Some times the only option is to anchor into a support beam. These are full of PT cable and rebar. Seeing as these are the load-bearing skeleton of the structure it is very important to ensure they will not be compromised in any way. Fortunately, GPR can locate all the steel in the support and locate safe areas for anchors to be placed. If you are a building owner or manager make sure any work being done to beams is always scanned.