Abstract
Door gaard beams have been developed through the utiliza-tion of ultra high strength steel. At first, the sheet We-tal gauge was reduced in proportion to the strength of theultra high strength without changing the shape of the beamsection. This caused beam buckling and did not meet gaardbeam specifications. Analyzing this phenomenon in accor-dance vrth the buckling theory of thin plates, a designcriteria that makes effectave use of the advantages of ul-tra high strength was developed.