Comparative approach to seismic vulnerability of an elevated steel tank within a reinforced concrete chimney

Abstract

This study provides a framework for investigating the seismic response of an elevated steel water tank within a reinforced concrete chimney, to assist optimal tank placement and analyse different tank geometries. Elevated tank design procedures in different guidelines and codes are adequate for specific cases, none of which meets the exact requirements of this case study, in which the supporting structure mass is large relative to the storage tank. The tank is located at an elevation 63 m below the mid-height of the 200 m chimney, resulting in a different behavior than a simple cantilever. Furthermore, for certain H/R ratios, coupling effects may exist between the fundamental period of the chimney and that of the sloshing wave. An equivalent model is examined that is simple enough yet able to accurately produce the design acceleration, dynamic amplification, damping and torsional effects at the chosen tank location, and to capture site effects. An analysis of the tank at ground level is conducted according to AWWA D100-11. Then, the tank at elevation 63 m is analysed within the framework of three existing methods using code spectra and site-specific spectra. A novel fourth method is then proposed which, contrary to the existing methods, can accurately capture the conditions of this case study by combining the benefits of all methods. The workflow described here can be readily applied to other cases of elevated tanks for which the standard procedures are inadequate.