No Phil Swift here, but Carbon Fiber Plastics are Pretty Cool
Reinforced fiber polymer composites are finding their way into bridge repair and maintenance. Upon doing preliminary research for a candidate solution report regarding the repair of worn-down bridge components, I found several options allowing structural deficiencies to be resolved. Weakened steel gusset plates and primary members suffer from cracks within their microstructure. Another common problem regarding our steel infrastructure (especially structures exposed to the elements) is rust and corrosion. My topic of choice involves the multiple chemical treatments applied after peening, grinding, or sand blasting. These chemical compounds prove to reduce wear created by oxidation and weathering. Sadly, my report is going to end up neglecting gusset plate and member reinforcement/repair as their solutions are not related enough for a direct comparison. Although this is true, I can indeed mention it here(the final report regarding the chemical treatments will be shared later).
With members (beams) found on bridges as well as gusset plates, several major failures can occur due to applied loading. In short, the most relevant of these failures, in relation to what I had mentioned, is this. With tensile forces acting on a beam, failure due to exceeding both the elastic limit and yield point are possible. If the material passes the elastic limit, the stress is enough so that the material (in this case steel) never “reforms” or returns to its original shape; think of this as stretching a slinky too far. Passing the yield point is where the material becomes plastic (significant strain or deformation with added force). With more added stress, the ultimate strength is reached, and then failure. Often a safety factor is used in combination with the yield stress, so the amount of stress seen by the member is several times smaller that the value of the yield point (if designed properly). This way there’s a low chance the member fails (unless there was a load combination never planned for). With deteriorating steel, nearly every strength value is decreased, leaving a smaller margin for failure. Beams are like your teeth, and rain, snow, and oxidation are like candy. If you neglect them, they rot, fail, and break (I know, weird analogy). “New” technology in the form of Adhesively Bonded External Carbon Fibre Reinforced Plastic, is the equivalent of a fluoride treatment or braces. With the microstructure repaired, strips of this material can be attached to structural members. The material properties of this material are quite staggering.
According to a report from the Swiss Federal Laboratories for Materials Testing and Research (EMPA), the “CFRP strip of approximately 0.8 mm thickness” has a strength of 3300 MPa. For a unit conversion for all of us U.S. folk, that’s 68,921,945.9 pounds of force held per foot squared of cross-sectional area. Regardless of how much the strength of a member or gusset plate decreases due to microstructure crack removal, the material aims to make up for and even surpass the original strength of the member when it was originally built. On top of that, these strips do not corrode and are quite easy to handle as they have a much lower specific weight than steel. The cost is relatively low and installation does not require bridge closure. Also, according to the EMPA, the “CFRP strips subjected to compressive stresses do not fall off on low load level” like bonded steel plates. The method of attaching these strips was originally invented in France according to the EMPA. As far a usage, most of Western Europe and Japan (currently in the same state of nationwide structure deterioration that we are in, hint hint) are known to use them heavily.
