Response of bluff and streamlined bridge girder in the wind as function of natural frequency tuning

The extended abstract must contain: The title of the paper; The name, e-mail and affiliation of the author(s); The contact person, inserted as a note, containing: name, affiliation, mail address, e-mail address, telephone number, fax number. The extended abstract must be prepared following the instructions provided in the present document; it should be no longer than four A4 pages (including figures, tables, references and everything else) and clearly illustrate: - The background of the work; - The methodology; - The results which have been obtained. The language of the conference is English. In order for the abstract to be typed, this template can be used with Microsoft Word, Open Office swriter or any word processor able to elaborate rtf-type documents: it already contains all the rules to be followed. Otherwise, the pdf template can be downloaded; Authors who will choose this latter possibility are urged to strictly follow the ABSTRACT The analysis of the aero-elastic stability of engineering structures creates an important part of indus- trial aerodynamics for many years. It is still of great interest also nowadays due to the development in theory and experimental techniques. During previous decades motivated by the very well known Tacoma Narrows bridge collapse many questions regarding the physical phenomenon have been an- swered in sufficient manner. Sophisticated methods for the aero-elastic instability prediction have been evolved and successfully applied to real structures. The majority of them are based on the so called aero-elastic derivatives representing the coefficients of self-excited forces induced by the wind-structure interaction. In terms of the trend of these coefficients one can declare the aero-elastic characteristics and usability of the considered cross-section shape. On the other hand, it is known that the aero-elastic derivatives (AD's) are quantities that depend on the experimental conditions. Paper by Noda et al. (2003) demonstrated the effects of oscillating amplitude on them. He found that for dif- ferent cases of the torsional amplitude there exist different courses of the aerodynamic derivatives. In order to eliminate possible discrepancies in the aero-elastic instability prediction, it is recommended to perform the measurement and thus highlight the role of the oscillation amplitudes. In this paper, the experiment elucidating the influence of the natural frequencies and other physical properties on the stability of the test girders has been performed. The phase shift, flutter frequency and the range of the critical velocity with respect to the frequency ratio have been determined. The aero- elastic instability analysis of two cross-sections (rectangular and bridge-like) including also AD's has been performed using a wind tunnel experiment. The special attention has been paid to the response of the girders at the critical state. The first examined deck is of a rectangular shape with the height-to- width ratio of 1 : 5. The geometrical similarity of a bridge-like girder has been maintained while the aspect ratio is respected. Both decks have been equipped with pressure sensors allowing to observe the wind forces in direct way. Both sections have been tested on the special testing stand. This stand was originally developed respecting an easy and quick tuning of the model eigen-frequencies and enabling the excessive deflection amplitude in both heave and torsion, see Net al. (2007). In Contact person: R. KrInstitute of Theoretical and Applied Mechanics, v.v. i. Academy of Sciences of the Czech Republic, Proseck´