Load Sharing in Transversely Post-Tensioned Pre-cast Box Girder Skew Bridges

Railway operators often use precast concrete box girders for railway bridges. In many cases, these box girders are placed side by side without a concrete deck on top. Sometimes these box girders are post-tensioned transversely to hold the girders together. The load distribution among the girders is easy to calculate when there is no transverse post-tensioning. Once the transverse post tensioning is introduced, the load sharing among the girders becomes more challenging to quantify. The way such a bridge is modeled will significantly affect the results of the analysis, especially when the bridge is at a skew. The assumptions made regarding the post-tensioning and how it is modeled will have a significant effect on the results due to the skew effect combined with how these girders interact. American Railway Engineering and Maintenance-of-way Association – AREMA – limits the skew angle for precast concrete slab and box girder railway bridges to 15 degrees while it allows skews up to 30 degrees for precast concrete I-girders and T-girders and 60 degrees skew angles for Cast-in-place concrete slabs and girders. AREMA does not specify limits for the skew angle of steel bridge structures. These limitations are established by way of surveying railway operators regarding their inventory of bridges rather than a scientific study analyzing the effects of such skew angles on the different types of bridges. In this paper the effect of transverse post tensioning on load sharing of precast box girder bridges is investigated and discussed for square and skew bridges. The effect of the skew on the behavior of such a bridge is also discussed and investigated through a finite element model.