Evaluation of response modification factor (R) of elevated concrete tanks

This paper discusses the failure mechanism of elevated concrete tanks with shaft and frame staging (supporting system) along with seismic behavior of these construction types. In order to modify the current code-based seismic design methodology, computer models have been established to determine the response modification factors, R, of the shaft and frame staging elevated tanks. The computational models have been subjected to an ensemble of earthquake ground motions. The effects of multi-component earthquakes, fluid–structure interaction and the P–Δ effects on the inelastic response of elevated tanks have been studied by conducting linear and nonlinear response history analyses. According to results of analyses and observed inelastic behavior during past earthquakes, the R factors for shaft and frame staging elevated concrete tanks have been evaluated regarding the seismicity of the site. Moreover, the shortcomings associated to the current simplified seismic analysis and design procedure have been addressed and a more rational modeling has been suggested especially for the shaft staging systems to enhance distribution of the ductility demand.