Nonlinear seismic response of ground supported cylindrical reinforced concrete tanks

Abstract

Seismic behavior of Liquid Containing Structures has been studied for decades. Being able to have these structures functioning during and after an earthquake is imperative for well-being of a society hence importance of their design. Response Modification Factor known as “R factor” is one of the key parameters in seismic design. However, in case of LCS’s, a justifiable guideline to determine the R factor is yet to be developed and current codes have utilized empirical values in design of these structures. The design intend for LCS’s is to meet the serviceability limits as opposed to life safety and collapse prevention which is the case of design of buildings. This study aims to investigate the effect of various parameters such as material nonlinearity, tank dimensions, base condition, concrete compressive strength, characteristics of seismic excitation records on the seismic behavior of concrete tanks. In this study, a finite element method is developed to investigate the seismic behavior of circular ground supported reinforced concrete tanks. First, the accuracy of current practice is investigated by employing the analytical and numerical methods, experimental studies. Finite element technique and pushover analysis are utilized to set up the pushover curve and achieve over-strength and ductility factors. The response modification factor (R) is then evaluated based on the nonlinear static analysis. Second, using the nonlinear dynamic analysis (time-history), the seismic behavioral aspects of full liquid tanks are studied taking into account the material nonlinearity, wall flexibility, effect of impulsive component, fluid-surface interaction and vertical ground acceleration. Thereafter, a parametric study is conducted to study the influence of tank dimensions, base fixity conditions and earthquake frequency content on the response modification factor. This study shows the over-strength and ductility factor of RC ground-supported tanks are significantly influence by tank size, height, height/diameter ratio and fundamental period. Also, fixed based tanks and shallow tanks have higher R values compared to hinged based and tall tanks respectively. The time history results show that the effect of material nonlinearity, vertical ground acceleration, base condition and earthquake frequency content on the dynamic behavior of liquid ground supported tanks is significant.