National Concrete Pavement Technology Center

About the research

The load capacities of the U-bolt connections used in steel overhead sign trusses for the Iowa Department of Transportation (DOT) are not known because the bolts are used in ways that do not match the available manufacturer data. Although these U-bolt connections appear to have performed satisfactorily in the past, there has been a growing safety concern in recent years because of the need for overhead sign trusses to support larger signs at greater span lengths.

The objective of this project was to develop effective and efficient methodologies to realistically estimate the capacity of the U-bolt connections specified in the actual steel overhead sign truss (SOST) design standards. To achieve this objective, a comprehensive literature search on the utilization and modeling techniques for U-bolt connections was first conducted. Three laboratory tests were then conducted on two types of specimens with loading directions of 0° and 90° for the Type-A specimen and 0° for the Type-B specimen.

The data collected from the tests were used to calibrate the finite element model. The calibrated model was then used in a parametric study to calculate the yield and ultimate capacity of both types of specimens with various material properties and load resultant directions.

Finally, interaction diagrams were developed with limitations for design usage to estimate the capacity of the U-bolt connections with different material types and load directions.