On the thickness determination of rectangular glass panes in insulating glass units considering the load sharing and geometrically nonlinear bending

Abstract

The number and size of windows has increased in large cruise ships, especially on the top decks. They have therefore become a weight and stability-critical component of the structure. Their thickness is determined according to the classification rules which are generalized for all type of passenger ships. That is, the provided formulae are based on linear-elastic, small deformation, plate theory and therefore more suitable for smaller windows in non-weight critical applications. However, majority of the windows are large insulating glass units (IGUs) that exhibit two effects that the rules do not currently consider: development of membrane stresses in the glass panes at large deflections due to the von Kármán strains (geometric nonlinearity) and interaction of the glass panes due to the internal cavity pressure between them (load sharing). Both increase the load bearing capacity of the IGUs. Therefore, extension to the thickness determination is needed for achieving the lightweight design. This paper uses nonlinear Finite Element Method to study the IGUs static response under uniformly distributed load considering the effects. The response consists of principal stress and deflection of the panes, and the cavity pressure. Validation is carried out by experimental results from scientific literature. Case study on typical panes from cruise ships indicate that considering the two beneficial effects, the thickness of the glass panes in the IGUs may potentially be reduced between 26–54 % with respect to the classification rule-based design. That is, by using the same allowable principal stress criterion between the linear and nonlinear predictions.