Ultimate strength of a stiffened plate with initial imperfections under complex loading

The ultimate strength of a ship stiffened plate with initial imperfections under uniaxial compression and lateral pressure is studied by nonlinear finite element analysis. The results of the Smith's experiments carried out for the structural ultimate strength and progressive collapse analyses are used to assess the accuracy of the nonlinear finite element analysis. A stiffened plate of a AFRAMAX double hull oil tanker designed according to the IACS' Common Structural Rules is analyzed using a one bay (1/2+1/2) finite element structural model able to simulate the influence of adjacent panels. The obtained ultimate strength results of the panel with initial imperfections under complex loading show the importance of the effect of initial imperfections and lateral pressure that clearly reduce the ultimate capacity of the stiffened plate. A comparison with the predictions of the Common Structural Rules indicates that the design formulation actually over-estimate the ultimate strength of the panel, as the initial imperfections are not explicitly defined and the real loading conditions of the structural element are simplified.