Inter-story displacement angle: refers to the ratio of the maximum horizontal displacement between stories to the story height δ u/h under the action of the standard value of frequent earthquakes calculated by wind load or elastic method. According to the mathematical formula, when the angle θ is very small, θ=tanθ, so θ = Tan θ = δ U/h, and the limit of the floor displacement angle is mainly an index to control the overall stiffness of the structure.

What you are talking about is actually the concept of displacement ratio, which is the ratio of the maximum horizontal displacement and interlayer displacement of the vertical members of a floor to the average displacement of the floor under the action of the specified horizontal force considering accidental eccentricity. The displacement ratio mainly reflects the torsion of the structure and the non-uniformity of the structural stiffness.