Theories of Aerodynamic Forces on Decks of Long Span Bridges

Long span bridges are one of the most challenging kinds of structures in civil engineering. Wind loading and wind effects are highly important aspects when designing this typology. The interaction between wind and structure, studied by using aeroelasticity theory, allows us to understand several classes of structural instabilities that may appear. Also, wind tunnel data, obtained by conducting careful testing of reduced models of bridges, produce useful information about prototypes' characteristics. A fundamental aspect of bridge design under aeroelastic constraints is identification of aerodynamic forces; several models for this purpose are presented in this paper. First, a model based on a two-degrees-of-freedom plane plate moving in an incompressible fluid is reviewed; this approach, although useful in airfoil engineering, is not valid any longer in civil engineering, as bridge decks are bluff bodies. Second, a linearized theory, also based on a two-degrees-of-freedom model is analyzed; in this case, obtaining aerodynamic forces requires identification of a set of coefficients, called flutter derivatives, that can be found by carrying out testing of reduced models of a segment of bridge deck. Finally, an extension of that approach, leading to a linearized theory of a three-degrees-of-freedom model is presented.