Why Effective Thickness Matters
A laminated pane contains glass plies connected by an interlayer. The interlayer can transfer shear between the plies, so the pane may behave somewhere between separate glass layers and a fully composite section. Effective thickness gives engineers a practical way to represent that behavior in calculation review.
Load Duration and kmod
Wind, barrier, maintenance, snow, live, and permanent actions do not all represent the same loading duration. VitraLab uses load-duration strength factors for stress resistance review, so the selected action duration can affect the design stress capacity used in the check.
Omega and Shear Coupling
For laminated glass effective thickness, VitraLab uses action-specific shear-coupling assumptions for the interlayer. These omega-based assumptions affect the effective thickness used for stiffness and stress calculations, but they are not the same thing as kmod.
Different Thickness for Stress and Deflection
For laminated glass, stress and deflection are not necessarily reviewed with one identical thickness value. VitraLab separates the stiffness used for deflection from the effective thickness used for stress so the output can reflect the selected action type and glass build-up more clearly.
User-Controlled Action Category
The user remains responsible for selecting the appropriate action category for the project. This is important because a wind check, barrier check, maintenance check, and permanent load check may use different strength-duration factors and different laminated effective-thickness assumptions.
What VitraLab Shows Publicly
VitraLab explains the engineering basis at a high level for transparency, but it does not publish the full internal tables, coefficients, or implementation details. Outputs should still be reviewed against the project specification, applicable standards, and engineering judgement.
Practical Review
When reviewing a laminated pane, check the glass ply thicknesses, interlayer type, load category, support condition, governing load case, ULS stress, SLS deflection, and any warning notes together rather than looking only at nominal glass thickness.
Frequently Asked Questions
Is laminated glass checked using total nominal thickness?
Not always. Laminated glass behavior depends on glass ply thickness, interlayer behavior, load duration, and shear coupling assumptions.
What is the difference between kmod and omega?
kmod is used for load-duration effects on glass strength. Omega is used for laminated glass shear coupling and effective-thickness calculations. They are related to the action basis, but they are not the same value.
Does VitraLab publish the omega tables?
No. VitraLab explains the workflow at a high level, but does not publish the full internal tables or implementation details.
Can the user choose the load category?
Yes. The tool gives the user control over the relevant action inputs and duration assumptions, which should be selected to match the project basis.