A stiffened plate is regarded as an assembly of the plating, due to simplicity in fabrication and the excellent strength to the weight ratio, stiffened plates are frequently used as structural components in ships and offshore structures. In all such application, it is always a paramount for structural designer/analyst to determine actual load carrying capacity of the structure.
In the present study, the ultimate strength of stiffened plates subjected to predominately axial compression is evaluated using Non-linear finite element analysis. Parametric studies covering a wide range of dimensionless parameters are carried out. The Parameters investigated are: the transverse flexural slenderness of the plate, the stiffener web slenderness, stiffener flange slenderness, and plate aspect ratio. From the parametric study, it is found that transverse flexure slenderness of the stiffened plate is more influential parameter as compared to other dimensionless parameter. It is observed that ultimate buckling strength decreases as the value of plate transverse flexure slenderness increases. Failure mode is also changed from plate induced overall bucking to plate buckling with increase in plate transverse flexural slenderness, which results in increasingly unstable post buckling behavior.
Strain hardening effect is evaluated and it is found that, strain hardening yields higher ultimate buckling strength. Ignoring the strain hardening effect, as it is common practice in marine industry, may cause underestimation of steel plated structure.
It is the matter of fact that thick hot rolled plate shows variation in material properties along the thickness direction. Effects of this phenomenon on ultimate buckling strength of stiffened plate are investigated and found to be significant. Furthermore, combined effect of strain hardening and variation in material properties along the thickness direction, yield remarkable increase in ultimate buckling strength of the stiffened plates. Therefore, in order to evaluate the ultimate buckling strength of stiffened plate accurately, variation in material properties along the thickness direction must be considered in the design and analysis of marine stiffened plates.
Effects of fabrication related imperfection are evaluated and it is found that imperfections have severe effects on the ultimate buckling strength of stiffened plate. Even at certain value of imperfection stiffened plate buckle before reaching to its yield strength. It is also found that as the plate flexural slenderness is increasing imperfection effect becomes more dominant and post buckling response also become sharply unstable.
A comparison of the numerical analysis results with design guidelines formulated by Det norske Veritas (DnV) and the American Petroleum Institute (API) is made. This comparison indicates that, in case of plate induced overall buckling, the guidelines results have good agreement with numerical results.