This study investigates the behavior of the topside of an offshore platform under special loads. Topside is designed for a combination of loads arising from types of equipment, fixed and rotating machinery, and cranes, apart from the gravity loads. While the wind loads are calculated using a gust factor and applied at different levels of the deck, a preliminary analysis is carried out using SAP2000 nonlinear. The design check carried following the code confirmed that the chosen sections satisfy the design requirements, both in strength and serviceability criteria. The topside of a typical offshore platform is highly vulnerable to fire, hydrocarbon explosion, causing extreme pressure and temperature in the confined areas. Pressure caused by the hydrocarbon explosion is rapid and results in an impulsive force of short duration. It damages the structural components and affects the overall performance of the topside considerably. The blast load is applied as an overpressure on the beams and columns and analyzed using ABAQUS explicit. The current study investigates the structural adequacy of members, constructed with X52 steel and functionally graded material (FGM). A comparison of the results showed that FGM offers more resistance to the displacement of beams and columns. Under the action of blast overpressure, members with FGM showed a significant reduction in both the plastic stain and Von-Mises stress at the beam-column connections in comparison to that of X52 steel. FGMs are used to model the deck plate and stiffeners to improve the impact strength, and compared with X52 steel and aluminum. A typical offshore crane hook is falling from 20m height considered for the analysis. Functionally graded materials showed improved impact strength, reduced plastic strain, and central deflection of the deck plate due to the enhanced mechanical properties of the material.

Keywords: Special loads, Hydrocarbon explosion, FGM, X52 Steel, Blast load