Lateral-Torsional-Roll Response of Long Precast Concrete Girders: Uncracked Buckling Load

Abstract

Lateral buckling of precast and prestressed concrete girders that are not fully restrained against twisting rota¬tions at their ends may occur during lifting and handling. Typically, the critical load at which this instability oc¬curs has been estimated by ignoring torsional deforma¬tions. Although that approach permits a closed-formed solution, it is unconservative. This study includes the torsional deformations and develops a series solution for the simplest case of an end-supported girder. The solu¬tion is then extended to include overhangs. A balance between accuracy and usability is struck by truncating to a one-mode solution. By comparing with two known special cases, the first term is found to be sufficiently accurate while clearly illustrating the effect of torsional flexibility on girder stability. Accounting for torsional deformations reduces the predicted buckling load by an amount that can be conveniently defined with a knockdown factor applied to the traditional buckling load that ignores torsion. In this sense, the effect of torsion is separated from lateral bending. Downward (major-axis) deflection improves stability, whereas that net upward camber does the op¬posite. Use of lightweight concrete reduces the safety factor against lateral buckling.