Behavior of Larger-Diameter Strands in the Disturbed Region of Prestressed Concrete Girders

Traditionally, the Tennessee Department of Transportation has been using American Association of State Highway and Transportation Officials – Prestressed/Precast Concrete Institute Bulb Tee (AASHTO-PCI BT) sections for its prestressed concrete bridges. These sections have limited bottom flange widths where the prestressing strands are located. To increase span capacities of these sections, other States have adopted new sections with a wider flange width. Producers in Tennessee have raised concerns about the cost of the new steel forms to accommodate these new sections. As an alternative, this research examines the use of larger diameter strand in conjunction with high-strength concrete and standard AASHTO sections as an innovative and cost effective approach to increase girder capacity to the maximum shipping limit.

Development and transfer lengths for larger diameter strands were found to be much shorter than current models predict. A methodology is proposed for the determination of development length for any size strand. In this study, the effectiveness of casting strand ends within an end diaphragm is demonstrated.

A full-scale bridge beam with larger diameter strand with a composite deck was cast and tested. The behavioral results of this beam were compared to existing models. The existing models were found to accurately predict the behavior of the beam.

This dissertation finds that larger diameter stands can be successfully used in bridge beams. Using these strands will result in reduced bridge costs for spans under 160 feet.