08-10-2014, 04:15 PM
Elevated water tanks supported on shaft-type stagings performed unsatisfactorily in past earthquakes. Codes recognize the lack of redundancy, overstrength and ductility in shaft-type stagings, and recommend larger design forces. In this study, strength and ductility demands of shaft stagings of eight tanks damaged during 2001 Bhuj (India) earthquake are re-assessed based on elastic and inelastic analyses considering soil structure interaction and sloshing motion of water inside the tank container. Shaft sections are found to fail at a higher base shear when soil-structure interaction is considered, than their fixed base counterparts. Also, ductility demands are less when soil-structure interaction is accounted for. Further, failure mode of a shaft (i.e., flexure or shear) depends on its aspect ratio and natural period of the tank. The study identifies that shaft supported elevated water tanks designed considering (a) the effect of soil-structure interaction, and (b) both flexure and shear capacities depending on their aspect ratio, are likely to show improved performance