Insulation glass can be defined in several ways: single glass, laminated glass or any combinations. Up to 3 gap's - so 4 panes are possible. For supporting the edges, simple boundary conditions, elastically supported borders, point fittings, clamps, balustrade clips or as well free borders, where all panes are only internally fixed by spacers can be chosen.
The program is specially developed to consider any shape of DGU's and possible load combinations together with climatic loads:
- temperature changes within the sealed volume filled with gas
- barometric air pressure changes
- changes in amplitude
- together with any outside load like wind, line or point loads in addition
Temperatur change
When sun is shining the gas inside the gap is heated up and will expand. This will lead to outside bending of the panes.
In winter this cooling will have the opposite effect; the glass will bend inside.
These effects must be considered (in Germany) and are related to possible production situations of the DGU.
The winter condition is related to a production by 27°C and a minimum temperature for the filling gas in winter of 2°C. So a difference of -25°C is regarded.
The worst case for the summer condition is set to a production temperature of 19°C and a maximum heat of 38°C what results in a difference of +19°C.
Barometric air pressure changes
The air pressure differences are now assumed to have the same unfavourable effect.
If the reference altitude for the winter load case is assumed to be 990 mbar at sea level (and thus the enclosure of this condition in the cavity), the required pressure difference of +40 mbar results in a maximum change for the summer to 1030 mbar, which will bend the panes inside.
For the summer load case, a pressure difference of -20mbar is required. Assuming production in winter at 1030mbar, this results in a change in air pressure to 1010mbar in summer.
Changes in height
These are the values to consider if the production (combined with a sealed conditions inside the DGU) and installation was not on the same amplitude (height above sea level). If the previously closed DGU is installed much higher (or must be carried of mountains to reach the site), this maximum difference shall be regarded too.
For summer this is set to +600m as it reduces the outside pressure and will therefore increase the arching outside (worst case), if real values are unkown.
For the winter loadcase this is set in Germany for the worst case scenario to –300m, if the real amplitude changes are not known and if possible.
For a production site at sea level:
|
Loadcase |
Production |
Installation | Pressure change [mbar] | Temperaturedifference [°K] | Note |
|
Winter |
Sommer +27° / 990 mbar |
Winter +2° / 1030 mbar |
+40 | 2-27= -25° | DGU arches inside |
|
Summer |
Winter +19° / 1030 mbar |
Sommer 39° / 1010 mbar |
-20 | 39-19 = 20° | DGU arches outside |
These load cases are recognised in MEPLA as follows:
|
Loadcase |
Inside pressure pi [N/mm²] |
Ambient pressure pa [N/mm²] |
Temperature difference ΔT | Height difference ΔH [m] |
|
Winter |
0.099 | 0.103 | -25° |
when lower installed than produced ΔH = -300m Standard |
|
Summer |
0.103 | 0.101 | +20 |
when higher installed than produced |
Please note, that the normal outside pressure is not zero but 1013 mbar! An outside pressure set to zero will indicate, that you’re dimensioning a DGU for the space shuttle – so really in space where there is vacuum outside.
Calculation method
In any case MEPLA will calculate the real physical behaviour within the gap’s regarding the closed volume, the pressure and temperature of the filling gas for reaching the equilibrium. So this method is valid for any pane shape.
And this is done too, when no climate load is given. All fractions of external loads are transferred via the calculated inside pressure of the filling gas from the first to the second and the next panes. If internal spacers are set, they will carry as well some fractions of this load due to their constant spacing effect.
To solve this situation will be much more complex, when in addition large deflections, point fittings or contact conditions, what’s all possible to use together.