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Finite Element Analysis of the Wolf Creek Multispan Curved Girder Bridge
Lydzinski, John C.
Baber, Thomas Thaxton,
Jose P. Gomez
Year: 2008
VTRC No.: 08-CR6
Abstract: The use of curved girder bridges in highway construction has grown steadily during the last 40 years. Today, roughly 25% of newly constructed bridges have a curved alignment. Curved girder bridges have numerous complicating geometric features that distinguish them from bridges on a straight alignment. Most notable of these features is that longitudinal bending and torsion do not decouple. Although considerable research has been conducted into curved girder bridges, and many of the fundamental aspects of girder and plate behavior have been explored, further research into the behavior and modeling of these bridges as a whole is warranted. This study developed two finite element models for the Wolf Creek Bridge, a four-plate girder bridge located in Bland County, Virginia. Both models were constructed using plate elements in ANSYS, which permits both beam and plate behavior of the girders to be reproduced. A series of convergence studies were conducted to validate the level of discretization employed in the final model. The first model employs a rigid pier assumption that is common to many design studies. A large finite element model of the bridge piers was constructed to estimate the actual pier stiffness and dynamic characteristics. The pier natural frequencies were found to be in the same range as the lower frequencies, indicating that coupling of pier and superstructure motion is important. A simplified "frame-type" pier model was constructed to approximate the pier stiffness and mass distribution with many fewer degrees of freedom than the original pier model, and this simplified model was introduced into the superstructure model. The resulting bridge model has significantly different natural frequencies and mode shapes than the original rigid pier model. Differences are particularly noticeable in the combined vertical bending/torsion modes, suggesting that accurate models of curved girder bridges should include pier flexibility. The model has been retained for use as a numerical test bed to compare with field vibration data and for subsequent studies on live load distribution in curved girder bridges. The study recommends consideration of the use of the finite element method as an analysis tool in the design of curved girder bridge structures and the incorporation of pier flexibility in the analysis.