QUESTION: We have a job where a structural beam in a parking garage has been found to be deficient. What are our options for repairing this beam?
ANSWER: One way to repair this is using carbon fiber systems. These systems are a carbon fiber fabric and epoxy where the carbon fiber acts as external reinforcement and are used when the internal reinforcement is missing or damaged. But these are passive systems — they are only taking load after the carbon fiber is installed. So if there is deflection, these systems are not going to do anything to reverse that or to pick up the dead load of the structure. You would have to go with something more active like external post-tensioning where PT tendons or rods are anchored at the ends of the beam and draped down to midspan and stressed to take the load and reverse the deflection. And almost any strengthening method only works if the concrete is sound. If there is ongoing corrosion, carbon fiber isn’t going to stop that. An engineer would have to inspect that beam to tell you if it will be successful. Remember that a situation like this is a safety issue so don’t get yourself into a situation where you are accepting the responsibility. The owner has to make some accommodations to get the job done properly.
This question and answer was generated during the Breakfast with the Experts at the 2015 World of Concrete, sponsored by BASF. If you have problems on your jobs that you would like to pose to the experts, plan now to attend one or more of the 2016 breakfasts. Another question: "Getting Consistent Concrete at the Jobsite."