Example Basis
- Primary topic
- EN 16612
- Engineering basis
- TGU load sharing
- Review status
- Project-specific verification required
Published Example Reference
The reference is the triple glazed insulating glass unit worked example in EN 16612:2019, Annex C, Tables C.3 to C.5. This page does not reproduce the standard's pages or tables. It records an independently written calculation explanation and the values used to test the VitraLab implementation.
Geometry and TGU Build-Up
The example unit is 660 mm by 2200 mm at a 45 degree slope. Its build-up is Pane 1 at 6 mm, Cavity 1 at 12 mm, Pane 2 at 4 mm, Cavity 2 at 12 mm and laminated Pane 3 with an equivalent calculation thickness of 5.04 mm. The aspect ratio is 0.3 and the example uses the Table B.3 volume-change coefficient k5 of approximately 0.0676.
Load Conversion and Annex C
Why the 45 Degree Loads Are Converted
The public calculator offers Horizontal or Vertical orientation. For this Annex C example, the actions at 45 degrees are first resolved into effective pressures normal to the glass, so a separate inclined-glass input is not needed. Those converted pressures are then used in the cavity calculation.
Snow and Self-Weight Conversion
The stated snow action is converted as 0.6 multiplied by cos(45 degrees), giving 0.30 kN/m². The pane self-weight actions are converted in the same way, giving approximately 0.1061, 0.0707 and 0.1414 kN/m² for Panes 1, 2 and 3. With wind included, the external action used on Pane 1 in the combined example is 1.0861 kN/m².
Coupled Two-Cavity Factors
Using the pane volume changes and both cavity volumes gives the relative volume-change factors. The reproduced coupling values are φ1 = 0.03133, φ2 = 0.02720 and β = 0.5153. Unlike a pair-by-pair approximation, the middle pane couples both cavities in one calculation.
Isochore Pressure Check
For the example isochore pressures of -4.3 and -5.8 kN/m², the independently calculated resultant pane pressures reproduce approximately +0.49 kN/m² on Pane 1, -0.02 kN/m² on Pane 2 and -0.48 kN/m² on Pane 3. Small last-digit differences can arise when rounded intermediate values printed in the example are reused.
Combined Load Result
For the worked wind, snow and self-weight state, the calculation reproduces the published rounded resultant pressures: 0.72 kN/m² on Pane 1, 0.20 kN/m² on Pane 2 and 0.38 kN/m² on Pane 3. The calculation test also checks the intermediate coupling factors rather than comparing only the final three values.
Engineering Use
What the Match Demonstrates
The match demonstrates that the implemented Annex C pressure-distribution equations reproduce this stated worked example when its converted actions and assumptions are used. It is a software regression benchmark, not independent certification of EN 16612 or verification of every possible TGU configuration.
Engineering Use
Project design still requires confirmation of pane build-ups, equivalent thickness, cavity widths, sealing conditions, design temperatures, atmospheric pressure, supports, actions and applicable National Annex requirements. Horizontal and Vertical project cases must use their actual directional load components rather than automatically adopting the example's 45 degree values.
Frequently Asked Questions
Does the calculator need a 45 degree orientation option for this test?
No. The benchmark uses the effective normal pressures obtained after resolving the example's snow and self-weight at 45 degrees. The calculator can therefore remain set to Horizontal or Vertical.
Are the EN 16612 pages or tables reproduced here?
No. The standard is referenced by edition, annex and table number, while this page uses original explanatory wording and independently calculated values.
Why are there two cavity-pressure variations in a TGU?
A TGU has three panes and two sealed cavities. Movement of the middle pane couples the pressure response of both cavities, so they must be solved together.
Does matching one worked example validate every TGU design?
No. It provides a strong regression benchmark for the stated calculation route, but other geometries, build-ups, environmental states and project requirements still need engineering review.
Engineering content is prepared and maintained by VitraLab Engineering. Worked examples show how the current calculator treats a defined case; they do not replace project-specific verification.