Shape Memory Alloys for Earthquake Building Protection

摘要

Use of Shape Memory Alloys (SMA) is more and more frequent in engineering because of their unique properties of completely recovering the imposed deformations after heating, or automatically returning to the unloaded configuration via a super-elastic process after very large strains (till around 10%). The process is regulated by a phase change in the material, shifting between martensite and austenite. Along this transformation, some SMA change their elastic properties by a factor three and damping coefficient by a magnitude. Super-elastic materials exhibit stable hysteresis loops under cyclic loading and dissipate energy without residual deformation thus providing in perspective self-centering capability for use in buildings earthquake protection. The present study investigates the performance of SMA-based devices for seismic protection of reinforced concrete structures. In countries with high seismic hazard, vulnerability assessment of existing constructions and seismic retrofit implementation is a major challenge for both scientific community and public administration. This paper illustrates seismic retrofit of an existing school building in Italy, using dissipating steel braces. Both SMA-wire dampers and mixed devices combining SMA elements and classical buckling-restrained axial dampers are considered for seismic upgrading. Adopted technique effectiveness and reliability are investigated by comprehensive nonlinear static and dynamic analyses. Numerical results show that super-elastic SMA dampers are effective for mitigating building response to strong earthquakes and providing systems self-centering capability with negligible residual strains.