This paper deals with the economic optimization of reinforced concrete framed structures typically used in road construction. It shows the efficiency of heuristic optimization by the simulated annealing algorithm (SA), the threshold acceptance method (TA) and the tabu search method (TS). The evaluation of solutions follows the Spanish Code for structural concrete. Stress resultants and envelopes of framed structures are computed by an internal matrix method program. Design loads are in accordance to the national codes for road bridges. The algorithm is applied to a 13 m horizontal span RC box road frame. This example has 50 discrete variables, 3 geometrical, 3 types of concrete and 44 reinforcement bars and bar lengths. The evaluation module includes the ULS of fatigue plus other commonly checked limit states of service and ultimate flexure, shear and deflections. The comparison of the three heuristic methods shows lower deviation from the best solution for the threshold accepting algorithm when compared with SA-TS methods. Structural results are reasonably slender, i.e. top slab of 0.95 m depth (1/14 slab/span ratio) and walls of 0.40 m thickness (1/15 wall/height ratio); and they indicate the importance of the inclusion of the fatigue limit state, since its ignorance leads to more economic but unsafe designs.
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