Rotational Centers of Plates Regulating Distortion of Box Girders

In thin‐walled prismatic members, three different points regulate the cross‐sectional properties. Among these, the centroid and shear center are important for beams with nondeformable cross section, while the rotational centers of plates are important for beams with deformable cross sections. This paper provides methods for determining the rotational centers of plates regarding the distortional problems of thin‐walled, multicell box girders, and proves that the rotational centers of plates can be explained by the same concept as the shear center. The general characters of distortion and location of the rotational center of each plate are derived for typical box girders with a trapezoidal section. A method for resolution of an eccentric load into components of pure bending, pure torsion, and pure distortions is also given.