Imperfection insensitive thin steel tubular shells under bending

Thin cylindrical shells are highly sensitive to imperfections, and the presence of even small geometric imperfections reduces their capacity significantly. This high sensitivity reduces the inherited benefits of thin cylindrical shells and has long been an obstacle for the effective and efficient use of thin cylindrical shells. The current practices, to deal with this imperfection sensitivity, are through the use of knockdown factors and stiffeners. These methods, which are also used for designing wind turbine towers among many other structures, diminish the structural benefits and increase the cost of construction. Recently, a new approach has emerged to reduce the sensitivity of thin cylindrical shells to imperfections, and to increase the load carrying capacity. In this approach, wavy cross-sectional shapes are explored instead of circular cross-sections. The wavy cross-section shapes reduce the slenderness (RR/tt) of the cylindrical shells because the local radius of curvature is reduced and consequently, the imperfection sensitivity of thin cylindrical shells is also reduced. Past studies have been carried out using the wavy shape cross-sections and they present highly promising results. These studies did not investigate the effect of residual stresses, which is the essential part of wavy cross-sectional cylindrical shells. Furthermore, an application of wavy cross-sectional thin cylindrical shells in tall wind turbine towers is explored to illustrate the benefits of wavy cylinders.

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