Seismic Analysis and Design of Liquid Storage Tanks

Abstract

Liquid Storage tank is one of the most critical components of petrochemical industries, nuclear plants and other critical plants. Analysis and design of such structures considering various critical load is very important for its safety. Due to importance of liquid storage tank being remain operational, such structure are designed following standardize codal provision guideline in most of the countries. However, analysis and design of liquid storage tank to seismic loadings is challenging and requires careful consideration, as damage to such structure has a greater impact on plants, environment and human life. There are various seismic design guidelines available for the liquid storage tank. Use of such guidelines warrant in depth understanding of dynamic behaviour of the liquid storage tank. Therefore, it is important to study the seismic behaviour of the liquid storage tank and to assess seismic hazard associated with it. Major objective of the present study is to analyze and design a liquid storage tank storing – product following various national and international seismic codes. A tank of 22 MLD capacity located in seismic zone – v as per Indian seismic code IS:1893, is considered. Liquid stored inside the tank is modelled as a spring-mass analogy comprising of impulsive and convective modes of oscillation defined by IS:1893(Part-II)-2014. API 650 design stipulations are mostly used world wide for gravity and seismic loading of the liquid storage tank. In the present study tank is designed using one-foot method following API 650 guidelines. However, seismic analysis is carried out using both IS:1893(Part-II)-2014 and API 650 guidelines with an objective to check efficiency of Indian seismic code guidelines. Seismic response parameters such as time period, base shear and bending moment are evaluated for liquid storage tank. It has been found that Indian seismic code guidelines are at par with API 650 guideline since seismic response parameters differs only by 7-8%. Tank is found to be self-anchored under API 650 guideline and found to be stable under seismic and wind loads. Erection plan and detailed structural drawings related to fabrication and erection are prepared for the liquid storage tank. A computational model of the liquid storage tank is prepared in a licenced commercial software SAP2000. Finite element analysis is carried out under the static conditions for the tank. A good agreement in terms of stress in the shell and thickness of the shell is found when the results of FEA and manual calculations are compared. Various parametric studies in terms of type of liquid stored in the tank, geometric aspect ratio and seismic zone may be carried out that will be useful to day-to-day design of liquid storage tank.