Why Load Combination Basis Matters
A glass pane can be governed by wind, dead load, barrier load, maintenance load, snow, live load, or an accidental point action. The governing result depends not only on the load magnitude, but also on whether the action is leading, accompanying, favourable, or unfavourable.
ULS Combinations
For ordinary ultimate limit state review, VitraLab uses EN 1990 STR/GEO design-value combinations. Unfavourable permanent action is treated as dead load, leading variable actions use the relevant design factor, and accompanying variable actions are reduced using ψ0 where applicable.
SLS Combinations
For serviceability review, VitraLab keeps SLS deflection separate from ULS stress. Serviceability rows show the corresponding action combination so the user can see which wind, snow, live, barrier, or maintenance case is driving deflection.
Barrier and Maintenance Loads
Barrier line, barrier area, barrier point, maintenance area, and maintenance point actions are kept visible as engineering actions in the result tables. Where another variable action accompanies them, the table shows the reduced accompanying action with the relevant ψ symbol.
Accidental Design Situations
For accidental point actions, VitraLab follows the EN 1990 accidental format at a practical result-table level: dead load where relevant, the accidental action Ad, the main accompanying variable action with ψ1, and other accompanying variable actions with ψ2 where they are included.
EN 16612 Glass Response
After the action combination is formed, VitraLab checks the glass response using the selected support condition, laminated glass equivalent thickness basis, action-dependent strength duration, and the relevant linear, nonlinear, or automatic plate-response route.
Engineering Review
The displayed combination is intended to make the result auditable. Engineers should still check the project consequence class, National Annex, specification, support details, load category, and whether any project-specific load factors or serviceability criteria are required.
Frequently Asked Questions
Does VitraLab use EN 1990 load combinations?
Yes. The current default ULS basis follows EN 1990 STR/GEO design-value combinations, while EN 16612 is used for the glass response checks.
What does ψ0 mean in the result table?
ψ0 identifies an accompanying variable action in an ordinary ULS or SLS combination.
How are accidental loads shown?
Accidental point actions are shown as Ad. Main accompanying variable actions use ψ1, while other accompanying variable actions use ψ2 where applicable.
Is this a replacement for engineering judgement?
No. The tool is intended to make the load-combination basis visible and reviewable, but the engineer must still confirm the project basis and National Annex requirements.