## 1 Introduction  
Seismic resistant systems such as special and ordinary moment-resisting connection frames have often been designed to generate considerable plastic deformations in the main frame members (_i.e._, beams and columns) under strong earthquakes [1; 2; 3], in spite of providing more stiffness to resist lateral loads. These plastic deformations may result in serious trouble in the repair of not only structural damage but also residual drifts [4; 5; 6]. The conventional steel slit dampers employed in such seismic resistant systems have been widely used as easy-to-replace energy dissipation devices because they are designed to allow the concentration of inelastic deformations for the purpose of protecting the main frame members. This design approach can make significant improvement regarding safety and economy, and can also improve acceptable seismic performance. Although these steel energy-dissipating dampers do improve damage control and member protection, their permanent deformation under strong earthquakes can bring about unexpected residual inter-story drifts in the entire building frame [5; 7; 8]. In addition, extra costs are necessary to replace dampers that have been damaged beyond repair with new ones. A recent study found that the owners of residential buildings in Japan would be better advised to rebuild entire structures rather than repair them when maximum residual inter-story drifts are greater than 0.5% [9]. Therefore, additional seismic restrainers combined in parallel to the retrofit energy dissipation damper should be required for aseismic design achieved by supplementing strength and stiffness to the structure with the aim of reducing inter-story drifts.  
One of the best ways to ameliorate seismic performance with respect to vibration control and recentering capability is accomplished by applying smart materials to the damper system [4; 10; 11; 12; 13; 14; 15; 16; 17]. Superelastic shape memory alloys (SMAs) have been widely utilized for self-centering and passive vibration control devices on the grounds that they possess their own material behavior characterized as a flag-shaped hysteresis under cyclic loading [17; 18; 19; 20]. In this study, bending bars fabricated with superelastic SMAs are installed on the steel slit damper and aligned vertically. The superelastic SMA bending bars, acting as seismic restrainers, instantly supply self-centering forces to the integrated damper system, and thus contribute to reducing permanent deformations mainly attributed to plastic yielding on the steel slit damper. Besides the reinforcing effects attained by these bending bars, energy dissipation capacities demanded for seismic resistance and supplemental damping are further improved in the cyclic behavior of the integrated damper system.  
The steel slit dampers presented here are designed based on experimental models provided in the reference [21]. The analytical specimens treated in this study are classified according to the types of steel slit dampers and the installation of the SMA bending bars. For the concept of the pilot study (so-called pre-study), this paper mainly focused on the inelastic behavior of new recentering damper systems, which was reproduced by refined three dimensional (3D) finite element (FE) analyses without relevant experimental tests. The FE models for steel slit dampers are calibrated to experimental results for the purpose of validating the adequacy of 3D FE modeling. After completing FE analyses, both models compared to each other are evaluated in aspects of seismic performance, such as ultimate strength, permanent deformation, and recentering ratio. The analysis results indicate that superelastic SMA bending bars sufficiently redeem the slit damper system from damage by improving performance and capacity. Finally, stress and strain curves measured at the critical points are also displayed as compared with the behavior of steel and SMA materials in order to verify reliable prediction.