When structure is defined and Internal Forces from Analysis part is available Steel Unity Check procedure can be performed. If Unity check results is too high or too low it is possible to change sections manually or from Steel toolbar or Codechecking menu group to choose Steel Design button or the same menu item. This procedure will choose sections for each member which will return Unity check results as much as possible nearest to one. Section selection will be done inside sections group from which initial section was choose.
The steel design is providing rational selection solution for the global optimization problem.
For the static indeterminate structures, steel design is providing rational selection of the sections for the one of possible redistributions (because of a changed stiffness ratio) of the internal forces and unity check criteria for cross and stability check. An adequate algorithm to determine the optimal stiffness ratio in combination with other criteria (like deflections check) is not available. Prior to the rational selection, global optimization of the sections should provide the single/optimal solution, is not supporting using implemented steel design functionality.
Fig 1. Rational selections vs optimal solution
Within the calculated results (in fact ith redistribution of forces), the satisfactory selection of sections (UC<1) is providing by:
- Collecting all sections of same section group (IPE, HEA, ...);
- Sort them by section area from smallest to largest;
- Finding section which gives UC closest to 1.0.
After recalculating of results, redistribution of forces appears. For this redistribution of forces other satisfactory selection of sections could be found. Iterative procedure could be continued until rational selection of sections is found.