Seismic performance of steel mega braced frames equipped with shape-memory alloy braces under near-fault earthquakes

This paper has two main objectives. The first objective is to compare the dynamic behavior of mega shape-memory alloy (SMA) braced frames subjected to far-fault and near-fault ground motions. Therefore, four mega SMA braced frames with various stories located in the vicinity of an active fault were considered. Fourteen near-fault records with two well-known characteristics of these records, i.e. forward directivity and fling step, were selected to test near-fault earthquake characteristics. Furthermore, other seven far-field records were selected for comparison. Through the nonlinear dynamic analyses, the results showed that for high-rise frames, the near-fault earthquakes resulted in more demands than the far-field, but for low-rise frames, far-fault records imposed more demands. It was also found that mega configuration and SMA stiffening at large strains played key roles in seismic vibration control of frames. The second objective of this paper is to study the superior performance of SMA braces over the buckling restrained braces by exploiting the super-elastic characteristic of the SMA. Identical buildings equipped with buckling restrained braces were also studied for comparison purposes. The results revealed the excellent performance of SMA braces under near-fault records by reducing both interstory drift and residual displacement of the top floor.