Practical Nonlinear Seismic Analysis of Tanks

Abstract

Liquid-storage tanks, designed as per the minimum requirements of API Standard 650 (1996), AWWA Standard D100 (1996), or any other design standard, should not be expected to remain fully elastic, or undamaged, when subjected to design ground shaking. Forces prescribed in design standards are only a fraction of those obtained from a linear elastic (no damage) response analysis. Force reductions are based on the expected overstrength and ductility of the system. However, there are no practical methods to quantify the effects of these reductions on potential damage to tanks. Some type of nonlinear analysis is needed to assess the tank's desired performance objectives. This paper presents a simplified nonlinear analysis for performance-based seismic design of tanks. It also presents a method of strengthening tanks by energy-dissipating base anchors. The simplified nonlinear analysis is illustrated for an unanchored tank, a tank anchored with traditional anchors, and a tank anchored with energy-dissipating anchors.