9m × 8m grid, 280mm PT flat slab. I get different governing combinations depending on whether I use the basic or refined method for v_Ed. Is there a clean workflow people trust, or is it always case-by-case?
The control perimeter at 2d from the column face. Prestress reduces v_Ed non-uniformly, so the refined method (β from moment-transfer, not the 1.15 default) governs at internal columns.
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Refined method (cl. 6.4.4) almost always governs at internal columns for PT slabs, because the prestress reduces v_Ed non-uniformly across the control perimeter. The thing people miss: the eccentricity factor β changes when spans are unequal — your 9/8 ratio is enough to push β above the 1.15 default. Compute β from the moment-transfer, don't take the code default. And remember the prestress secondary moments feed M_Ed at the column — include them or you'll under-read the shear.
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