Cyclic Testing of Storage Tank Plate-Shell Connection

Abstract

Earthquake-induced uplifting/settlement at the base of liquid-storage tanks causes yielding in the bottom plate. Limited amount of yielding is a source of deformability and damping in tanks, but excessive yielding during repeated cycles can rupture the bottom plate and cause the liquid to leak from the tank. This study is conducted to experimentally determine the amount of plastic yielding that can be allowed in the bottom plate during the expected number of load cycles. Four test specimens for this study were obtained from a tank that was demolished after 66 years of service. A novel test protocol is developed for engineers to account for the large number of load cycles expected during a magnitude M 9 earthquake in the region of interest. From the results of cyclic tests, it is determined that (1) the bottom plate can sustain 20 cycles of ±0.335 rad (±19°) plastic rotation without rupture; and (2) the plastic moment capacity of the bottom plate increases by 32% due to strain hardening. These results are significant in performance-based seismic design and evaluation of liquid-storage tanks.