Center for Transportation Research and Education

About the research

Although they have appeared to perform well, the actual load capacities of U-bolt connections used in Iowa Department of Transportation (DOT) steel overhead sign trusses (SOST) are not known because they are used in ways that do not match available manufacturer data.

A previous phase of this research initiated the determination of the load capacity of these U-bolt connections through limited laboratory tests and parametric studies performed on finite element models. It was noted at the conclusion of that work that additional laboratory tests should be performed on high-strength U-bolts subject to static loading in multiple directions and that the fatigue performance of the U-bolt connection should be investigated to understand the impact of repeated loads near the yield load. In order to resolve the concerns left from the previous phase of this research, this study will investigate the fatigue behavior of the U-bolt connections, evaluate the fatigue capacity of the U-bolt connections used on SOST, and validate the analytical results developed in the previous research. To achieve the proposed objectives, an 8-task, 36-month research plan was developed, which includes field monitoring, analytical simulation, and multiple stages of laboratory testing. The research results will assist engineers in effectively and efficiently designing overhead sign support sign structures without concern for the capacity and safety of the U-bolt connections.