Performance-based design of blast resistant offshore topsides, Part II: Modelling and design

A simplified analytical model for deck plates of offshore topsides structures is proposed. Based on the theory of virtual work and an assumed deformed shape function in Cartesian coordinates, a set of equilibrium equations in terms of energy are developed. The equations are formed as a static case and a dynamic case with unsolved variables defined as generalized coordinates. When these equations are re-arranged, they are equivalent to a modal analysis, which can be solved using Lagrange’s equation method. The generalized coordinates in the static case can be solved manually while in the dynamic case, the ordinary differential equations are solved numerically by developing a computer program using a symbolic software package, MAPLE. The proposed method is comparable with finite element analysis results up to a certain threshold at which development of membrane strain and plasticity modes become dominant. When comparing the results to the reported experimental data, the proposed shape functions for deformations in the lateral directions are modified in order to accommodate the observed behaviour. The results compare favourably with test data and finite element analysis as a control case.Despite inconsistent ductility ratios between the proposed method and the finite element analysis at very high overpressures, the method shows good correlation of results at practical design values. Hence, the proposed method would be a useful tool for preliminary appraisal methods especially for design engineers involved in evaluating the performance of deck plating subjected to a range of hydrocarbon explosion scenarios.