RESPONSE OF BRIDGES TO STEADY AND RANDOM WIND LOAD Wind analysis of the Hardanger Supsension Bridge

With more and more increasing span lengths of bridges due to better material quality and improved construction techniques new effects must be included in the design process. A major issue is the increased susceptibility of such structures to wind induced vibrations. Especially steel bridges – and consequently a majority of suspension and cable stayed bridges – allow for extraordinary slender main girder cross section. The price to pay for these material savings and architectural highlights is a balancing act concerning the wind design, because one can no longer state a priori that the final construction will withstand the acting wind forces. Instead, sophisticated analysis methods must be applied to determine critical wind velocities for all types of known wind effects. By considering the typical cross section of modern long-span bridges a close resemblance to aircraft wings is obvious. Therefore, many analysis techniques originally applied in aeronautics have crossed over to bridge engineering. Although many problems can be reduced to simplified models there are some aspects which can only be treated numerically by referring to sophisticated computer models – a field of activity which is nowadays often called Computational Wind Engineering (CWE) [1]. This term comprises the characterization of interaction of wind and cross-section by numerical Computational Fluid Dynamics (CFD) methods on the one hand, and structural analysis based on the resulting aerodynamic coefficients on the other. This so-called wind buffeting analysis must take into account the random properties of wind events, which are described by wind power spectrum and coherence. On the other hand, detailed information of the considered structure must be provided, which is done in the form of eigenmodes and –frequencies. This information is combined in a statistical analysis method to provide information about the structure peak response due to a given wind profile. In this paper the application of CWE methods is presented for the investigation of the Hardanger bridge, a suspension bridge planned in Norway. First, detailed CFD calculations are performed to obtain an aerodynamic characterization of the used cross sections for main deck and pylons. The obtained information is used in the following to perform wind buffeting calculations for the prediction of response to fluctuating wind. All calculations were performed with a commercial software package which is capable of CFD calculations [2, 3] as well as wind buffeting analysis [4].