Elastic Stability of Planar Steel Frames with Unsymmetrical Beam Loading

Unsymmetrical loads along the frame beams produce unequal axial forces in columns together with primary bending moments in the frame members. The combined effect of these two factors on the elastic buckling loads of the frames is studied. The case of one concentrated load acts at different locations on the frame beams is chosen as an example to study the effect of aforementioned factors. The analysis is applied on different types of structural systems such as braced and unbraced multistory frames. Parameters such as fixed and hinged bases, beam to column bending stiffness ratios, and beam span to column height ratios are considered. In addition, the effect of the axial stiffness of the bracing elements is taken into account. The matrix displacement method of analysis has been used throughout the study. The geometric nonlinear behavior of the members is considered by using the stability functions to modify the stiffness matrix of the individual members. Results clearly show that the combined action of the primary bending moments along with the variation of loads ratios on columns has considerable effect on the elastic buckling loads of the braced planar frames.