عملکرد لرزه ای مخزن های ذخیره مایع کره ای: یک حالت مطالعاتی Seismic performance of spherical liquid storage tanks: a case study

Introduction Seismic loading can induce large damages in industrial facilities and their complex components (e.g. Babič and Dolšek 2016; Demartino et al. 2017a, b, c). The loss of the structural integrity of these structures can have severe consequences on the population, the environment and the economy (Krausmann et al. 2010; Rodrigues et al. 2017). Looking at power/ chemical/petrochemical plants, storage tank containers are widely employed. These hold liquids, compressed gases or mediums used for the short- or long-term storage of heat or cold. Liquid storage tanks and piping systems are considered as critical components of those industrial facilities (Vathi et al. 2017; Bakalis et al. 2017). The seismic response of tanks has been widely studied in the past, starting from the pioneering studies of Housner (1957, 1963). In particular, Housner (1957) frst presented the simplifed formulae to compute the dynamic pressures developed on accelerated liquid containers and successively (Housner 1963) studied the dynamic behavior of ground-supported elevated water tanks considering equivalent spring–mass systems. Current practice for the seismic design of storage tanks is mainly based on Appendix E of API 650 (2007) standard and on Eurocode 8 (1998). Generally speaking, there are many diferent types of equipment used for the storage of liquids and gases. The characteristics of the diferent tanks adopted mainly depend on: (a) the quantity of fuid being stored, (b) the nature of the fuid, (c) the physical state of the fuid and (d) the temperature and pressure. In industrial plants, gases are usually stored under high-pressure, often in liquid form since the volume is largely reduced. Spherical storage is preferred for storage of high-pressure fuids. A sphere is usually characterized by even distribution of stresses on the surface and by the smaller surface area per unit volume than any other shapes. These tanks are usually named Horton sphere and are used for storage of compressed gases such as propane, liquefed petroleum gas or butane in a liquid–gas stage. The seismic analysis of spherical storage tanks requires to account for the fuid–structure interaction and for the soil–structure interaction. The frst phenomenon is generated by the presence of a free surface allowing for fuid motions. This phenomenon, referred to as “liquid sloshing”, is generally caused by external tank excitation, and may have a signifcant infuence on the dynamic response (Patkas and Karamanos 2007). The second phenomenon is related to the interaction between the structure and the soil (Mylonakis and Gazetas 2000). In particular, in the case of tanks, EN 1998-4 with reference to foundations on piles, recognizes the importance of kinematic interaction and the efects of dynamic soil–structure interaction.