Finite element methodology for the evaluation of soil damping in LNG tanks supported on homogeneous elastic halfspace

Abstract

Influence of foundation conditions and typology in above-ground full containment liquefied natural gas (LNG) storage tank design makes it necessary to evaluate its structural response due to dynamic actions. Typical above-ground full containment LNG storage tanks are constituted of an outer tank made of reinforced and pre-stressed concrete, which provides support, protection and secondary containment in case of failure of the inner tank and a 9 % Ni steel inner tank, which acts as principal and main containment. Conceptual description of full containment LNG storage tanks is included in applicable normative EN 14620-1. Foundation is a structural element, which acts as a dynamic excitation transmitter in case of earthquakes and modifies structure response. This effect is known as soil-structure interaction due to dynamic energy exchange, which affects the overall structural response. The soil-structure interaction under seismic loads has been implemented on the LNG storage tanks for, at least, the last 30 years. The term is widely used to consider the site effect taking into account the local soil characteristics instead of the simplified approach in a fixed-base analysis. A methodology based on the use of finite element modeling for evaluation of soil-structure interaction under horizontal seismic action is presented and results obtained are compared to methodology included in Veletsos and Damodaran Nair (J Struct Div ASCE 101:109–129, 1975) of characterizing the soil as the standard Voigt solid, which assumes the characteristics of a simulated 1 degree of freedom (DOF) oscillator. Besides, comparison with current formulae extracted from codes EN 1998-1 and ASCE 7-05 will be performed.