Challenge

Design a large tubular steel tower structure subjected to demanding static, cyclic and dynamic loading. The design required consideration of wind and seismic loading, fatigue, structural resonance, welded construction, highly loaded bolted-flange connections and anchoring to a reinforced-concrete foundation.

Engineering Approach

The complete structural load path was analysed from the upper structure through the tubular welded sections and bolted-flange connections to the foundation anchoring system. The reinforced concrete foundation was designed. Structural stress and fatigue analysis were combined with assessment of wind and seismic loading, structural dynamics and resonance, welded joints and highly loaded bolted connections. Critical bolted-flange connections were investigated using both analytical methods and nonlinear contact FEA, including bolt preload, flange separation and the redistribution of bolt loads as the joint progressively opened under external loading. Analytical predictions were compared with the nonlinear finite-element results to provide an independent assessment of the joint behaviour.

Outcome

The completed tower design satisfied the required structural, fatigue and dynamic performance criteria under the specified operating, wind and seismic load cases. Critical bolted-flange connections were demonstrated to maintain the required structural performance, with close agreement between analytical predictions and nonlinear FEA.