Seismic performances of overhead Water tanks

Abstract

This research mainly deals with study of seismic performance of circular shaped overhead water tanks (OWTs) made of concrete material. Out of the two types of staging provided for OWTs, framed staging is considered. Moreover, the performances of OWTs resting on different soil strata such as hard soil, medium soil, and soft soil are taken into consideration in addition to the OWTs with fixed base. Initially, to understand the seismic performance, eight tanks of different storage capacities have been studied. Since there is no specification for seismic analysis of overhead water tanks in the Indian code IS1893 (part 1):2016, the guidelines Indian Institute of Technology Kanpur-Gujarat State Disaster Management Act (IITK-GSDMA) has been adopted for seismic analysis of OWT. It provides guidelines for structural idealisation of tanks for both empty and full conditions. It idealise the filled OWT as two degree of freedom system and they are impulsive and convective mode. The OWTs in empty and in filled conditions are investigated in linear as well as nonlinear performances. Albeit Empty OWTs are not important in normal structural design, they become important in seismic design. Lateral stiffness of the OWTs is calculated as per the guidelines using Structural Analysis and Design Program (STAAD-Pro) software. The damping ratio of tanks performing within the elastic limit is taken as 5%. While seismic response quantities such as base shear, base moment, roof displacement, sloshing wave height and hydrodynamic pressure are calculated for both filled and empty conditions in linear performance, the response reduction factor is investigated in nonlinear performance of OWTs. Six ground accelerations are selected based on the strong motion characteristics for determining the linear performance newline newline newline