Iron-based shape memory alloy (Fe-SMA) for fatigue strengthening of cracked steel bridge connections

Abstract

Smart iron-based shape memory alloys (Fe-SMAs) are used in this study to retrofit fatigue-cracked riveted connections in steel bridges. The prestressed strengthening technique is found to be an effective approach to overcome fatigue-related damage in riveted connections. Because of the property of Fe-SMAs known as shape memory effect, these alloys can be prestressed without difficulty. The activated (i.e., prestressed) Fe-SMA strips (two 50-mm wide × 1.5-mm thick) are anchored to the flanges of a steel I-beam in either side of the connection. Thereafter, a test setup is specifically designed to examine the SMA-strengthened cracked double-angle connections. First, a static test is performed on the unstrengthened connection without any crack. Subsequently, two high-cycle fatigue (HCF) tests are conducted on a pre-cracked connection. The pre-cracked connection with no strengthening is subjected to fatigue loading with a load ratio of R = 0.1. After practically N=2×106 loading cycles, the crack propagates up to 50% of the connection depth, whereas the fatigue crack growth rate gradually decreases because of the reduction in connection rigidity. Finally, the SMA-strengthened connection is subjected to the HCF loading. It is observed that the fatigue life is substantially enhanced, and the fatigue crack is arrested by the activated Fe-SMA strips.