Sculptural form finding with bending action
Paper in proceedings, 2017
This paper demonstrates a method development for integration of bending action into the form finding process. The aim has been to facilitate the designer with means to compromise between structural efficiency and sculptural freedom for grid shell type of structures.
The analysis is carried out using Dynamic Relaxation (DR) and to achieve bending capability, the base element implementation is a 12 degrees of freedom beam where the DR is solving for both translations and rotations . For purpose of validation, stress based utilization is calculated based on Eurocode 3 equations which are simplified to allow for separation of axial and bending utilization . A stress based sizer is also implemented to enable comparison based on tonnage.
The methods presented are derived from the principles behind stiffness control and force-density control form finding, commonly applied for compression and tension structures respectively . The common denominator being that they are all driven by a form finding load case, where the user can specify various combinations of axial- and bending utilization limits for the elements, to which the form adapts as it tries to find equilibrium of internal and external forces and moments.
None of the methods was found to satisfy all requirements for a useful general purpose shell design tool. The main issue was found to be wrinkling of the initial geometry when the need for drastic change in element length, required for a structurally unsound free form surface changing shape in the form finding process, is being opposed by the relatively high axial stiffness of a beam. This is not usually an issue when form finding with elastic springs that undergo large deformations in the process.
Conclusively there might be merit for a form finding element that allows for large axial deformation to avoid the wrinkling problem but has the bending properties of a beam. From a workflow point of view, the implementation of elements with bending capability was demonstrated to be useful for form exploration, particularly when combined with automatic sizing. The separation of bending and axial utilization was also found useful from a form evaluation point of view.