Seismic performance enhancement of base isolated RC building incorporating Cu-Al-Be and FNCATB based SMA

Abstract

Abstract The introduction of smart materials used for enhancing the seismic performance of buildings has gained popularity in recent times. Shape memory alloy (SMA) is a classic example of smart material which is used to enhance performance and overcome various drawbacks of traditional base isolation systems such as the lack of recentering ability and very high isolator displacement which causes the pounding effect. SMA possesses a distinctive characteristic to endure exceptionally high levels of strain during the loading phase, and upon unloading the strain, no permanent deformation is perceived. In most of the studies and applications, nitinol (Ni-Ti) is used as SMA material. However, it has a higher manufacturing cost and is unable to retain its superelastic property in extremely low temperatures. Due to such limitations, different combinations of materials are studied and tested to be used as a replacement for Ni-Ti SMA and out of which copper-aluminium-beryllium (Cu-Al-Be) and a ferrous-based alloy (FNCATB) materials are significant as these SMAs are relatively less expensive to produce and also their superelasticity property is shown in a wide range of temperatures. So, in this study, the optimal seismic performance of a multi-storeyed base isolated RC building is evaluated under a set of real earthquake loads with these two SMAs. The base isolation is modelled in combination with rubber bearing and SMA (Cu-Al-Be and FNCATB), known as shape memory alloy rubber bearing (SMARB). The top floor acceleration and the isolator displacement are evaluated using these two types of SMAs and the responses are compared. The optimal values of normalized forward transformation strength of SMA materials (FS0 ) are evaluated through a bi-objective optimization study to minimize the top floor acceleration as well as the isolator displacement of the isolated building. An evolutionary optimization algorithm, particle swarm optimization is used to solve the optimization problem. The results obtained in this study indicate that the Cu-Al-Be SMA is marginally more effective in reducing the isolator displacement and the FNCATB SMA performs more efficiently in controlling the top floor acceleration of the isolated building. The optimal value of FS0 is also higher for the Cu-Al-Be based SMARB isolation system.