“Computational Civil Engineering - "Intersections" International Journal

260 C. IonescuAs an example, when using the OPTSTAR software, in the optimization of areinforced concrete structure, the following inconveniences occur:• Stiffness modulus, used for assessment of the tension and deformationstate, is constant all along the optimization process progress and equal tothat of the cement concrete according to the class of concrete. As a result,the reinforcement bars has no function in this process. Practically, it is likeoptimizing plain concrete structures.• As demonstrated in the literature, stiffness modulus varies as a function ofstress condition of the element, as well as along the element function of theinitiation and development of fissures.• Restrictions used in optimization process and imputed in OPTSTARsoftware (i.e. tensions, displacements, specific deformations etc.) cannot beused, due to the variety of computation hypothesizes for reinforcedconcrete (i.e. working stages); tensions are determined in stage I,displacements in stage II, and the stiffness modulus implies dimensioningof the cross-sections, meaning stage III.Generally, the logic of the design process reveals the existence of six phases:problem definition, selection of the system parameters value, creation of the designstructure, bridge structure evaluation, selection between the solutions, and technicalverification. In this rational mode, each phase generates a clear and correctperspective and feedback might appear between phases due to problem refiningeffort and a partial overlaying or a fusion might exist between successive phases.For the optimal design process of a bridge a logical sequence of the major stages isadvised, as presented in Figure 1. Search for the optimal solution is done unifying,through continuity, three larger processes: classical design concept (which includesthe six phases presented above), optimal design based on finite elementcomputational software, and optimal structure selection from more optimalstructures (each within its class) using multi-criteria decision.4. CONCLUSIONS1. Methods for design of bridge structures are iterative in nature, but iterationsemerge mainly in the analysis of the design problem and they are not inherentto the design itself.2. Through proper definition of the design problem, it can be seen that many ofthe iterative procedures of the design process might be eliminated if thesystemic approach is used.