Geometry for simple reciprocal frames

Daniel is right, it depends on curvature.
If you have a barrel vault then U beams will be shifted more than U directions.
Diamond grid is a bit better though (a bit).
If you think about Zollinger system instead of Recirpocal all beams are at the same eccentricity for a barrel vault. (1) (1.2 MB)

This post might help: