# Second Order Effects and Elastic Critical Loads of Plane, Multistorey, Unbraced Frames

*The paper describes an approximate method of allowing for the second order effects produced by axial forces in the members of multistorey, plane frames, unbraced against side-sway. The displacements and axial forces, given by a standard linear elastic analysis, are used to calculate an equivalent system of loads which, when applied to the frame, produce approximately the same additional deformations us would be cuused by the out-of-balance axial forces. A second linear elastic solution is then performed with the equivalent set of loads applied to the frame, and the complete solution obtained by superposition of the two linear elastic solutions. A check on the validity of the method is the accuracy with which the results can be used to estimate the elastic critical load of the frame.
T.M. Roberts*