Seismic Analysis of Ground-Supported Tanks Using the Vertical Response Spectrum

Vertical ground motions can have a significant impact on the structures vertical response for several types of nonbuilding structures. Tanks and vessels, hanging structures, and horizontal cantilever systems are some examples. The forthcoming ASCE 7-16 code requirements for vertical response spectrum will now account for nonbuilding structures that are sensitive to vertical ground motions. The code requirements are based on Chapter 23 of 2009 NEHRP Provisions, except that the response spectrum will be defined at the MCE_R level. The NEHRP Provisions are based on several previous studies. This paper is oriented toward seismic analysis of ground supported tanks using a vertical response spectrum. While cylindrical tanks have a well-defined and simply determined vertical period, rectangular tanks require the use of peak spectrum response due to the lack of quantified vertical period approximations. A brief discussion of the approach will follow with several examples. Examples will consist of a comparison of vertical response spectrum, ASCE 7-10 code requirements, and reference code requirements (ACI, AWWA and API) for both circular and rectangular ground supported tanks.