Seismic performance evaluation of Cu-Al-Mn shape memory alloy concentrically braced frame

Abstract

Cu-Al-Mn is one of the shape memory alloys (SMAs), which has been newly studied in recent years. This material can be used instead of typical Ni-Ti SMA since it can reduces material cost and dependence on temperature and loading rate, also, increases machinability and cold workability. In the present study, the seismic application of Cu-Al-Mn bars was evaluated as a part of the steel brace, selecting a 2D two-story split-X braced frame. FEMA P-695 methodology used to compare the collapse performance of two systems in the special concentrically braced frame (SCBF) and Cu-Al-Mn SMA braced frame (SMABF). Then the seismic response of the two systems was investigated at the different levels of earthquake intensity under nonlinear incremental dynamic analysis. The results showed that the SMABF had an allowable and more significant margin collapse compared to the SCBF system. The fragility curve of the two systems showed that the Cu-Al-Mn brace decreased the collapse probability of the frame. The collapse probability of Cu-Al-Mn brace was reduced by 82% and 45% at the maximum considered earthquake (MCE) and 1.5 times of MCE, respectively, compared to the collapse probability of the SCBF system. The SMABF had an allowable maximum inter-story drift ratio, having more distribution over the height of the frame in collapse point under all records but under 21% of records, the maximum inter-story drift ratio of the SCBF reached over 2.5%. The Cu-Al-Mn brace reduced the axial strain demand of the brace and inter-story drift of the 1st floor and residual drift. The result showed that the decreasing percentage of axial strain was 36% on average under the MCE intensity level of earthquakes. Also, the application of Cu-Al-Mn SMA in the braced frame increased the maximum top acceleration about 69% at the MCE level. Therefore, increasing acceleration in this system must be considered in the design of non-structural components. Despite the effectiveness of this new material, low ductility and poor energy dissipation were two weak points of this system. Therefore, this new alloy suggested using with other damping systems, or boundary frame with rigid connections to provide extra energy dissipation.