Nonlinear Behavior of Structural Plane Frames

The deformations that occur in an actual structural frame may significantly influence the joints’ equations of equilibrium and hence the theoretical load-carrying capacity. The finite deflection theory is introduced to deal with the influence of finite displacements on the behavior of structural frames. The method is applied to rigid-jointed pitched roof portal frame and the results are presented in the form of nondimensional graphs. The bowing functions (b₁ and b₂) and stability functions (s and c) influence significantly the behavior of this type of frame at high load parameter which indicates their importance for the estimation of the theoretical load-carrying capacity. The classical phenomenon of elastic critical load needs to be reconsidered since the load-deflection curve does not produce the buckling phenomenon. In general, the nonlinear behavior of structural frames as influenced by instability, bowing and finite deflections are studied. A relaxation method has been developed for solving the problem because direct solution is not possible.