In this paper, we discuss the buckling stress relation expression of the box beams representing the automobile body frame which is composed of thin plates under axial compression load and torsional torque. First, it is shown that the well-known buckling stress relation expressions of the rectangular plate under combined stress have similarities, and they are related by one coefficient. Based on these well-known expressions, the buckling stress relation expression of the box beams is proposed. And the accuracy of this expression is validated by comparison with the results of the finite element method (FEM). As the results, it is shown that the proposed expression of the box beams under compression and shear stresses are sufficiently useful.
