LAUSR

Abstract For the first time, this paper investigates the stability and stiffness analysis of a single column in a specific case with the connected oblique beam. In this case, the modification factors are analytically derived such that the stiffness of oblique beam is included in the calculation of the well- known parameters G T and G B . The effective length factor for such column can be obtained by these modified G T and G B . It is noted that the effective length factor of the column in the mentioned specific case is assessed for the first time in this research. In the following, a single span- one story steel frame is investigated to determine the lateral stiffness of the frame. In this frame, the applied lateral load and the structural frame are not on the same plane. Accordingly, it is also focused on the investigation of the effects of hinge existed in the beam as well as the changing of column base connection from fixed to hinged forms. The structure is considered as a 3- dimensional steel frame for the analysis upon the least work principle. All effective factors are taken into account including axial and shear loads as well as bending and torsional moments. At the end of the analysis, a relation is obtained through response surface method. The lateral stiffness can be calculated by the derived relation based on the specifications of the steel frame such as geometrical properties of the employed sections, specification of the used material and deviation angle of the beam.