Ferrous SMA (FNCATB) based Superelastic Friction Bearing Isolator (S-FBI) subjected to pulse type ground motions

Abstract

A new variant of ferrous Shape Memory Alloy with Fe-Ni-Co-Al-Ta-B (FNCATB) composition have been proposed that shows huge superelasticity under a wide temperature range. This shows the potential as a much superior and economic alternative for seismic applications. With this as the eventual goal, the FNCATB wires are employed as restrainers in conjunction with the pure-friction bearing, referred as super-elastic Friction Base Isolator (S-FBI). The FNCATB based S-FBI shows superior performance over the conventional Frictional Pendulum System (FPS) and the Nitinol based S-FBI, with a much less (1/17-th) volume requirement, estimated from the pertinent isolator parameters, the optimal choice of which are obtained through ad hoc optimization. The performance assessment is based on nonlinear dynamic analysis under a suite of recorded near-fault ground motions. An experimental force-deformation dataset for the FNCATB are fitted in the existing Wilde's model to describe the super-elasticity. The FNCATB S-FBI offers considerable improvement, either in the isolation efficiency or reducing the base displacement with slight or no compromise in the other. The performances are also supported by a set of performance indices adopted from benchmark seismic control problem. An energetic assessment also corroborate to these findings. A Short Time Fourier Transform (STFT) based analysis of floor accelerations demonstrate the superior high frequency suppression characteristics of the FNCATB over the Friction Pendulum System (FPS) and Nitinol based S-FBI. The ferrous composition while coupled with less volume requirement implies to superior economic viability that can be studied through detailed cost-benefit analysis.