Plated girders have been extensively used in steel bridge construction since the 19th century. Over the past century, the effective width method was developed to take the nonlinearities resulting from shear lag and plate buckling into account. This method leads to having a cross-section with a reduced area in which the stress can linear be considered. The section properties of the reduced cross-section can be used for determining the resistance and the longitudinal stress in the plated girder. The reduction of the cross-section area takes place in two steps. First, the section area is reduced in local scale for subpanels that have class 4, and local effective section properties will be determined. Second, the local effective cross-section is reduced to consider the overall buckling, which can be plate-like buckling, column-like buckling, or their interaction.
The longitudinal compressive stress that can be determined from effective section properties in a box girder with pure bending moment will be higher since the effective section includes a reduced second moment of inertia and an increased distance between the neutral line and the compression flange. This master thesis aims to assess whether effective section properties accurately determine the compression stress magnitude in box sections with pure bending moment that remain unaffected by local buckling and experience overall buckling in the form of pure column-like buckling in the compression flange.
The findings indicate that if the subpanels of the isolated compression plate are stocky, and the overall buckling failure has the form of pure column-like buckling, the stress, and behavior remain within the elastic region up to column-like buckling failure. There does not exist any sudden increase in compression stress magnitude in the plate. The analytical method that can address the maximum magnitude of the compression stress in the plate has contribution of the gross section area of the plate.
If such a stiffened plate with pure column-like buckling failure and stocky subpanels serves as the compression flange of a box girder, the same conclusion was reached regarding determining the first moment of inertia. However, in the presence of the slender web in the cross-section, the effective area of the web, in combination with the gross section area of compression flange should be considered for determining the section properties with which the maximum longitudinal stress can be determined.