Overview
- Primary topic
- Eurocode 10
- Engineering basis
- prEN 19100
- Review status
- Project-specific verification required
Why Laminated Glass Needs a Coupling Model
A laminated pane contains glass plies separated by one or more polymer interlayers. Its bending stiffness, deflection and ply stress depend on the shear transferred between those plies. EET represents this coupled response without treating the physical build-up as either one homogeneous glass plate or a set of completely independent plies.
Equivalent Thickness in the Current EC10 Calculation
EET does not assign one universal substitute thickness to a laminated pane. For each applicable action and coupling basis, VitraLab determines the stiffness effective thickness hef;w used for plate response and deflection, together with ply-specific stress effective thicknesses hef;σ,i. When an IGU pane is laminated, the same response is used in the DGU and TGU Annex C calculation. The value of hef;w is also reused when the optional natural-frequency calculation is selected.
Method
Action-Specific Interlayer Shear Modulus
Interlayer shear modulus depends on the product, load duration and design temperature. VitraLab therefore requests Gint values for the active action categories rather than applying one value to every load. Permanent, wind, snow, live, maintenance, barrier and accidental actions can require different project or product data.
Calculated or Partial Shear Coupling
For a covered prEN 19100-2 Table A.1 route, the Calculated or Partial Shear result combines the action-specific Gint with the resolved Table A.1 coefficient to determine the coupling parameter, equivalent thicknesses and ply response. Those results belong to that action, duration and temperature basis. If Table A.1 does not cover the case, VitraLab does not extrapolate it: the separately labelled VitraLab EET Plate Method uses the conservative No Shear effective-thickness state and returns REVIEW.
Full Shear and No Shear Comparisons
VitraLab also reports Full Shear and No Shear comparison scenarios. Full Shear represents the fully coupled bound, while No Shear represents uncoupled plies. These comparisons help engineers understand sensitivity to the selected interlayer assumption but do not replace verified product data.
Double and Triple Laminated Panes
The current calculator supports double and triple laminated panes, including laminated panes within DGU and TGU. For a triple laminate, the two entered interlayer thicknesses may differ, but the implemented Formula A.6 scope uses one common action-specific Gint for both interlayers. Ply and interface response is retained across the complete build-up.
Applicability
Action Routes and Table A.1
VitraLab resolves Table A.1 applicability separately for each active action and uses exact or bounded-interpolated coefficients only where the reviewed route permits them. It does not extrapolate beyond that mapping. Uncovered cases are identified as a VitraLab EET Plate Method route, use the conservative No Shear effective-thickness state and require engineering REVIEW. The related Eurocode 10 glass structures guide summarises the wider implemented calculation boundary.
Ply Stress and Governing Resistance
The calculation retains signed stress for every laminated glass ply and evaluates the applicable glass-ply/interlayer interface normal stresses using the implemented Annex A.6 Formulae A.9 and A.10. The report identifies the governing ply for resistance verification while retaining the remaining ply and interface results, so one governing value does not hide the through-thickness response.
Engineering Review and Draft Status
The 2024 prEN 19100 documents are drafts submitted for enquiry and may change before publication. Annex A is informative, and use may depend on the applicable National Annex and project requirements. Engineers must verify interlayer product data, temperature, duration, glass treatment, supports, loads, consequence class, response-route coverage and every reported review note. EET is a structural response model; it is not product approval, certification or evidence that an interlayer is suitable for the specified exposure.
Worked Example: EC10 EET 6 / 1.52 / 6
The selected geometry follows an exact Table A.1 four-edge uniform-load route. This is an illustrative software example, not independent validation or an interlayer product recommendation.
- Pane size
- 1000 × 2000 mm
- Orientation and support
- Vertical, four edges supported
- Build-up
- 6 / 1.52 / 6 laminated glass
- Glass design basis
- Annealed, main glass surface, CC2
- Applied action
- +0.500 kN/m² wind, 3 s duration
- Interlayer and coupling
- Gint = 0.400 N/mm²; Calculated / Partial
- Governing combination
- ULS - Wind+ alone
- Design action
- 0.750 kN/m²
- Calculated response
- 4.922 N/mm² stress
- Utilization or ratio
- 0.197 utilization
- Governing combination
- SLS - Wind+ alone
- Design action
- 0.500 kN/m²
- Calculated response
- 1.348 mm deflection
- Utilization or ratio
- 0.088 of 15.385 mm limit
The exact Table A.1 route resolved η = 0.352 and hef;w = 8.475 mm. For comparison, Full Shear produced 2.467 N/mm² ULS stress and 0.332 mm SLS deflection, while No Shear produced 6.255 N/mm² and 1.899 mm. This sensitivity shows why the selected Gint, action duration and temperature basis require project verification. Open the EC10 calculator to reproduce or change the inputs.
Frequently Asked Questions
What is EET for laminated glass?
EET is an equivalent-thickness method used to represent the stiffness and ply-stress response of a laminated glass build-up while accounting for the selected degree of interlayer shear coupling.
Why does VitraLab request different Gint values by action?
Interlayer shear modulus depends on load duration, temperature and product data. Different actions can therefore require different values rather than one modulus for every calculation.
What do Full Shear and No Shear mean?
Full Shear is the fully coupled comparison bound and No Shear is the uncoupled-ply comparison bound. For covered Table A.1 routes, Calculated or Partial represents the resolved action-specific coupling. For uncovered routes, VitraLab uses the conservative No Shear effective-thickness state and reports REVIEW.
Does the current implementation support triple laminated glass?
Yes. The current EC10 implementation supports double and triple laminated panes and retains the calculated stress for every glass ply. Formula A.6 uses one common action-specific Gint for both interlayers of a triple laminate, although their thicknesses may differ.
Is the EC10 laminated-glass calculation based on a final standard?
No. It is based on the reviewed 2024 drafts of prEN 19100-1 and prEN 19100-2. The calculation and its inputs require engineering review and must not be treated as certification to a final adopted Eurocode.
Can a generic interlayer modulus be used for every project?
No. Engineers should use verified product data appropriate to the action duration and design temperature, and review any conservative fallback assumption explicitly.
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.