Experimental and numerical analysis of small-scale panels with indented stiffeners

During the construction process of the ship's hull, the ultimate strength of the stiffened panels is reduced due to both initial imperfections and residual stresses. In service, these stiffened panels are exposed to damage that causes permanent deformations and localized residual strength, reducing additionally the ultimate strength of damaged panels, which must be considered in the design process to preserve the structural integrity. The paper provides analyses of the effect of damaged stiffened panels on the ultimate strength considering the residual stresses caused by indenting depth and different locations. Experiments were performed using small-scale models representative of a full-scale bottom panels from a cargo compartment at the midship of a typical Suezmax tanker. Experimental tests of the indentation were conducted on the intersection plate-stiffeners, where the force-displacement responses were analyzed. After the indentations, the panels were submitted to uniaxial compression experimental tests, in order to evaluate the loss of ultimate strength compared with the equivalent intact panel. Finite element models were developed by ABAQUS software in three steps sequentially: panel indentation, indenter taking off, and uniaxial compressive loading. Plastic strains and residual stresses caused by the indentation are incorporated in the ultimate strength analysis of the panels. Initial imperfections and maximum denting depth of the panels were measured in the small-scale models for the numerical-experimental correlation. Both indentations and ultimate strength presented a good agreement. A parametric study was performed using the numerical model to determine the residual strength due to the damage and its relationship with both dent depth and location.