A practical approach for assessing damage to bolted steel connections after fires and earthquakes

This study improves the tap-tone method to provide a quantitative evaluation of damage in bolted steel connections. The analysis utilized Fast Fourier Transform (FFT) techniques to assess the soundtracks that captured the tap-tone frequency. This methodology was applied to high-strength bolts within steel joints and connections subjected to elevated temperatures, as well as to evaluate the seismic performance of these connections. The findings indicate that the tap-tone frequency may increase with higher bolt pretension and torque strength; however, it can significantly decrease due to a large drift in the connections and exposure to high temperatures. Specifically, when the drift exceeds 2 %, the frequency may decline from 5 kHz to approximately 2.5 kHz. In cases of fire damage at 800 °C, the frequency may drop below 1 kHz. These results provide a foundation for rapid damage assessment of bolted steel connections subjected to great earthquakes and fire.