Vertical cylindrical welded steel tanks are widely used for fluid and bulk storage in industrial and agricultural plants. They usually consist of a thin bottom plate, a cylindrical shell with uniform or stepped thickness and a closed-roof or open-top (with or without floating roof). With the development of economy and oil industry, more and more oil storage tanks are put into service in recent decades, especially large tanks.As typical thin-walled structures, tanks are very susceptible to buckling under wind load especially when they are empty or partially filled. Over the past few decades, buckling failures of cylindrical steel tanks and silos during windstorm have occurred in many countries and regions. Buckling of tanks sometimes even occurs under moderate wind load during their construction. Because of serious economic losses and environmental problems due to the destruction of storage tanks, studies about buckling of tanks under wind load have been conducted extensively over the past few decades.