Experimental Study on Steel Girder Strengthened with Adhesively Bonded Iron-Based Shape Memory Alloy

A strengthening system for steel girders using adhesively bonded iron-based shape memory alloy (Fe-SMA) was developed and experimentally tested. The Fe-SMA was fully bonded to the bottom flange of a steel girder without additional anchors. The Fe-SMA strip was activated using a small torch to a target temperature of 140 ℃. During activation, the specimen first exhibited downward deflections when it was heated, which was mainly thermal deformation, and when the specimen cooling down, an upward deflection gradually developed, owing to the Fe-SMA prestress. The final upward deflection was 0.73 mm, which indicated a prestress of approximately 200 MPa in the Fe-SMA strip. Static and fatigue tests of the strengthened specimens were conducted in a four-point bending test setup. Test results showed that the strengthening system worked reliably after 3 million cycles of fatigue loading. The strengthening system was beneficial for the flexural and fatigue behavior of the steel girder.