Finite element modeling of RC beams externally strengthened with iron-based shape memory alloy (Fe-SMA) strips, including analytical stress-strain curves for Fe-SMA

Research into the application of iron-based shape memory alloys (Fe-SMA) for strengthening existing structures has boosted in recent years. The shape memory effect of this material can be used to introduce prestressing forces, improving the behavior of the retrofitted structures. However, knowledge about these alloys is still limited and more research is needed. This paper proposes analytical stress-strain curves for Fe-SMA based on the modified Ramberg-Osgood models for nonlinear materials, and taking into account the differences observed according to the material's initial state. The degree of roundedness and the level of strain hardening vary depending on the initial state, achieving in all cases a satisfactory agreement between analytical expressions and experimental curves. Moreover, these curves have been implemented into a nonlinear finite element model developed to reproduce the response of reinforced concrete beams strengthened upon shear using external Fe-SMA strips that have been previously tested by the authors. The numerical results of the finite element analysis show a very good correlation with the experimental behavior observed during the tests.