Effective Length Factor for Transverse Buckling of Single-Column Bridge Bents

Design for stability requires quantifying the effective length of columns. While guidance adopted from building design is sufficient for many cases in bridge design, conservative assumptions are often made when assessing the effective length for transverse buckling of single-column bents. The torsional stiffness of some superstructure types can restrain the rotation at the top of the column, reducing the effective length. However, due to a lack of guidance, this restraint is often neglected in design. Equations for the effective length factor of transverse buckling of single-column bents were derived by solving the governing differential equation. The equations were verified by comparison with eigenvalue buckling results from matrix structural analysis software. With an idealized fixed base, the proposed effective length factor varies from K=2 when the superstructure torsional stiffness is zero to K=1 as the superstructure torsional stiffness approaches infinity. Effective length factors that account for base flexibility were also derived. The equations developed in this work provide for a more accurate evaluation of the effective length of single-column bents and will enable more efficient designs.