Fe-SMA over a short period. Fe-SMA effectively mitigates concrete cracking, enhances load-bearing capacity, and improves overall beam stiffness without adverse effects. Moreover, the yield capacity of composite beams strengthened by Fe-SMA plates under the recover stresses of 214 and 314 MPa increased by 35.2% and 40.8%, respectively. Further, the maximum deflection increased by 4.5% and 12.8%, respectively, compared to the reference beam under identical loads, with reduced midspan deflection (δM) and overall deformation. Additionally, Fe-SMA exhibits an advantage over CFRP in controlling δM and overall deformation of composite beams when utilizing materials with equivalent initial pretension to enhance the bending capacity of composite beams.