Calculation and Use of Laminated Glass

Technical Article

Different glasses and layer structures are available for glass structures which are used for different purposes. The following types are usually used: float glass, partly tempered glass, and toughened safety glass.

Float glass is a basic glass product and its name describes the production process. These glasses have no self-equilibrating stresses and can therefore also be called annealed glass. These glasses are used, for example, in window construction, facade construction, interior design and in furniture construction.

Partly tempered glass and toughened safety glass are products that are manufactured by refining float glass. By subsequently heating the glass and then a defined cooling process, products with a residual stress state are created. The process creates a parabolic prestressing profile across the cross-section, which leads to a higher strengths of the glasses and greater flexural tensile stresses can be absorbed.

A distinction is made here between partial or full prestressing of the cross-section. Of course, different bending rigidities are achieved, but other properties such as the fracture pattern also change. Toughened safety glass has a small crumbled fracture pattern, which significantly reduces the risk of cuts. In contrast to float glass, however, partly tempered glass 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 displayed.

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 coupling 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.

Consider in Calculation

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

  • Calculate 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:

  • Calculate the double-thickness pane (rigid composite)

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

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

Figure 01 - Entering the Layer Structure

The option to consider the shear coupling 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 you activate the shear coupling. 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 of Composition 

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

Summary

The computer-assisted calculation with their available options helps to display systems that might be too complex or even not editable by manual calculation.

Keywords

Laminated glass Laminated safety glass Shear coupling PVB foil

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