With the advance of engineering know-how, high strength steel, and the fabrication of steel structures, there has been a tendency of steel structures being designed and fabricated thinner and more flexible.
However, incessant accidents and collapses of such structures have made the engineers of the world reconsider the ultimate strength of the structures and called for establishing more accurate design codes.
One of the simplest thin-walled structures would be a plate girder that consists of a webplate, flanges, and stiffeners.
Even a precise investigation on the behavior of plate girder panels will reveal complicated and rather random performances due to the nature of the parametric loading and imperfections.
In this paper, an application of perturbation method is discussed to take into account the stress redistribution and the change of various rigidities due to the large deflection of webplates and the elasto-plastic behavior of flanges. Special attention is paid on the effect of residual stress of flanges upon the load carrying capacity of girders.
The numerical computation was performed by means of finite differences to take into account many boundary conditions solving for unknown displacements.
The analytical results were compared with those from the experiments conducted at other institutions.
As a result of the analysis, it was found that the existence of large residual stress of flanges is not desirable for the load carrying capacity of plate girders, and that the postbuckling performance may significantly differ depending on the individual properties of the panels.

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