Tolerances of initial deflections of steel plates and strength of I cross-section in compression and bending☆

Abstract A further step towards the strength-based assessment of fabrication tolerances of steel plates is attempted. The procedure presented derives from the idea that the strength reduction of an I cross-section due to initial deflection should not exceed, irrespective of the web-plate slenderness and of the type of loading, the maximum strength reduction for the case of uniform compression. Thus, despite the degrading influence of initial deflections, any I cross-section could be exploited up to a certain percentage of the strength of the cross-section with an initially flat web plate. The theoretical ultimate loads are calculated using the large deflection theory of thin elastic plates. Employing the so called ‘energy measure’ of imperfections a less conservative correspondence between the predominant single mode initial deflection, adopted for specifying the tolerances, and of the most dangerous one — corresponding to the initial buckling mode of the plate — applied in calculations of strength, is established. The application of the approach to the case of an unstiffened steel plate girder of I cross-section shows that the currently applied tolerances may be substantially relaxed.