Experimental study of GFRP stiffened plates with and without large opening under combined axial and pressure loading

Abstract

GFRP stiffened panels forms the basic component of ship hulls, decks, submarines, offshore oil platforms etc., GFRP stiffened panels used in ship hulls and decks are subjected to axial loading due to buoyancy and pressure loading due to cargo. GFRP stiffened plate dimensions considered in this study are the scaled down dimensions of a cargo ship. Aluminium moulds with and without opening are fabricated for casting GFRP stiffened panels. GFRP stiffened panels with integral stiffeners are manufactured using hand lay-up process. A unique lay-up pattern was adopted to achieve the monolithic behaviour of stiffeners and plate. Fabrication of GFRP stiffened panels by manual hand layup process leads to formation of indentations. These imperfections are determined using the LVDTs attached to imperfection measurement setup. The measured imperfections are compared with the allowable imperfection values available for steel in BS 5400, because limiting imperfection values are not available for FRP. Openings are necessary for access and maintenance in ship hulls, decks etc. The presence of openings can lead to loss in strength and stiffness of the GFRP stiffened panels. In this study, GFRP stiffened panels with and without opening are tested for different combinations of axial and pressure loading. Axial loads are applied using two hydraulic jacks and measured using two load cells which are fabricated to prevent eccentricity while applying axial load. Pressure loads are applied using inflatable air balloons with and without opening fabricated for this study. Load capacity, failure strain, failure patterns of GFRP stiffened panels under different load combinations are presented. Failure locations of GFRP stiffened panels with and without opening various load combinations are discussed. Reduction in load capacity, span to deflection ratio and loss in stiffness due to opening is calculated.