Working platforms and support caissons of offshore steel structures are often designed with plate boxes or plate girders. The important shear walls or shear webs must often be perforated to allow utilities, etc., to pass through. The failure mode of these large perforated shear panels is typically shear buckling, usually in the plastic range. The paperpresents results of a finite element buckling analysis with inelastic material behaviour and gives general guidelines for the ultimate capacity design of perforated shear plates. The parameters affecting the ultimate capacity of square plates with circular perforations under uniform shear stress were investigated using the incremental structural analysis program NISA83. Nonlinearities in material properties and geometry were taken into account in the calculation of ultimate capacities of each perforated shear plate.The parameters investigated in the study were hole size for a concentric hole and hole location for a constant hole size. Only single unreinforced round holes were considered. Three capacities were calculated for each variation of these parameters: the ultimate in-plane capacity, the elastic buckling capacity, and the ultimate elastic-plastic buckling capacity.In order to check the input data and to provide concise display of the results, a graphic postprocessor was developed as part of the research. The program NISPLOT uses colour graphics to generate plots of the nodes, element mesh, the deflected shape, and stress patterns of the loaded plates. The plots were reduced to black and white for this paper. Key words: girders, holes, steel, ultimate capacity, buckling.