During a fire, a lightly loaded column in a frame may fail due to the additional compressive force generated in the column if its free thermal expansion is restrained. Using the finite element method, a computer program has been developed to analyze the behavior of steel structures under fire conditions. This program is used to conduct a parametric study to assess the behavior of a column restrained by the rest of the structural system in a frame. A simple method is proposed to quantify this effect. Additional axial force in the column from both the computer analysis and the simple method are compared and close correlation is obtained. A case study is performed on a restrained column in a real fire. Observation of the failure temperature after fire confirms the applicability of the simple method. It is concluded that column thermal restraint should be taken into account when carrying out fire resistant design for columns. The proposed simple method is capable of predicting this response.