عنوان مقاله [English]
Today, there has been an increasing interest in use of seismic isolation to protect the structures against earthquakes. The most common type of seismic isolation is called base isolation, in which the isolation layer is installed under foundations to separate the structures from the ground and reduce the earthquake forces. However, the use of this type of seismic isolation faces some difficulties such as construction in congested urban areas or construction of near sea structures. Furthermore, for seismic retrofitting of existing buildings, the installation of the isolation under foundations is difficult or even impossible, so it needs to be located on the middle floors of the buildings. This method of isolation design is called floor or middle story isolation. Despite the advantages of seismic isolations, they have some limitations such as instability in large deformations, residual displacement and the need to replacement after severe earthquakes. The use of shape memory alloys (SMA) in regard to their unique properties is considered as an appropriate solution to overcome the above problems. These smart materials show high strength and strain capacity, high recentering ability, high resistance to corrosion and to fatigue. The purpose of this study is to investigate the effect of combination of middle story isolation utilized by natural rubber bearing (NRB) and iron based shape memory alloys in steel structures; and to compare the performance of such structure with and without the presence of the shape memory alloy in the middle story isolation system. Then, a three story steel structure has been modeled and evaluated. For this purpose, a structure with floor isolation and iron based shape memory alloy were modeled in OpenSees computer program. The structures were then subjected to seismic loading. The results were presented in the form of story drift, floor acceleration, floor shear forces, and base shear. The outcome of this research shows that the use of these alloys in the middle story isolation reduces the overall base shear and floor shear forces. The overall story drift, floor acceleration and displacement are reduced; with the exception at the isolation level. Thus utilizing the natural rubber bearing isolator along with the iron based shape memory alloy can be considered as a desirable system for the seismic protective design of buildings.