Repair and strengthening of offshore platforms topside girders using externally bonded fibre reinforced polymers

Abstract

Offshore structures play an important role in the current economy, from oil and gas to facilitating offshore renewable energies. It is inevitable that steel structures residing in an offshore environment will corrode over time due to salt accumulation. Such structures, often utilizing plate girders as structural members, frequently require repair to operate safely and efficiently. The conventional method of repair involves entire sections being replaced and welded underwater. This method has proven to be a costly approach due to the operational losses of a shutdown during repair. In this study, the practicability of an alternative repair method using fibre reinforced polymer (FRP) composites along with an associated adhesive is investigated. Various studies have been conducted on this topic, however this project aims to fill the gaps in the understanding of FRP repaired steel beams which have been stiffened with transverse web stiffeners located at loading points. This is a very applicable scenario to the offshore industry and prevents supporting beams from undergoing lateral torsional buckling. Three compact plate girders are tested under four-point bending; an intact section, a damaged section and a damaged section repaired with FRP. Testing was undertaken on the Amsler machine in the UWA Structures Laboratory. For the purpose of this study, corrosion is imitated through cutting a section of web and both flanges in the midspan. A strength regain ratio (SRR) is utilised to compare the extent of capacity regained through repair.