Elastic and Inelastic Buckling of Portal Frames

The critical vertical and horizontal loads that will cause sidesway buckling of an inelastic portal frame hinged at the base are determined. The elastic portal frame subjected to both lateral and vertical loads is shown to be similar to the elastic beam column in that it would not buckle. Similar to the inelastic beam column, the inelastic portal frame has well-defined vertical and lateral buckling loads. A trial method incorporating the numerical integration procedure for inelastic columns was developed for obtaining the sidesway deflection under given loadings. The effects of various loadings on the frame are shown, as related to the design criteria. For various loadings, the current (1963) AISC design specifications are shown to vary from accurate to slightly unsafe.