Seismic Performance of R. C. Elevated Water Storage Tanks

Abstract

The primary basis for construction of structures for strong ground shaking is that it shall not collapse. However, permissible damage for structural components is permitted. If a structure is permitted to be damaged in the case of severe ground shaking, it shall be constructed for seismic forces considerably lesser than those expected in the event of severe shaking if it is to remain linearly elastic. Response reduction factor, R is the factor that should be used to lower the actual base shear in order to obtain the required design lateral force. In the case of seismic design of water tanks, different values of the “R” factor are suggested by various countries, such as IBC-2000 gives the value of the “R” factor varying from 2 to 4, whereas ACI 350.3 has given the values from 2 to 4.5, whereas AWWA (D-100) recommended the values in between 3 and 4. According to Eurocode 8, the behaviour factor, also known as the “R” factor, varies between 1 and 5. The values in the Indian code for seismic analysis, IS1893-(Part 2), range from 2 to 4.Hence, it is tempting to look into the real aspect of the ‘R’ factor evaluation. IS 1893, an Indian seismic code, calculates a design shear force for an elastic structure and divides it by twice R. In other words, the term “R” refers the amount of over-strength and ductility that a structure is predicted to possess. Thus, by considering the elements, over strength factor, redundancy factor, and ductility factor, the structure can be constructed for much lesser force than is predicted by the violent shaking, preventing the structure from collapsing. Available literature shows a sound recommendation does not exist for the values of “R” given in the seismic design codes of various countries, including India. There is currently no basis for the R-values in the codes. According to the available literature, limited research has been done on the influence of viscous dampers on “R,” which reflects a structure's ability of dissipation of energy through inelastic behaviour. The finite element (FE) approach must be used in conjunction with the study of material properties, the study of nonlinear hinge properties, the investigation of the seismic response of water tanks for different water heights, and the effect of including braces in staging to reduce the seismic response of the water tank to examine the nonlinear response of tanks under dynamic time-history and push-over analysis.