Assessment of different rotation prevention systems for bridge deck construction through field monitoring

During bridge deck construction, the construction loads often transfer through the formwork system and overhang brackets to the bridge girders, leading to significant torsional moments acting on the exterior girder. These torsional moments can cause excessive rotation on the exterior girder, resulting in many safety and maintenance issues, such as thin deck, reduced concrete cover, and cracking in the service stage. To prevent the exterior girder from excessive rotation, different types of rotation prevention systems are currently used in the United States. One of the traditional rotation prevention systems is the block-tie system, which uses transverse tie bars, or diagonal tie bars, combined with timber blocks to reduce the exterior girder rotation. Another rotation prevention system is the pipe-tie system, which is a combination of transverse ties and diagonal pipes. However, the effectiveness of these systems has never been evaluated through field bridge monitoring. In this study, three bridges were instrumented with different types of rotation prevention systems. Also, the transverse rotation and strain in rotation prevention systems were recorded during bridge deck construction using a bridge monitoring system. Besides, the maximum rotations and strain values were compared amongst these three bridges. The results show that the block-transverse-tie and block-diagonal-tie systems are not as effective as pipe-system for limiting the exterior girder rotation. Therefore, the pipe-tie system is recommended for bridge deck construction in order to mitigate the issues caused by excessive exterior girder rotation.