A Comparison between Different Editions of API650 Seismic Provisions for Cylindrical Steel Storage Tanks Considering the Fragility Curves

Seismic safety of liquid storage tanks is of considerable importance due to its application in different industries. In Iran, most of these storage tanks are designed based on API650 code provisions. Despite designing tanks according to API standard, the lesson learned from previous earthquakes, shows different kind of damage occurring on them. This study is an investigation on evaluating different revisions of API650 seismic codes from years 2001 to 2013. The failure modes considered are Buckling, Overturning, Sliding and Shell Yielding. For this, three steel cylindrical tanks has been checked by different revisions of API650 under different PGA from 0.1 to 2 and various failure modes are taken into account respectively for each tank. According to these information, the fragility curves are derived and compared among all the revisions of API650 code. According to the resultsit seems that API650 in edition of 2001, Presents buckling criteria as the main criterion.This criterioncompared to the overturning criteria even in unanchored tanks­determinedvery conservative.In these samplesthere were no overturning criteria prior. In 2005, 2009 and 2013 editions of API650 for unanchored tanks, presented overturning criteria as the main criterion considering the sliding and total stress failure criteria but for anchored tanks total stress failure criteria controlled much more conservatively. Generally buckling criteria not reported in prior.