Testing Begins on Hybrid-Composite Railroad Bridge Built Near Pueblo

A full-size locomotive pulling 26 heavy-axle-load coal cars traversed the first composite railroad bridge near Pueblo in November. The live-load test was conducted on the 2.7-mi Facility for Accelerated Service Testing Loop at the Transportation Technology Center, a transportation research and testing facility operated by TTCI, a subsidiary of the Association of American Railroads.

The bridge supporting the locomotive is a 30-ft span comprised of eight hybrid-composite beams, said John Hillman, senior associate with Teng & Associates in Chicago and the structural engineer for the project.

Hillman is also the founder and president of HC Bridge Co., a firm specializing in the development of hybrid-composite structural alternatives.

"I’ve always been fascinated by the simplicity and elegance of the load paths in arch structures," said Hillman. "When I was introduced to vacuum-assisted resin transfer methods for composite manufacturing, it seemed logical to me to combine this versatility with the strength and economy of conventional building materials, yet still benefit from the lightweight and corrosion resistant nature of composite materials."

With this goal in mind, Hillman set out in the mid-1990s to design and build a lighter, more durable bridge structure. Known as the Hillman-Composite Beam, or HCB, these beams are designed to be stronger, lighter and more corrosion resistant than the standard concrete and steel beams traditionally used in infrastructure.

"The response of the bridge matched exactly the predicted strains and displacements calculated in accordance with the limits specified in the American Railway Engineering and Maintenance-of-Way Association design codes," said Hillman. "With the performance of the HCB validated and recognized by the rail community, the next step is production of a prototype for extended testing in Pueblo. Our ultimate goal is for the HCB to become the standard bridge technology for revenue service on the Class 1 railroads."

In its simplest embodiment, the HCB is comprised of three main subcomponents shell, compression reinforcement and tension reinforcement. The compression reinforcement consists of self-consolidated concrete pumped into a profiled conduit within the beam shell. The tension reinforcement consists of Hardwire steel reinforcing fabrics that run along the bottom flanges of the beams.

Essentially, the beam functions like a tied arch in a glass box, and Hillman said he used this principle to improve load performance and decrease weight. The concrete arch is tied at each end with multiple layers of Hardwire steel reinforcements, which run along the bottom flange. The unique high-strength steel fabrics, which consist of thin, twisted, 450,000-psi, high-tensile steel cords, are 11 times stronger than a typical steel plate.

"Fifty years ago, we started using prestressed concrete for railroad bridges, and that was considered new technology at the time," said TTCI’s Principal Engineer Duane Otter. "Since that time, they have become a mainstay for railroad bridge construction. Looking ahead, we see the HCB technology as having the potential to become a new mainstay."

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