Many of the railroad bridges in the United States were built in the early 1900s or before. Time and tonnage have taken their toll on these structures, and railroads today are confronted with the necessity to replace them or upgrade them with selective replacement of critical components.
The beam system consists of three main components. The first of these is the plastic beam shell that encapsulates the other two components. The second component is the compression reinforcement that consists of a portland cement grout or concrete arch that is pumped or pressure injected into a continuous conduit fabricated into the beam shell. The third component is the tension reinforcement that is used to equilibrate the internal forces in the compression reinforcing. This tension reinforcing could consist of unidirectional carbon or glass fibers or steel fibers anchored to the ends of the concrete arch. The objective of this project was to develop a cost-competitive alternative to conventional steel or reinforced concrete beams that would be lighter in weight and resistant to corrosion. The concept that was explored is a composite structural beam system using both plastic and concrete components.
This concept exploration project included the fabircation and testing of a prototype bridge beam, and cost comparisons with steel and concrete beams. The results demonstrated the concept had real potential. Accordingly, a follow-on contract was awarded (HSR-43), to fabricate and field test a bridge span of these hybrid-composite beams at the Transportation Technology Center in Pueblo, Colorado.
