Calculating canopy and open structure wind loads using single-surface pressure assumptions misses the net pressure effect created by wind acting on both exposed surfaces simultaneously — a simplification that understates the real loading condition these structures experience.
Why Open Structures Load Differently Than Enclosed Buildings
Canopies, carports, and other open or partially open structures experience wind pressure on both their upper and lower surfaces simultaneously, since there is no enclosed interior to separate the two. This creates a net pressure effect that is fundamentally different from how an enclosed building’s facade experiences pressure on a single exposed surface.
Where the Single-Surface Simplification Enters
Engineers accustomed to enclosed building wind load calculations, where a single exterior surface pressure is the primary consideration, may apply a similar single-surface logic to an open structure like a canopy — evaluating pressure only on the upper surface, for instance, without accounting for the simultaneous pressure acting on the underside.
Why This Understates the Real Loading Condition
The net pressure on an open structure reflects the combined effect of pressure on both surfaces acting together, which can produce a higher net force than either surface’s individual pressure would suggest in isolation. A calculation that only evaluates one surface is not simply incomplete — it is calculating a fundamentally different, and lower, loading condition than what the open structure will actually experience.
Applying Correct Open-Structure Methodology
After explaining how open structures require net pressure calculation across both surfaces, the fix is applying the specific open-structure provisions the code provides for this category, rather than adapting enclosed-building logic to a structure type it was never designed for. Wind Master applies the correct open-structure methodology to canopies and similar elements, calculating net pressure across both exposed surfaces rather than defaulting to single-surface enclosed-building assumptions.
Validate your open-structure calculations — Audit your net pressure methodology.