Optimizing Cross Frame Plan Orientation in a Horizontally Curved Steel Bridge - Is it Worth it?

Unlike straight bridges where cross frames are considered “secondary members”, the interaction of bending and torsion in horizontally curved bridges renders these components primary load carrying members. The effect of curvature on behavior has been understood to be more critical during the construction of these structures due to a lack of a large, hardened, concrete deck that helps to stiffen and stabilize the entire system. Therefore, cross frames play a more important role in providing stability to the girders, helping to restrain lateral torsional buckling and to resist lateral loads in curved bridges during construction. This work examines the effects of using what is termed skewed bracing on the behavior of horizontally curved I-girder bridges having nonskewed abutments during construction. For this, the performance of this bracing system is compared against that for more common type of bracing for horizontally curved bridges, bracing oriented normal to girder web, using three-dimensional, nonlinear finite element analysis. The main objective of this research is to examine optimizing bracing plan orientation in horizontally curved, I-girder, bridges to maintain geometric control and acceptable stress levels during construction while concurrently possibly reducing the number of required intermediate braces. Studies completed on a single-span bridge having small radius of curvature indicated better load sharing between the girders during construction when skewed bracing was used. As a result, exterior girder deformations and rotations, which generally are the largest, decreased when compared against those in a bridge having normal bracing.

View content