Date of Award

January 2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Iraj Mamaghani

Abstract

Seismic response plays an important role in the design of liquid-filled thin-walled steel cylindrical tanks because of the small thicknesses of the walls as compared to their diameter. The liquid-filled thin-walled cylindrical tanks are vulnerable when they are subjected to earthquake accelerations. This dissertation aims to estimate and improve the seismic buckling strength of the liquid-filled thin-walled steel cylindrical tanks under earthquake excitation. The structural response to the base excitation is modeled using the concept of effective earthquake forces. The time steps in numerical analysis are divided to be small enough to accurately capture the periods of oscillations. The finite element method (FEM) is compared with experimental results and theoretical equations available in the literature to ensure the accuracy of the numerical analysis. Based on the extensive parametric study, seismic design equations and design curves representing the interaction effects of the diameter-to thickness (D/t) and height to diameter (H/D) ratios for the liquid-filled thin-walled steel cylindrical tanks of various geometries subjected to different earthquakes are presented and discussed. Results reveal that the D/t ratio is an important parametric factor of the seismic buckling strength of the liquid-filled thin-walled cylindrical tank. The dynamic buckling capacity of the tank decreases significantly when the D/t ratio increases. An increase in the H/D ratio also seems to have a negative effect on the seismic buckling strength; however, its effect is less significant compared to the D/t ratio. The effects of geometrical imperfection on the seismic buckling strength of liquid-filled thin-walled cylindrical tanks. This study discovers that the seismic buckling strength of the tanks decreases significantly as the amplitudes of initial geometric imperfection are included. This study also introduces the improvement of seismic buckling strength of liquid-filled thin-walled cylindrical tanks due to vertical stiffeners. It is concluded that the vertical stiffeners improve the seismic buckling strength of the liquid-filled thin-walled steel cylindrical tanks when they are subjected to horizontal earthquake excitation. This study concludes that vertical stiffeners can improve the seismic buckling strength by at least 10% of the critical peak ground acceleration (PGA) of unstiffened liquid-filled thin-walled steel cylindrical tanks. Finally, this study proposes the new design criterion of the liquid-filled thin-walled steel cylindrical tanks which is the double-skin thin-walled composite tanks (DSTWCTs). The DSTWCT is constructed to have the same diameter (D) and height (H) as a single-skin thin-walled tank (SSTWT) with an equal volume of steel. DSTWCT consists of two skins which are inner and outer walls. The inner wall diameter of DSTWCT is equal to the diameter of SSTWT. The seismic design and numerical finite element models of DSTWCT are proposed. It is concluded that the seismic buckling capacity of DSTWCT substantially improves when the gap between double skins of DSTWCT is filled with concrete up to 50% of the height of the tank. The location of the seismic buckling of DSTWCT occurs at the hollow sections just above the surface of infill concrete and moves to the higher location as the concrete-filled ratio increases which in turn results in improved seismic buckling strength and ductility. Chapter six presents the conclusions and future study.

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