New Aspects Concerning Inelastic Instability of Steel Structures

Plastic design procedures necessitated a reconsideration of the problem of inelastic instability of steel structures. Theories developed for members of continuously strain-hardening materials cannot be applied indiscriminately to structural steel sections since this material exhibits an extended yield level at a constant stress before the onset of strain-hardening. Besides, residual stresses introduced by rolling and fabrication procedures have a marked influence on the buckling strength. Recent developments in the field of column and plate buckling will be discussed with respect to the previously mentioned effects. The column- buckling problem has been solved for the entire elastic and inelastic range. For plates, a solution for the beginning of strain-hardening has been derived using the theory of orthotropic plates with appropriate moduli developed from theoretical and experimental considerations. After mentioning the shortcomings of the linear buckling theory in some cases of plate and shell buckling, it is indicated that this theory is unable to predict the static strength of plate girders.