Preliminary assessment of the design requirement against blast load for ship superstructure

This paper attempts to rationalise, and assess, the existing design requirement for the sizing of the outer plating of a ship superstructure against an external air blast. First, a review of the current design guideline, specifically on how the blast load parameters were specified by the Rules and Regulations of Lloyd's Register and the assumptions behind the use of the scantling equation, is provided by the way of a design case study. Next, a non-linear SDOF model that incorporates a new plastic membrane phase is developed in this paper, together with three-dimensional FE simulations, to model the large inelastic deformation of the platings. The required plate thickness needed to resist a specified load intensity is then compared for the three different methods, viz. Lloyd's Register design rule, SDOF and FE. As expected, it will be shown that existing design guideline achieves the purpose of maintaining water or gas-tight integrity of a plating; however, there exists significant unnecessary redundancies (or over design) with implications on light-weighting. Additionally, the results will be summarised in the form of a failure map that will be useful to designers.