AN EMPLOYEE WAS RIGGING A BUNDLE OF ANGLE IRON PIECES ON THE BACK OF A FLAT BED TRAILER. AS THE ANGLES WERE PICKED, THEY WERE NOT RIGGED EVENLY. WHEN THE OPERATOR SET THE PIECES BACK DOWN ON T HE TRAILER, THE RACK SUPPORTS THEY WERE SETTING ON BECAME UNSTABLE AND FELL TAKING THE RIGGER WITH.