Elevated water tanks are most commonly used to store water and to supply at certain height for pressurizing the water distribution system. A major irregularity along the height of the structure is due to large water mass on the top and complex phenomenon of dynamic interface between the fluid and the walls of the tank with the horizontal acceleration causing the sloshing, which determines the need for specific conditions. These issues pose significant problems in terms of design and modeling of such structure, making it particularly inspiring from a structural analysis point of view. The seismic performances of these storage tanks are a matter of special importance extending beyond the economic value of the tanks. The seismic behavior of the elevated water tanks is different from that of a ground supported tank or underground water tank. Therefore, in the present paper, a seismic analysis using response spectrum method is carried out for steel elevated water tanks. The study is made on cylindrical elevated water tank with and without the bracing configurations (2-storey, 3-storey and 4-storey) considering different earthquake zones (zone 2 to 5) and soil conditions. The analysis is carried out using STAAD-PRO V8i (SELECT series 4) software. The results for bare and braced frame tanks, which are in terms of base shear, time period and displacement for different seismic zones and soil conditions, are compared. The water tanks with 3-storey and 4-storey showed better performance than 2-storey in terms of displacement. The braced frame steel elevated tank showed an increased overall stiffness than the unbraced one.

Water tanks, especially elevated water tanks, are considered as significant services in several cities. Their safety performance during strong earthquakes is of serious concern. They should not fail after earthquake, so that they can be used in meeting essential needs like arranging drinking water and putting out fires. The failure of these structures and the subsiding of water may pose threats to the health of a city due to the shortage of water or difficulty in putting out fire during critical conditions. There have been various studies investigating the dynamic behavior of fluid storage tanks, however, most of these studies have focused on the ground level cylindrical tanks. Very few studies have concentrated on the behavior of elevated tanks (Malhotra et al., 2000; Ramazan and Adem, 2007; and Anumod et al., 2014). Therefore, attention here is generally focused on the dynamic behavior of supporting structure of elevated cylindrical water tank. A lot of research has been done and various mechanical models for tank analysis have been created. The most famous of them are Housner’s equivalent two-mass model, Haroun’s three mass models, and Malhotra et al. (2000) simplified method which is one of the standard analytical methods and is primarily useful for finding initial responses and controlling accurateness of results of numerical models. In the present study, linear dynamic analysis is carried out using response spectrum method. It is considered the most basic response value used in the earthquake-resistant design of structures. IS 1893 (Part 1, 2002) draft copy code is used for the analysis. The response spectrum of a linear system is frequently used as a tool to express the periodic properties of an earthquake motion which is considered the backbone of dynamic analysis. There are computational advantages in using the response spectrum method of seismic analysis for prediction of displacements and member forces in structural systems. The method involves the calculation of only the maximum values of the displacements and member forces in each mode using smooth design spectra that are the average of several earthquake motions.

Structural Engineering Journal, Dynamic analysis, Cylindrical storage tank, Response spectrum method