Effect of Skew Angle on the Rotation of Exterior Girders During Construction

Abstract

Bridge designers tend to extend the deck slab width beyond the exterior girders, over a distance called the overhang, to increase the width of the bridge without adding extra girders. Moreover, the screed machine used in finishing the surface of the deck slab usually rests on the edges of the overhang. The machine weight combined with the weight of the fresh concrete leads to torsional moments in the exterior girder. Hence, excessive rotations in the exterior girder arise and they lead to issues such as lose of concrete cover, instability of the superstructure and non-uniform deck slab thickness. Many Departments of Transportation are facing this problem and there are no specific guidelines to compute this rotation. Contractors usually use temporary bracing systems such as timber blocks and diagonal or transverse ties to reduce the rotation. However, these methods were found to be not very effective. The bridge geometrical parameters play a significant role in this phenomenon, and one of these parameters is the skew angle. Skewed bridges are popular because of the geometrical conditions imposed by roads alignment and the geographical barriers to cross, which leads to a non-perpendicular crossing. In these cases, skewed bridges are more economical than an equivalent straight bridge. This study focuses on the effect of skew angles on the rotation in steel girder bridges. The purpose of this study is to examine different skew angles using Finite Element Analysis (FEA) of bridges subjected to construction loads. SAP2000 is used to develop the FE models of these bridges. The findings of this research will provide designers and contractors a better understanding of the effect of skew angles on the rotation of exterior girders and opens the way for future research to develop methods to reduce the rotation to satisfactory limits.