## 1 Introduction  
Shape memory alloys (SMAs) are metallic smart materials capable of sustaining large inelastic strains that can be recovered by heating or by unloading [1], exhibiting the shape memory effect and the superelastic effect, respectively. The origin of this behavior is their ability to form two crystal structures through the rearrangement of atoms within the crystal lattice, the austenitic, and the martensitic [2]. SMAs also exhibit some other characteristics which are the following: ductility, low elastic anisotropy, superb corrosion and abrasion resistance [3], excellent fatigue performance, and their thermo-mechanical properties can be controlled by the selection of the material composition and various heat treatments [4]. In structural engineering applications, systems with SMA-based elements can be used as dissipation devices exploiting their energy dissipation capacity and their recentering capability, enhancing the stability and reliability of steel framing structures and preserving their structural integrity and functionality. Numerous other publications concerning the application of SMAs in civil structures may also be cited. An excellent relevant work is [PERSON] et al. [5], which provides valuable information about the subject, while the work by [PERSON] et al. [6] may also be quoted. In the following paragraphs, recent advances in scientific research on SMA applications in framing systems are summarized, highlighting the potential regarding their deployment as diagonal braces. [PERSON] et al. [7] investigated experimentally (via reduced scale tests) as well as analytically the possible benefits of the use of SMA braces for the control of the seismic response of a single-bay frame, and its advantage over the use of steel braces of the same stiffness and yield force characteristics. At the same time, an analytical verification study was also presented, based on the FE modeling of the cyclic behavior of SMAs. Both approaches were focused on the effect of pre-straining the SMA braces, and the results obtained revealed an optimum level of pre-strain range from 1 to 1.5%. A consistent reduction in the response (due mainly to recentering) in the presence of SMA braces was reported. The need for further studies regarding SMA models under pre-strain conditions was also pointed out. Furthermore, [PERSON] et al. [8], studied three- and six-story concentrically braced frames equipped with SMA braces, to establish their seismic response compared to traditional relevant structures. The authors developed an analytical model of the former type of frames in detail, and two suits of ground excitations were introduced to evaluate their performance, in terms of inter-story and residual drift. The results of the investigation showed that the use of SMA braces satisfactorily addresses the lack of ductility and energy dissipation issues reported in traditional solutions. The development of more precise simulations of SMA systems was also suggested. [PERSON] and [PERSON] [9] evaluated the seismic response of steel-braced frames employing shape memory alloy braces. Various buildings of several heights and different bracing systems were selected to examine the overstrength, ductility, and response modification factors of braced frames utilizing SMAs. Static pushover analysis, incremental nonlinear dynamic analysis, and linear dynamic analysis were carried out to predict the behavior and calculate overstrength, ductility, and response modification factors. The effects of building height, number of spans, and different types of bracings including diagonal X and Chevron are considered. Comparing the response modification factor of varying system configurations, the study indicated that the seismic response of Chevron bracing is preferable when compared with other types of bracing. The first objective of the work presented by [PERSON] and [PERSON] [10] was to compare the dynamic behavior of mega SMA braced frames subjected to far-fault and near-fault seismic excitations.