Seismic Assessment of RC Framed Staging of Elevated Water Tanks

Abstract

Elevated water storage tanks are one of the most crucial structures to be considered under seismic action due to the complex behaviour of fluid–structure interaction. The modelling of this fluid–structure interaction can be carried out by rigorous application of Finite Elements Analysis (FEA) with Computational Fluid Dynamics (CFD). But in case of professional practice and design, these methods are very tedious and time-consuming for day-to-day application. Following the Housner model of elevated storage tanks, previous studies suggest that if the time period of the convective (Tc) and the impulsive (Ti) mode are well separated by factors above 2.5, then the complex fluid–structure interaction can be uncoupled to perform approximate analysis. Also, it eliminates the risk of coupled resonating condition of fluid and structure. The present Indian Standard (IS) seismic code for liquid storage tank follows this idealization for simplified analysis. But, the aspect ratio or height to diameter ratio (hs/Ds) of the tank staging and number of panels in it plays a significant role on the assumption where Tc/Ti can be smaller than 2.5. Hence, this present study reveals the range of hs/Ds for which the Tc/Ti value lies above 2.5 to conduct simplified analysis following the IS provisions and to avoid the coupled resonance. The tank is considered as elevated circular concrete water storage tank with flat roof.