AN ABSTRACT OF THE THESIS OF Sujan Shrestha, for the Master of Science degree in Civil Engineering, presented on March 3, 2015, at Southern Illinois University, Carbondale. TITLE: POST BUCKLING RESPONSE OF SWAY COLUMNS UNDER MECHANICAL AND THERMAL (FIRE) LOADS MAJOR PROFESSOR: Dr. Aslam Kassimali, Ph.D. The post-buckling response of sway columns under mechanical and thermal loadings are presented by using the geometrical nonlinear analysis. For thermal analysis, the columns are assumed to be fully restrained in their axial directions. The method of analysis uses Beam-Column theory which is based on an Eulerian (corotational) formulation. Numerical solutions are shown for the post-buckling response of sway columns. The numerical investigations of the geometrically nonlinear analysis of sway columns were carried out with three different boundary conditions of sway columns as suggested by AISC, under mechanical loading and temperature changes. The sway columns considered are the cases `c', `e' and `f' in Table C-A-7.1 of AISC Manual (2011). These were modeled and analyzed to predict the post-buckling response under the mechanical and thermal loads. Furthermore, for each of these support conditions, the effects of slenderness ratios on the post-buckling response were analyzed by considering the slenderness ratios of 50,125 and 200. Also, the effects on post-buckling strength were observed keeping the same slenderness ratios but varying rotational end conditions of sway columns. Many useful conclusions can be drawn from this study. The more important conclusions are: 1) As all unrestrained sway columns undergo excessive deformation under mechanical loading, they do not possess significant post-buckling strength once the loading reaches the buckling load. 2) All restrained sway columns undergo much smaller deformations under thermal loading as compared to mechanical loading; thus significant post-buckling strength is achieved even after reaching the buckling temperature. This post-buckling strength can be considered during the design of structures which will aid in safe and economical structures. 3) Slenderness ratios play an important role on post-buckling strength only in thermal analysis but not in mechanical analysis. Increase in slenderness ratio tends to decrease the post-buckling relative deformation of the columns under thermal loading but has no such effect under mechanical loading. 4) Rotational end conditions also play significant role on post-buckling strength during thermal analysis but not during mechanical analysis. Keeping the slenderness ratio constant and varying the rotational end conditions, the post-buckling strength of all sway columns remains same under mechanical loading but is different under thermal loading.