Evaluation of seismic ground motion scaling procedures for linear time-history analysis of liquid storage tanks

Abstract

Liquid storage tanks are vital life-line structures, especially following destructive seismic events. However, at present there is no accepted procedure to scale ground motions to perform time-history analysis for these very short period structures. Current standards and design codes e.g. ASCE/SEI 7-10, Eurocode 8 and NZS 1170.5, for conventional structures, e.g. buildings and bridges, minimise in a pre-defined range of periods the difference between the response spectra of chosen records and the target spectrum. This period range has limits related to the fundamental period of the structure in the excitation direction being considered. However, these design specifications have important differences in their scaling procedures and consequently affect the calculated seismic response of the structure. Additionally, these procedures were not formulated for time-history analysis of liquid storage tanks. This is evident in the case of the restriction imposed by NZS 1170.5 for very stiff structures, which includes most tanks. This restriction leads to reduced structural loading giving non-representative results. The research reported here concerns the seismic response of storage tanks, in terms of base shear, overturning moment and wall stresses, when subjected to scaled ground motions using the procedures of three design specifications. It was found that the Eurocode 8 approach produces the highest seismic response on storage tanks. ASCE/SEI 7-10 gives intermediate results in terms of applied load and seismic response compared to the other two specifications. The study also shows that the restriction imposed by NZS 1170.5 for tanks, produces an underestimate of the seismic load on storage tanks.