Sensitivity analysis and optimum design curves for the minimum cost design of singly and doubly reinforced concrete beams

This paper reports on the application of the Lagrangian Multiplier Method (LMM) to the minimum cost design of both singly and doubly reinforced concrete rectangular beams under limit state design conditions. Cost objective functions and stress constraints are derived and implemented within the optimisation method. Cost sensitivity analysis, detailed testing and comparisons with conventional design office methods are performed and the results reported, showing that the Lagrangian Multiplier Method can be successfully applied to the minimum cost design of reinforced concrete beams. The proposed approach is effective and reliable without the need for iterative trials. Optimum design curves have been developed that can be used without prior knowledge of optimisation. Despite the simplification of the cost model and the assumptions made, satisfactory and reliable results have been obtained and confirmed by using standard design office procedures