PCI eLearning Course T520: Girder Stability-Introductory Material and Hanging Girders-Mast 1989, Lateral Stability Part 1

Mast 1989, Lateral Stability Part 1

Pdf Summary

The lateral stability of long prestressed concrete beams has become increasingly important as beam spans have grown. Many designers only consider lateral stability of the finished structure, leaving the problems of stability during construction to the fabricators and contractors. This special report addresses the issue of lateral stability during handling and shipping. The author presents a theory for the lateral bending stability of prestressed concrete girders that are free to roll at the supports. The factor of safety is dependent on the height of the roll axis, the initial lateral eccentricity, the lateral stiffness, and the maximum permissible tilt angle of the beam. The theory is compared to the PCI Design Handbook provisions for lateral stability during lifting. The author provides an example and a simple computer program for solving more general cases. The conclusions of the report state that the stability and safety of a hanging beam are dependent on the initial lateral eccentricity, height of the roll axis, theoretical lateral deflection of the center of gravity of the beam, and maximum permissible tilt angle. The net factor of safety is the lesser factor of safety calculated from the two equations derived in the report. The effect of lifting point location on beam stability is also discussed, with moving the lifting point in from the end being the most effective method of improving lateral stability. The report also mentions other methods for improving lateral stability and modifying beam cross sections. A preview of Part 2 of the report, which extends the analysis to beams supported on flexible supports, is included.

Keywords

lateral stability

prestressed concrete beams

beam spans

construction stability

lateral bending stability

roll axis

lateral eccentricity

tilt angle

lifting point location

beam cross sections