Overall buckling of lightweight stiffened panels using an adapted orthotropic plate method

The ultimate longitudinal bending strength of thin plated steel structures such as box girder bridges and ship hulls can be determined using an incremental–iterative procedure known as the Smith progressive collapse method. The Smith method first calculates the response of stiffened panel sub-structures in the girder and then integrates over the cross section of interest to calculate a moment–curvature response curve. A suitable technique to determine the strength behaviour of stiffened panels within the Smith method is therefore of critical importance. A fundamental assumption of the established progressive collapse method is that the buckling and collapse behaviour of the compressed panels within the girder occurs between adjacent transverse frames. However, interframe buckling may not always be the dominant collapse mode, especially for lightweight stiffened panels such as are found in naval ships and aluminium high speed craft. In these cases overall failure modes, where the buckling mode extends over several frame spaces, may dominate the buckling and collapse response. To account for this possibility, an adaptation to large deflection orthotropic plate theory is presented. The adapted orthotropic method is able to calculate panel stress–strain response curves accounting for both interframe and overall collapse. The method is validated with equivalent nonlinear finite element analyses for a range of regular stiffened panel geometries. It is shown how the adapted orthotropic method is implemented into an extended progressive collapse method, which enhances the capability for determining the ultimate strength of a lightweight stiffened box girder

Simulation of ship grounding damage using the finite element method

AbstractThis paper presents a comparison with experimental data of the resistance of stiffened panels to penetration damage. It also carried out comparisons between numerical simulations and experiments investigating the grounding of ships. The finite element method and FEA software are used to predict penetration damage and this modelling simulation is then extended to investigate damage to a ship’s double bottom structure in different grounding scenarios. The progressive failure of the double bottom is investigated in terms of plastic deformation and also the evolution of damage including material rupture. Three different levels of complexity were used in modelling the double bottom structure concerning the inner and outer shell plating; longitudinal stiffeners in the shell plating, and structures with stiffening in longitudinal floors. The analysis was carried out in the ABAQUS explicit code.The results presented include the crushing force as a function of time, an investigation of the energies involved in the plastic deformation and rupture of the double bottom structure, and comparisons with experimental data where available

奥付

Marine-grade aluminium alloy is an established structural material for medium- to high-speed commercial craft and has also been used as the primary hull material for several naval vessels. The analysis of large high-speed craft operating in deep ocean environments requires rigorous methodologies to evaluate the ultimate strength of the hull girders. Representative plate load-shortening curves form part of simplified hull girder ultimate strength methodologies; for the case of a high-speed aluminium vessel, the curves need to account for the effects of parameters including alloy type, geometric imperfection, softening in the heat-affected zone, residual stresses, lateral pressure and biaxial load. This paper examines the strength of a series of unstiffened aluminium plates with material and geometric parameters typical of the midship scantlings of a high-speed vessel, using a non-linear finite element approach. The parametric studies show that these factors can have a significant influence on the strength behaviour of the plates both prior to and after the collapse point has been attaine

A Timoshenko beam finite element formulation for thin-walled box girder considering inelastic buckling

A Timoshenko beam finite element model is formulated based on the Lagrange and Hermitian interpolations, in which the transverse shear deformation is explicitly evaluated. To account for the local inelastic buckling, the finite element formulation is coupled with a Smith-type progressive collapse method where the nonlinear responses of local structural members can be assessed. The effect of shear lag is accounted by an effective breadth theory. This coupled model enables an efficient prediction of the flexural behaviour of a thin-walled box girder under lateral loading. To demonstrate its capability, a case study is completed on a single-skin box girder under four-point bending. Equivalent finite shell element analysis is carried out for validation. The proposed method shows a close correlation with the shell element model in both strength and stiffness predictions. It is found that the effect of shear lag is significant in this case study, which substantially reduces the stiffness of the box girder