Earthquake Resistant Design of Anchored and Unanchored Liquid Storage Tanks Under Three-Dimensional Earthquake Excitation

Abstract

In the past major damage to liquid storage tanks has been caused by earthquakes and leakage or spillage combined with fire led to considerable harm in addition to the damage of the tanks. Hence, earthquake resistant design of liquid storage tanks has been an essential topic in the field of earthquake engineering. It is necessary to have proper codes for engineers dealing with the construction of liquid storage tanks. Present codes do not provide fully satisfactory procedures for an earthquake resistant design of anchored and especially unanchored tanks. For example the American Standard API 650 [5.1–1] which is based on the work of Wozniak [5.1–2] does not in general provide a conservative estimate of the dynamically activated loads. The maximum axial compression force in the tank wall which is further increased by uplift of tank bottom edge of unanchored tanks is substantially underestimated in many cases. A design rule is proposed by Priestley et al. [5.1–3] in the New Zealand recommendations for the seismic design of storage tanks. In these recommandations an excellent summary of the design rules of earthquake excited tanks is given. The maximum axial membrane force, increasing due to uplift of unanchored tanks, is estimated by a simple iterative procedure based on results of Clough [5.1–4] and experiments. The modification of the effective flexibility of the interaction vibration mode (common vibration of the flexible tank wall and the liquid), increasing the natural period due to uplift, is, however, not taken into account.