Lateral stability of reinforced-concrete beams with initial imperfections

The paper presents the results of an analytical study aimed at investigating the lateral stability of reinforced-concrete (RC) beams with initial geometric imperfections. Based on the experimental results in the literature, a general buckling moment expression was developed, linking the limit moment of a RC beam with an initial sweep and twist to the critical moment of its geometrically perfect configuration. This expression takes into account the initial geometric and material non-linearities of the beams, the elastic-inelastic material properties of concrete and steel, the cracking of concrete due to restrained shrinkage and in-plane flexure, and the contribution of longitudinal reinforcement to stability. The formula was applied to three standard types of Aashto I-girders to determine the critical unbraced length of each type. Finally, an analytical equation was developed for estimating the lateral deflections of RC beams with initial geometric imperfections. The limit moment and lateral deflection equations were shown to provide close and conservative estimates for RC beams.