Calculation and use of laminated glass

Technical Article

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In the field of glass construction, there are various glasses and layer structures that are used for different purposes. In the classic case, these are: Float glass, tempered glass, and toughened safety glass.

Float glass is a basic glass product that is designated according to its method of production. These glasses have no residual stress and can therefore also be called technically stress-relieved glass. These glasses are used, for example, in window construction, facade construction, interior design and in furniture construction.

TVG and ESG, on the other hand, are products that are manufactured by finishing float glass. By subsequently heating the glass and then defining a defined cooling process, products with a residual stress state are created. The process creates a parabolic prestressing profile across the cross-section, as a result of which these glasses have higher strengths and greater bending tensile stresses can be absorbed.

A distinction is made here between partial or full prestressing of the cross-section. Of course, different bending stiffnesses are achieved, but other properties such as the fracture pattern also change. ESG has a small crumbled fracture pattern, which significantly reduces the risk of cuts. In contrast to float glass, however, TVG shows a rough fracture pattern, which may be decisive for the residual capacity of overhead glazing, for example.

Laminated and laminated safety glass

Laminated glasses are a combination of several glasses that are connected by an intermediate layer. Depending on the required requirements for the glass pane, different properties can be mapped.

Laminated safety glass also places even greater demands on the intermediate layer. In this case, the required safety should be fulfilled in case of breakage and thus a risk of injury should be reduced.

When calculating stresses and deformations, a shear bond must not be considered according to DIN 18008-1 if it is favorable for the structure, but must be taken into account if it results in larger stresses or deformations.

Consideration in calculation

The simplest procedures for applying the standard for the case without shear coupling are as follows:

  • Calculation of a single pane with half load
  • Calculate the equivalent cross-section thickness
    $\mathrm d^\ast\;=\;\sqrt[3]{{\mathrm d^3}_1}\;+\;{\mathrm d^3}_2$

and the case with shear coupling:

  • Calculation of double-thickness pane (rigid bond)

For computer-aided calculations as in RFEM, more comfortable solutions are implemented.

Especially in RF-GLASS, the layer structure can be selected via a database and constructed according to the real specifications.

Figure 01 - Input of layer structure

The option to consider the shear bond between the panes can be selected in the "Details" check box. As an additional option, the option of a 2D or 3D calculation is available when the shear coupling is activated. The background of these two options is that in a 2D calculation, an equivalent cross-section is automatically created and the system is calculated with the plate theory.

Figure 02 - Details about the layer structure

In the 3D calculation, solid elements are created by the individual layers, whereby the effect of the shear bond is represented exactly on the basis of the defined stiffness. This option produces the most realistic results, but also requires the most computing time.

Summary

The computer-assisted calculation supports the engineer with their available options to display systems that might be too complex or even not possible to work by manual calculation.

Keywords

Laminated glass Laminated safety glass Shear coupling PVB foil

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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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