Eight-year natural environmental exposure and sustained-loading of reinforced concrete beams with iron-based shape memory alloys
Yunus Emre Harmanci, Christoph Czaderski, Moslem Shahverdi
Abstract
Low-cost iron-based shape memory alloys (Fe-SMA) are recently proving to be favorable alternatives for strengthening reinforced concrete (RC) members. Unlike carbon fiber reinforced polymers (CFRP), Fe-SMAs eliminate the need for labor-intensive anchorages and exhibit plastic behavior similar to reinforcing steel, rendering them especially promising for prestressed near-surface mounted (NSM) applications. However, due to their recent development, not many long-term experimental studies have been yet available and thus the long-term durability of Fe-SMA-strengthened RC members remains relatively unexplored. To this end, the structural behavior of two RC beams strengthened with NSM Fe-SMA were investigated, exposed to a natural environmental conditions and sustained loading above their cracking load level for 8 years, followed by four-point bending until failure. Results were compared with a previous investigation of identical beams and Fe-SMA strips without exposure to environmental factors or sustained loading. Additionally, a comprehensive cross-section analysis (CSA) was conducted for both long-term exposure and four-point bending. Despite notable creep effects caused by the 8 years of sustained loading that accounted to approximately 55% of the total mid-span deflections, no significant differences were observed in terms of load-carrying capacity, ultimate deflections, or strains, compared to the unexposed beams. The employed CSA effectively captured the long-term and bending behavior. Additionally, a parameter study and global sensitivity analysis were conducted to identify influential parameters affecting structural performance, concrete compressive strength was found as the most dominant influencing parameter.