Resolution of flat bottom tank outlier Original Research Article

This paper contains the results of an outlier resolution evaluation for a large flat bottom tank, 40 ft 6 in. in diameter and 32 ft 8 in. in height. The tank was an outlier in both the USI A-46 and IPEEE programs due to insufficient strength of the bolt chair to transfer the bolt load to the side of the tank. The bolt chair evaluation resulting in the outlier was linear elastic. A more sophisticated non-linear analysis was performed of the bolt chair using the program ANSYS. The evaluation resulted in the conclusion that the bolt chair was able to transfer almost the entire yield strength of the bolt without excessive deformation that could ultimately cause overall tank failure. This evaluation tremendously increased the seismic capacity of the tank and resolved the outlier for both programs. The tank outlier evaluation also included a evaluation of soil–structure interaction (SSI) effects on the seismic demand on the tank. However, the formal consideration of SSI had a small effect on the overall seismic demand.