Rational shape for the load contours in L-shaped columns is proposed using the inverse method of analysis. Determination of the ultimate loads from the appropriate interaction curves derived from the shape of load contours is shown. An alternate and simple method based on the concept of an equivalent square or rectangular column is proposed to determine the theoretical ultimate loads using the interaction diagrams in square or rectangular columns. Theoretical loads computed by the two proposed methods are compared with the test results of 45 columns. © ASCE.