An Optimization Index to Identify the optimal Design Solution of Bridges

Structural optimization has become an important tool for structural designers, since it allows a better exploitation of material, thus decreasing structure self-weight and saving material costs. Moreover, it helps the designer to find innovative design solutions and structural forms that not only better exploit material but also give the structure higher aesthetic value from an architectural point of view. When applied to real scale structures like bridges, this approach leads to the definition of voids patterns delimiting regions where fluxes of force migrate from force application point to boundary regions and suggests innovative layouts without renouncing to formal and structural aspects. Nevertheless, the criticality of this powerful tool is related to the ease of defining entire families of possible candidate solutions, by modifying input volume reduction ratio to reduce structural weight as much as possible or defining several starting trial solutions based on the judgment of designer. In this case, structural optimization still leads to the best material distribution, but finding the best compromise between material saving and structural performance is a designer choice. To face this aspect, a global optimization index (GOI) has been defined and applied to the structural optimization of a steel-concrete arch bridge built is San Donà in the province of Venice, Italy. On the basis of this work, a generalized version of the optimization index is proposed and its analytical formulation is discussed in detail in this thesis. The application of proposed optimization index is extended from topology optimization to other optimization techniques. Moreover it allows not only to identify best candidate solution originated by a unique reference model, but even comparing structural performances between candidates solution derived by several starting trial solutions. Through structural optimization procedure performed on three different type bridges, namely footbridges supported by concrete shell, Calatrava Bridge (steel arch bridge) and two cable-stayed bridges, the effectiveness of proposed optimization index is validated. The results show that the proposed optimization index provides to the designer a mathematical procedure able to highlight the best choice among several candidate solutions obtained by the optimization procedure. With the proposed optimization index, a suitable score for each design solution of specific starting layout is assigned, therefore the best overall layout solution which is the best compromise between material saving and structural performance can be highlighted among single-family multi-solutions or multi-families or multi-solutions.