Feasibility Assessment of an Innovative Isolation Bearing System with Shape Memory Alloys

The objective of this work is to investigate the feasibility of a new seismic isolation device concept based on the superelastic effect given by shape memory alloys. Seismic isolation is one of the most effective options for passive protection of structure, which modifies the global response and improves performances, in particular regularizing the structural response, shifting the fundamental period of vibration, and increasing the global energy dissipation. Shape memory alloys (SMAs) are characterized by unique mechanical properties due to a solid-solid transformation between phases of the alloy. They show high strength and strain capacity, high resistance to corrosion and to fatigue. Regarding the stress-strain constitutive law, the nonlinear hysteresis due to the superelastic effect, that for particular range of temperature can be described like a flag shaped relation, avoids residual deformation, provides some hysteretic energy dissipation and limits the maximum transmitted force. An isolation bearing system based on a SMA superelastic effect is intended to provide the nonlinear characteristics of yielding devices, limiting the induced seismic force and providing additional damping characteristics, together with recentering properties to reduce or eliminate the cumulative damage. Flag-shape hysteresis is characterized by much less energy dissipation with respect to other isolation device technology force-displacement relations, therefore its effectiveness has to be investigated. In this work the dynamic response of the proposed innovative SMA isolation devices has been compared with equivalent traditional bearing response through dynamic time history analyses. Results show that force and displacement demands in the two systems are quite similar for medium to high flag-shape dissipation capability range.