Experimental and numerical study of uniaxially compressed stiffened plates with different plating thickness

This paper presents a numerical - experimental research to evaluate the effect of corrosion in panels subjected to uniaxial compression and subsequent repair. The effects of corrosion are approximated by a uniform reduction in the plating's thickness. Currently, repairing a corroded offshore structure involves the change of the hull plating, which is excessively expensive and, therefore, other alternatives should be investigated in order to extend its useful life. The experimental study considers a set of five panels with an average scale of 1:3.5, representing a typical intact panel of a VLCC (Very large Crude Oil Carrier) converted into a FPSO (Floating Production Storage and Offloading) platform and two different plating reduction thickness levels. These experiments are reproduced through a numerical model that considers geometric and material nonlinearities. The geometrical imperfections in the surfaces of plates and stiffeners are reconstructed from measurements using techniques of laser scanning and optical capture. Thickness distributions are measured with an ultrasonic sensor in several predetermined panel sections points. True stress vs true strain curves for all panel's elements are obtained by tensile tests and employed in the numerical model. Once the numerical model is validated, the effect of the axial load eccentricity, the supported element load redistribution due to changes in the thickness, and the effects of the inclusion of intermediate repair on the plate are studied. The results show that the inclusion of an intermediate light stiffener allows recovering the panel load capacity and prolonging the useful life of offshore platforms. Likewise, it is concluded that the selection of the repair should be based on the local strength recovery of the plate, which is most affected.