Methodology for the parametric analysis and seismic design of isolated elevated water tanks

This paper describes a methodology of analysis and seismic design for the study of 828 parametric models of reinforced concrete elevated water tanks with seismic isolation in the base. Thus it was possible to estimate the interest responses such as, for example, the fundamental period of vibration, maximum lateral displacement, maximum shear forces and maximum bending moment, through a set of curves of normalized responses whose errors do not exceed 10% for all cases. This continuous special structure similar to an inverted pendulum was discretized using the lumped mass criterion. The modeling was made using uni-dimensional elements considering flexure and shear effects. The support of the tank was partitioned into ten elements and the tank into five elements. The isolation system is conformed by a rigid girder that connects the superstructure (tank and support) with the isolators, which are located in the circular perimeter of the base support. The elastic parameters were grouped in the following order: a) elevated tank: slenderness ratio (HD), diameters ratio (RD), diameter - thickness ratio (DE), water mass - structure mass ratio (RM), b) Isolation system: slenderness ratio (RHa) c) Water: the water-structure interaction effect was considered using Housner's method. The sensitivity analysis of the structural models, allowed us to observe that the maximum moments and the maximum shear forces are equivalent to 50% of the maximum responses obtained in their similar fixed base, and that the relative lateral displacements are lower than 1,2 % which means that the structure moves in the shape of rigid block.