Deer Isle Bridge: Field and Computed Vibrations

For the last several years the Deer Isle suspension bridge in Maine has been the subject of a field survey by the U.S. Federal Highway Administration. At this writing, both on‐site wind and vibration measurements are continuing. The present paper makes use of some of the currently available data from this survey and incorporates it with results of finite element analyses of the bridge to define with some accuracy a number of its prominent modes. The study is a part of ongoing research into methods for both sharpening and corroborating the prediction of the wind response of flexible bridges. The present research project also incidentally confirms the efficacy of cable bracing added to the bridge by its designer with the aim of defending it against wind‐induced oscillation. The results reported herein indicate that the computed frequencies and mode shapes using finite element modeling are in reasonable agreement with the results of the field‐data analysis. In addition to providing a comparison of computed parameters versus those observed in the field, the paper serves the purpose of establishing some information needed in using the Deer Isle field data in wind‐buffeting research.