Effect of Different Ways to Model Line Supports in Glass Structures
Due to the special properties of glass, you also have to pay close attention to detail points when modeling in an FE model. Glass has a very high compressive strength and is therefore generally only designed for its tensile stresses. A particular disadvantage of the material is its brittleness. Stress peaks that occur in the calculation must therefore not be readily neglected.
Different Calculation Options in RFEM
Various ways to arrange supports allow for such stress peaks to be generated or avoided. Considering certain points and knowing the program's functionality is therefore already necessary when defining the layer structure. Basically, there are two calculation options available: the "2D" or "3D" option. The "2D" calculation method describes an internal modeling of the layer structure via surfaces. The glass panes are displayed via surface elements in RFEM. When using LSG glasses, an equivalent thickness of the layer is determined. However, when considering shear coupling, if the stiffness difference is too large, this theory reaches its limits, so that the "3D" option must be applied. The layer structure is modeled and calculated as solid elements. The advantage of this more time-intensive method is that the stiffnesses of each layer are exactly considered in the calculation and that relations such as shear coupling can be actually considered. In some cases, RFEM already presets a calculation option, which can not be modified.
Selecting the Support Arrangement
If the calculation is based on the plate theory, it represents the simplest form for arranging supports. Supports are automatically assigned to the system line.
When you calculate according to the solid theory, however, there are several options available. Supports can be defined on each glass layer, but this may result in unintended restraining end moments occurring in the support area. It is important to pay attention to this phenomenon when entering data, because this setting is not immediately apparent in the result evaluation.
Comparison of Results and Conclusion
If you compare the results of both calculations of a simple laminated glass pane, supported on one edge and supported on all edges, it is clear that the design ratio of system 2 is even more favorable than with system 1. This stems from the fact that the support results in a restraint, leading to more stiffness being assigned to the support and therefore resulting in a smaller deformation and smaller internal forces in the mid-span. However, this lower ratio is a fallacy, since the frame of the glass or the fastening of the glass pane to the frame are usually not designed for these forces. But the results also show that the differences in the calculations are very small and therefore oftentimes not noticed. This article is thus intended to raise the user's awareness about constructing detail points before the calculation, especially in glass construction, in order to be able to design the model as precisely as possible in the FE program.
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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
Design of single-layer, laminated and insulating glass