Parametric analysis of the mechanical behavior of Cu-Al-Be shape memory alloy strands for applications in self-centering systems

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In this work, the mechanical behavior of Cu-Al-Be shape memory alloy (SMA) strands for applications in self-centering systems is discussed. The influence of the mechanical response from the wire level to the strand level is evaluated in order to define the strand configurations that provide the best mechanical properties for seismic control applications. Therefore, a comprehensive numerical analysis of 1 × 7 and 1 × 19 strand typology constructions is performed. Two boundary conditions and two different core materials are assessed: ends fixed or free to rotate; and strand core made of SMA or a soft material. A multilinear flag-shaped model is used as SMA constitutive law, which is integrated into four different linearized cable models. To validate the numerical analysis, four 1 × 7 strand specimens are fabricated and subjected to cyclic tensile tests with strain amplitudes of 3.5% and 5.5%. The results show that the cable models considering the Poisson effect are the most stable numerically, although they rely on asymmetric stiffness matrices. The energy dissipation capacity is controlled by the material damping ratio (3.2%) regardless of the strand configuration. Therefore, optimum conditions are obtained when most layers develop the maximum strain capacity of the material. Thus, the fixed ends condition is the best choice if maximum strength is desired, since the ductility gained by increasing the helix angle is negligible regardless of the core material. For this condition, the helix angle must be the same for all the layers. On the other hand, the free ends condition is the best choice if maximum strain is desired, since the strength decays rapidly as the helix angle increases. A self-centering device based on CuAlBe SMA strands has been modeled, obtaining promising results for seismic protection of structures.