Analysis of Unbraced Multistory Steel Rigid Frames

A compatibility method of analysis is developed for the study of the inelastic in-plane behavior of multistory steel rigid frames subject to sidesway. The method provides for the following conditions to be satisfied throughout the frame simultaneously: (1) The internal forces are in equilibrium with the external forces on the deflected frame; (2) the curvature of each portion of each member satisfies the appropriate nonlinear moment-thrust-curvature relationship; and (3) the distortions of all the parts satisfy the condition of continuity of the frame. The analysis is obtained by successive approximations. A special technique is developed to facilitate the analysis at the condition of ultimate load, and in the early stages of instability of the frame. Good agreement is obtained with tests conducted by others on three full-scale frames.