A Study On Ultimate Strength Of Lightweight Ship Structures

Nowadays energy saving and environmental protection is the consensus of human society. In order to regulate and reduce CO2 emissions from ships and improve energy efficiency of shipping,International Marine Organization(IMO) has developed and approved the Energy Efficiency Design Index(EEDI) as a new energy efficiency standards for new ships. It is very significance to reduce ship weight, increase ship cargo and improve EEDI by using lightweight structural material in new ships.Steel sandwich plate is a new material for shipbuilding. It has a lot of advantages such as lightweight and high flexural stiffness comparing to conventional steel panels. It is likely to substantially reduce the structural weight of ship hull if ship design and construction is by using steel sandwich plate instead of conventional stiffened panels. However up to now steel sandwich plate is mainly used for ship repair and not yet used for complete new ship. One of the main reasons for that might be the lack of rational design methods for establishing the full equivalence in strength requirements between steel sandwich plate and conventional stiffened panel because of the inadequate study on the mechanical characteristic steel sandwich plate. Therefore it is necessary to carry out the study on structural ultimate strength of steel sandwich plate and to develop the calculation method for the ultimate strength of steel sandwich plate of ship structure.In this paper a systematic research is performed on the ultimate strength of Steel/polyurethane/steel sandwich plate by means of the good combination of theoretical study, numerical simulation and model test. The main research work and achievements are summarized as follows:(1) A calculation method and program is developed for longitudinal ultimate strength of ship girder according to the guidelines of common structural rules. Its rational and reliability is demonstrated by series of numerical calculation and comparison analysis of ultimate strength of box girder model and ship structure. It lay the foundation to carry out the comparative study on ultimate strength of steel sandwich plate.(2) Based on the existing solution, a simplified method is presented for solving the critical buckling stress of steel sandwich plate in expression of three generalized variables by analyzing the mechanical properties of steel sandwich plate and simplifying the typical boundary conditions. The problem of coupled equations with three general variables is simplified to solve two independent equations with two generalized variables. It makes the theoretical solution of steel sandwich plate is simplified and similar to the classical theoretical solution of thin plate.(3) The series of studies are carried out on the typical failure mode and ultimate strength of steel sandwich plate. A calculation method is presented for analyzing the equivalent ultimate strength between steel sandwich plate and conventional stiffened panel. Numerical examples show that the structural weight is reduced if the steel sandwich plate is designed with equivalent ultimate strength to replace the longitudinal stiffened panel. The structural ultimate strength is improved if the steel sandwich plate is designed with same weight to replace the longitudinal stiffened panel.(4) The model test of steel sandwich plate under combined biaxial compression and lateral pressure is performed in initiated in the first time in China. The comparative study is carried out on simplified theoretical calculation results, finite element analysis results and model experimental results of steel sandwich plate and some useful conclusions are obtained.