Smart Structures and Systems, Vol. 8, No. 4 (2011) 399-412 399 Energy-balance assessment of shape memory alloy-based seismic isolation devices O.E. Ozbulut* and S. Hurlebaus Zachry Department of Civil Engineering, Texas A&M University, College Station, TX, USA (Received January 21, 2011, Revised May 15, 2011, Accepted August 5, 2011) Abstract. This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material. Keywords: shape memory alloy; superelasticity; energy balance; seismic isolation; bridges. 1. Introduction During strong earthquakes, substantial amounts of energy are imparted to the structures, which may lead to excessive deformations and failure. This input energy should be dissipated through either inherent damping mechanism of the structures or inelastic deformation in order to avoid collapse. Since the bridge structures usually have very low inherent damping, they can experience large deformations to dissipate the seismic input energy relying on inelastic deformations when subjected to strong ground motions. This may cause severe damage or complete collapse as occurred during the past earthquakes (Bruneau 1998, Hsu and Fu 2004, Liu 2009). Bridges are lifelines of the transportation network. Failure of bridges during an earthquake will increase travel time and distance within the network. Therefore, indirect economic loss can also reach to significant levels besides the direct loss resulting from bridge damage (Enke et al. 2008). Seismic isolation has been one of the most commonly used methods to minimize the damaging effects of strong ground motions over past decades. Seismic isolation aims to reduce earthquake energy that enters to the structure by providing flexible interfaces which decouple the support of a *Corresponding Author, Dr., E-mail: ozbulute@tamu.edu