Stability Approach of the Dimensioning of Glass beams

Jan Belis, Rudy Van Impe, Bram De Meester, Guy Lagae, Kali Babu Katnam

1. Introduction

From a safety point of view, laminated glass beams are obligatory for reasons of residual strength and adhesion of glass pieces in case of failure. Although the total slenderness of the glass-PVB composite can be reduced compared to monolithic sections, a study of the buckling behaviour of
laminated glass beams seems very useful here too. In the text below, glass beams with “real” imperfections are considered.

2. Numerical analysis
2.1 Parameters
For realistic glass beams, parameters like initial shape imperfections (Figure 1.) and relaxation of the interlayer (Figure 2) have to be examined.

2.2 Results
2.2.1 Influence of overall bow magnitude

The effect of the amplitude of initial shape imperfections corresponding to the first eigenmode on the resistance to lateral torsional buckling is examined in a numerical parametric study. The values of the amplitude parameter are discussed and results are shown in the paper.

2.2.2 Interlayer thickness

Under very short loadings, laminated glass beams have a slightly higher buckling resistance than monolithic specimens with the same glass thickness. As the total beam thickness is a major geometric parameter that influences the buckling behaviour, the small increase in overall thickness
of the laminate (due to the interlayer) causes a small gain in buckling load.

However, when relaxation of the PVB is taken into account, the importance of this effect is put into the right context. For the final effect on the buckling load, we refer to the paper.

2.2.3 Combined effect of shape imperfections and PVB relaxation

When both effects are combined, a “realistic” laminated beam will show a highly reduced residual buckling resistance compared to a perfect geometry opposed to an instantaneous loading.

2.3 Failure mechanism
Perfect glass beams are compared to glass beams with realistic imperfections.

For certain beam geometries, both cases
show an interesting contrast. Depending on the geometry and
imperfections of the glass, the risk of failure due to buckling increases
considerably. From the example in figures 3 and 4, it is clear that
buckling will always occur for toughened beams with this particular geometry. Even for ordinary float
glass, buckling can occur before fracture if the glass thickness is small.

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The Authors

Dr. Jan Belis dr. ir.-arch./Assistant Professor Ghent University - LMO Jan Belis holds a degree in civil engineering/architecture and a PhD degree in structural engineering from Ghent University, Belgium. Since 2006, he is assistant professor at the same institute. His r... Read more