Ultimate collapse strength assessment of damaged steel plated grillages

Abstract

Across many industries damage events leading to a breach in structural integrity continue to occur.An area where this can lead to particularly unsafe conditions is in the maritime environment, where it may be difficult to rescue crew and cargo. In order to improve structural safety through design for the survivability or to assess the residual strength of a damaged vessel in an emergency response or salvage scenario, it is critical to understand the influence of the damage. This paper investigates the use of FEA on ultimate collapse strength of damaged steel grillages and the influence of the damage aperture on the developing failure modes within the structure. The study finds that the presence of damage, in the form of a hole, can lead to the failure mode changing as damage aperture size is increased leading to significant changes to the ultimate collapse strength of the structure. It concludes that to assess the damaged strength of steel plated structures, it is critical that modelling methods are able to capture and account for such mode changes in order to accurately assess the true residual strength of the structure.

Compartment level progressive collapse strength as a method for analysing damaged steel box girders

“…This is the form of initial imperfection shape that has been applied to the grillage FEA model. In the study presented in Underwood et al [28], the resulting failure modes in the grillages were seen to be of an alternating direction as has been seen for the H400 grillage in Figure 7. Investigating the development of the H300 grillage failure mode shows how the initial imperfection shape is stable as the axial load is applied, leading to the failure developing with deflections in the same direction between stiffeners.…”

“…Assessment has been undertaken through the analysis of two damage events introduced into the panel as diamond cut-outs, using the same method as in Underwood et al [27,28], ignoring any potential residual stresses caused by the impact and extra material as this is assumed not to affect the strength of the panel. The first is a small damage event positioned with its centre at the middle of the central stiffener with the breadth of the damage equal to the longitudinal stiffener spacing giving a damage area ratio of 0.3.…”

“…Underwood et al [29] propose that the progressive collapse method could be developed, using the response surface method kriging, to capture the strength characteristics of the damaged steel structure and can then be used to determine the failure load. An investigation into the ultimate collapse strength of damaged grillages has demonstrated the need to assess damaged structure at this level of idealisation due to the influence of the damage on the developing failure mode of stiffened steel structures [28]. It is proposed that progressive collapse assessment can be implemented at a multiple frame or compartment level by idealising the structure into grillage elements, with the damage strength characteristics efficiently developed through FEA and stored within the response surface.…”

“…The modelling arrangement and boundary conditions used within the FE modelling have been created drawing on previous work undertaken by the authors to model damaged stiffened panels [27,28,29 and 30] and guidelines for the use of FEA for the ultimate strength assessment of stiffened panels [32, 16 and 33]. All FEA has been undertaken using the commercial FEA software ANSYS v14.0.…”

“…In their own work to investigate the residual strength of a damaged warship, Ren et al [19] [27,28], has highlighted these problems. In particular the failure cannot always be assumed to be interframe and as such new methods need to be developed which can capture these failure modes.…”