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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 9/10
Edited by: B.H.V. Topping
Paper XVI.1

Feasibility and Optimality in Structural Design

U. Kirsch

Department of Civil Engineering, Technion-Israel Institute of Technology, Haifa, Israel
(currently Visiting Professor and Carnegie Research Fellow, Department of Civil Engineering, Heriot-Watt University, Edinburgh)

Full Bibliographic Reference for this paper
U. Kirsch, "Feasibility and Optimality in Structural Design", in B.H.V. Topping, (Editor), "Proceedings of the Fourth International Conference on Civil and Structural Engineering Computing", Civil-Comp Press, Edinburgh, UK, pp 125-132, 1989. doi:10.4203/ccp.9.16.1
Some relationships between optimal and feasible structural designs are presented. In many structural design problems, where the objective function is not sensitive to changes in the design variables, the object is to find an improved feasible design rather than the theoretical optimum. Interior optimization methods that converge to the optimum from the interior side of the acceptable domain are most suitable for this purpose. Several methods, intended to introduce improved feasible designs are discussed in this paper. These methods are particularly useful for problems with a narrow feasible region or in cases where it is necessary to determine whether a feasible region exists. Necessary conditions for feasible solutions are derived and a procedure to convert an infeasible design into a feasible one by modifying the preassigned parameters is introduced. It is shown that the optimal value of the modified parameters can often be determined directly. Several examples illustrate the relationships between feasibility and optimality. It is emphasized that optimization methods are most useful in the search for improved feasible solutions for various practical design problems.

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