Elevated Water Tank Inelastic Seismic Analysis

by Laurel Harrington, Seattle Water Dep, Seattle, United States,
C. W. Roeder, Seattle Water Dep, Seattle, United States,

Document Type: Proceeding Paper

Part of: Lifeline Earthquake Engineering


In 1988, the Seattle Water Department hired CYGNA, a consulting firm, to assess the seismic reliability of their water system, since major earthquakes can occur in the area. Their study included elastic analyses to determine the earthquake resistance of elevated steel water tanks. Magnolia Bluff tank, a radial cone bottom tank built in 1947 with a capacity of 1 million gallons, is typical of these tanks. Elastic analyses are sometimes not a good indicator of inelastic response. Thus, the inelastic analysis presented in this paper was performed to evaluate the inelastic response and compare it to the predicted elastic behavior. Force versus deflection curves based on the deflection of the center of mass of the tank were computed. This approach allowed the tank to be analyzed as a single degree of freedom system, while still accounting for both brace and frame action.

Subject Headings: Water tanks | Inelasticity | Seismic tests | Seismic effects | Water supply systems | Steel structures | Load and resistance factor design | Elastic analysis

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