SEISMIC ANALYSIS OF OVERHEAD CIRCULAR WATER TANKS – A COMPARITIVE STUDY

Abstract

This paper compares the results of seismic analysis of overhead circular water tank carried out in accordance with IS: 1893- 1984 and IS: 1893-2002 (Part-2) draft code. The analysis is carried out for elevated circular tank of 1000 Cu.m capacity, located in four seismic zones (Zone-II, Zone -III, Zone-IV, Zone-V) and on three different soil types (Hard rock, Medium soil, Soft soil). Further, three different tank-fill conditions - tank full, tank 50% full, tank empty are also considered in this study. The seismic responses of circular tanks are computed and compared based on the theoretical procedures of IS: 1893-1984 and IS: 1893- 2002(Part-2) draft code. The analysis was performed using SAP-2000 software package also. The parameters of comparison include base shears, base moments, impulsive and convective hydrodynamic pressures on tank wall and base slab. The results of the analysis showed an increase in base shear, base moment, hydrodynamic pressure and time period with increasing zone factor for all soil types and tank fill conditions considered. The increase in base shear and base moment are found to be in the range of 54% -260% in the analysis performed using draft code over the values of IS: 1893-1984. The hydrodynamic pressure increased in the range of 54%-280% with the use of draft code over the values obtained based on IS: 1893-1984. The results of SAP-2000 are found to be in agreement with those of the draft code.