| Stiffened steel panels are the basic strength members in ship and offshore structures. Due to their simplicity in fabrication and excellent strength to weight ratio, stiffened steel panels are also widely used for construction of land based structures such as box girder and plate girder bridges. Since the overall failure of a ship hull is normally governed by buckling and plastic collapse of the deck, bottom or sometimes the side shell stiffened panels, it is of crucial importance to accurately calculate the ultimate strength of stiffened panels in deck, bottom and side shell for more advanced structural design of ship structures.The buckling of a plate mostly occurs in elastic regime with high strength steel adopted widely, and the plate reaches ultimate strength due to losing capacity when equivalent stress where maximal in-plane compressive stress appears arrives at yield in post-buckling phase. The elastic large deflection solution and rigid plastic solution are combined to achieve theoretical formula of ultimate compressive strength of a plate in the present paper, which agrees well with the result by the finite element calculation (ANSYS) and existing experiential expressions.The reduction factors derived from curve fitting based on calculation results by the finite element program (ANSYS) considering all kinds of damages such as cutouts, corrosion, cracks, denting, initial deflection and residual stress are introduced to modify the effective width of perfect panel in the present paper. The modified Perry-Robertson equation is applied to calculate ultimate compressive strength of damaged stiffened panels founded on so-called beam-column method, and the width of effective plate adopts above reduced effective width of a damaged plate. Several conclusions are achieved in the present research as follow:1. An explicit formula of ultimate strength is achieved according as combination of elastic large deflection method and rigid plastic method for perfect plates.2. The explicit formulae with damage parameters as variable of reduction factors for ultimate strength of damaged plates are achieved by curve fitting based on a mass of numerical computation for parametric imperfection and damage of plates.3. The effective width of damaged attached plates adopt the effective width of damaged plates in ultimate strength computation of damaged stiffened panels.4. The reliability of ultimate strength of corroded stiffened panels is analyzed.
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