Steps:1. Dig out hole where rail was mounted using a flat-head screwdriver. Clear the area of debris using a shop vacuum (figure A).
2. Using the mounting bracket of the rail as a guide, drill a hole into the concrete using a hammer masonry bit (figure B).
3. Drive a 5/16-inch threaded rod through the rail bracket and into the new hole. Decide how much of the rod to leave above the surface and mark for your cut (figure C). Leave enough room to add a lock washer and a nut.
4. Remove the rod and clamp it to a sawhorse with a woodworker's clamp and C-clamp. Cut it to length using a hacksaw (figure D). Smooth the cut edge with a file.
5. Mix up a small amount of quick-set cement to patch the hole below the rail base. Pack the cement in the hole, then set the railing in place.
6. Insert the rod through the base and the cement and into the hole you drilled (figure E). Tap the rod down by holding a block of wood on it and smacking the wood with a hammer.
7. Place a lock washer and nut on the threaded rod (figure F). Partially tighten the nut using a socket wrench. If possible, secure the back side of the bracket by driving a new lag screw into the existing anchor.