Grating effect on flutter instability

Flutter stabilization of girders should be one of the major subjects for long-span bridges. In the former studies by authors, various geometric-shaped sections have been studied from the viewpoint of flutter stabilization, such as elliptical section, rhombus section, trapezoidal section and so on. Recently, the aerodynamic characteristics of grating-installed bridge decks have been focused for future super long-span bridges. However, systematic and detailed studies on the efficiency of grating on flutter stabilization are inadequate. For example, it remains unsolved yet in terms of flutter characteristics in relation with their opening ratio (OR) and their location of grating installed on bridge deck. The aim of this paper is to clarify the influence of the opening ratio and the location of grating for plate-like bridge deck on flutter instabilities based upon their aerodynamic derivatives and flutter analysis. A series of wind tunnel tests have been conducted for various grating conditions, such as changing the OR in the range of 0%, 20%, 40%, 60%, 80% and 100%, and their locations. Furthermore, a “step-by-step” analysis is applied to clear the role of each aerodynamic derivative on flutter instability and flutter mechanism. Depending on the grating conditions on the bridge deck, peculiar flutter type was observed in addition to the conventional torsional branch-coupled flutter. It was the hybrid branches-coupled flutter, that is with both heaving- and torsional-branch instability at a certain high-reduced velocity range. These particular flutter instabilities were discussed according to their aerodynamic derivatives.