Composite Beam System for High Speed Rail Bridges Uses Hardwire For Tensile Reinforcement

04 June 2004

Teng & Associates have further developed a structural Plasticon-Optimized Composite Beam System for use in bridge structures.

The ""Hybrid-Composite Beams"" are comprised of three main sub-components that are a shell, compression reinforcement and tension reinforcement. In the preferred embodiment, the shell is comprised of a fibre reinforced plastic (FRP) box beam.

The compression reinforcement consists of portland cement concrete which is pumped into a profiled conduit within the beam shell. The tension reinforcement consists of Hardwire, anchored at the ends of the compression reinforcement. The orientation of these sub-components is further evident as demonstrated graphically in the figure at the top right.

John Hillman, lead engineer and developer of this system from Teng & Associates, said ""We were expecting to encounter most of our difficulties in lay-up from Hardwire, not the glass fabrics. By the time we were done, we found the opposite to be true. Hardwire was much easier to work with than the glass; no masks, no gloves, easier to cut, easier to control tolerances and positioning in the mould, Hardwire is the perfect material for our application. We were also concerned that placing 90 degree bends at both ends of a hard length piece would result in an impossible fit. After studying the required lay-up, we were able to cut and bend the Hardwire to extremely close tolerances with simple hand shears and a manually operated brake press. The ease in fabrication was just the icing on the cake. The structural properties and lay-up qualities of Hardwire make it the only logical choice for the tension component of the Hybrid-Composite Beams.""

A study funded by the High-Speed Rail IDEA Program of the Transportation Research Board has recently been completed that addressed cost metrics, design limit states and fabrication issues related to the manufacturing of the hybrid-composite beam. This study also included the design, fabrication and load testing of the first prototype hybrid-composite beam.

The HSR-IDEA project findings confirmed that the hybrid-composite beam can be manufactured with minimum tooling costs and that the girders can be predictably designed to satisfy the strength and serviceability requirements for railroad and highway bridge structures. Cost metrics indicate that the hybrid-composite beam does appear to offer a cost-effective alternate to concrete or steel beams. What distinguishes the hybrid-composite girder from beams of conventional materials is that the FRP materials are claimed to offer greater corrosion resistance and potentially longer life, and because of their reduced weight, shipping and erection costs for the hybrid-composite girders offer a distinct advantage.

Finally, Hillman adds that because satisfying serviceability requirements typically drives the design of the hybrid-composite girders, these girders can provide additional strength capacity beyond what is required by design codes. With these and other inherent benefits, the hybrid-composite girder offers an attractive alternative to consider in the construction of new railroad and highway bridges as well as the reconstruction of the existing bridge inventory.

The Composite Bean System has been presented at a number of engineering events over the past year, and having been refined and developed with the support from developers and vendors, Teng & Associates are now in discussions with several end users - representing both railroad and highway applications - regarding pilot projects to introduce the technology into service.

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