Behavior of Horizontally Curved I-Girders during Lifting

Several stages of performance need to be considered during the design of curved I-girders, including both the construction stage and the in-service conditions. Girder stability during the early stages of construction can be difficult to assess because the girders, at times, have little or no bracing present. One stage when there is no bracing present occurs when the girders are picked up from the ground or transport trucks by cranes and lifted into place. To better understand girder response during this critical stage, field studies were conducted on horizontally curved I-girders to measure rotations and stresses during the lifting process. This paper provides details of a semianalytical solution to predict the buckling and deformational responses of straight and curved girder segments during lifting. The deformations can be compared with rotational limits that were established to minimize problems with making connections to previously erected girder segments. The total rotational deformations of a horizontally curved girder result from two distinct components: (1) rigid-body rotation and (2) rotation caused by the girder cross-sectional twist owing to torsion from the girder’s self-weight. A spreadsheet design tool, UT Lift, was developed to provide critical information for evaluating the rotational behavior of a horizontally curved I-girder during lifting and to estimate its lateral-torsional buckling capacity. An example of UT Lift’s capabilities is presented along with background information on its development. Recommendations are given for safely lifting and erecting horizontally curved steel I-girders.