Dynamic behaviour controlled the engineering design and this condition was extensively analysed using the dynamics suite within CSCS’s Masterseries software. Vortex shedding from the tubes and balls generates complex modes of vibration in the structural form. Frequencies vary with wind speed, object size and shape. Phasing of the oscillations in different parts of the sculpture causes periodic spikes in the most prominent amplitude of vibration, leading to considerable loads in the main stem. This design condition resulted in the engineering details of the form.
High fatigue resistance with suitable residual strength was required for both the tubes and the welds. High strength grade S460-equivalent Ovako 280 tube was specially imported from Sweden for the main stem. Selection of the appropriate Execution Class and appropriate certification of welders was ensured. All welds were tested and certified. Fail-safe systems are incorporated in the structure to cater for “unknown unknowns” in this unusual project, in part due to the position of the work high above public pedestrian areas.
New residents of the development were each presented with a handmade miniature replica of the sculpture in matching steel and gold leaf materials.
Photos: Keith Hunter