Large windows or openings with static or dynamic load onboard ships [IGF-No. 16765 N]

Responsible research centres: Technical University Hamburg-Harburg (Prof. Fricke)

Time period: 01.11.2010 - 28.02.2013

Final report: CMT 22/2013


Project summary

Large windows are used in passenger vessels and mega-yachts to an increasing extent. Typical design loads are water pressure in way of front bulkheads during shipping of green water or during immersion of windows in emergency cases with heeling of the ship as well as shear and normal stresses due to hull girder bending especially in the aft and forward part of the side shell plating.

In this project, the load carrying behaviour under lateral pressure as well as the structural behav-iour under shear load was investigated experimentally and numerically. The experiments were performed with five test models – ship-typical steel structures with large windows – in original scale. The window dimensions as well as the type of framing (clamped/ bonded) were varied. All steel walls were about 3000 mm wide and 2800 mm high and vertically stiffened. Models 1-3 were fitted with windows 1500 mm x 1200 mm, whereas larger windows 1900 mm x 1600 mm were used for models 4 and 5. The panes of model 1 and 2 were clamped, the remaining panes were bonded.

All test models served for elastic in-plane shear tests and afterwards for ultimate load tests with lateral pressure on the window panes and the surrounding steel structure. The tests were accom-panied by finite element computations.

The shear tests have shown that the contribution of the windows to the stiffness depends strongly on the shear stiffness of the steel structure and may be quite large. The shear stiffness of the fifth test model, which was designed like a continuous strip of windows, was increased by the window panes by a factor of almost ten. Procedures were established to determine the stiffness including glass panes numerically and analytically. The stiffness of the steel structure with regular window arrangement can be estimated analytically on the basis of beam theory, whereby the shear stiff-ness in way of the web intersections has to be considered correctly. If finite element analyses are preferred, recommendations for modeling are given. The contribution of windows to the stiffness is mainly determined by the stiffness of the bonding or rubber gasket. Also here an analytical calcula-tion is possible as an alternative to an FE computation, which, however, requires an iterative pro-cedure which was programmed as Scilab script.

The ultimate load tests have shown that the load-carrying capability of the glass panes is frequent-ly not utilized, if the panes slip out due to the deflection of glass and steel. This failure mechanism occurred with clamped windows as these show a typical overlap of about 1 cm which is smaller than the bonded width. Furthermore it was observed that hardly visible defects in the glass surface on the tensioned side significantly reduce the glass strength. Compared to the four-point bending tests performed by the glass producer, the strains measured during the ultimate load tests reached values which correspond to the stresses at the lower scatter band of the glass strength.

Numerical investigations have shown which measures can effectively increase the ultimate strength of ship windows. An increased overlap, as required in ISO 11336-1 for large yachts since 2012, is an effective measure. Furthermore stiffening of the structure as well as of the interlayer in laminated glass windows can be effective, however the advantages and disadvantages have to be evaluated. If glass panes with different thicknesses are used in laminated glass, the thickest glass pane is to be arranged at the loaded, i. e. outer side.
Altogether the project has brought several new findings, clarified diverse questions and resulted in procedures for the determination of the contribution of glass windows to the stiffness of the ship structure. Insofar the objections are reached.

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