Project Overview
The Christmasville Road Bridge is the oldest precast, prestressed concrete bridge in the United States. Still in service 73 years after its construction, the bridge’s superstructure remains in “Fair” condition, a testament to the durability of its design and construction.
As the first precast, prestressed concrete bridge, the bridge faced several challenges during developments. The Freyssinet system was employed; however, at the time, there were no U.S. bridge design specifications for prestressed concrete and no established fabrication facility in Tennessee. Despite these obstacles, engineers pioneered an innovative approach to beam construction.
The beam cross-sections were precast concrete modular blocks, cast in segments and assembled in a stressing bed being prestressed into complete beams. These adjacent beams were then transported to the job site to form the superstructure. The gap formed by the beam shape was filled with concrete to encapsulate the prestressing strands running along the exterior of the individual beams. Notably, this project utilized individual 7-wire prestressing strands, which are the industry standards employed today.
Although the bridge was not designed to meet any formal design codes at the time, its longevity—remaining in service for over seven decades with continued use expected—demonstrates the remarkable resilience of precast concrete construction. This pioneering structure stands as an enduring example of innovation and durability in bridge engineering. |