Simplified Earthquake Analysis of Intake‐Outlet Towers

Abstract

A simplified procedure is presented to determine the maximum earthquake forces in intake‐outlet towers directly from the design earthquake spectrum without the need for a response‐history analysis. All the significant effects of tower‐water interaction and tower‐foundation‐soil interaction are included in the analysis. The hydrodynamic effects of outside and inside water are approximated by added mass functions, which can be determined to a useful degree of accuracy without requiring rigorous three‐dimensional analysis of the two fluid domains. The simplified response spectrum analysis (SRSA) procedure utilizes convenient methods for computing: (1) The first two natural frequencies and modes of vibration of the tower; and (2) the modifications to the vibration period and the damping ratio of the fundamental vibration mode due to tower‐foundation‐soil interaction. The procedure is demonstrated to be accurate enough for preliminary design and safety evaluation of towers.