Assumption bulging frequency of the real scale tank by micro-tremor measurement and the eigenvalue analysis

Abstract

Damage to tanks has been reported every time an earthquake with a seismic intensity of 6 or higher occurs, such as the 2011 Tohoku Pacific Coast Earthquake (Great East Japan Earthquake), the 2016 Kumamoto Earthquake, and the 2022 Fukushima Prefecture Earthquake.[1-5] . The damage assessment revealed that there are two main types of damage that can occur inside the tanks. The first case is damage to the roof and upper sidewalls of the tank, and the second case is damage to the sidewalls and corners, mainly at the bottom of the tanks. The first is caused by the sloshing phenomenon (liquid level motion due to resonance between the natural frequency of the liquid content and the dominant frequency of seismic waves) due to longer-period seismic motion. On the other hand, the second type is caused by the bulging phenomenon[6,7] (coupled vibration between tank wall and liquid content), and is mainly caused by vibration of the tank structure due to short-period seismic motion