evaluation of modification factor for concrete cylindrical tanks using pushover analysis

in this paper the response modification factor due to ductility and saved strength of cylindrical concrete elevated and ground tanks is obtained using finite element method and nonlinear push over analysis considering the lateral effective modes of tanks. to modeling the behavior of the tank materials, the five parameters william-warnke and prefect elastoplastic models are used for concrete and reinforcement rebars respectively. in the calculations the reinforced bars are modeled both exactly and as percentage of concrete surface area. in addition it is assumed that the foundation of the structure is absolutely rigid and contained water has linear behavior. the response modification factor is obtained for different performance levels by changing different parameters such as height, thickness, radius, and percentage of the reinforcementbars of the shaft and shell, thickness and dimensions of stiffener and water level. the obtained results show that the factor for the elevated tanks changes between 4and 5 and the factor for the ground tanks varies between 1 and 2.5 these changes depend on the performance levels for the tanks.