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.
The objective of the present work is to propose a new seismic isolation device based on superelastic material components manufactured using shape memory alloys. Seismic isolation is one of the most effective options for the passive protection of structures. Shape memory alloys (SMAs) are characterized by unique mechanical properties due to a solid-solid transformation. An isolation bearing system based on a SMA superelastic effect is intended to provide nonlinear flag-shaped lateral displacement-shear force hysteresis, additional damping, and recentering properties to reduce or eliminate the residual deformations.The device concept is based on two separate systems, one to transmit the vertical load and another to act as a lateral restrainer. This article presents in detail the mechanical components of the innovative device focusing on its main properties.The system theoretical response is computed, resulting very attractive from the earthquake engineering point of view, because of its capability in reaching the design goals, i.e., modification of the structural response, ability to undergo large displacement demand without loss of strength, energy dissipation, and recentering after the seismic event.
The mechanical behavior of superelastic springs is investigated in this study. The goal is to evaluate the device response and to exploit the material superelastic behavior, main concerns being material and geometrical response nonlinearity. The investigation is made of two parts, i.e., an experimental campaign and a numerical model proposal. Experimental tests have been performed on superelastic SMA coil springs considering load history in tension and compression for three different spring geometrical configurations. Tested specimens experience a maximum elongation larger than the original spring axis length. The response is not symmetric and under compression it is affected by buckling instability. Nevertheless, experimental results show a very good superelastic behavior with no damage and with negligible residual displacements. Numerical analyses have been performed to reproduce the experimental campaign results. A simple finite element model is proposed. Experimental and numerical result agreement is very good. The numerical model turns out to be a powerful design tool even for the very complex geometrical and material nonlinear conditions under investigation. Hence, it is proposed as a useful tool for spring design validation and response prediction.
The objective of this work is to investigate the feasibility of a new seismic isolation device concept, in which the restoring force is given by the superelastic effect of shape memory alloys. Seismic isolation is an option for passive protection of structure when an earthquake occurs, because it modifies the structural global response and improves performance. Dynamic responses of proposed innovative SMA isolation system and of traditional bearing device are compared through dynamic time history analyses. Results show that the SMA system is effective in reducing force and displacement demands, dissipating the input seismic energy and limiting the residual displacements.
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