Lateral elastic postbuckling analysis of elastically rotationally restrained I beam-columns

Using a variational approach the field equations and the associated boundary conditions governing the lateral elastic postbuckling response of rotationally restrained I beam-columns under uniform bending and axial compression are established. The stability of the critical state associated with a symmetric bifurcation point is thoroughly discussed including the warping effect of the cross section and geometric nonlinearities due to a nonlinear bending moment-curvature relationship. Moreover, the initial postbuckling path is readily determined via an approximate analytic technique. It is found that the beam-columns exhibit postbuckling strength and, therefore, are not sensitive to initial geometric imperfections. However, the postbuckling equilibrium path is quite shallow, and hence the load-carrying capacity of such beam-columns above the critical state is rather limited.