Anchorage systems normally include, at a minimum, a building structure and an anchorage device to which the worker will tie off. Anchors are fixed to a strong structural member. Anchors are not effective if they are attached to weak materials. Many anchors are removed when they are no longer needed. Other anchors are designed to be left in place for future use (e.g., repeated servicing), or are covered over during the job (e.g., with roofing shingles), or are cut flush with the surrounding surface (e.g., concrete bolt-style anchor protruding from a wall).