Temperature Effect on Seismic Responses of SMA Knee-Braced Frames

Shape-memory alloy (SMA) knee-braced frames (KBFs) are a type of seismically resilient frame buildings. Knee braces (KBs) in this system are the SMA buckling-restrained braces, which provide both self-centering and energy-dissipating capacity. SMAs are known for their noticeable thermal-mechanical property, but there remains a lack of understanding regarding the temperature effect on the seismic responses of SMA KBFs. Hence, this study aims to address this issue at both component and system levels. Cyclic loading tests were conducted on reduced-scale SMA KB specimens under five distinct ambient temperatures ranging from $-20°\mathrm{C}$ to 20°C. The experimental data were then used to quantify the relationship between the hysteretic parameters of interest and the ambient temperature. At the system level, a multistory steel frame located in Tangshan City, China, was selected as the example structure. The probability density function was built to describe the temperature variation of the selected region, and the parameters of the function were determined using the maximum likelihood estimation method. The probabilistic analytical framework that considered the temperature effect was described. Then, this work conducted seismic design at the reference temperature (20°C). In what followed, within varying temperature conditions, nonlinear time-history analysis and multistripe analysis were conducted. The seismic response indexes under discrete temperature levels were compared. Finally, the temperature effect was understood by generating the joint fragility curves under various levels of temperature and seismic intensity. The findings indicated that the temperature effect on SMA KBs was noticeable. However, the temperature effect on SMA KBFs was minor, even though the extent of temperature variation was up to 60°C.