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 approximately by added mass functions, which can be determined to a useful degree of accuracy without requiring regorous 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.