Transverse Analysis and Field Measurements of Segmental Box Girder Wings

摘要

Parapets placed on bridge deck surfaces, commonly known as barriers are purposes omitted from the structural analysis model for design or load rating. Barriers should not be considered primary structural members because they are designed to withstand the impact of a vehicular collision. After a forceful collision, a barrier may sustain some structural damage and would no longer support or strengthen the bridge deck. However, when completely intact, these secondary structural members do, significantly, absorb and distribute any applied load, thus acting as fully functional structural members. The amount that appurtenances, specifically parapets, contribute to deck strength is of interest to permitting agencies, such as the Florida Department of Transportation (FDOT). For a concrete segmental box girder bridge, load ratings for oversized load permits are currently determined with a calculation that involves the transverse analysis of the bridge without factoring in the extra strength of fully intact appurtenances. Moreover, within the transverse analysis, the maximum moment generated from the live load is typically calculated from Homberg charts. These generalized influence surfaces were designed based on plate surface models and are conservative. When added to the standard 'error on the side of caution' design methods, this moment estimation and the lack of consideration for the appurtenances create a conservative transverse load rating for the bridge. With 3D finite element bridge models, created using LUSAS, it is shown, qualitatively and quantitatively, how much of an effect the barrier has on the live load distribution for three concrete segmental box girder bridges located in the Florida Keys. Data obtained from these models is directly compared to measurements obtained from FDOT load tests on the actual bridges and also to predictions made from Homberg influence surfaces. Modifying the current method of test rating, for structurally sound bridges, with fully functional appurtenances should interest permitting agencies and would prove beneficial to those transporting oversized loads.