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Behavior of Horizontally Curved Steel I-Girders During Lifting

Andrew Clayton Schuh

2008

The analysis of curved I-girders can be challenging because of the interaction of torsional and bending stresses. The St. Venant torsional stiffness of I-shaped girders is relatively small due to the open section. The warping stiffness of the girder therefore plays an important part in resisting the torques that can result from horizontal curvature. In highly curved girders, the warping stresses can become large and perhaps even greater than the bending stresses. There is little guidance, however, from AASHTO or other literature regarding how to account for these stresses or how to consider girder safety and serviceability during critical stages for girder stability such as the early stages of construction when all of the bracing is not installed. The potentially critical construction stage covered in this thesis is the lifting of curved I-girders. Field studies were conducted where data was collected for the validation of a 3-D finite element model. The model was used to improve understanding of curved girder behavior during lifting.

Upon validation, the finite element model was used to conduct a parametric study of the buckling behavior of a curved girder during lifting. Specifically, the effect of the locations where the crane’s lifting apparatus is attached along the girder length is investigated. The serviceability aspect of this parameter i.e. potentially excessive rotations is also discussed. Recommendations are presented to provide guidance for the safe lifting of horizontally curved steel I-girders.

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