Abstract

This thesis presents a comparative study of the seismic response of anchored and unanchored steel tanks and, in particular, it evaluates the safety of the tank shell against buckling. The study inspected design check methodologies outlined in current codes and standards for steel tanks under seismic loads. Numerous tank dimensions were selected for an extensive parametric study, and these tanks were evaluated under varying earthquake intensities. Tank shells were originally designed using a factor of safety of 2, according to the prevailing codes. The buckling phenomenon of steel liquid-filled shells was carefully evaluated, and a comparison was made between the two types of shell buckling: membrane buckling and elastic-plastic buckling. It was shown that the elastic-plastic buckling stress may limit the seismic design, especially at higher values of total liquid pressure. Moreover, the elastic-plastic buckling capacity is eventually depleted when the ratio of total-to-hydrostatic pressures is equal to the employed factor of safety (reduction factor). The validity of the assumption of rigid or flexible tank wall was carefully examined under a wide range of peak horizontal and vertic􀀳l ground accelerations. The maximum axial stress in the shell was computed for both anchored and unanchored tanks where, for the latter, amplifications due to tank uplift were taken into consideration. The maximum axial stress and the allowable buckling stress were compared for each tank, and several tanks were found unsafe. It was clear that the factor of safety adopted in ourrent design codes fur determ.inlng the shell thickness must not be applied to all tanks. Tanks with larger height-to-radius ratio when subjected to high peak earthquake accelerations tend to be unsafe, if originally designed under such a factor of safety. A formula was suggested to initially modify the factor of safety according to the height-to-radius ratio and the expected peak earthquake acceleration. There is a limit though as to the accepted increase in the initial factor of safety for the evaluation of shell thickness, otherwise the design may be rendered impractical. This occurs mostly in unanchored tanks with large height-to­radius values and intense earthquake accelerations; in this case, anchoring of the tank shell becomes the sound solution. The results of the present study can be the core for enhancing seismic design methodologies in commonly used codes for steel liquid storage tanks.

School

School of Sciences and Engineering

Date of Award

2-1-2003

Online Submission Date

1-1-2002

First Advisor

Medhat A. Haroun

Committee Member 1

Ahmed A. Rashad

Committee Member 2

A. Samer Ezeldin

Committee Member 3

Ezzat Fahmy

Document Type

Thesis

Extent

266 leaves :

Library of Congress Subject Heading 1

Tanks

Rights

The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

Call Number

Thesis 2002/7

Location

mmbk

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Included in

Engineering Commons

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