Patents Assigned to Frederick Johnson
  • Prestressed rock truss
    Patent number: 4274762
    Abstract: A roof support system for mines in which prestressed rock trusses are bolted to the roof of the mine with roof bolts which each extend beyond the width of the mine gallery and the method of installing said trusses into position.
    Type: Grant
    Filed: February 26, 1979
    Date of Patent: June 23, 1981
    Assignee: Frederick Johnson
    Inventor: Stanley F. Johnson