Vol.10, No.2 EARTHQUAKE ENGINEERING AND ENGINEERING VIBRATION June, 2011 Earthq Eng & Eng Vib (2011) 10: 253-262 DOI: 10.1007/s11803-011-0063-3 Seismic analysis of a LNG storage tank isolated by a multiple friction pendulum system Zhang Ruifu † , Weng Dagen ‡ and Ren Xiaosong ‡ State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China Abstract: The seismic response of an isolated vertical, cylindrical, extra-large liquefied natural gas (LNG) tank by a multiple friction pendulum system (MFPS) is analyzed. Most of the extra-large LNG tanks have a fundamental frequency which involves a range of resonance of most earthquake ground motions. It is an effective way to decrease the response of an isolation system used for extra-large LNG storage tanks under a strong earthquake. However, it is difficult to implement in practice with common isolation bearings due to issues such as low temperature, soft site and other severe environment factors. The extra-large LNG tank isolated by a MFPS is presented in this study to address these problems. A MFPS is appropriate for large displacements induced by earthquakes with long predominant periods. A simplified finite element model by Malhotra and Dunkerley is used to determine the usefulness of the isolation system. Data reported and statistically sorted include pile shear, wave height, impulsive acceleration, convective acceleration and outer tank acceleration. The results show that the isolation system has excellent adaptability for different liquid levels and is very effective in controlling the seismic response of extra-large LNG tanks. Keywords: LNG; tank; earthquake; isolation; bearing Correspondence to: Zhang Ruifu, B303, School of Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China Tel: +86-21-6598 3701; Fax: +86-21-6598 2668 E-mail: zhangruifu@gmail.com † PhD Candidate; ‡ Professor Supported by: Foundation of Basic Research Program of State Key Laboratory from Ministry of Science and Technology of China Under Grant No. SLDRCE10-D-01; Foundation of Shanghai Engineering Technical Research Centre Under Grant No. 10DZ2252000 Received November 26, 2010; Accepted April 11, 2011 1 Introduction Extra-large tanks are lifeline projects which are being built in increasing numbers to store liquefied natural gas (LNG). The volumes of these tanks are very large and have capacities of about 160,000 m 3 . The LNG tank consists of an inner steel tank, which contains the LNG, and an outer concrete tank that encases and protects the inner tank. Insulation is placed between the two tank walls (Fig. 1). Most extra-large LNG tanks have a fundamental frequency between 2 and 10 Hz which involves the range of resonance typical of most earthquake ground motions (Tajirian, 1998). The seismic analysis of these structures is a complicated and challenging task because the multi-layer construction of the tank and the soil- structure interaction must be considered. Extra-large LNG tanks present a great risk if they fail during an earthquake. It has been observed that common tanks may easily be damaged during an earthquake, which had been proven in many actual events. Typical damage to tanks in past earthquakes such as 1989 Loma Prieta, 1994 Northridge, Chi-Chi Taiwan and 1999 Kocaeli, was in the form of cracking at the corner of the bottom plate and compression buckling of the tank wall (elephant foot buckling) due to uplift, sliding of the base, anchorage failure, sloshing damage around the roof, failure of the piping systems and plastic deformation of the base plate (Abali and Uckan, 2009; Chalhoub and Kelly, 1990). Damage to liquid storage tanks in past earthquakes has prompted experimental and analytical investigations of the seismic response of these structures. Originally, Housner (1957) developed a mathematical model in which the mass of the liquid part that accelerates with the tank wall is called “impulsive” and the mass of the liquid part that causes a sloshing motion of the free surface near the tank roof is called “convective.” A different approach to the analysis of flexible containers was developed by Veletsos (1974). He presented a simple procedure to evaluate the hydrodynamic forces induced in flexible liquid filled tanks. Later, Veletsos and Yang (1976) estimated the maximum base overturning moment induced by a horizontal earthquake motion by modifying Housner's model to consider the first cantilever mode of the tank. They presented simplified formulas to obtain the fundamental natural frequencies of liquid filled shells using the Rayleigh-Ritz energy method. Haroun (1980) and Haroun and Housner (1981; 1983) modified Housner’s model and took into account the flexibility of